Nuclear Restoration Services (NRS) Hunterston A site aqueous discharges variation application

We received an application from NRS Hunterston A site, on 28 February 2024 for a variation to permit EAS/P/1173609. NRS have requested the permit be varied to allow the following:

Radioactive aqueous discharges to no longer be concurrent with a flow of cooling water at seven cubic metres per second (7 m³/s).

Radioactive aqueous discharges to be independent of tide times.

Radioactive aqueous discharges to be made at the end of the cooling water culvert at grid reference NS 1773 5176, removing reference to grid reference NS 1809 5166 within the permit.

NRS have submitted a number of documents in support of their application. The documents include the application form as submitted by the applicant, along with technical and non-technical supporting documents. These documents, listed below, are available on request from SEPA or can be downloaded below. 

• HNA/2860/TC/REP/1578 Options Assessment for the Disposal of Aqueous Radioactive Waste
  
  After reviewing the submitted documents, we requested further information regarding short-term releases. The following documents were provided in response to that request:
• HNA/2812/ED/CS/1556 Check of Discharge to Sea Line Flow with New Pipework Extension Direct to Sea
• HPS/TSSD/SR878 Best Practicable Means (BPM) Report for Aqueous Discharges to Sea following Fuel Free Verification
• ENE – 0328A/R1 Dispersion of aqueous effluent from Hunterston power stations, Eden Nuclear and Environment.
• Dispersion of aqueous effluent from Hunterston power stations Annex- Additional Scenarios ENE-0328A/R2, dated 30/05/2024
• Addendum to BPM Report (HPS/TSSD/SR878) for aqueous discharges to sea following fuel free verification HPS/TSSD/ES/ENV/DR2735

SEPA shared the application  with both the Office for Nuclear Regulation and Food Standards Scotland in accordance with our Memoranda of Understanding with these organisations as well as with Scottish Ministers in accordance with our working arrangements. No comments were made.

Background to the consultation

The Hunterston A site uses the same discharge arrangements as Hunterston B which is operated by EDF. Consequently, due to the discontinuation of the main cooling water system on the EDF Hunterston B site (as outlined below), Hunterston A must vary the site EASR permit with regards to the aqueous discharges from the site.

During the generating and defueling phases of the power station, Hunterston B uses a significant volume of sea water as a tertiary cooling water system. The EASR permit for the management of radioactive substances specifies a large volume flowrate of water (7 m³/s) to make radioactive discharges to sea, which can only be achieved using the Main Cooling Water system.

Following removal of all nuclear fuel from the site, EDF states there will be no justification for the continued use of the Main Cooling Water system, which requires significant electrical power and maintenance resource to operate. Consequently, EDF has reviewed the credible options with a view to establishing the most appropriate, sustainable options for future radioactive effluent discharges.

A contractor was appointed to undertake dispersion modelling of the effluent discharges from both Hunterston A and Hunterston B, and there has also been a number of internal optioneering sessions. Following an option elimination process, it was established that there were three main options available, and these have been reviewed as part of the Best Practicable Means assessment. The work undertaken concluded that Hunterston A should continue to use the existing pipework from the site to the existing cooling water culvert. At this point a small bore pipe from the Hunterston A site will be threaded through the existing large cooling water culvert. It was found that this option represented the best value for money and the least environmental risk. This option requires a variation to the EASR permit for the management of radioactive substances due to the removal of nominal cooling water flowrates for discharges.

In addition, the dispersion modelling indicated that a tidal window provides little benefit to dilution and dispersion of the radioactive discharges in the Clyde Estuary at the existing discharge point. NRS has deemed that a tidal window constraint within the permit is therefore disproportionate to the risk and has requested its removal. The existing permit condition requires that radioactive aqueous discharges are only made during the interval of one hour after high tide and one hour before low tide.

The application does not seek to change the existing authorised radioactive aqueous discharge radionuclides or activities or the authorised location of the discharge point.

The Hunterston B site, operated by EDF uses the same discharge arrangements as Hunterston A. Consequently, EDF has applied to vary the Hunterston B EASR permit in the same manner. SEPA is carrying out a simultaneous consultation on the EDF Hunterston B EASR variation application.