Office for Nuclear Regulation

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Dungeness B planned inspection

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 no-break electrical supplies system 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 an electrical specialist.

Interventions Carried Out by ONR

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

The interventions for other parts of the inspections were for licence compliance covering the following licence conditions:

Explanation of Judgement if Safety System Not Judged to be Adequate

During the plant walkdown, we identified a potential design weakness in that the operation of the Essential Diesel Generators (EDG) appeared to be dependent on a single 110Vac fuseboard, which could not be inspected or maintained due to the impact on EDG availability. 

An exchange of information since the inspection does provide some confidence that the licensee should be able to demonstrate that failure of the fuseboard is not significant and that the nuclear safety function of the system as a whole is not compromised.  I have therefore arranged a further intervention with the licensee to clarify the significance of this fuseboard within the safety case and therefore do not recommend any further regulatory action at this stage.

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

For LC 10, the inspection reviewed the training arrangements and training records for site staff associated who either operated or maintained the no-break electrical supply system and found these to be adequate and therefore assigned this an IIS rating of 3 for LC 10.

For LC 23, the site had appropriate technical specifications in place for the no-break electrical supplies system and it demonstrated compliance with these through the check-sheets completed for a sample of shifts.  Compliance with LC 23 was judged to be adequate and therefore was assigned an IIS rating of 3.

For LC 24, the inspection focused on the implementation of the operating instructions for recovery from a fault within the system.  Whilst the engineer who demonstrated the procedure was competent, the instructions that he was using were not wholly appropriate to the task and potentially the same issue could arise elsewhere.  An action was placed on the site to revise the instructions and to identify whether it was an issue for other procedures.  Compliance with LC 24 was judged to be below standard and therefore was assigned an IIS rating of 4.

For LC 27, the safety mechanisms, devices and circuits (SMDC) were associated with individual equipment items and were maintained with those items.  The extent of SMDCs was also found to be adequate and hence compliance with LC 27 was judged to be adequate and therefore was assigned an IIS rating of 3.

For LC 28, the intervention included the adequacy of instructions for maintenance and their implementation.  The scope of maintenance was consistent with the safety case, although it was found that not all fuseboards were inspected or maintained.  Instructions were generally found to be adequate, but we found some anomalies with their implementation.  Actions were identified to address the shortfalls.  Compliance with LC 28 was judged to be below standard and therefore was assigned an IIS rating of 4.

For LC 34, the Systems, Structures and Components in SBI07 do not form any barriers to contain radioactive material and radioactive waste.  LC34 was therefore not applicable to SBI07.

The LC 17 inspection considered supply chain arrangements and focussed specifically on the Spares Management Improvement Programme.  Overall Dungeness B was taking positive action to improve spares management at the site and was making progress.  There remained a performance gap to close which will require on-going management intervention by the Supply Chain Manager and continuing commitment from supply chain staff.  The spares management improvement programme at DNB remains work in progress and is overseen by the Spares Management Board.  The Spares Management Board will decide when a normal state of affairs is achieved and this is expected to be later in 2015.  DNB’s approach to resolving the issue associated with spares management is considered appropriate however noting that the improvement programme remains on-going compliance with LC17 is assigned an IIS rating of 4.  ONR will continue to monitor progress at the routine meetings with the Corporate Supply Chain Team.

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.