3.1 The Environmental Safety Case

3.1.1 Definition and Purpose of the ESC

An ESC is a set of claims about the environmental safety of facilities for the disposal of solid radioactive waste. It also includes the arguments and evidence that support those claims.

You should refer to requirement R3: Environmental safety case, in part 2 for a high-level explanation of the role of the ESC in regulating a radioactive waste disposal facility. There is also further information at the end of part 3 about how we use the ESC at different stages of the lifetime of a disposal facility.

The purpose of your ESC is to demonstrate that people and the environment will be adequately protected from the radiological and non-radiological hazards associated with the disposal of radioactive waste during the full lifetime of your disposal facility, including the period after the site is released from radioactive substances regulation.

To achieve this purpose, your ESC should have the following objectives:

• show how you have addressed or will address all the relevant requirements of this guidance
• demonstrate to us that your disposal system will achieve the required standard of environmental safety, given the proposed or accepted radioactive waste inventory
• demonstrate to us that you have considered how exposures to radiation can be kept as low as reasonably achievable, taking into account environmental, social and economic factors, and that you have developed your disposal facility to achieve this (in other words, that exposures to radiation are optimised)
• provide a basis for any controls and limits on the construction, operation and closure of your facility necessary in order to achieve the required standard of environmental safety. Where relevant these controls and limits will be reflected in the environmental permits that we issue to you
• help you manage your disposal facility and make decisions in a way that ensures that the required standard of environmental safety is achieved and maintained and that exposures of members of the public to radiation continue to be optimised

You should use a systematic approach to ESC development. Examples of good practice in safety assessment and safety case development for radioactive waste disposal include but are not limited to IAEA SSG-23; NEA MeSA Initiative; IAEA MODARIA Programme Tecdoc-1904, Safety Report Series No. 126. Your ESC may comprise a collection of documents, datasets and other materials. Together, these should present the claims, arguments and evidence you rely on to show that the required standard of environmental safety is met.

You must have an appropriate management system in place to show that you have designed, constructed, operated and closed (or will design, construct, operate and close) your disposal facility in line with the assumptions you have set out in your ESC.

3.1.2 Responsibility for the ESC

You are responsible for the environmental safety of your facility. Therefore, you are responsible for preparing and updating the ESC for your facility.

You should review and update your ESC throughout the lifetime of the disposal facility, in accordance with your environmental permit and when you think it is necessary for operational reasons (see requirement R3: The environmental safety case). Your reviews should take account of operational experience.

If your understanding of your disposal system changes, you must update all your claims and safety arguments that are affected by the changes. You must also update the other aspects of your ESC that are affected by the changes, for example, changes to your assessment input data may require you to revise your waste acceptance criteria.

Your management system should include a change control process to manage any changes to your ESC. You should consider the most appropriate format for reporting updates to your ESC, taking account of any instruction and guidance we have given you.

We will use your ESC to help us regulate your disposal facility throughout its life. We explain how we will use your ESC later in this part of the guidance.

You are responsible for undertaking proportionate research and development, for example to:

• monitor scientific or technological developments relevant to your ESC
• ensure and demonstrate that your planned technical operations can be practically accomplished to provide the required protection for people and the environment
• investigate and understand the processes on which the environmental safety of the disposal system depends

You are responsible for carrying out all necessary investigations of sites and of materials to assess their suitability and obtain data necessary to support your environmental safety assessment.

3.1.3 Scope of the ESC

Your ESC should address all the relevant requirements in part 2 of this guidance. You should take a proportionate approach to addressing these requirements. The emphasis your ESC places on each requirement may change at different stages in the lifetime of your disposal facility.

Your ESC should cover both the period while your disposal facility is subject to radioactive substances regulation and a sufficient period after your permit is surrendered to capture the potential peak risks.

Your ESC should set out and justify how you expect your disposal system will evolve, taking account of natural processes and climate change; also known as the ‘expected evolution’. You should set out and consider variants of the expected evolution to investigate uncertainties in the evolution of your disposal system. Your ESC should also consider appropriate ‘what-if’ scenarios, for example to demonstrate the robustness of your disposal system.

Your ESC should assess the impacts on people and the environment from both the radiological and non-radiological properties of the radioactive waste and materials in your disposal facility.

If your disposal facility is on a nuclear licensed site, the licensed site will need to meet the requirements of the GRR. Your ESC should then form part of the SWESC that the nuclear licensed site will be required to submit under the GRR. The relationship between your ESC and the SWESC is explained in the GRR.

3.1.4 Relationship with Operational Health and Safety and Nuclear Safety

Your ESC should focus on protecting members of the public and the environment, not on protecting workers, nor avoiding and mitigating the immediate consequences of accidents during operations.

If your site holds a nuclear site licence, protecting workers and avoiding and mitigating the immediate consequences of accidents during operations are regulated by the ONR. ONR will require you to prepare and maintain a nuclear safety case demonstrating that your arrangements for protecting workers and avoiding and mitigating the immediate consequences of accidents are adequate (see guidance produced by ONR, for example, Technical Assessment Guide on The purpose, scope, and content of safety case NS-TAST-GD-051).

If your site does not hold a nuclear site licence, these and other similar obligations are regulated by the HSE and (the non-RSR parts of) SEPA.

Any arguments you make in your ESC must be compatible with your arrangements for and arguments about the protection of workers and the avoidance and mitigation of the immediate consequences of accidents.

For nuclear licensed sites, these aspects of your nuclear safety case may influence the claims and arguments in your ESC, especially when optimising your disposal facility (see requirement R7: Optimisation of radiological protection of the public). In this case, your ESC should explain this influence and demonstrate that a satisfactory level of environmental safety is still achieved. The need to protect workers and avoid and mitigate the immediate consequences of accidents does not reduce the need to protect the environment, and you must still address all the relevant requirements in this guidance.

Similarly, the claims and arguments in your ESC may influence your arrangements for, and arguments about, the protection of workers and the avoidance and mitigation of the immediate consequences of accidents.

Some accidents could have consequences for the environmental performance and safety of your disposal facility. For example, an accident could damage a barrier that you rely on to contain radionuclides after closure, or it may make it difficult to operate or close the facility as planned. In the event of such an accident occurring your ESC should explain how you will ensure your facility continues to provide satisfactory environmental performance. You should take action to prevent accidents from occurring and also implement appropriate mitigations to limit the impact of accidents on the long-term environmental safety of your disposal facility, for example by protecting relevant structures, systems and components of the facility such that they are not damaged. You should also explain and have procedures ready for how you would remediate any damage.

Although you do not need to assess the immediate radiation doses arising from accidents for compliance with your environmental permit, you should make such assessments and ensure that people are protected as you satisfy the requirements of other regulators. If an accident does occur while you hold your environmental permit, you will need to account for any immediate and long-term environmental effects.

3.1.5 Graded Approach to the ESC

You should take a graded approach when developing your ESC. This means that the level of analysis and documentation in your ESC should be proportionate to the magnitude of the radiological and non-radiological hazards and risks associated with the radioactive waste that your disposal system is designed for.

Using the graded approach does not change any of the protection standards or numerical criteria set out in this guidance. We expect all facilities to comply with these standards and criteria.

When determining the level of effort that you should expend on your ESC, you should consider criteria including:

• the hazard and risk posed by the radioactive waste intended for or disposed of in your disposal facility
• how much experience there is (both in the UK and internationally) with the types of practices, procedures and designs used to construct your disposal facility
• the level of knowledge available about the performance of similar facilities or practices, and the uncertainty in this knowledge
• the complexity of your disposal facility and the safety arguments you rely on

3.1.6 Management System Description

All of your work in developing your ESC and in siting, constructing, operating, closing, monitoring and otherwise controlling your disposal facility must be conducted in accordance with an appropriate management system that ensures the work is of the highest quality and is undertaken by suitably qualified and experienced personnel. You should:

• have and apply an appropriate management system that addresses requirement R2: Management system and environmental safety culture, for controlling work
• describe your management system in your ESC
• specify how your programme for developing, reviewing, updating and using your ESC is managed, who is responsible for different aspects of the ESC how the ESC is checked, reviewed, updated, approved and used
• describe your approach to specifying and managing the work required to develop your ESC, including where work is conducted partly or wholly by the supply chain
• describe the actions you will take to update your ESC in response to new information
• describe how you will provide and allocate financial and human resources to the ESC and to the safe management of radioactive waste and provide confidence that it will be possible to implement the controls assumed in your ESC
• explain your approach to ensuring that those managing and developing the safety case and the radioactive waste are suitably qualified and experienced and receive appropriate training

Your management system should ensure that you keep appropriate records of your work on the ESC and on the management of radioactive waste. The records of your work should be traceable and auditable. Your ESC should explain the approach that has been adopted to ensure the environmental safety of the facility. It is important that you record the reasons why decisions were made, and that this information will be available and easily traceable for both present and future generations.

In addition to being subject to internal reviews and audits, your ESC should be subject to independent peer review by suitably qualified and experienced experts. The nature of the reviews will depend on regulatory requirements and be proportionate to the hazards and risks posed by the waste and the facility in question. Peer reviews and your responses to any issues raised should be documented as part of your ESC.

Your management system should explain how your ESC is implemented. In other words, how you ensure that management of the radioactive waste and of your site is consistent with your ESC and how the various controls and limits that are necessary are documented and enforced. You should:

• describe your arrangements for managing and retaining data and records
• specify how data and records are stored, and which data and records need to be retained - the data and records should be stored in a manner appropriate for the time period over which they need to be retained
• ensure your arrangements address requirement R12: Preserving and accessing knowledge, information, and data

You should consider what information and equipment is required to be able to understand and interpret stored data and records.

3.2 Presentation of Your ESC

3.2.1 Overview and Content of Your ESC

You should present your ESC using a structure that allows you to set out your claims, arguments and evidence clearly. It should be clear how you have addressed the relevant requirements of this guidance.

Depending on the complexity and level of detail, your ESC may comprise a hierarchy of documents. These must be effectively cross referenced, such that your claims, arguments and evidence can be easily followed. If you use a document hierarchy, you should include an overview report that summarises the main arguments and evidence and provides an overview of the hierarchy that you have used.

Your ESC content should cover all the components discussed in this guidance; how you choose to structure this content is up to you. However, the relationships between the components of your ESC are important and these are illustrated in Figure 3.1 (adapted from Figure 2 of IAEA SSG-23).

Figure 3.1 – Environmental safety case components showing the relationship between them [adapted from IAEA SSG-23].

The following subsections discuss each of the components that make up your ESC. We describe what we expect the content of these components to comprise and, where applicable, how you should use quantitative and qualitative assessment criteria.

3.2.2 ESC Context

You should clearly describe the context of your ESC or your revisions to your ESC. You should explain why you have produced or revised your ESC, for example, for a permit application, to vary or surrender a permit, or as a periodic update. You should include an explanation of how you have applied the graded approach as part of the context of your ESC or revision to your ESC.

The ESC context should, as appropriate, summarise and reflect relevant aspects of the following:

• the legal framework
• the policy and strategy
• international commitments
• international safety standards and guidance
• the environmental permitting process and the stage at which your disposal facility has reached

You should discuss the context for your ESC with us at an early stage before submitting the ESC itself so that there is a common understanding of the objectives and scope of the ESC and what is required and expected. You will need to show that you have identified the legislative and policy contexts and understand their implications for your ESC. You should develop the ESC at a level of detail appropriate to the risk and the stage of disposal facility development.

3.2.3 Environmental Safety Strategy

Your ESC should include an environmental safety strategy that provides further details on how your disposal system provides the necessary isolation and containment of radioactive waste in accordance with the preference in UK Policy 2024 and IAEA requirements for ‘concentrate and contain’. This should summarise your approach to ensuring and demonstrating environmental safety.

The goal of your environmental safety strategy is to set out the high-level approaches you propose to take to satisfying the requirements set out in this guidance and ensuring environmental safety. Your environmental safety strategy by itself does not need to demonstrate that your disposal facility satisfies the requirements; that is done by the whole of your ESC and the control of your operations according to your management system.

In your environmental safety strategy, you should provide a summary of:

• your disposal facility siting and design explaining at a high level your disposal concept
• how your disposal facility provides isolation and containment of the radioactive waste
• the components of your multi-barrier system and any other engineered or natural components of your disposal system with important environmental safety functions
• how your facility design provides defence in depth, robustness and passive safety
• your strategy for demonstrating that your disposal system will provide the environmental safety functions claimed
• the most important arguments and lines of reasoning that your ESC uses to demonstrate environmental safety
• the timeframes for your safety assessments and how uncertainties that are relevant to environmental safety are addressed
• how your management arrangements ensure your disposal facility is operated in line with your ESC and the main management controls that contribute to environmental safety

Although your environmental safety strategy should explain how the location of your disposal facility contributes to environmental safety, it does not need to explain your site selection process.

You should begin to identify your environmental safety strategy at an early stage during the planning of your facility and continue to develop it as your plans advance.

3.2.4 Disposal System Description

In your ESC, you should provide an appropriately detailed description of your disposal system which provides the basis for understanding disposal system performance and for your safety assessments (see later section of this part of the guidance). You should describe:

• the characteristics of your site
• the inventory of waste that you either intend to dispose of and or have disposed of
• the characteristics of the waste, including:
  • the radionuclide inventory
  • the waste form
  • heterogeneity
  • any non-radioactive hazardous properties

• the design of your disposal facility, including your multi-barrier system
• areas of the disposal facility that you either plan to construct and or that you have constructed
• how you either plan to operate your disposal facility and or how you have operated it
• how you either plan to close your disposal facility or how you have closed it
• how your disposal system may evolve with time, including the effects of climate change

When describing your disposal system, you should highlight aspects of the system that have significant effects on environmental safety. You should also identify and discuss uncertainties in your knowledge, the possible consequences of these uncertainties and how you manage the uncertainties.

Aspects of your disposal system that you should consider when describing the characteristics of your site include:

• geology
• hydrogeology
• hydrology
• geochemistry
• natural resources, for example, oil and gas and mineral deposits
• the characteristics of the surface environment at and near to the site, including but not limited to topography, land uses, fauna and flora, the presence and habits of human populations

You should keep your disposal system description updated as new information becomes available. Use your knowledge of your disposal system and the uncertainties in your knowledge to guide your future research, data collection and environmental safety assessment activities.

3.2.5 Environmental Safety Assessment

3.2.5.1 Introduction

The term ‘environmental safety assessments’ is used here to refer to all assessments that you may need to perform, including, but not limited to, those shown in Figure 3.2 (adapted from Figure 4 of IAEA SSG-23). Your environmental safety assessments should address all aspects of your disposal system that could be significant to radiological protection of people, protection of the environment and protection of groundwater.

Figure 3.2 – The seven key environmental safety assessments.

In your environmental safety assessments, you should:

• consider both the radiological and non-radiological impacts of your facility and consider impacts on people and the environment
• evaluate the environmental safety of your disposal system, including protection of groundwater
• present the results of your assessments to allow us to consider the environmental safety of your dispose facility against the appropriate regulatory criteria as set out in part 2 of this guidance

Your assessments should include evidence that you have an adequate understanding of the behaviour of your disposal system both now and in the future. The results of your assessments should show how your disposal system meets the required standards of environmental safety.

The sub-sections below describe certain aspects relevant to all of the environmental safety assessments, and then focus on each assessment included in figure 3.2 in turn. The sub-sections included are:

• representative persons
• scenario development
• the environmental safety assessments as a whole
• radiological environmental safety assessment for the period of RSR
• radiological environmental safety assessment for after the period of RSR
• non-radiological environmental safety assessment
• criticality assessment for the operational phases and after the period of RSR
• engineering assessment
• isolation assessment
• management system assessment

3.2.5.2 Representative Persons

You will need to define one or more persons to be used for determining compliance with the dose constraint. These are the representative persons. These individuals, who will almost always be hypothetical, receive a dose that is representative of the more highly exposed individuals in the population.

The radiological impact on the public should be estimated using the individual effective dose to the representative persons, which is the sum of the committed effective dose from intakes of radionuclides (i.e. from internal exposure by ingestion and inhalation) and the effective dose from external exposure. Doses from internal exposure are calculated using dose coefficients from intakes of radionuclides by ingestion and inhalation, which provide the committed effective dose per unit activity of intake, expressed in units of sieverts per becquerel (Sv/Bq).

In considering dose to the representative persons, you should take a number of factors into account:

• the dose assessment must account for all relevant pathways of exposure
• the dose assessment must consider spatial distribution of radionuclides to ensure that the groups receiving the highest dose is included in the assessment
• habit data should be based on the groups or populations exposed and must be reasonable, sustainable, and homogeneous
• dose coefficients have to be applied according to specific age categories

When selecting characteristics of the representative persons, you should address three important concepts: reasonableness, sustainability, and homogeneity. You should define the representative persons such that the probability is less than about 5% that a person drawn at random from the populations will receive a greater dose.

Your prospective dose (and risk) assessments should be carried out in a manner that provides confidence that they are appropriate, covering all reasonably foreseeable situations and exposure routes using realistic information on habits and land use.

Where the hazard presented by the waste warrants a detailed assessment, you should provide a probability distribution of dose from each risk assessment that you undertake. This probability distribution should cover the range of potential doses that the representative persons could receive and the probability that they receive any given dose.

You should consider three age categories in your scenarios when estimating annual dose to the representative persons for prospective assessments. These categories are 0–5 years (infant), 6–15 years (child), and 16–70 years (adult). For practical implementation of this recommendation, you may use dose coefficients and habit data for a 1-year-old infant, a 10-year-old child, and an adult to represent the three age categories.

You will need to show that your choice of potentially exposed groups is reasonable and suited to the particular circumstances. The location and characteristics of the potentially exposed people considered should be based on assessments of releases or potential releases of radioactivity and on assumptions about changing environmental conditions.

Your assumptions about the habits and behaviour assumed of potentially exposed people should be based on present and past habits and behaviour that have been observed or that are judged relevant. You should not exclude from consideration any pattern of behaviour which a reasonable person might adopt, whether or not anyone actually engages in such behaviour at a given time. You should not assume behaviour which a reasonable person would regard as extreme and which habit surveys have not revealed.

Metabolic characteristics similar to those of present-day populations should be assumed. Other parameters used to characterise the representative persons should be generic enough to give confidence that the assessment of risk will apply to a range of possible future populations.

If specific habit data for the exposed populations are not available, you may derive values from appropriate national or regional population data. A distribution of these data may be used in probabilistic assessments, or a value on the distribution may be selected for deterministic calculations.

Using the 95th percentile of behaviour in deterministic calculations is a cautious assumption for defining an intake rate. Care should be exercised to avoid selecting extreme percentile values for every variable to prevent excessive conservatism in the assessment. The overall selection of parameter values should provide a reasonable and sustainable representation of the exposures.

Any one representative person may be exposed to all the discharges of radioactive waste and emissions of radiation from the site in combination. The habits data should therefore address all potential combinations of habits that may lead to exposure from each element of discharge and emissions separately and in combination.

You should agree with us how to include uncertainties in the estimation of dose for compliance purposes. To demonstrate adequate radiological protection your ESC should show both compliance with the relevant quantitative standards and optimisation of radiological protection.

3.2.5.3 Scenario Development

Your environmental safety assessments need to address the performance of your disposal system for both present and future conditions. When considering future conditions, you will need to consider many different factors that could affect the performance of your disposal facility, including, but not limited to:

• future human actions
• climate and other environmental changes
• events and processes

You can address these considerations through the formulation and analysis of a set of scenarios. Your scenario development is a significant part of the development of your quantitative safety assessments.

Scenarios are descriptions of alternative possible evolutions of your disposal system. The development of your scenarios forms the basis of your environmental safety assessments that make up an important part of your environmental safety case.

The scenarios that you develop may represent or bound a range of similar possible evolutions of your disposal system. Your choice and the rationale for your choice of an appropriate range of scenarios and your associated environmental safety assessment cases are important, as they will strongly influence your assessment of the performance of your disposal system.

Scenarios represent structured combinations of features, events and processes relevant to the performance of your disposal system. You will need to consider different types of scenarios that should include your expected evolution scenario, variants of your expected evolution scenario (which will include disturbing events and processes) and “what-if” scenarios to explore more extreme, or even unrealistic, events and processes.

The “what-if” scenarios you include in your environmental safety assessments are useful to explore particular properties of your disposal system, for example one or more of the natural or engineered barriers. The aim of your what-if scenarios that assume extreme conditions, is to examine the robustness of different aspects of your disposal system.

When constructing your scenarios you should use robust and systematic methodologies, such as methods based on:

• screening of features, events and processes (FEPs)
• analysis of the safety functions that your structures, systems and components are intended to fulfil

Regardless of the method you use for developing your scenarios, all features, events and processes that could significantly influence the performance of the disposal system should be addressed in your assessments. Using such a structured methodology should allow you to demonstrate that all potentially significant migration pathways for the migration of radionuclides have been considered as well as taking account of the possible evolutions of your disposal system.

Your scenario development should be clearly documented, setting out your claims, arguments and evidence. It is important to clearly identify your expected evolution, variant and what-if scenarios and the rational for how these are to be used in your environmental safety assessments.

The design of your disposal system will determine the time frames your environmental safety assessments need to consider. Regardless of these timeframes, you will need to consider who might be affected in the future (representative persons). You should assume that humans will be present in your scenarios and that they will make use of local resources. As it is not possible to predict future human behaviour with any certainty, you should assume that humans in the future will have similar habits to present humans, or habits that have been observed in the past. Where your consideration of climate change means conditions at your site will be different in the future, the habits of humans at this time should be consistent with the expected climatic conditions.

When developing your scenarios you should clearly document all of the events and processes that you have included and where necessary the probabilities of their occurrence. Your environmental safety assessments will need to take this information into account when evaluating doses and risks to your identified representative persons.

3.2.5.4 The Environmental Safety Assessments as a Whole

Your environmental safety assessments should have both quantitative and qualitative components. You should use quantitative assessments where you understand enough about a particular aspect of your disposal system and where you are able to quantify uncertainties. If you don’t understand enough or if a detailed quantitative assessment would be disproportionate or inappropriate, you may place a greater emphasis on qualitative arguments.

Your environmental safety assessments should be consistent with your ESC context, environmental safety strategy and disposal system description. This does not mean that every assessment you do has to represent every detail of your disposal system. Your assessments will inevitably include simplified representations of some parts or all of your disposal system. You should identify and justify the levels of simplifications in your assessments.

You should aim to represent the disposal system in a realistic way, but where this is not possible or would be disproportionate, you should err on the side of caution (i.e. your mathematical models should be realistic or over-estimate the possible impacts on people and the environment). It may be appropriate for individual assessments to be more cautious or to focus on a particular aspect of the disposal system.

As appropriate, you should consider the concentrations of radionuclides that might build up in environmental media and the harm to humans that could result.

Your environmental safety assessments should extend in time at least until the time of peak impact (for example, dose and risk). You should justify the length of time assessed in your assessments and demonstrate why impacts will not increase further after the period you have considered.

Where your assessment considers a particular event (such as a natural disruptive event), you should justify the assumed timing of the event.

For inadvertent human intrusion events you should present assessment results from the point in time immediately following the end of RSR. You may also need to present results at a range of points in time to capture the maximum assessed doses to take account of both radioactive decay and in-growth.

3.2.5.5 Radiological Environmental Safety Assessment for the Period of RSR

You should assess the environmental impacts that will or could occur while the permit is in place. This includes the period over which your disposal facility is operational, during closure and during any post-closure period of control for the purposes of radiological protection.

Your assessments should be informed by the results of monitoring at and around your site. You should assess the radiological impacts to members of the public from all of the releases from your disposal facility during the period of RSR. These could include:

• permitted discharges, for example of leachate to surface or marine waters
• releases to the environment across the barriers of the disposal facility, for example older areas of an existing facility that were not designed to modern standards
• external irradiation from radioactive waste both before and after emplacement

You should use monitoring data and your assessments to understand the distribution of any radionuclides released from your facility during the period of RSR, for example to groundwater. You should use this knowledge in your assessments of the environmental safety of the disposal system in the period after RSR (see below)

Your assessments should demonstrate that during the period of RSR doses arising from your site, combined with those from any sites close by, if applicable, during the period of RSR do not and will not exceed the dose constraints for members of the public set out in standard 2.

You should also carry out assessments of the radiological impacts on wildlife so that we can consider how your results relate to the dose rate criteria set out in requirement R13: Protecting wildlife.

You do not need to present assessments of the immediate impacts of potential accidents in your ESC. However, in the event of an accident where it could affect the long-term environmental performance of your disposal system, you will need to factor the consequences into any future assessments.

3.2.5.6 Radiological Environmental Safety Assessment for After the Period of RSR

You should assess the radiological impacts that could occur in the future, including the far future, after you surrender your permit. These are referred to as ‘planned potential exposures’ by the ICRP. You should consider potential impacts to people and the environment, including groundwater.

The timeframes for your assessments will depend on how the disposal facility and the surrounding environment may evolve over time. The timeframes you choose may also need to reflect:

• the scenarios you are considering for inadvertent human intrusion
• whether natural processes could uncover the radioactive waste in your disposal facility and how long this might take

For the purpose of your assessments, you must assume that there will be no control over, nor restriction on the use of your site after the period of RSR (see requirement R3: The environmental safety case).

You should identify the pathways by which members of the public could be exposed to radiation from the expected evolution of your disposal facility and assess them against the risk guidance level (see standard 3).

As appropriate, you should consider the concentrations of radionuclides that might build up in environmental media and the harm to humans that could result. We will consider your assessment results and judge the acceptability of any releases of radionuclides from your disposal facility.

You should assess the consequences of inadvertent human intrusion into the disposal facility (see requirement R16: Protecting against inadvertent human intrusion into near-surface disposal facilities after the period of RSR) and of natural disruptive processes uncovering the radioactive waste (see requirement R17: Protecting against natural disruptive processes acting on near-surface disposal facilities after the period of RSR).

You should assess the consequences of inadvertent human intrusion and of sub-surface natural disruptive processes affecting the disposal system barriers. This should include considering how the timings of such events affect your results. Your assessment should consider how the consequential degradation of the barriers affects the long-term performance and environmental safety of the disposal system including the time and the magnitude of peak risk (see requirements R16 and R17).

You should compare your assessment results with the risk guidance level (see standard 3) and the dose guidance range (see standard 4). Figure 3.3 illustrates the lifetime of a site and the relevant standards that apply.

3.2.5.7 Non-Radiological Environmental Safety Assessment

You should assess the non-radiological impacts that could occur until the time when your disposal facility will no longer pose an environmental hazard.

You should refer to our guidance for conventional landfills for further information. However, as explained in the following paragraphs, for your RSR permit you do not need to comply directly with the guidance for conventional waste landfills. Instead, you should meet the standards set out in this document.

In all cases you should demonstrate that the:

• disposal system provides adequate protection of people and the environment against non-radiological hazards associated with the radioactive waste
• level of protection against non-radiological hazards is consistent with that achieved by national standards for non-radioactive waste, in accordance with requirement R15: Protecting against non-radiological hazards

In your assessment you should consider any substances that have the potential to be harmful to people or the environment. Your list of substances should include any substances that would be regulated for a non-radioactive waste disposal facility. For example, asbestos, lead, mercury and all chemicals on the relevant published list. We have published a “List of Hazardous Substances as determined in accordance with Schedule 2 of the Water Environment (Controlled Activities) (Scotland) Regulations (CAR)”. This list is based on recommendations from the Joint Agencies Groundwater Directive Advisory Group (JAGDAG) in JAGDAG Hazardous Substances/ Non-Hazardous Pollutants Consultation June 2018.

As part of your assessment, you should consider both the potentially harmful substances present in the radioactive waste and substances that might result from the degradation or reaction of precursors present in the radioactive waste. To identify substances present, you should draw on inventory records and investigations, and on relevant monitoring data.

There may be substances present in the radioactive waste that are not directly harmful to the environment or to human health, but which affect disposal system performance. For example, some substances may react or form complexes with certain radioactive or non-radiological substances and enhance their transport. You should consider these substances in your ESC. Where appropriate, you should account for these substances and their possible effects in your assessments.

As appropriate, you should consider the concentrations of non-radiological hazardous substances that might build up in environmental media and the harm to humans that could result. We will consider your assessment results and judge the acceptability of any releases of non-radiological hazardous substances from the disposal facility.

As far as is appropriate, you should use assumptions and mathematical models for non-radiological substances that are consistent with those you use to assess the potential impacts of radioactive substances.

In your assessment, you should consider the pathways that may result in impacts to humans and the environment during the evolution of your facility (for example, releases to groundwater and gas release). You should also consider the variant scenarios developed in your assessments for radioactive substances.

You do not need to assess the impact of non-radiological hazards in radioactive waste brought to the surface by inadvertent human intrusion.

Protecting groundwater should also be a focus of your assessment. You should refer to part 4 for further guidance on what you need to do to demonstrate that groundwater is protected.

• In your ESC, you do not need to consider wider non-radiological environmental impacts associated with your disposal facility, for example, noise and traffic (because these would be considered in an Environmental Impact Assessment, and where relevant under other permits).

3.2.5.8 Criticality Assessment

As part of your ESC, you will need to consider the possibility of a local accumulation of fissile material that could cause a neutron chain reaction (see requirement R18: Criticality risk during and after the period of RSR for near-surface disposal facilities). Your assessment should consider controls implemented at the waste packaging stage (for example, limits on the quantity of fissile material in an individual waste item, waste container or waste package) and/or controls exercised during the emplacement of waste in the facility (for example, physical separation of packages with a high loading of fissile material). Any controls that you require for packaging radioactive waste will need to be reflected in your waste acceptance criteria and compliance arrangements (see requirement R11: Waste acceptance). We may specify permit conditions relating to waste emplacement as appropriate.

You will need to consider the full range of processes that might lead to or have consequences for criticality both before and after the closure of your disposal facility. These should include any processes that might remobilise and concentrate fissile material and/or other material that could influence a neutron chain reaction such as neutron multiplication. For example, mobilisation of neutron poisons out of waste containing fissile material might influence neutron multiplication within the system.

The detail of the assessment should be proportionate to the amount and concentration of fissile material disposed.

3.2.5.9 Engineering Assessment

You should provide an assessment that sets out the arguments and evidence to support the claims and assumptions that you make in your ESC regarding the construction, quality and performance of engineered structures, systems and components. You should demonstrate that you have applied good scientific and engineering practice. Your engineering assessment should be developed in accordance with your management system (see requirement R2: Management system and environmental safety culture) and should address the relevant aspects of requirements R4, R6, R7, R8, R9 and R10. The outputs from this engineering assessment should be used appropriately to support your other assessments and your environmental safety case.

Your engineering assessment should:

• be consistent with the other assessments in your environmental safety case- in particular, the timeframes that you consider for your assessment of engineering and properties of your disposal system should be informed by your isolation assessment and your environmental safety assessments
• be consistent with your current plans for the construction, operation and closure of the disposal facility
• include a justification of any claims and assumptions you make about the constructability of the engineered components of your disposal system and how well they will perform and how long they will perform for
• describe and take account of the evolution of the properties of the engineered barriers over an appropriate period and the uncertainties in these properties to support your environmental safety case

You should inform your engineering assessment using operating experience, wider practical engineering experience and observation, as well as relevant research, modelling and other (for example, analogue) studies into the long-term behaviour of materials. For example, studies on the evolution of concrete over time, modelling and or experimental data on the performance of waste forms such as ceramics, metals and glasses. You should show that you have considered the relevant features of the disposal system and the events and processes that could affect their performance. The processes you may need to consider include, but are not limited to:

• physical (for example, thermal, hydrological, mechanical, radiological)
• chemical (for example, corrosion, dissolution)
• biological (for example, microbial)

You should consider the uncertainties associated with the properties, behaviour and performance of the engineered barriers and other components of the disposal system at an appropriate level of detail.

Your engineering assessment should be proportionate. For a small inventory of relatively low hazard and/or risk, a simple analysis may be appropriate. However, for disposal facilities for larger inventories and higher hazards and or risks, we expect a detailed engineering assessment, including a thorough assessment of uncertainties.

You should carry out proportionate research and development to support your ESC, which should include appropriate studies and data collection to enhance knowledge of the properties and performance of your engineered barriers, structures and components. You should use this knowledge and data to update your engineering assessment, your understanding of the disposal system and your environmental safety case.

3.2.5.10 Isolation Assessment

You should present an isolation assessment for your disposal system to address requirement R8: Isolation. Your isolation assessment should form the basis for the scenarios that you develop describing the evolution of your disposal facility, inadvertent human intrusion and natural disruptive processes in your environmental safety assessments. When developing your isolation assessment, you should take account of the guidance provided on inadvertent human intrusion and natural disruptive processes.

Your isolation assessment is an integral part of your environmental safety case and your claims, arguments and evidence that your disposal facility will provide sufficient isolation for the length of time that the disposed radioactive waste inventory could cause exposures or risks to people (if they were to come into contact with the waste) greater than the standards set out in this guidance. Your isolation assessment should capture all the relevant information when considering how your disposal system will evolve and the types of human actions that might lead to inadvertent human intrusion into your disposal facility.

As set out in the isolation requirement, your isolation assessment should include, but not be limited to, a description of all the natural processes affecting your disposal system, how you expect it to evolve and the scenarios that could lead to inadvertent human intrusion.

When considering inadvertent human intrusion scenarios, your isolation assessment should identify the range of human activities that could lead to direct exposures to the disposed radioactive waste and/or disrupt the barriers of your disposal facility. These might include, but are not limited to, construction, borehole drilling, agriculture, scavenging for materials, archaeological or other excavations and mining. The relevant activities will be different for different locations and types of disposal facility. For example, agriculture activities on the cap of some near-surface disposal facilities may disturb them but might not disturb a deeper facility.

When considering inadvertent human intrusion events, you should consider the degree of physical isolation that your disposal facility design provides.

For near-surface disposal facilities you should assume that activities leading to inadvertent human intrusion into the radioactive waste will occur and you should assess the consequences accordingly (see requirement R16: Protecting against inadvertent human intrusion into near-surface disposal facilities after the period of RSR). You do not need to evaluate all possible inadvertent human intrusion scenarios where you can show that a sub-set of scenarios provide suitable bounding cases.

3.2.5.11 Management System Assessment

Your management system assessment should:

• include evidence to show that your management arrangements and data retention arrangements address requirements R2: Management system and environmental safety culture and R12: Preserving and accessing knowledge, information, and data
• provide the required assurance that your management arrangements will provide the required quality for all safety related activities - this includes all of the other assessments within your environmental safety case, as well as the quality of the work to construct, operate, close and monitor your disposal facility
• support and provide confidence in the claims, arguments and evidence you use to make your ESC
• include evidence of the use of reviews and internal audits of processes and procedures for the control and quality assurance of the development and use of your ESC and of your disposal facility (see IAEA GSG-16 for guidance on assessing and improving management systems)

3.2.6 Iteration and Design Optimisation

You should follow an iterative approach to the design of your disposal system and the development of your ESC. Your ESC needs to show how and why you have reached the environmental safety decisions you have, which environmental safety decisions you are making now and how you are making them. It should also show how you will ensure that appropriate environmental safety decisions are made in a systematic way in the future.

You must show how such decisions remain consistent with past decisions or have to deviate from them in light of new evidence or analysis. Your design decisions should be guided by the requirement to optimise for radiological protection of the public, in particular with respect to the long-term environmental safety.

Requirement R7: Optimisation of radiological protection of the public, sets out what you should consider when optimising your disposal facility design.

Your ESC needs to demonstrate that you have optimised and continue to optimise your disposal facility design such that public exposure to ionising radiation from the disposal of radioactive waste is kept as low as reasonably achievable, taking into account environmental, economic and social factors.

You should set out your arguments that the disposal facility design presented in your ESC is optimised. This should include setting out the other options you considered and why you did not choose them.

You may set out optimisation arguments for decisions about individual structures, systems and components of your disposal system. Where you do this, you should explain how you managed the whole environmental safety case development process to ensure that the decisions about one component give the desired outcome for protection and for the disposal system as a whole. We expect you to have followed and documented an iterative process to design optimisation.

When you are developing or updating your ESC you should use your optimisation process to identify areas where further research and development work are required and indicate how you will incorporate the results of this work into your process of optimisation. Your ESC should document this process so that it is included in the ESC that you formally submit for regulatory approval.

You should explain how your optimisation process takes account of new information and how you will use the process when you need to make new decisions.

Optimisation is fundamentally a judgement process, conditioned by decisions that have already been taken. In order to achieve an optimised disposal facility, you will also need to make good engineering decisions about the technical and management solutions that you adopt and apply your management system to ensure the quality of work that your ESC relies on. You should, as appropriate, follow good practice and consider the use of requirements management systems in developing your disposal system and justifying that it is optimised. You should set out your approach in your ESC.

3.2.7 Management of Uncertainty

You should demonstrate that you have identified and where appropriate investigated all the significant uncertainties in your ESC. You should produce and maintain a register of all your significant uncertainties.

A systematic approach to managing uncertainties is an important part of your ESC. When developing your ESC and when updating it you should implement a clear plan and forward programme for managing significant uncertainties.

Your plan should clearly set out objectives, approaches and anticipated timescales for work aimed at managing and resolving uncertainties.

Your consideration of uncertainty should not be limited to numerical uncertainties in input data or results. You should also consider other types of uncertainty. For example, there will be uncertainty in the future evolution of the site and facility, and in your conceptual understanding of some aspects of your disposal system and how it will evolve. There may also be uncertainties relating to the design of your facility and further issues may derive from new information, changed circumstances, regulatory review and peer reviews. You should make sure that you account for such uncertainties in your ESC.

When presenting the results of your assessments, you will need to account for uncertainties explicitly and analyse their possible consequences. This should cover both the period when the site is subject to radioactive substances regulation and the period after the site’s environmental permit has been surrendered.

During the development of your ESC, you should use your knowledge of the uncertainties in your ESC to identify future information needs (for example, information you will need to optimise your disposal facility) and guide any research and data collection work (for example, site characterisation).

You should develop, describe and apply an appropriate strategy for undertaking environmental safety assessments that addresses the uncertainties in the performance of your disposal system. Your strategy should be appropriate to the level of hazard and risks associated with your disposal system. Your strategy could include carrying out one or more of the following:

• probabilistic calculations in which input parameters are sampled from probability density functions
• deterministic calculations with fixed values of input parameters for a range of values within a probability density function
• calculations for a cautious or bounding value of a particular parameter
• calculations for different scenarios or cases, for example to address uncertainties in conceptual models or modelling uncertainty or where uncertainties are difficult to quantify

You should develop, describe and apply an appropriate strategy for uncertainty and risk management. You should, as appropriate, undertake activities to reduce uncertainties and risks. Such activities might for example include research, revised modelling, design changes, revised waste acceptance and management practices. You should document the options considered and the reasons for selecting the chosen approach.  

If you choose not to take steps to reduce a specific uncertainty, you should explain your reasoning.

Simplifications in environmental safety assessments are unavoidable. As part of the ESC, you need to show that any simplifications adopted either have an insignificant effect on the outcome of the assessment or are cautious.

3.2.8 Integration of Safety Arguments

Your ESC should synthesise all of your claims, arguments and evidence into a coherent whole. You should show how the structures, systems and components of your disposal system work together to provide environmental safety and meet the relevant requirements set out in this guidance.

Your integration of safety arguments could address various aspects such as the following:

• evidence that your organisation has appropriate leadership, management and culture for safety
• evidence of the development and use of a suitable management system by suitably qualified and experienced staff
• estimates of the impacts from exposure to ionising radiation from your disposal facility for comparison with the relevant quantitative criteria, including an explanation of how uncertainties have been addressed
• an explanation of how non-radiological impacts have been considered in your assessments, including comparison of releases with appropriate quantitative criteria
• evidence of compliance with relevant requirements for groundwater protection
• multiple lines of reasoning including evidence of appropriate facility design, optimisation, robustness, defence in depth
• results from monitoring and evidence of operational experience at relevant (e.g. similar) facilities
• discussion of complementary environmental safety indicators
• an acknowledgement of uncertainties and any limitations in your ESC, a description of the effects they might have, and description of a programme of work aimed at addressing and reducing these uncertainties and limitations as appropriate
• a discussion of any findings or information that are not in line with the claims, arguments and evidence you present in your ESC and of their significance and an explanation of why you still have confidence in your arguments
• how you will ensure that you will operate your disposal facility in accordance with appropriate limits, controls and conditions

3.2.9 Limits, Controls and Conditions

You should use your ESC to propose limits, controls and conditions to be applied to your disposal facility. Your proposed limits, controls and conditions should be consistent with your environmental safety assessments and take account of other relevant factors and should be documented in your ESC. We will review your ESC and proposed limits, controls and conditions and use the information as a basis for any permit we issue.

The limits, controls and conditions proposed in your ESC should ensure that any assumptions and arguments you rely on remain valid and, therefore, that your facility provides, or will provide, the requisite standard of environmental safety and protection. When you undertake periodic reviews and updates of your ESC you should, if necessary, also propose updated limits, controls and conditions consistent with your updated ESC.

Examples of such limits, controls and conditions may include, but are not limited to:

• maximum inventories of radioactive and non-radioactive constituents of waste to be accepted
• maximum activity concentration limits for radioactive constituents and concentration limits for non-radioactive hazardous substances
• waste packaging specifications, including the types, sizes and properties of waste containers and packages and details of waste conditioning and packaging processes
• requirements for characterisation and monitoring
• waste emplacement requirements
• construction quality assurance standards to be used in controlling construction

You should clearly identify all such proposed limits, controls and conditions along with suitable justifications and statements of how you would ensure that they would be complied with. How you have calculated or defined each proposed limit, control and condition should be explained clearly and in appropriate detail.

Limits, controls and conditions may be based on the claims, assumptions and results from your environmental assessments, and any other relevant part of the radioactive waste management system (for example, transport safety requirements).

3.3 Guidance About Modelling

You should apply the guidance in this section to all relevant mathematical models. This will include mathematical models related to design, optimisation, characterisation and monitoring, and environmental safety assessments.

3.3.1 Using Models in the Development of Your ESC

You should develop and use appropriate conceptual and mathematical models to understand and assess the environmental safety of your disposal system.

The conceptual models you use for your environmental safety assessments should be based on your disposal system description. As far as possible, conceptual and mathematical models should be consistent between different assessments. You should aim as far as possible to make your models realistic so that they represent your best estimate of the behaviour of your disposal system.

You should update your conceptual and mathematical models as your understanding of your disposal system changes.

The complexity and detail in your mathematical models should be proportionate to the hazards and risks presented by the waste you have disposed and propose to dispose of. Your mathematical models should also be appropriate to the complexity of your disposal system and the quality of the available data. You should not produce complex numerical models unless you understand and have enough data about your system to support the models.

It is often helpful to use a combination of deterministic and probabilistic mathematical models to address different types of uncertainty. You should use your models to undertake structured sensitivity and uncertainty analyses.

When presenting and interpreting mathematical model results, especially for the far future, you should recognise that they are not predictions. Rather, they show how your system may behave, given certain input parameters or ranges and assumptions. They are aids to help you (and us) understand your system and how different properties, events or design decisions may affect its behaviour. You should use mathematical model results for the far future to support judgements about environmental safety in conjunction with other lines of reasoning.

You should adopt a systematic approach to developing and using conceptual and mathematical models. You should clearly record and describe:

• the objectives of the modelling
• your considerations of alternative conceptual and mathematical models and your reasons for choosing the models you have
• the input data you used, the source of that data, why you chose that input data and how you have ensured it is in line with other conceptual and mathematical models
• any assumptions, simplifications or omissions you make in your models, which should be justified, including an evaluation of their significance
• the level of confidence you have in your models, and your reasons for this
• the sensitivity and uncertainty analyses that you have done
• the work you have done to improve the confidence you have in your models

You should explain why your conceptual and mathematical models are fit for purpose, how you have built confidence in the results of your models and the work you have done to improve your confidence. This may include:

• describing your management system and approach to quality assurance for your models
• describing the verification and validation steps you have undertaken
• describing your peer-review arrangements and the results of peer reviews of your modelling work
• comparing your mathematical model results to site-specific measurements
• comparing your mathematical model results to the results of other models
• using your models to model analogues of your disposal system (or part of it) and comparing your model results with measurements and observations
• describing the sensitivity and uncertainty analyses you have done
• applying your mathematical models to benchmark (e.g. international comparison project) problems

We encourage you to discuss your modelling objectives and approach with us.

You should regularly review your modelling objectives to see whether they still meet the needs of your ESC. You should review your conceptual and mathematical models and update them as needed to take account of new information or understanding.

To the extent possible, you should verify and validate your mathematical models. The effort you expend on model validation should be proportionate to the importance of the model to demonstrating the environmental safety of your disposal system. You should describe your approach to verification and validation and justify that you have sufficient confidence in your model results for the role they play in your ESC. You should establish that there are no significant errors in your models.

Full validation of a mathematical model is not possible. For example, it may not be practicable to collect the necessary experimental or monitoring data, or you may be modelling processes that will only occur far in the future and cannot be measured.

You should evaluate whether alternative conceptual models would significantly affect your environmental safety assessments and, if this is the case, assess the implications of these alternative conceptual models. The results from your assessments using alternative conceptual models should contribute to your overall understanding of uncertainty.

3.3.2 Deterministic and Probabilistic Approaches

It is often helpful to use a combination of deterministic and probabilistic mathematical models to address uncertainty. You may combine these approaches, such that a model may be deterministic for some parameters and probabilistic for others.

A deterministic mathematical model is one in which single values are used for all input parameters and a single value calculated for all results.

A probabilistic mathematical model is one in which probability density functions are specified for some or all input parameters. The probability density functions are used to capture uncertainty, for example, in the value that a certain parameter might have. Before the model is run, the probability density functions are sampled to select input parameter values for that model run. The model is run many times and the results for all runs combined to produce probability density functions of results.

For each run of a deterministic model, you will have to choose a specific set of parameters from the range of possible values. When choosing these, you should provide arguments and evidence supporting your choice. Where appropriate, you should complete several runs of the model with different parameter values to understand the range of possible outcomes.

When compiling data to use in probabilistic assessments, you will need to specify probability density functions. You should explain and justify the function, parameters and values chosen for the probability distribution.

When using probabilistic models, you should justify your selection of parameters, take due account of possible correlations between parameters, justify your approach to sampling probability distribution functions, and show that you have run enough simulations.

You should show that the spatial and temporal discretisation of your mathematical models is fit for purpose and such that they do not introduce modelling artefacts (e.g. inappropriate averaging or dilution).

If you undertake probabilistic assessments, you should present the probability density function of effective dose and risk to the representative person in your environmental safety case. When interpreting results from probabilistic models, you should consider whether certain model runs might have involved unrealistic combinations of parameter values.

3.3.3 Choosing Model Input Data

You should aim to use input data that is as realistic as possible. You should give preference to site-specific input data, where possible. Where you use conservative or site-generic input data, you should make this choice clear. Your choice of input parameter values should not lead to underestimation of impacts (e.g. dose or risk).

When doing uncertainty and sensitivity analysis or assessing ‘what-if’ scenarios, you should choose input data appropriate to the expected variation in the parameter or phenomenon you are investigating.

Your input data should be consistent between mathematical models unless there are good reasons otherwise.

You may ask experts to elicit input data for your mathematical models. If you do this, you should:

• explain the choice of experts and the method of elicitation used
• document their judgements and the reasoning behind them
• identify any biases and seek to eliminate or minimise them

3.3.4 Making Comparisons with Quantitative Standards

You should compare the results from your environmental safety assessments with the standards set out in part 2 of this guidance and the groundwater standards described in part 4. Which you use will depend on:

• the assessment you are doing
• whether the calculations are for scenarios during or after the period of regulation and what exposure situation is being assessed

Parts 1, 2 and 4 of the guidance explain when each should be used.

When comparing calculated doses or risks with the standards in this guidance, you should sum the dose or risk over all pathways to which the representative persons could be exposed. When calculating doses or risks from a number of cases or scenarios, you should consider whether the doses or risks should be aggregated. Such aggregation would be necessary, for example, if the representative persons could receive impacts from more than one exposure pathway.

The mathematical model results you compare with the standards should include those for the time of peak radiological impact.

When comparing the results of your environmental safety assessment calculations with our standards you should also present the assessed impacts as a function of time after waste disposal. You should explain whether your assessment results are for cautious calculations or not.

When comparing results from deterministic assessments with the relevant standards, you should explicitly include the range of uncertainty in the calculated result as determined by a sensitivity analysis (or importance analysis) in the comparison. When comparing results from probabilistic models with the relevant standards, you should present the full range of results obtained and identify and use appropriate statistical measures including the expectation value. You should provide explanations for results that are significant outliers and/or that exceed relevant regulatory criterion. You should demonstrate that there is at least a 95 percent level of statistical confidence that the mean value of risk complies with the relevant standards. Other statistical measures are also important factors in demonstrating the adequacy of the results of your assessment.

When you present calculated risks, you should also present the values of the assessed probability and conditional impacts separately.

If aggregating calculated risks for a number of cases or scenarios, you may assign each scenario or case a probability of occurrence, before summing and comparing them with the risk guidance level. Alternatively, you may compare the result of each case or scenario with the risk guidance level, assuming that the probability of occurrence is one. The approach that you follow must be documented in a fully traceable way.

Your mathematical models may give rise to calculated doses that are high or even above the point at which the effects of radiation are purely stochastic (around 100 mSv). If this occurs, you should investigate and explain whether these model results could be realistic and in what circumstances they might arise. You should present this information as part of your environmental safety case.

The standards apply regardless of whether you have conducted simplified, conservative assessments or more detailed assessments

3.4 Use of the ESC in Regulating Disposal Facilities

This section provides guidance on how your ESC is used in regulating a disposal facility over its full lifetime, including during the:

• environmental permit application process
• period of regulation
• environmental permit surrender process

You should start discussing the ESC with us before entering the permit application process (see requirement R1: Early engagement).

3.4.1 During the Environmental Permit Application Process

3.4.1.1 Obtaining an Environmental Permit

If you do not yet have an environmental permit but you intend to develop a disposal facility for radioactive waste you should obtain permit pre-application advice (including ESC pre-submission advice), in line with requirement R1: Early engagement, from SEPA at the start of planning and design of your radioactive waste disposal facility. You should agree an appropriate point with us to apply for an environmental permit. If you wish to seek a change to an existing permit you should also agree when this would be done with us.

You should:

• apply for an environmental permit for your radioactive waste disposal facility using the relevant application form and guidance on our website
• submit your ESC to support your environmental permit application

We will generally consult interested parties (for example, the planning authority, potential host community, other regulators) and other members of the public on new applications for radioactive substances activity permits for radioactive waste disposal facilities. We may also consult on applications for variations to existing permits. Therefore, you should engage with and involve interested parties and members of the public when developing your ESC. You should seek to secure and maintain the confidence of interested parties by presenting your ESC in a way that people will understand and involving them in its development. Different styles and levels of documentation may be needed to present your ESC to different audiences, but these should be consistent. The expectations of interested parties should be taken into account (see IAEA GSG-16, paras 5.27 - 5.30).

Our reviews of your ESC and of any associated permit application will depend on the stage you have reached in developing your disposal facility. We will focus on the most important hazards and risks. We will give greater scrutiny to higher hazard and higher risk proposals, such as the disposal of higher activity waste. Facilities and activities must be appropriate to the sensitivity of the site. We will give greater scrutiny to disposals in locations that may be sensitive, for example to climate change, and where people might come into proximity with radiation.

We will perform an initial phase of review to determine if your ESC and any associated permit application are complete and of sufficient quality to facilitate further, more detailed review. Our more detailed ESC reviews will consider the claims, arguments and evidence presented in your ESC against this guidance.

Our reviews will be independent, traceable, evidence-based and made against our published and applicable guidance by suitably qualified and experienced personnel.

During our reviews you may need to provide us with further information. We may conduct or commission assessment studies on key issues as part of our reviews.

The results of our reviews will be documented and used by us to provide you with advice and to determine your environmental permit application. We will document the rationale for our judgements on whether the arguments presented in your ESC are adequately supported and whether they are in accordance with our regulatory requirements, standards and other guidance.

Your ESC, including quantitative environmental safety assessments, will need to be detailed and comprehensive enough to support any claims that you make. Quantitative assessments are important in our consideration of your ESC, but regulatory acceptance of your case will involve judgement taking account of many factors. Therefore, both the qualitative arguments supported by the quantitative assessments provided in your ESC will be important in informing the judgements we make.

Depending on the comments received during the initial consultation stage on the environmental permit application, we may consult interested parties and members of the public on our proposed decision, as the determination process draws to a close.

If you are issued with an environmental permit for a radioactive waste disposal facility it will be on the basis of a particular version of your ESC. However, we expect you to keep your ESC under review (see requirement R3) and, therefore, your ESC will evolve over time. You must inform SEPA if, based on your developing ESC or otherwise, you want to make significant changes to the way you operate your disposal facility.

3.4.1.2 Environmental Permit Conditions for a Disposal Facility

SEPA specifies limits and conditions in environmental permits to ensure that people and the environment are protected to a standard consistent with legal requirements and this guidance.

As described above, you should propose your own limits, controls and conditions that reflect the environmental safety assessments in your ESC. We will use these proposals to develop the limits and conditions in the environmental permit for the waste disposal facility. We might wish to impose, for example, inventory limits or allowable activity concentrations for specified radionuclides.

These limits and conditions are not restricted to radiological aspects. They could be related to chemical and physical characteristics of the waste.

We may also place limits and conditions in the environmental permit relating to features and techniques which support significant claims and arguments in your ESC, as well as conditions relating to how the facility may be operated and closed (for example, quality assurance of elements of the construction, effluent management). These may include measures that you need to take before you begin particular operations or phases of work (for example, first waste emplacement, commencement of closure).

You may impose additional limits, controls and conditions (e.g. on waste producers) to those set out within your environmental permit, so long as they do not conflict with your environmental permit.

As a minimum, you should ensure your ESC contains the following information about your proposals, to enable SEPA to set environmental permit limits and conditions:

• maximum inventories of radioactive and non-radioactive constituents of waste which can be accepted
• maximum activity concentration of radioactive constituents and concentration limits for non-radioactive constituents of the waste
• other proposed WAC
• limits on any planned discharges from your disposal facility

Your ESC should also provide enough information to justify the method you propose to use for managing waste acceptance and disposal facility capacity. The IAEA has published technical information on how activity limits can be set using a ‘sum of fractions’, or the summation rule approach (IAEA-TECDOC-1380, 2003). Other approaches may be used. When using such approaches you should ensure that they are appropriate to your waste and that you take appropriate account of waste heterogeneity.

You should present a reasoned forward programme of work which could include, but not be limited to:

• further development and updating of your ESC
• reducing and managing uncertainties
• the further development, operation and closure of your disposal facility
• review and continuous improvement of your management system

We may decide to place requirements relating to these and other factors within your environmental permit.

3.4.2 During the Period of Regulation

3.4.2.1 Maintaining the ESC

You should maintain your ESC as a live document during the period of RSR. Updates to your ESC should reflect growing knowledge about the disposal system. They should also increasingly reflect the facility as-built, and wastes as disposed of, rather than as planned. The aim is to show that the disposal system as realised in practice is providing and will continue to provide proper protection to people and the environment.

You will need to ensure that there is legal clarity over the documents that comprise the ESC referred to in your environmental permit. Your ESC documents should be controlled documents, subject to formal change control. You should agree with SEPA any significant changes to your ESC in accordance with any requirements in your permit. You should engage with us as your ESC evolves so that it is always clear which version(s) of the ESC documents are used for regulatory purposes. You must develop, operate, close and control your disposal facility in accordance with your environmental permit and the relevant ESC documents.

You should revise your ESC in accordance with requirement R3: The environmental safety case. The updates to your ESC should consider:

• knowledge and experience gained during the construction, operation and closure of the facility
• understanding gained from site characterisation work and monitoring
• learning from regulators and operators of other relevant facilities, both nationally and in other countries
• learning from accidents and events during the operation of your and other relevant facilities nationally and in other countries
• developments in environmental safety assessment techniques and in scientific and technical understanding
• technological advances e.g. in the management of radioactive waste
• changes to national and international guidance and standards
• changes in policy and legislation
• results of research and development studies (for example, on specific techniques or optimisation)

You should discuss and agree with SEPA how and when updates to your ESC will be structured and made available to promote traceability and transparency. You should maintain a detailed audit trail of changes to the ESC.

You should use updates to your ESC in your ongoing decision-making. This decision-making may relate to environmental safety, waste management, the provision and allocation of resources, organisational change, environmental safety assessment, waste acceptance criteria or research, development and demonstration work.

You should submit your updated ESC to us in accordance with requirement R3: The environmental safety case, and your environmental permit.

We will periodically review your environmental permit, and this will be informed by our reviews of your updated ESC. If necessary, we will revise relevant limits and conditions specified in your permit.

Whether or how we update the environmental permit will depend on how the ESC has changed and the outcome of any public consultation or other relevant (e.g. judicial) process. The process of reviewing an environmental permit may be initiated in response to a permit variation application or may be initiated by us.

1. 1. 1. 1. Long-term preservation of the ESC

You are responsible throughout the period of RSR for preserving relevant versions of your ESC and all other relevant records in accordance with requirement R12: Preserving and accessing knowledge, information, and data. You should provide access to the records for interested parties where this is compatible with any security restrictions. You are also responsible for making suitable arrangements to promote the preservation of information about the disposal facility in the period after RSR.

3.4.2.2 Long-Term Preservation of the ESC

As described above, you should maintain a management system that includes details of your quality assurance processes, including for construction. It should ensure the quality of all environmental safety-related work throughout the planning, construction, operation, monitoring and closure of the disposal facility.

For construction, proposals should cover the design, specifications of materials selected, a stability assessment (if relevant) and the CQA plan. The construction of infrastructure must be in accordance with the approved construction proposals unless:

• any change to the approved construction proposals would have no impact on the performance of any element of the design
• a change has otherwise been agreed by us

For CQA, you should take account of our Landfill site management plan guidance  as far as it is relevant to your disposal facility:

The scope of your management system should include all aspects that your ESC relies on. This includes the quality of data that supports your ESC as well as ensuring that the facility is constructed, operated and closed in accordance with the claims made in your ESC.

3.4.2.3 Quality Assurance Checking During Construction, Operation and Closure

As described above, you should maintain a management system that includes details of your quality assurance processes, including for construction. It should ensure the quality of all environmental safety-related work throughout the planning, construction, operation, monitoring and closure of the disposal facility.

For construction, proposals should cover the design, specifications of materials selected, a stability assessment (if relevant) and the CQA plan. The construction of infrastructure must be in accordance with the approved construction proposals unless:

• any change to the approved construction proposals would have no impact on the performance of any element of the design
• a change has otherwise been agreed by us

For CQA, you should take account of our Landfill site management plan guidance  as far as it is relevant to your disposal facility:

The scope of your management system should include all aspects that your ESC relies on. This includes the quality of data that supports your ESC as well as ensuring that the facility is constructed, operated and closed in accordance with the claims made in your ESC.

3.4.2.4 Monitoring and Surveillance Programmes

Your ESC should be used to help specify programmes for monitoring and surveillance of your disposal facility and surrounding area. Your programmes should be developed and implemented to provide evidence that the disposal facility is performing as expected and that system components are fulfilling their environmental safety functions.

Monitoring activities should include establishing background radiation levels and measuring potential releases to environmental media (for example, soil, surface water, ground water and atmosphere) as well as monitoring other relevant parameters that might be used to reflect aspects of disposal system performance such as surface waters and groundwaters, land deformation, land use, engineered barrier characteristics, temperature etc. You should provide and justify a reasoned monitoring plan and programme and carry out monitoring systematically throughout the lifetime of your disposal facility. On the basis of monitoring data, you should review system performance and, if necessary, consider and implement corrective actions.

In particular you should consider monitoring the effects of construction and operation of your disposal facility on the groundwater levels and chemistry around your disposal facility and comparing these to the effects assessed in your ESC to help improve your understanding of your disposal system.

You should also consider monitoring the borders of your disposal system so that you can identify any changes that might be a consequence of the migration of contaminants onto your site from other sources

3.4.2.5 Controlling the Waste That Is Disposed Of

You should have arrangements in place to ensure that radioactive waste disposed of to your disposal facility is consistent with your ESC and complies with your permit conditions. This should be achieved by implementing a suitable waste acceptance system that includes measures to control disposals both for the facility as a whole (facility waste acceptance limits) and for individual waste consignments (waste acceptance criteria) (see requirement R11: Waste acceptance).

You may review and propose revisions to the WAC at any time, so long as you retain consistency with your permit and ESC. When you update your ESC, you should also review the WAC and propose any changes to them to maintain consistency with your ESC.

Your arrangements should include proportionate measures to confirm that waste consignments conform to the WAC (for example, inspection of consignments and paperwork, auditing of waste consignors). You should also have arrangements for dealing with waste consignments that do not conform to your WAC.

3.4.2.6 Applying for a Variation to the Environmental Permit

You should use the application form and guidance on our website if you wish to apply for a variation to your environmental permit. If necessary, you should submit a revised ESC in support of your application.

We will consult on your permit variation application and our proposed decision, if this is required by our policies and procedures for consultations.

We will consider any revised ESC you submit against the requirements of this guidance as part of determining your environmental permit variation application. We will scrutinise the claims, arguments and evidence in your revised ESC as part of our determination.

Your varied permit will make reference to your ESC - this will be to the version of the ESC submitted and assessed as part of your application.

3.4.3 During the Permit Surrender Application

3.4.3.1 Application for Surrender

You should engage with and take account of the views of interested parties when considering the surrender of your permit. You must discuss and agree with us the process to follow for applying to surrender your environmental permit.

Permit surrender cannot take place before we are satisfied that you have closed your disposal facility in accordance with your permit and your ESC. It may be the case that permit surrender cannot take place until after a further period of:

• control for the purposes of radiological protection (for example during which radioactive decay and other attenuation processes allow the radiological protection standards in this guidance to be met for your disposal facility)
• monitoring to demonstrate that the closed facility is evolving in line with your ESC

The period of control for the purposes of radiological protection must be agreed with us and may be many years, decades or even longer after closure, depending on the type of radioactive waste facility and the nature of waste disposed of within it. You should:

• use the application form and guidance provided by us to apply to surrender your environmental permit
• submit a final ESC in support of your permit surrender application - the final ESC should reflect the as-built and closed waste disposal facility, including an accurate record of the radioactive waste disposed

We will consult on your surrender application and our proposed decision if this is required by our policies and procedures for consultations.

We will consider your final ESC against the requirements of this guidance (and any amendments to it) as part of determining your surrender application. For nuclear sites, there may be aspects of the scope of your permit surrender application which we will assess against separate guidance (see Management of radioactive waste from decommissioning of nuclear site: Guidance on Requirements for Release from Radioactive Substances Regulation).

3.4.3.2 After the End of Regulation

Once your application for permit surrender has been granted, we will have satisfied ourselves that the closed waste disposal facility meets the requirements of this guidance and, therefore, people and the environment are sufficiently protected for the long-term. There will be no need for any on-going human action to maintain environmental safety.