Office for Nuclear Regulation

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Dungeness Reactor 21 Statutory Outage 2014 - Graphite Structural Integrity Inspection

Executive summary

Purpose of intervention

An intervention was performed by ONR inspectors on 23rd and 24th April 2014 to determine the adequacy of the graphite inspections being performed during the Reactor 21 2014 periodic shutdown. Furthermore, the opportunity was taken to determine the progress of in-vessel inspection of boiler support welds.

Interventions carried out by ONR

Explanation of judgement if safety system not judged to be adequate

NA

Key findings, Inspector's opinions and reasons for judgements made

Overall my intervention on the graphite core inspections and the boiler support bracket inspections at Dungeness B (DNB) Reactor 21 did not find any issues that would prevent consent for return to service being granted.

The preparations made prior to the graphite core inspections and the evident interaction between the power station and the design authority based at Barnwood were of particular note. It was clear that these interactions had strengthened the link between the operational safety case and the plant condition which are important aspects of operational safety.

An issue has been raised to determine the as-built DNB brick shape and geometry, and compare it with that used in average core weight loss methodology.

On the basis of what I observed during the intervention, I judged that the requirements of LC28 were being met and I allocate an overall IIS rating of 3, adequate standard.

Conclusion of intervention

At the time of the intervention the schedule of graphite core inspections and in-vessel steel work inspections as defined by the outage intent document had not been completed. Once the inspection schedule has been completed to the satisfaction of the safety case requirements, assessment reports will consider whether the results are consistent with the relative safety cases.

I recommend that the relevant project inspector, who will be writing the project assessment report, considers those forthcoming assessment reports. Their conclusions will help to inform their decision as to whether to recommend that Consent to return to service is granted.