Regulatory Standards & Requirements

In this part of our guidance, we set out the regulatory standards and requirements that apply to disposal facilities for solid radioactive waste.

2.1 Radiological Protection Standards

This section summarises the radiological human health protection standards referred to in this guidance. However, please note that other standards also apply for the protection of wildlife and groundwater that appear elsewhere in this guidance.

When applying these radiological protection standards, all disposals of radioactive waste made on a single permitted site will be considered as a single source. Your assessments of dose or risk from all disposals will be assessed together for the purpose of comparison with the appropriate regulatory standard.

For the purpose of dose assessment where there are multiple sources (two or more separately permitted facilities at a single location) guidance on the appropriate dose constraint to use is also provided below.

2.1.1 Standard 1: Dose Limits

The dose limits specified in legislation and UK policy 2024 for protection of individual members of the public from ionising radiation are:

• 1 millisievert (mSv) for doses that can be received in a year by any member of the public from all controlled and authorised sources of radiation
• 15 mSv in a year for exposures of the lens of the eye
• 50 mSv in a year for exposures to the skin (averaged over 1 square centimetre)

Meeting these limits is a legal requirement but, in this guidance, we require you to meet the more protective dose constraints and other standards (see below) which ensures these limits are complied with.

2.1.2 Standard 2: Dose Constraints during the Period of RSR

The dose constraints specified in legislation and UK policy 2024 for protection of a member of the public from any authorised source, or group of sources, of ionising radiation during the period of RSR are:

• 0.3 mSv per year from any single authorised site
• 0.5 mSv per year from the aggregated exposures from a number of separately authorised sources in the same location (e.g. neighbouring but separately authorised sites)

Normal operation of your disposal facility should not exceed the annual dose constraints in any year during the period of RSR. Compliance with the dose constraints means not exceeding them. You should also apply optimisation during this period to further reduce exposures of people to ionising radiation (see requirement R7: Optimisation).

You should compare your dose assessments with the 0.3 mSv per year dose constraint. The assessment of effective dose should take into account both direct radiation from the disposal facility and external and internal radiation from all liquid or gaseous discharges from the disposal facility. For existing disposal facilities, you should take into account any impacts from radionuclides migrating from your facility into the surrounding environment that contribute to doses received by the public. Where the disposal facility is permitted with other facilities under a single permit, the sum of the doses from all the facilities should be compared with the 0.3 mSv per year dose constraint.

If your disposal facility is one of a number of separately authorised sources of radiation at a single location, you also need to compare the sum of the doses with the 0.5 mSv per year dose constraint. The assessment of the total effective dose should take into account external and internal radiation from all discharges from your disposal facility, together with external and internal radiation from planned discharges from any other separately permitted sources and sites at the location.

2.1.3 Standard 3: Risk Constraint and Risk Guidance Level After the Period of RSR

UK Policy 2024 requires that for the period after permit surrender, the risks to the public of a fatal cancer or heritable defect must not exceed a risk constraint of 1 in 100,000 per year (or 10^-5 per year). Compliance with the risk constraint means not exceeding this level of risk.

Furthermore, operators should seek to achieve a risk guidance level of 1 in 1,000,000 per year (or 10^-6 per year), of a fatal cancer or heritable defect to a member of the public. The term ‘guidance level’ is used because it describes the standard we are seeking consistency with but not absolute adherence to. Compliance with the risk guidance level means consistency with this level of risk.

The risk guidance level has been set lower than the risk constraint to account for uncertainties inherent in exposure projections far into the future. By adopting this as our regulatory standard we ensure the risk constraint is complied with.

A representative person is an individual, usually hypothetical, receiving a dose that is representative of the more highly exposed individuals in the population (see ICRP Publication 101a ‘Assessing Dose of the Representative Person for the Purpose of the Radiation Protection of the Public’). When defining a representative person for applying the risk guidance level, you should not differentiate between members of the public and workers. This is because after the period of RSR no planned work involving radioactive substances will be being carried out and hence nobody will be classified as a worker with respect to radiological protection legislation.

The risk guidance level is the radiological assessment standard which applies to assessed risks from radioactive substances arising from the ‘expected evolution’ of your disposal system. Your assessment should therefore consider the impacts from radionuclides that are dispersed in the environment due to the gradual break down of barriers and the associated transport of radionuclides in groundwater or gas.

The risk guidance level is also the criterion against which variants of the expected evolution should be compared. You should use variants to explore the impact of events occurring that do not form part of the expected evolution, other uncertainties and sensitivities of your disposal system to provide a greater understanding of how your disposal facility might perform.

When comparing results from your assessments with the risk guidance level you should explain any biases that you include. While it is appropriate to make conservative assumptions in your estimation of risks, compounding conservatisms can make it difficult to get an understanding of the expected risks posed by your facility. As the risk guidance level is a cautiously low level of risk already, understanding your expected estimates of the risks and the uncertainties will provide an important input to assessing your environmental safety case.

You should ensure peak risks are clearly identified and included in your assessment. The timing of peak risks will vary depending on the radiological inventory, the disposal system and on the events and processes acting on it.

To calculate the radiological risk associated with a potential exposure situation you should multiply the estimated effective dose that could be received, by the estimated probability that someone would receive this dose and the estimated probability that death or heritable defect would occur as a consequence of the exposure (the risk coefficient). Assessed risks should be summed over all situations that could lead to exposure of the same person to radiation.

You should use a risk coefficient of 0.06 per sievert (Sv) to assess stochastic effects. This corresponds to recommendations set out in UKHSA advice (HPA, 2009 ‘Radiological protection objectives for the land-based disposal of solid radioactive wastes’).

The risk guidance level applies to situations where only stochastic effects of radiation exposure are being considered. That is, only if the estimated annual effective dose is less than 100 mSv and the estimated equivalent dose to each tissue is below the relevant threshold for deterministic effects (tissue reactions). If your calculations result in doses that exceed these deterministic thresholds your disposal concept may not be acceptable for the inventory proposed.

Your calculations of risk will be important in helping judge the environmental safety of your disposal facility. However, you will also need to include supporting qualitative claims, arguments and evidence in your ESC.

2.1.4 Standard 4: Dose Guidance Range After the Period of RSR for Near-Surface Disposal Facilities

For the period after permit surrender potential exposures must not exceed a dose guidance range of around 3 mSv per year (for exposures lasting more than one year) to 20 mSv (for exposures of one year or less). Compliance with the dose guidance range means not exceeding the applicable dose.

The dose guidance range should be used for the assessment and evaluation of specific scenarios in the period after the end of regulation that could involve direct contact with radioactive waste. In these scenarios the emphasis is on avoiding or mitigating the consequences of the potential exposures. The dose guidance range should be used for the assessment of:

• Inadvertent human intrusion into the radioactive waste itself after the period of RSR (see requirement R16)
• Certain scenarios resulting from natural disruptive processes and events after the period of RSR that uncover radioactive waste and could lead to direct encounter with the waste (see requirement R17).

For these scenarios the assessed effective dose to a representative person in the period after RSR should not exceed the range from around 3 millisieverts per year (3 mSv per year) for exposures lasting more than one year to 20 millisieverts (20 mSv) for exposures of one year or less, where there is no recurring exposure in subsequent years.

Disposal facilities should be located and designed so that the waste remains contained and isolated for a long enough period of time given the inventory that has been or will be disposed. A disposal facility should not allow the waste to be uncovered, for example by erosion, before the hazards posed by it have reduced sufficiently to comply with both this standard and the risk guidance level. We require that such scenarios are assessed for near-surface disposal facilities to ensure that the radiological consequences to people in the future are acceptable.

Similarly, while a disposal facility may include elements in the design to prevent inadvertent human intrusion, at least for a limited period of time, we require that such inadvertent human intrusion scenarios are assumed to occur for near-surface disposal facilities after the end of RSR. The dose consequences from these inadvertent human intrusion scenarios should be compared to this standard to ensure that people in the future are protected (see requirement R16).

If your facility cannot comply with the dose guidance range, this indicates that your proposed radioactive waste inventory is not suitable for your particular disposal concept or facility design, or is not suitable for near-surface disposal at all, and that you will need to explore alternative long-term management options.

2.2 Requirements

2.2.1 Requirement 1: Early Engagement

You should engage early with us if you intend to:

• develop a new facility for the disposal of solid radioactive waste
• make changes to an existing facility which may require a variation to your environmental permit
• make significant changes to your ESC

SEPA can provide you with advice prior to your permit application or ESC submission and we may charge for this service. Depending on the type of advice required, a formal contract may be needed.

How early engagement should start will depend on many factors including:

• type of facility and the stage of development it is at
• environmental setting
• availability of resources
• how mature plans are for the proposed facility or change
• how significant, complex or novel the proposed facility or change is

A structured and proportionate programme of engagement should be agreed with interested parties and periodically updated, starting from early in the development of the disposal concept and extending over as many years as is appropriate.

We cannot provide regulatory certainty that we will grant or vary your environmental permit until the permit determination process is completed. However, seeking pre-application advice will help you understand our regulatory requirements and expectations, and the process to be followed, before you make a formal application.

Early engagement also offers other benefits; it should help:

• us prepare for the permit application
• inform our contribution to other decision-making processes, for example, land use planning or nuclear site licensing
• enable us to participate in the operator’s or developer’s discussions with communities and other interested parties before any consultation on your application for an environmental permit
• inform the operator or developer of how we will engage with other regulators
• inform the operator’s or developer’s investment decision
• guide the development of innovative waste disposal concepts and how such concepts could be regulated
• reduce the uncertainty in the operator’s or developer’s programme, including time and cost.

2.2.2 Requirement 2: Management System and Environmental Safety Culture

You should develop and maintain an effective management system, including written arrangements which show how you will design, construct, operate and close your disposal facility. Your management system should control the development of your ESC, the development of your disposal facility and the disposal of radioactive waste to ensure compliance with the limits and conditions in your environmental permit (for example, the maximum disposal limits for the site).

Your management system should be consistent with international good practice (for example, ISO 14001, ISO 9001, IAEA GSR Part 2, IAEA GSG-16) and address important aspects, including:

• leadership, including policy; organisational structure; roles, responsibilities and accountabilities
• planning, including objectives; risk management; production and maintenance of your ESC
• support, including adequate resources; suitably qualified and experienced personnel; training and continuous learning; succession planning; communication; interactions with waste consignors; knowledge, information, data and records management; intelligent customer capability; supply chain management
• operation, including decision-making; control of work; change control; emergency response; waste acceptance at the disposal facility
• performance evaluation, including quality assurance; internal audits
• improvement, including corrective actions; reviews

You should:

• be able to demonstrate that your organisation is a competent operator (for example, technically and financially competent) and fully capable of assuring environmental safety throughout the period of RSR
• keep your management system ‘fit-for-purpose’ by regularly reviewing and updating your written arrangements
• adapt your management system as you progress through each stage in the lifetime of the disposal facility
• develop, foster and maintain a positive environmental safety culture, including appropriate individual and collective attitudes and behaviours to environmental safety, which is supported by your management system, and require your suppliers to do the same

Senior management should recognise that the attitude of individuals and the environmental safety culture within an organisation are influenced through leadership. To improve the environmental safety culture and help individuals to develop professionally, managers at all levels are required to demonstrate their commitment to environmental safety as a priority in resource allocation, business planning, documentation and in all waste management activities (see IAEA GSR Part 2 for examples). Your senior management should demonstrate a proactive and long-term approach to environmental safety issues in decision making on radioactive waste management (as recommended in IAEA GSG-16). For example, decision making should include, but not be limited to, asking questions such as:

• can discharges be prevented or reduced?
• has the ‘waste hierarchy’ been properly applied?
• does a proposed activity increase the risks of barrier failure or leaks – can the proposed activity be further optimised to avoid or reduce this?
• can the activity be undertaken with reduced environmental cost?

You should consult with us and follow any guidance on management systems and environmental safety culture, for example the ‘Guide to the standard conditions for radioactive substances activities’.

2.2.3 Requirement 3: Environmental Safety Case

An ESC is a set of claims about the environmental safety of a facility for the disposal of solid radioactive waste, together with the arguments and evidence that support those claims.

Your ESC should demonstrate that people and the environment will be adequately protected from the radiological and non-radiological hazards and risks associated with the disposal of waste during the full lifetime of the disposal facility, including the period after the site is released from RSR.

Your ESC should set out why you believe your disposal system will provide the required levels of isolation, containment and protection of people and the environment from the hazards and risks posed by the waste you intend to dispose of and is consistent with sustainable development. These arguments should be based both on qualitative and quantitative evidence.

Your ESC should include quantitative assessments to demonstrate compliance with the dose constraints during the period of RSR (see standard 2). Your ESC should demonstrate consistency with the risk guidance level (see standard 3) and show that the dose guidance range will not be exceeded after the period of RSR. Your ESC should also demonstrate that groundwater is protected (see requirement R14: Protecting groundwater). You must demonstrate all of the above and that you have met all of the other requirements in this guidance.

Uncertainties associated with quantitative assessments will increase for periods further into the future and, at some point, such assessments might no longer serve as a reasonable basis for decision-making. Your ESC needs to provide assurance, beyond quantitative assessments, that the environmental safety requirements (for example, on isolation, containment and disposal system design, construction, operation and closure) will be met. We will take account of a wide range of factors, including all the NS-GRA requirements, when we judge the acceptability of your ESC and proposals for waste disposal.

Your ESC does not have to be a single document (see IAEA SSG-23; IAEA SSG-1 Rev. 1 for guidance) and may consist of information in different forms (for example, paper documents, digital documents, photographs, audio, video, databases). You should list all the information that makes up the ESC and provide a clear explanation of how this information is structured and collectively forms the ESC.

Where the disposal facility is situated on a nuclear licensed site, the ESC for the disposal facility should form part of the site-wide environmental safety case (SWESC – see GRR for details) for the whole nuclear site. In cases where contamination of ground or groundwater arising from the radioactive substances activity extends beyond the boundary of the authorised premises, such areas should be considered in the scope of the SWESC. This ensures that all potential sources of exposure to people and impacts on the environment are considered.

You should:

• submit an ESC in support of an application for an environmental permit to dispose of solid radioactive waste in a disposal facility
• maintain the ESC as a live document during the period of RSR.
• review and, where necessary, revise the ESC:
  • periodically and at each major stage in the lifetime of the disposal facility or a significant change to it (e.g. new phase of operations, extension, closure)
  • whenever there are significant changes to how the facility is operated or the type of waste you intend to dispose of
  • to take account of new information (for example, operational experience; monitoring, changes in policy, legislation, standards or guidance, site understanding, developments in science and technology)

You should implement management arrangements for the production and maintenance of your ESC, including a change control process (see requirement R2: Management system and environmental safety culture).

You should submit a revised ESC to us:

• as part of a permit variation application (for example, due to plans for a significant change to the facility, how the facility is operated or the type of waste disposed of), unless the proposed variation is supported by the existing ESC
• following completion of a scheduled review and revision of your ESC, if required by your environmental permit
• following a substantial review of the ESC (for example, as a result of significant new information), if agreed with us
• prior to the closure of all or part of your facility
• as part of a permit surrender application

The ESC submitted prior to closure of part or all of your facility should show that the as-built facility with the disposed inventory meets the requirements of this guidance. Your ESC at this stage should consider any additional measures to further optimise your facility during closure. This includes your proposals for backfilling, capping, sealing access tunnels and shafts, for example.

Controls may need to remain in place for the purpose of assuring radiological protection following closure. These assurance measures may for example include monitoring or restrictions on access to or use of the site. These controls will need to continue within the period of RSR, until we determine and grant your application to surrender a permit. The ESC should describe these controls and provide evidence that they will be sufficient and practicable for protecting people and the environment, and that resources will be provided sufficient for the controls to endure and be effective for the period proposed.

You should propose an estimated duration of control for the purposes of radiological protection within your ESC. However, unless there were exceptional circumstances SEPA would not accept a proposal for a period of control for the purpose of radiological protection lasting longer than 300 years after closure of the facility. This is because of the major societal changes that may take place over such long periods of time.

When you apply to surrender your environmental permit, your ESC (and SWESC where relevant) should show that the risks presented by all radioactive waste remaining on site and any non-radioactive hazardous properties of the radioactive waste, including contamination that may have arisen before or during operations, are consistent with the relevant standards and any applicable surrender requirements.

See part 3 for further guidance on the scope and content of an ESC.

2.2.4 Requirement 4: Site Characterisation

You should carry out a programme of site characterisation to gather data about the natural and man-made features of the site and to understand how the site and surrounding area has evolved and may evolve in the future.

Your site characterisation programme should:

• adequately determine baseline conditions (also see requirement R5: Monitoring)
• inform development of conceptual and mathematical models of the site and its characteristics
• inform the environmental safety assessments included in your ESC
• inform the development and selection of disposal concepts and engineering design

These are just examples - your characterisation programme might have additional aims.

Your site characterisation programme should provide enough detail but should reflect the:

• radiological and non-radiological hazards and risks presented by the waste
• uncertainties in understanding and the conceptual and mathematical models of the site
• complexity of the environmental setting

Your site characterisation programme will need to record and describe information about the site and surrounding area, including, but not limited to, the:

• geology
• geotechnical properties of the geology
• geochemistry
• background radioactivity
• hydrogeology
• hydrology
• topography
• soil characteristics
• climate
• plant and animal distributions
• human behaviours, activities and settlement patterns, in the past as well as the present
• actual or potentially valuable or exploitable natural resources at and near the site

You should identify the potential for, and effects of, a changing climate and processes such as erosion, seismic events, uplift and ground subsidence and assess how these could affect your conceptual and mathematical models and the environmental safety assessments included in your ESC.

If you carry out any intrusive site investigation activities, you should minimise the disturbance of the geological formations as far as reasonably practicable. This is due to the potential for adverse effects on the natural features which you may later rely on to perform an environmental safety function. Boreholes, wells or other ground penetrations should be suitably decommissioned and sealed, with suitable records kept.

You should consider a phased or iterative approach to site characterisation to support the development of conceptual and mathematical models of your site and the environmental safety assessments included in your ESC, for example:

• early phases of site characterisation should focus on understanding the site and its wider setting to assess whether the site appears broadly suitable and how an ESC might be developed
• later, more detailed, phases of site characterisation should aim to refine the understanding of the site and its surroundings and provide the data for further development of your ESC
• further site characterisation should be undertaken as necessary over the lifetime of the disposal facility to maintain the conceptual and mathematical models and ESC

You should, as appropriate, develop conceptual and mathematical models of the site and its regional setting which cover the current state of the site and the processes affecting site evolution. The extent and level of detail of your models should reflect the complexity of the site and be proportionate to the hazard and risks posed by your disposal facility.

You should review and update your site characterisation programme periodically to take account of new information, advances in investigation or monitoring technologies and emerging priorities for data gathering to reduce uncertainties that are potentially significant to the environmental safety of your disposal system.

You should present each phase of site characterisation as part of a structured forward programme that demonstrates how continually acquiring information will help to develop your conceptual and mathematical models of your site, including its evolution, and support your ESC.

2.2.5 Requirement 5: Monitoring

You should develop, implement and maintain a proportionate programme to monitor the site and the disposal facility for changes caused by site investigation, construction, operation, closure, and evolution of the disposal system, including the impacts of climate change. Monitoring activities must be designed and carried out so that they will not compromise the environmental safety of your disposal system.

You should carry out an appropriate level of baseline monitoring starting before the site is significantly disturbed, for example, by site investigation or construction work. It should continue for long enough to acquire data that adequately represents the baseline condition (including seasonal or other natural variations) against which future changes at the site can be assessed. The same measurements may form part of your site characterisation programme (see requirement R4: Site characterisation).

Baseline monitoring should include:

• measurements of background radioactivity at the site, including natural radioactivity and any contamination from historic discharges, weapons testing and nuclear accidents
• relevant radiological and non-radiological parameters that may change as a result of constructing, operating and closing the facility

During the period of RSR, you should carry out monitoring to show that:

• you are complying with the limits and conditions of your environmental permit
• the disturbance caused by intrusive site investigation, construction, operation and closure activities is not compromising the integrity of the disposal facility
• your conceptual and mathematical models of the site remain fit for purpose
• the disposal system performance is consistent with the claims made in your ESC
• the disposal facility and wider environment are evolving as expected

Monitoring may also be carried out for other purposes, for example, to meet other legal obligations or comply with other regulators’ requirements.

You should regularly review your monitoring programme and update it as necessary.

You should clearly set out how you will assess the results of any monitoring, including the levels of specific parameters or identified changes that will trigger action. Where trigger levels are used, you should have management arrangements in place setting out the appropriate course of action if a trigger level is reached or exceeded.

You should recognise that the monitoring of the disposal facility during the period of RSR does not cease when waste emplacement stops. Your monitoring programme will need to continue until the disposal facility permit is surrendered. As the disposal facility’s lifetime stage changes, the aims and requirements of the monitoring may also change. The monitoring plans you develop should account for this evolution and should be updated accordingly during the facility lifetime.

Monitoring for public reassurance after release from RSR is not required, although this does not prevent such monitoring from being undertaken so long as it does not compromise the environmental safety of the disposal system. If you intend to carry out any reassurance monitoring after release from RSR, you should take care not to damage the barriers which perform an environmental safety function. The provision of environmental safety cannot rely on monitoring or other actions by future generations after the period of RSR.

Further guidance on monitoring may be found in:

• Environmental radiological monitoring in Scotland – Radiological Monitoring Technical Guidance Note 2
• Monitoring and Surveillance of Radioactive Waste Disposal Facilities – IAEA SSG-31

2.2.6 Requirement 6: Disposal System Design

You should design the disposal system (see Glossary) so that it is in accordance with this guidance and good practice nationally and internationally and provides the necessary environmental safety functions for the radioactive waste that you intend to dispose of. Your environmental safety strategy (covered further in part 3) should describe your high-level approach to the design of the disposal system. This should be proportionate to the hazard and risk posed by the radioactive waste in your inventory.

In developing the design of your disposal system, factors you take account of should include, but not be limited to:

• geographical and geological features, including the hydrogeology
• the potential future effects of climate change, for example, from rising sea levels
• the engineering feasibility of your design to be implemented

You should design your disposal system so that events and processes that could prevent or hamper closure of the facility as planned are avoided. Such events and processes might, for example, include flooding or a loss of waste containment before closure. Failure to close the facility as planned could have negative effects on long term protection of people and the environment.

You should demonstrate that the design of the disposal system is optimised. Your design should take account of the amount and type of radioactive and other waste to be disposed (see requirement R7: Optimisation).

Your processes for engineering design, assessment and validation should be fully integrated within your ESC. You should conduct, where appropriate, tests, trials and demonstrations of your engineering methods under relevant conditions. Confidence will need to be established in the ability for example to emplace waste and install engineered barriers to meet design specifications. Engineers and other personnel carrying out design work must be suitably qualified and experienced and understand how the design will inform the ESC.

There will be a number of structures, systems and components of the disposal system which contribute to environmental safety (see part 3). An important aspect of your design will be the multiple barriers that you propose to isolate (see requirement R8: Isolation) and contain (see requirement R9: Containment) the radioactive waste (see IAEA SSR-5 requirement 7).

The barriers can be physical (engineered or a natural part of the geosphere) or they may have other properties which help to slow down the migration of certain radionuclides, for example, chemical properties of the waste form. The barriers should be diverse, to minimise common failure modes impairing more than one of the barriers. They should also be complementary so that together they provide the required level of environmental safety. There is a distinction between these barriers and the environmental safety functions they provide. A given barrier may contribute to the environmental safety case in a number of ways, and these safety functions may be wholly or partly separate from one another. For example, the host geology may provide a physical barrier and may also have chemical properties that help to slow down the migration of certain radionuclides. There may be circumstances where one of these functions is impaired without the other necessarily being affected.

The barriers should be designed to perform their required environmental safety functions for the period of time that you claim in your ESC. You should present the arguments and assessments supporting these claims in your ESC.

In your ESC, you should include a description of:

• the barriers which form the disposal system design
• how long they are expected to perform
• how you plan to show that the barriers are performing as required, and will continue to for their design life, to the extent that this is possible
• how your arguments and assessments of your barrier performance take account of how the barriers will degrade over time
• the outcome of ‘what-if’ scenarios for the barriers (for example, loss of barrier) in your environmental safety assessments that support your multi-barrier design approach and any adjustments you have made to optimise the disposal system design
• how the disposal system design provides defence in depth so that environmental safety is not unduly dependent on any single component (for example, barrier)
• the feasibility of implementing the proposed disposal system design (including ease of construction)
• how the layout of the disposal system has been designed to allow for optimised disposal of the waste and to ensure that there are no significant risks related to nuclear criticality (where there are fissile materials present in the waste)

During the period of RSR, your disposal system design should aim to use passive features that do not depend on human actions or on any active engineered system, for example, requiring the operation of electrical circuits or mechanical moving parts, as far as reasonably practicable. This ‘passive safety’ will help reduce risks to people and the environment both during this period of RSR and afterwards. However, in some settings active engineered systems and/or human actions may be necessary in this period. For example, before closure active ventilation systems may be needed in disposal facilities accessed by a shaft or tunnel.

When designing your disposal system, you will need to:

• consider whether the controlled release of any radioactive effluents (liquids or gases) is necessary during the period of RSR
• describe what systems are required to manage such discharges, for example, ventilation or leachate management systems
• demonstrate that your systems represent best practicable means (BPM) (see requirement R7: Optimisation)

After the period of RSR, your disposal system should rely entirely on passive safety.

Proposals for changes to the design of your disposal facility (e.g. revised barriers, extensions) should be made under a formal change control process in accordance with requirement R2: Management system and environmental safety culture. Their implications for environmental safety should be assessed in accordance with the guidance provided in part 3.

2.2.7 Requirement 7: Optimisation of Radiological Protection of the Public

Radiological protection must be optimised during all stages of radioactive waste management, including during the design, construction, operation, closure and post-closure management of a disposal facility. This means making sure that people’s exposure to ionising radiation is kept as low as reasonably achievable (ALARA), taking into account environmental, economic and social factors.

For a radioactive waste disposal facility, optimisation should consider both normal exposures during the period of RSR and potential exposures after the period of RSR.

Optimisation is also a requirement of health and safety legislation that is enforced by HSE at non-nuclear sites or by ONR on nuclear licensed sites. This legislation requires that risks to the health and safety of workers and other persons from exposures to ionising radiation are reduced so far as is reasonably practicable. As such, you will need to consider the protection of workers as part of the process of optimisation for the radiological protection of the public.

Optimisation involves the iterative assessment of options to see what further radiological protection improvements can be made, for example, different design features or alternative operating techniques; unless the costs and other disbenefits are grossly disproportionate, you should adopt any identified improvement. The option identified by the optimisation process can be considered to be the BPM.

Optimisation does not mean minimising exposures regardless of the consequences of doing so. You should take into account wider environmental, economic and social factors when deciding what can reasonably be achieved. You should view optimisation as part of a wider appraisal of options, recognising that there will be competing claims for limited resources, and that no option is completely risk free. The result of optimisation should identify the option(s) resulting in an acceptably low level of exposure to the public, but not necessarily the option with the lowest possible exposure. Your process for optimisation of radiological protection should consider any reasonable measures that could reduce exposures of the public to ionising radiation.

The effort and resources you put into optimisation should be proportionate to the magnitude of the exposure or potential exposure / risk. There is no lower level of exposure below which optimisation is not required, but there are diminishing returns as the exposure is progressively driven lower.

As well as considering economic and social factors, you should also consider protection of the environment in achieving a balanced outcome from the optimisation process. This means taking account of a wide range of environmental factors, including the impact of radioactivity on wildlife (see requirement R13: Protecting wildlife) and the impact of the non-radiological hazards associated with radioactive waste (see requirement R15: Protecting against non-radiological hazards).

By considering what is ALARA and taking account of and balancing social, economic and environmental factors, you should choose options and make decisions that are sustainable. Optimisation requires evaluation of a wide range of diverse factors.

Optimisation is an ongoing process that should continue throughout the period of RSR and take into account the whole lifetime of the disposal facility. You should carry out optimisation:

• as part of your ESC development for the planning and design of a disposal facility
• periodically at each stage when you review your ESC
• to support the choices you need to make between sufficiently different alternatives

For an existing disposal facility, choices may be constrained by past decisions, but you should still ensure exposures are optimised, including whenever you are reviewing and updating your ESC, making a modification to the disposal facility, changing your operations, or changing the wastes that you accept for disposal. Where environmental safety requirements are not met, measures shall be put in place to upgrade the environmental safety of the facility, economic and social factors being taken into account.

The primary goal when disposing of solid radioactive waste is to protect people and the environment, including after the disposal facility has been closed and the period of RSR has ended. During the period of RSR, safety will be subject to active and ongoing regulatory scrutiny by a range of regulators. You should, therefore, focus optimisation on those aspects of the design and its implementation that make a difference to long-term environmental safety.

When comparing options, you should consider the:

• probability of individuals (representative persons) receiving exposure
• the timing and duration of the exposures and the geographical area affected
• the number of people exposed, and the magnitude of their individual doses

If you decide to calculate collective doses to help distinguish between different options, you should use these with caution because of the large uncertainties that can make any comparison of options meaningless (see ICRP 103 for guidance on the appropriate use of collective doses).

For a new disposal facility, optimisation begins by considering the inventory of the waste that is intended to be disposed of in the facility and the characteristics of the site, as this will influence the overall design concept. For example, whether it is constructed as an underground facility accessed by a tunnel or a disposal vault accessed from the surface. You should make initial strategic decisions based on the level of radiological hazard and other characteristics of the inventory. You may choose to select an overall design concept specific to a particular inventory, or one which provides greater flexibility for the type of waste it can receive. You should set out and fully justify these choices in your ESC. You should also describe the comparison of options you have undertaken to justify your claims regarding optimisation.

Features of the disposal facility where the comparison of options could be undertaken include:

• the depth, design and layout of the facility in relation to its surroundings
• each barrier of the multi-barrier system
• the waste form and package design
• the construction methods
• operations including waste handling and emplacement
• the materials and methods of backfilling around the waste packages
• the engineering measures used to seal and or cap the disposal facility
• the measures used to collect and discharge aqueous or gaseous emissions
• the measures applied to discourage access or reduce the probability of inadvertent human intrusion

The waste forms and package designs acceptable for disposal at your facility should be clearly justified in the ESC (see requirement R3: Environmental safety case) and reflected in the WAC (see requirement R11: Waste acceptance criteria). In cases where the site location or disposal concept is not yet determined, your management system should include a way of providing reassurance that the waste forms and package designs will be suitable for disposal in future.

As you develop the design of a disposal facility, you should document the process to create a written record of the decisions made and show that you have properly carried out optimisation (see requirement R12: Preserving and accessing knowledge, information, data and records). There should be consistency between the optimised design of the disposal facility and the ESC, where the claims, arguments and evidence for their environmental safety functions should be fully set out. There should be a clear link between the documentation that reports the outcome of the optimisation process and the ESC.

We have issued general guidance on optimisation and BPM (SEPA, 2019). While this guidance is mainly directed at facilities that generate radioactive waste from operational activities, it provides further information on the practical application of optimisation.

2.2.8 Requirement 8: Isolation

The aims of disposal are to isolate radioactive waste from the accessible environment (the subject of this requirement) and to contain the waste and the associated radioactive substances (see requirement R9: Containment) so that there are no unacceptable consequences.

You should ensure that your disposal system provides adequate isolation. This means that, for the necessary length of time, your disposal system physically separates your disposed radioactive waste from the accessible biosphere, i.e. those parts of the environment that people or wildlife are, or may be, in contact with.

As IAEA SSR-5 states, for near-surface disposal facilities, isolation has to be provided by the location and the design of the disposal facility and by operational and other controls for the purposes of radiological protection. For geological disposal of radioactive waste, isolation is provided primarily by the host geological formation as a consequence of the depth of disposal.

Your disposal system should 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. It should prevent, as far as is reasonably practicable:

• inadvertent human intrusion into the disposal facility
• natural disruptive processes exposing the waste during the period you are relying on isolation

Isolation may be provided by a combination of factors including, but not limited to:

• depth of the disposal or distance to the accessible environment
• properties of the overlying geology and the wider geological environment that might restrict the ability to drill boreholes or excavate material (for example, hardness of rock)
• a low potential for investigation or exploitation of natural resources (for example, minerals, thermal energy)
• poor accessibility of the terrain (for example, beneath the sea, below steep topography)
• remoteness of the location (for example, from human settlements or activities)
• design features of the facility, including the cap for a surface facility, that contribute to isolation (for example, facility layout, waste emplacement strategies, use of durable materials)
• management controls applied during the period of RSR that increase separation between the radioactive waste and people (for example, fencing or surveillance of the site)

Your ESC should include your arguments and evidence that support your case that your disposal system provides adequate isolation of the radioactive waste over a sufficient length of time. You should document the information related to inadvertent human intrusion and natural processes that you rely on in the environmental assessments you use to support your ESC. You should include, but not be limited to:

• a description of the features, events and processes, both surface and subsurface, relevant to your disposal system. You should take account of the potential effects of climate change on your disposal system over the lifetime of your disposal facility. The potential consequences of climate change include changes in rainfall intensity and patterns (which can affect watercourses and aquifers), changes in sea level, changes in rates of erosion including coastal erosion, glaciation and tectonic movements.
• a description of the ’expected evolution’ of your disposal system that incorporates your best understanding of the processes acting on your disposal system including the effects of climate change
• a justified list of the events and processes that could affect the degree of isolation provided by your disposal facility
• a description of and justification for inadvertent human intrusion scenarios that could lead to intrusion either directly into radioactive waste or other parts of the disposal facility. You should consider how the evolution of the disposal system may influence the nature of inadvertent human intrusion
• an estimate of the expected timeframe when events and processes might lead to radioactive waste being uncovered
• consideration of the uncertainties associated with all of the above

We refer to this description of the isolation provided by your disposal facility, including the supporting arguments and evidence included in your ESC, as your ‘isolation assessment’.

2.2.9 Requirement 9: Containment

The aims of disposal are to contain waste and the associated radioactive substances (the subject of this requirement) and to isolate them (see requirement R8: Isolation) from the accessible environment so that there are no unacceptable consequences.

Containment of radioactive substances should be provided by a combination of natural and engineered barriers and other environmental safety measures. These may include, but are not limited to, the:

• waste form
• waste packaging
• backfill materials
• physical structures which form part of the facility
• properties of the host geology and the wider geological environment

In accordance with the graded approach required by the International Safety Standards, the ability of your disposal system to provide containment of the waste should be commensurate with the hazard posed by the waste.

Disposal facilities do not need to provide complete containment of waste forever - this is neither practicable nor necessary because the hazard associated with waste generally declines with time. You should ensure that the radioactive substances are contained for long enough so that people and wildlife are not exposed to unacceptable levels of radioactivity. Containment should contribute significantly to ensuring that exposures of people are as low as reasonably achievable, taking into account environmental, social and economic factors.

In the case of heat generating waste, you should design the disposal facility to provide adequate containment of the waste and the radioactive substances at least for the period while heat is being producing at a rate that could otherwise adversely affect disposal facility operations and or closure, the radiological performance of the disposal system or pollute the environment. Waste with levels of radioactivity high enough to generate significant quantities of heat by radioactive decay are not suitable for near-surface disposal.

When considering the ability of a disposal facility to contain radioactive substances, you should assess the potential for the barriers to be degraded or eroded.

You should use both quantitative and qualitative arguments and evidence that support any claims made in your ESC about how the barriers and other environmental safety measures will contain the waste and limit the migration of heat and radionuclides.

You should demonstrate how the performance, durability and longevity of your disposal system’s barriers contribute to containment, and how you will make sure, using quality control and assurance systems, that the design specifications for engineered structures, systems and components will be fulfilled. You should also demonstrate how the barriers are compatible with each other and with the waste.

Where your disposal system’s ability to contain radionuclides relies significantly on the properties of the surrounding geology for containment, you will need to provide detailed evidence of the robustness of its performance in your ESC.

This requirement does not rule out the discharge of radioactive effluents (liquids or gases) from a disposal facility as a controlled release under an environmental permit during the period of RSR.

2.2.10 Requirement 10: Construction, operation and closure

You should construct, operate and close your disposal facility according to your environmental permit, the disposal system design considered in the approved ESC, approved construction proposals and the procedures described in your management system. You must ensure that:

• at the point of closure, the engineered barriers have been installed correctly and are intact such that there is confidence that they will perform their required environmental safety functions
• you preserve the environmental safety functions of any natural barriers your ESC relies on

Your approach to construction, operation and closure must provide environmental safety as well as fulfilling your other legal obligations, including operational safety, security and nuclear safeguards.

The methods you use to construct, operate and close your disposal facility should meet the design requirements and quality standards identified in your ESC and your management system. They should also be flexible enough to allow for variation in actual conditions when compared to design assumptions. Any changes that are made should be controlled by your management system.

You must not start construction of engineering or other infrastructure until we have confirmed that we are satisfied with your construction proposals and associated plans for construction quality assurance (CQA). You should submit a CQA validation report, in accordance with any requirements in your permit, as soon as practicable following the construction of the relevant infrastructure.

In accordance with your management system, you should inspect, test, monitor and maintain all engineered barriers that will perform an environmental safety function as claimed in your ESC. Records of inspections, tests and maintenance should be created and preserved in accordance with requirement R12: Preserving and accessing knowledge, information and data.

If you find that barriers are not installed or functioning as anticipated, you should assess the implications for the ESC. If necessary, you should take corrective actions to make sure that the claims made in your ESC can be fulfilled or modify your ESC accordingly to reflect the differences. The implications of the changes to the ESC will need to be communicated to us.

While your facility is being operated, and until permit surrender, the assessed effective dose from your disposal facility to a representative person should not exceed the relevant dose constraint (see standard 2).

If an accident releases radioactivity into or around the facility, you should assess the implications for your operations, your closure plan and for your ESC. Your management system should include arrangements for appropriate mitigation should such an accidental release of radioactivity occur.

You should have plans in place to close your disposal facility; this could be in a single step or in phases where appropriate. The closure plan should describe how closure will be optimised (see requirement R7: Optimisation) and how any uncertainties associated with implementation of the closure plan will be managed. You should periodically review, and where necessary update, the closure plan while the facility is being constructed and operated.

Your plans to close your disposal facility should be consistent with the assumptions in your ESC. Delay to the backfilling, sealing or capping of the disposal facility, or part of the disposal facility, after the last waste emplacement should be avoided. If for some reason you consider a delay to be desirable, this would need to be fully justified in your ESC. You will need to demonstrate that the integrity of the waste packages and other site infrastructure are adequate and that the long-term performance and hence environmental safety of your disposal facility will not be adversely impacted.

If you wish to make changes to the plans or schedule for construction, operation or closure that are assumed in your permit or ESC, you will need to update your ESC appropriately (see requirement R3: The environmental safety case and part 3 of this guidance).

In situations where construction, operation and closure activities overlap, you should plan and carry out your activities to ensure the safety of people and the environment.

2.2.11 Requirement 11: Waste acceptance

Waste acceptance at your disposal facility needs to be adequately controlled to ensure that people and the environment are protected from ionising radiation and other hazards posed by the waste. To achieve this, you should define waste package specifications and waste acceptance criteria and limits and other relevant considerations for the waste that can be accepted into your facility. Your ESC should clearly set out any assumptions, limits and constraints regarding the waste that can be accepted including activity limits for individual packages as well as the total inventory that can be disposed to the facility. SEPA may incorporate some of these limits and constraints in your environmental permit and may also include additional constraints.

You should use your ESC to develop and maintain waste acceptance criteria (WAC) that can be applied to individual consignments of waste intended for disposal at your waste disposal facility. While the WAC should ensure that waste consignments are consistent with your ESC, they also need to ensure compliance with environmental permit conditions. In practice the ESC and the permit should be aligned as the permit conditions will be informed by your ESC, however, there may be additional permit conditions that you will need to factor into your WAC.

You may include additional criteria in your WAC to ensure that waste can be managed in accordance with other legislative or regulatory requirements (for example, requirements relating to health and safety, transport of the waste and pre-disposal management). You should collate and apply the WAC required for environmental safety with any WAC required for other purposes.

You should review and, where necessary, revise the disposal facility WAC following any updates to your ESC. You should submit any proposed WAC to us when you:

• apply for an environmental permit for disposal of radioactive waste
• submit an ESC to us
• submit a revised version of your ESC to us (for example, in support of an application to vary your environmental permit)
• are required to at any other time or as agreed with us (for example, if you make a substantial change to the WAC)

Your disposal facility waste acceptance limits and package specific WAC should address any features of the waste, waste form (including any encapsulant) or waste package that could affect the performance of the disposal system. These features could include:

• radionuclide content, activity and distribution
• fissile content and distribution
• non-radioactive hazardous substances and pollutants
• heterogeneity of waste, including high activity particles and interesting or noticeable objects that could attract people and hence increase exposures
• susceptibility to microbial action
• chemical stability
• thermal stability
• mechanical stability
• structural integrity
• potential for gas generation
• liquid content in the waste form
• potential for creating voids within the waste mass, resulting in, for example, uneven settlement, engineering stability issues or altered leachate or gas pathways
• potential for leachability

Your disposal facility waste acceptance limits and WAC should specify the radionuclides (or groups of radionuclides) and the maximum concentration and total activity of each that the facility can accept to ensure consistency with your ESC.

The IAEA has provided guidance on how activity limits and activity concentration limits can be set for near-surface disposal facilities, including the option of using the sum of fractions (the summation rule) approach (explained further in IAEA -TECDOC-1380, 2003). The IAEA approach or other approaches may be used.

Your disposal facility waste acceptance limits and package specific WAC should include requirements that make sure that all waste accepted for disposal is passively safe.

Your disposal facility waste acceptance limits and package specific WAC should include, where necessary, parameters relating to the evolution (e.g. degradation) of the waste form and the waste package under the conditions expected in the disposal facility, identified as a result of studies such as literature reviews, modelling or testing. This is to make sure that the waste form and waste package perform adequately during and after the period of RSR.

You should provide guidance to waste consignors on the application of your package specific WAC, for example, on specifications for the acceptable waste containers, levels of heterogeneity in the waste and acceptable unpackaged items that may be disposed of directly to the facility.

You should have controls in place to ensure that the disposal facility waste limits set out in your environmental permit are not exceeded and there is compliance with any other conditions relating to waste packages received by your facility. These should include arrangements to ensure that waste producers and waste consignors manage waste, so that when you receive it at your disposal facility, you can be confident it meets your package specific WAC. These controls should at least cover the following:

• interaction with the waste producers prior to receiving the waste, including providing advice and training as appropriate
• quality assurance of waste consignment information
• monitoring of waste packages
• audits of waste producer facilities
• ensuring that the waste has undergone a BPM assessment and adheres to the waste management hierarchy principles
• ensuring total waste acceptance activity limits for the facility are not exceeded
• arrangements to deal with any non-conforming waste consignments

Your management system (see requirement R2: Management system and environmental safety culture) should ensure that these matters are suitably controlled during the lifetime of your disposal facility.

We may specify environmental permit conditions for situations where:

• a waste consignment does not fully meet the WAC and
• you think that disposing of such waste within the facility would not breach any of the ESC constraints

These conditions may require you to submit a demonstration of environmental safety for the disposal to us, and to obtain formal approval before the waste can be received for disposal.

2.2.12 Requirement 12: Preserving and Accessing Knowledge, Information, and Data

You should set up and maintain during the period of RSR a comprehensive system for preserving and accessing knowledge, information and data about the radioactive waste and the disposal system. IAEA and NEA have issued relevant publications (for example, IAEA (2022) General Safety Guide GSG-16, "Leadership, Management and Culture for Safety in Radioactive Waste Management ", NEA (2019) “Preservation of Records, Knowledge and Memory (RK&M) Across Generations”).

Your system for preserving and accessing knowledge, information and data should include all relevant aspects that affect your ESC and compliance with your environmental permit.

Your arrangements should recognise and be appropriate for the following phases of the facility’s lifetime:

• site characterisation including determination of the environmental baseline
• design, construction and operation of the facility up to its closure
• from closure of the facility to an application to surrender the permit
• long-term archiving of records just prior to permit surrender

Your arrangements should transfer appropriate information on the disposal system and its environmental safety to an appropriate organisation (e.g. national government or archive) for preservation in the longer term after permit surrender.

Relevant knowledge, information and data could include, but is not limited to:

• site characterisation data (for example, geology, hydrogeology, geochemistry and other properties), monitoring data including details of baseline conditions and any interpretation of the data
• a description of the facility, its geometry and location
• sufficient versions of the ESC including the environmental safety assessments
• optimisation studies / BPM cases
• facility design documentation, as-built and any subsequent modifications
• waste inventory and waste package records, including where and when waste is emplaced in the facility
• details of facility closure
• measures to prevent or reduce the probability of inadvertent human intrusion

You should:

• not rely on knowledge, information or data held by individuals or other organisations (except those organisations whose archiving has achieved archive service accreditation status)
• as far as reasonably practicable, capture all required knowledge, information and data within a set of records
• produce and organise your records in a way that technical specialists who do not have site-specific knowledge can access and understand
• produce and organise summary information in a form that non-specialists can access and understand so they know if and when to involve technical specialists
• preserve the records in a way in which they are kept safe so they can be managed, accessed and understood over the long-term, taking account of relevant standards, guidance and codes of practice
• ensure that these records are protected from damage and loss (for example, storage of multiple copies at different locations, in different forms or media types)

You should set up retention arrangements for your records that specify how you will decide when they are no longer required (for example, superseded or no longer relevant). These should align with any permit requirements. After the facility is closed, but while it is still under RSR, your retention arrangements may specify a condensed set of relevant documentation which should be retained.

Just before permit surrender, you should transfer relevant records to a suitable organisation for long-term safe-keeping and management. For example, The National Archives or a facility which has achieved archive service accreditation status such as the Nuclear and Caithness Archives (Nucleus). These records should provide enough information so that future generations can have a fundamental understanding of your disposal system, especially its location and contents. We expect these records at least to include:

• a description of the closed facility, its geometry and location
• site characterisation (for example, geology and its properties)
• waste inventory and waste package records, including where and when waste is emplaced in the facility
• the final ESC for the as-built facility at the time of permit surrender
• monitoring results, including those during the closed phase of the facility

2.2.13 Requirement 13: Protecting Wildlife

You should protect wildlife from the harmful effects of ionising radiation resulting from the release of radionuclides from your disposal system. In this guidance “wildlife” means populations of wild animals and plants which depend upon designated habitats.

Your assessments should consider releases that could take place in accordance with your expected evolution and variants of it and scenarios that involve natural disruptive processes. There are specific requirements to protect habitat sites and species which have been designated for protection in conservation legislation. There are also international obligations to protect the environment, by considering wild animals and plants.

The IAEA (IAEA GSG-10) and the ICRP (ICRP-108, ICRP-124) have recommended the use of Derived Consideration Reference Levels (DCRL) for this purpose. Several research studies have also proposed dose rate criteria and assessment approaches (Copplestone et al., 2001; Andersson et al., 2008; Brown et al., 2016). These approaches use reference animals and plants as the basis for relating exposure to dose rate, and dose rate to radiation effects, for different types of animals and plants.

Based on these recommendations, we do not expect wildlife populations or the integrity of their habitats to be adversely affected if the total dose rate from all permitted discharges of radioactive substances is about 1 milligray (mGy) per day (40 microgray per hour (μGy/h)) or lower. You may use the current ICRP or IAEA DCRLs for specific reference animals and plants as alternative dose rate guidance levels.

You do not need to carry out more detailed assessments if, on the basis of a simple cautious assessment, the dose rates to wildlife from permitted discharges from your disposal facility are 0.25 mGy/day (10 µGy/h) or lower. More detailed assessments would consider the impact of combined permitted discharges and use more realistic assessment assumptions.

To demonstrate that wildlife is sufficiently protected during the period of RSR, you should assess the exposures of representative animals and plants that depend on habitats which may be affected by releases of radionuclides from your disposal facility. These representative animals and plants may be the same as reference animals and plants. You should make reasonable assumptions about potential future designated habitat sites and species for the period of RSR, based on the best information available at the time of the assessment.

You should also provide an assessment of the potential impact on wildlife from the disposal facility for the period after RSR (though you are not required to compare this with the standards above). You should take a proportionate approach to this assessment. You should consider how the disposal facility will evolve in the period after RSR and how wildlife may be affected. This includes the expected evolution of the disposal facility, variants of the expected evolution and scenarios that involve natural disruptive processes. As the location and status of designated protected habitat sites and species will be unknown after the period of RSR, you should make reasonable assumptions about potential wildlife receptors based on the best information available at the time of your evaluation.

You should demonstrate that your facility is suitably isolated, and waste contained, so that intrusion by animals and plants does not lead to a significant risk.

Your assessment of the impacts on wildlife is an integral part of your ESC. As such, your wildlife assessments should be considered as a factor in the optimisation of the design options for the facility.

We do not expect you to assess the impact of inadvertent human intrusion scenarios on wildlife.

2.2.14 Requirement 14: Protecting Groundwater

You should ensure that your radioactive waste disposal facility does not cause pollution of groundwater at any stage during your site investigations, facility construction, operation, closure, and long-term evolution after the period of RSR.

Any activity causing or liable to cause direct or indirect discharge of any hazardous substances or pollutants to groundwater is a controlled activity under the Water Environment (Controlled Activities) (Scotland) Regulations 2011 (CAR 2011). The development, operation and closure of a radioactive waste disposal facility is a controlled activity under these regulations as well as a radioactive substances activity under EASR.

Part 4 of this guidance explains what you must do to meet the above requirements.

2.2.15 Requirement 15: Protecting Against Non-Radiological Hazards

Some radioactive waste may be potentially harmful to people and the environment because of its non-radioactive properties. A wide range of substances such as asbestos, lead and methane may present non-radiological hazards. These may have been present in the waste package when it was initially disposed of, or may result from subsequent physical, chemical or biological changes following disposal. Properties such as heat generation, acidity or alkalinity may also be considered non-radiological hazards in some circumstances.

You should assess the impact on people and the environment of the non-radiological hazardous properties of the radioactive waste. Additional guidance about how you assess these hazards for groundwater is included in Part 4.

You should demonstrate that the disposal system will provide a level of protection against the non-radiological hazards in radioactive waste that is consistent with that which would be achieved by applying national standards for the disposal of non-radioactive waste.

For some radioactive waste, the non-radiological hazards may be greater or last longer than the radiological hazards. You should take an approach that is proportionate to all of the hazards presented by the waste.

Your ESC should:

• include claims, arguments and evidence that address any non-radiological hazards associated with the radioactive waste
• use methods and approaches appropriate to the nature and magnitude of these hazards and the risks posed

You should set WAC for relevant non-radioactive substances and properties which are consistent with the assumptions made in your ESC (see requirement R11: Waste acceptance).

You should include non-radiological hazards in your decision-making when optimising for radiological risks (see requirement R7: Optimisation).

 

2.2.16 Requirement 16: Protecting Against Inadvertent Human Intrusion into Near-Surface Disposal Facilities After the Period of RSR

Inadvertent human intrusion could occur after a disposal facility has been released from regulation and could include intrusion into:

• the waste in the disposal facility
• engineered barriers that are part of the disposal facility
• where applicable, any natural geological barriers that are part of the disposal facility

You should assess the range of inadvertent human intrusion scenarios that you have identified in your isolation assessment. Your isolation assessment should have described and justified those scenarios relevant to your disposal system. Your isolation assessment should have taken account of the evolution of the disposal system and how this might change the plausible inadvertent human intrusion scenarios.

The inadvertent human intrusion scenarios that your isolation assessment identified should have been based on present or past examples of human actions that might take place in your disposal facility setting. Your scenarios should also be based on known technology that is or has been used around the world.

You should take account of the inventory that has been or is proposed for disposal in your facility when evaluating your scenarios. For example, you should consider how interesting or noticeable objects within the waste could influence human behaviours (specifically by attracting people, and hence increasing exposures) after the inadvertent human intrusion occurs.

For your inadvertent human intrusion scenarios you should evaluate the potential radiation exposures for the people who are intruding into the waste and for people who might visit, occupy or live close to the site afterwards. You should assess the potential effective doses that would be incurred by an intruder and a person or persons representative of the more highly exposed individuals in the local population that might be affected by contamination following and inadvertent human intrusion event. You should compare your results with the dose guidance range (see standard 4).

You should use the results from the above assessments to develop or update your WAC (see requirement R11: Waste acceptance criteria) as necessary. You may need to set WAC for specific constituents of the waste that could have a high activity concentration in order to restrict the doses that could be received through scenarios involving direct intrusion into the waste or bringing waste to the surface.

In addition to your evaluation of the impacts on intruders on the local population at or shortly after the intrusion event, you should assess how such intrusion events could impact the long term performance of your disposal facility and protection of the public and the environment more widely. You should treat these assessments as variants of the expected evolution of your disposal facility and compare your results with the risk guidance level (see standard 3).

As well as comparing the results of your assessment to the numerical standards and setting WAC as described above, you should identify measures to reduce the probability and consequences of inadvertent human intrusion when optimising the design of your disposal facility (see requirement R7: Optimisation). Where reasonably practicable, you should implement any measures that you identify, unless the measures could themselves compromise the safety of the disposal system.

To further reduce the probability of inadvertent human intrusion, you should ensure arrangements are in place for the long-term safe-keeping and management of records about the disposal facility (see requirement R12: Preserving knowledge, information, data and records). You should also consider if it would be appropriate to make use of warning signs or markers, recognising that markers may be of limited effectiveness and also have undesirable effects.

This requirement does not require you to assess the risks from non-radiological hazards of the radioactive waste for your inadvertent human intrusion scenarios but you must address requirement R15: Protecting against non-radiological hazards.

You do not need to consider planned intrusion scenarios. This is because we take the view that a society that preserves full knowledge of the disposal facility is capable of exercising proper control over any planned intrusions into the disposal system.

In the region beyond your disposal facility, human actions such as drilling drinking water wells are not considered to be inadvertent human intrusion. Where appropriate, you should undertake assessments of such scenarios and compare your results with the risk guidance level (see standard 3).

 

2.2.17 Requirement 17: Protecting Against Natural Disruptive Processes Acting on Near-Surface Disposal Facilities After the Period of RSR

All near-surface disposal facilities will be subject to events and processes that degrade the natural and engineered barriers that isolate and contain the radioactive waste. These processes include continuous processes, such as weathering (including biological processes), and riverine and coastal erosion, as well as discrete events, such as flooding or seismicity.

The expected evolution of your disposal facility that you documented in your isolation assessment should have set out how you expect events and processes to affect your disposal facility over its lifetime. This assessment should also include assumptions on climate change based on discussions with the relevant regulators.

Natural processes that affect your near-surface disposal facility will eventually lead to its disruption, recognising that this may take a very long time for more isolated near-surface disposal facilities. Your ESC needs to make the case that your disposal facility will be isolated for long enough given the inventory that is to be disposed. We characterise the disruption of a near-surface disposal facility in 2 main ways:

• the uncovering of the radioactive waste at the ground surface as part of the expected evolution of the disposal facility
• damage to the barriers of your disposal facility beneath the ground surface such that they no longer perform as assumed in your expected evolution

The results of your assessment should be used to demonstrate consistency with the relevant dose and risk guidance levels and inform the optimisation of your disposal facility (see requirement R7: Optimisation). Where applicable and reasonably practicable, you should implement measures that could enhance the robustness of your disposal facility.

When evaluating and presenting potential exposures for the period after your disposal facility has been disrupted, any quantitative assessment should be supported by appropriate qualitative arguments that together make a reasoned case that potential exposures have been optimised. For long-term environmental safety assessments, reliance on qualitative evidence will increase as the assessment timescale increases. Where the assessment timescales are very long, you should use multiple arguments (for example, including natural analogues) to build confidence in your ESC.

1. 1. 1. 1. Uncovering of radioactive waste as part of the expected evolution

Your isolation assessment (see requirement R8: Isolation) should have identified the events and processes and expected timeframe when radioactive waste will eventually be uncovered at the surface. Your environmental safety case needs to demonstrate that the periods of containment and isolation are long enough, given the physical form and radioactivity of the radioactive waste inventory, to ensure that the radiological exposures to people that might arise at that time and thereafter will be sufficiently low. You should be able to provide confidence that at and after this time, levels of residual radioactivity should be very low, and the physical form of the waste will have degraded to be relatively homogeneous and unrecognisable such that it would not be interesting, noticeable or attract attention.

Your isolation assessment should have estimated when your disposal facility might be disrupted and should not have placed any reliance on the ongoing maintenance after the period of RSR, for example, of engineered structures such as sea or flood defences, or drainage systems.

You should use a proportionate approach to assess the potential exposures to ionising radiation at and after the estimated time your disposal facility is disrupted and the waste is uncovered at the surface. For cases where your disposal facility is expected to provide isolation for a very long period compared to how long your radioactive waste inventory remains hazardous, a simple argument supported by appropriate evidence may be sufficient.

To build confidence that waste will be isolated for long enough, you should consider other variant and what-if scenarios, for example:

• variant scenarios, for example, the occurrence of higher-than-expected erosion rates, possible due to uncertainty in climate change
• what if scenarios, for example, low probability extreme events that uncover the waste

When developing your post-disruption exposure scenarios for situations where radioactive waste is uncovered, you should take into account how exposure pathways for the relevant representative persons might be affected by the:

• form and distribution of the waste
• distribution of radioactivity within the waste, including the potential for high activity particles
• potential for interesting or noticeable objects that could affect the behaviour of people in the locality (specifically by attracting people and hence increasing exposures)

You should assess these potential exposures against the risk guidance level and the dose guidance range.

We will consider your assessment results and judge the acceptability of your ESC against the full range of NS-GRA requirements, not just the numerical standards.

1. 1. 1. 2. Disruption of barriers below the surface

Where appropriate, you should assess the effect on potential exposures that might arise due to subsurface natural events that you have not included in the expected evolution of your disposal facility. The nature, magnitude and probability of the subsurface natural events assessed should be consistent with your isolation assessment. You should consider how such events might disrupt the engineered or natural barriers your ESC relies on and evaluate the impact on the performance of your disposal system. These impacts should be addressed as either variants of your expected evolution or as ‘what-if’ scenarios.

You should justify any scenarios that you consider to be variants of your expected evolution and compare your result from any numerical assessments with the risk guidance level (see standard 3). For scenarios based on highly unlikely events, you should consider these to be ‘what-if’ scenarios to provide insight into the optimisation (see requirement R7: Optimisation) of your facility design to contain radionuclides (see requirement R9: Containment).

2.2.18 Requirement 18: Criticality Risk During and After the Period of RSR for Near-Surface Disposal Facilities

You should demonstrate that a local accumulation of fissile material, such as to produce a neutron chain reaction, will not occur. You should present arguments and evidence in the criticality assessment within your ESC to support your claim.

In your criticality assessment, you should consider controls implemented at the waste packaging stage and controls on the emplacement of waste in the facility.

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 the disposal facility. These should include any processes that might remobilise and concentrate fissile material and/or other material that could influence neutron multiplication. For example, mobilisation of neutron poisons out of waste containing fissile material might influence neutron multiplication within the system.

Your criticality assessment should be proportionate to the concentration and total inventory of fissile material disposed. For a disposal facility with a low concentration and total inventory of fissile material, a simple analysis may be sufficient to show that a criticality will not occur.