Office for Nuclear Regulation

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Hunterston B Power Station – Outage Intervention

Executive summary

Purpose of intervention

The purpose of this intervention was to undertake Licence Condition [LC] compliance inspections at EDF Energy Nuclear Generation Ltd’s [NGL’s] Hunterston B power station, in line with the planned inspection programme contained in the Hunterston B Integrated Intervention Strategy [IIS] for 2015/16.

Interventions carried out by ONR

This intervention is one of a number of LC28 compliance inspections performed by ONR during the periodic shutdown of Reactor 3 to inform the ONR decision whether to issue a licence instrument granting consent for the return to service of Hunterston B Reactor 3 following its 2015 statutory outage.  This intervention specifically focused on arrangements for graphite core examination, inspection and testing and the observations made during these periodic shutdown activities.

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

At the time of the visit, the licensee had completed 21 visual inspections and bore measurements, out of a target requirement of 31. We were satisfied that the licensee was in an appropriate position to undertake all planned inspections and measurements.  An assessment report will be produced subsequently to consider whether the work performed was sufficient and whether the findings are consistent with the current safety case.

I considered that personnel involved in undertaking inspections and measurements have had sufficient training to perform their various tasks.  I also examined some of the raw visual inspection data and I am content that it is of the necessary quality.

I observed the station’s graphite assessment panel which sentenced the 21 inspection and monitoring findings to date; I sought further information on the conclusions generated for one channel which will be considered as part of ONR’s assessment of the return to service safety case.

I noted the discovery of Key Way Root Cracking (KWRC) in Layer 6 of Channel 22:66. This was the first KWRC found in the main population of the AGR graphite bricks.

I also noted another potential KWRC in Layer 4 of Channel 42:76. This crack was yet to be sentenced by GAP.

In light of the observations made during the inspection, I have allocated an IIS rating of ‘3 - adequate’.

Conclusion of intervention

I conclude that the licensee is in a good position to complete its full scheduled programme of graphite inspection.  A forthcoming assessment report will consider whether the results are consistent with the graphite safety case, once the inspection schedule has been completed.