Office for Nuclear Regulation

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Dungeness B planned intervention

Executive summary

Purpose of intervention

This was a planned inspection at EDF Energy Nuclear Generation (NGL) Dungeness B (DNB) power station, undertaken as part of the planned intervention strategy for the Civil Nuclear Reactor Programme (CNRP) of the Office for Nuclear Regulation (ONR).

The intervention included a system based inspection of the ponds and flasks systems to demonstrate compliance with the safety case for these systems.  This inspection was performed by the ONR nominated site inspector with technical support provided by a mechanical engineering specialist and a civil engineering specialist.

Interventions Carried Out by ONR

The key interventions during the ponds and flasks system based inspection were for licence compliance covering the following licence conditions (LC):

The intervention for the remainder of the inspection was for licence compliance covering the following licence condition:

Explanation of Judgement if Safety System Not Judged to be Adequate

From the inspections against licence conditions and the plant condition, the systems fulfilled the majority of requirements of the safety case.  Seven actions have been placed where we judged that there was a shortfall against the requirements.  For the majority of these the shortfall was not sufficient for us to judge that the systems do not adequately meet the requirements of the safety case.  The exception to this was the crane brakes.

The crane brakes were identified as a safety mechanism and hence their operation was fundamental to the safety of the cranes.  However, NGL was unable to provide evidence of brake testing during the inspection.  Hence we concluded that the brakes did not fulfil the requirements of the safety case and that this alone was sufficient to reach the conclusion that the systems were not adequate.  NGL embargoed all crane operations in the ponds as a result.  Whilst this judgement that the systems were not adequate remains, based upon the findings from the inspection, the licensee has subsequently provided evidence and removed the embargo.  We were satisfied with the evidence provided and as such accepted NGL’s decision to lift the embargo.

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

For LC 10, training records were inspected for a range of staff involved in operations and maintenance associated with the ponds and flasks.  These were found to be adequate and hence an IIS rating of 3 has been allocated.

For LC 23, a sample of the records for compliance with the site’s technical specifications over the previous two months was inspected.  This demonstrated that the site had been compliant and hence this has been allocated an IIS rating of 3.

For LC 24, the adequacy of operations in the ponds was inspected by reviewing the instructions and witnessing walkthrough of a particular operation.  The overall control of operations within the ponds through the application of a quality plan was acceptable, but there were issues with the instruction for the specific operation that was witnessed.  Two actions were placed on the site to improve the particular instruction and to review all operating instructions.  The overall conclusion was that compliance with LC 24 was below standard and hence this has been allocated an IIS rating of 4.

For LC 27, the pond coolant pumps and crane brakes were found to be safety mechanisms.  Whilst the coolant pumps were found to be available, the site was unable to demonstrate that the crane brakes were available during the inspection, which led to an embargo on crane operations.  Whilst the site did demonstrate brake availability after the inspection had been completed, we concluded during the inspection, that compliance was below standard and hence this was allocated an IIS rating of 4.

For LC 28, records for inspections in the maintenance schedule for plant and structures in the ponds were inspected.  Generally the site provided evidence that plant had been inspected, examined, maintained or tested within the time interval in the maintenance schedule.  Shortfalls were identified in the licensee’s control of external inspectors and following up on defects identified during pond leak inspections and actions were placed to address these.  Compliance with LC 28 was found to be below standard and hence this has been allocated an IIS rating of 4.

For LC 34, the potential for leakage of radioactive material was primarily from leaks of pond water.  These were very small and any leakage that occurred was collected in sumps, which allowed them to be processed via an engineered route.  Compliance was therefore judged to be adequate and has been assigned an IIS rating of 3.

Finally the system based inspection requires an assessment of the plant condition, which was based on discussions with the licensee on its own assessment and a walkdown of the plant.  The licensee had identified a number of areas where the plant needed to be improved.  The civil structure was generally judged to be adequate, although the site should look at repairing leaks and deal with accumulations of boron crystals.  The mechanical systems generally reflected the state of the plant described by the licensee, although some minor areas for improvement were identified.  Overall the plant condition was judged to be acceptable.

During the SBI, we identified seven actions where we judged the performance to be below standard.  These have been recorded in an ONR issue to ensure that the actions are suitably discharged.

For LC 7, the sites arrangements and their implementation for reporting incidents had been inspected during a previous visit and found to be adequate.  To continue the inspection, this report covers the production and processing of investigations.  Some issues were found with this, but these were not sufficient to consider the compliance with LC 7 to be inadequate.  The overall compliance has therefore been judged to be adequate and assigned an IIS rating of 3.

The intervention was performed in line with ONR’s guidance requirements (as described in our technical inspection guides) in the areas inspected.

Conclusion of Intervention

From the evidence obtained during this intervention, no matters have been identified that are likely to have a significant impact on nuclear safety on the station at this time. Therefore, no additional regulatory action arising from this visit is considered necessary at this time.