Office for Nuclear Regulation

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NGL Dungeness B Neutron Scatter Plug Management Programme Level 4 Meeting held at Barnwood

Executive summary

Purpose of intervention

The purpose of this meeting was to update the Office for Nuclear Regulation (ONR) and the Environment Agency (EA) on EDF Energy Nuclear Generation Ltd (NGL):

  1. Work to use the Dungeness B (DNB) Main Active Waste Vault (MAWV) for emplacement of Neutron Scatter Plugs (NSPs).
  2. Progress on the DNB NSP Secondary Vault (NSPSV) project.

Interventions Carried Out by ONR

There are structural integrity issues with NSPs at DNB which have lead to NGL to decide not to reuse them in further fuel assembly rebuilds. This leads to a need to store activated NSPs unloaded from the cores in the NSP Recovery Facility (NSPRF) vault. However, there is limited capacity to store NSPs in the vault and given the level of arisings this will be exceeded in the near future.

The main nuclear safety and radioactive waste management issues in dealing with these NSPs is in the unloading operation from reactor, handling through the fuel route and their long term storage. Should the NSPRF vault reach its capacity, this would prevent the build of new reactor fuel using new NSPs due to there being no available storage space to store old NSPs.

There is a project underway to provide an additional NSP vault, the NSPSV. However, the current NSPRF capacity will be reached before the NSPSV can be made operational. To mitigate this threat NGL has proposed to move NSPs currently held in the NSPRF vault into the MAWV. This creates space within the NSPRF for storage of additional activated NSPs as they are unloaded from the reactor. ONR is monitoring all of these issues through a series of planned interventions.

NGL provided a summary of the background to NSP issues and their rational for the proposed management of historic NSPs through MAWV emplacement and the programme of work for the construction of the NSPSV. Main areas discussed were;

During the meeting, at the request of the EA, consideration was also given to the Best Available Technique (BAT) assessment that underpins the management options being proposed.

Explanation of Judgement if Safety System Not Judged to be Adequate

Not applicable.

Key Findings, Inspector's Opinions and Reasons for Judgements Made

No significant safety concerns were identified. The major risks identified were primarily commercial in nature. NGL have reviewed the NSPSV project to confirm that it will fully deliver its specified requirements.

The key question raised by the regulators focused upon the level of confidence NGL had in calculating volume capacity within the MAWV and number of NSPs it can hold, taking into account variables such as the packing factor and waste piling. NGL responded that they were confident that the MAWV could hold at least 400 NSPs, which is the estimated number that will be required to be transferred over the next five years. During this period they could implement the NSPSV to provide extra storage capacity if considered reasonably practicable to do so.

NGL were asked what level of confidence there was in the NSPSV being available in mid to late 2016 as stated in NGL documentation and what would be the implications if this date was not met. NGL's response was that they were on programme to complete all design substantiation and associated safety case work on the NSPSV. Annual video inspections of the MAWV would allow management of emplacement space within this vault and ensure construct the NSPSV came on line if the requirement for extra NSP storage capacity was identified.

Conclusion of Intervention

No safety issues are currently identified with the projects for emplacement of NSPs to the MAWV or design of a NSPSV. ONR will review the safety case and programme strategy presented in September following completion of the first NSP emplacement campaign to the MAWV.


NSPs are part of the fuel assemblies loaded into the cores. As fuel is burnt up they become activated.