Office for Nuclear Regulation

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Reactor 7 Graphite Core Inspection Arrangements during its 2018 Statutory Outage

Executive summary

Purpose of Intervention

Heysham 2  (HYB) Reactor 7 (R7) shut down for a statutory outage in May 2018.  During this shutdown, EDF Nuclear Generation Limited (NGL) carried out a series of inspection activities on the graphite core. This work is required by Licence Condition (LC) 28 - Maintenance, Inspection and Test Schedule (MITS). This included visual inspection, dimensional measurements and trepanning of samples. At this outage, NGL is also performing inspection of the peripheral graphite bricks. This was the first time such inspections of the peripheral bricks were carried out for this reactor, although similar inspections had already been carried out at HYB Reactor 8, Torness (TOR) Reactor 1 and Reactor 2. 

The objectives of this intervention were:

I judged this intervention based on the findings of the intervention, the quality of the data I observed and the knowledge and experience of the licensee’s staff. This intervention will inform the ONR decision on granting consent for the return to service of HYB R7 following its 2018 periodic shutdown.

Interventions Carried Out by ONR

Licence condition 28 (LC28) requires a licensee to perform an adequate programme of MITS.  This intervention was performed to ensure that NGL was compliant with LC28 in their graphite inspection work.  Two ONR inspectors, a graphite specialist and the project inspector, examined the visual data recorded during the graphite and peripheral brick inspections. The present intervention covers the following aspects that are relevant to the confidence with which the inspection results can be held and to ensure compliance with LC28:

This intervention report does not comment on the significance of those findings. This will be addressed by a separate ONR assessment once the graphite core inspections are completed. ONR’s assessment will however take note of the findings of this intervention.

Explanation of Judgement if Safety System Not Judged to be Adequate

N/A.

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

At the time of my site intervention, the licensee had completed all 16 visual inspections and bore measurements, out of a target requirement of 16. Two circumferential bore cracks have been observed, but no full height axial cracks.

I consider that the licensee’s arrangements with regards to graphite core inspection during this outage are both suitable and adequate. In my opinion, the visual records and the data that I sampled were of adequate quality for NGL to form a judgement and sentence the cracks. At the time of my intervention, the safety case commitments were on target and, at the time of my inspection, there was no reason to believe that these would not be met.

The licensee personnel that I met at station were knowledgeable and the training records that I sampled were up-to-date. From the training records that I sampled, I consider that the personnel involved in undertaking inspections have adequate training and experience to perform their various tasks.

Conclusion of Intervention

I conclude that the licensee is in an adequate 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.

I have allocated an ONR rating of ‘Green’ - Adequate.