Office for Nuclear Regulation

This website uses non-intrusive cookies to improve your user experience. You can visit our cookie privacy page for more information.

Heysham 2 Reactor 8 Periodic Shutdown: Graphite Core Inspection LC28

Executive summary

Purpose of intervention

The intervention took place at Heysham 2 on 11th October 2016 during its periodic reactor 8 shutdown as part of the licensee’s, EDF Energy Nuclear Generation Limited’s (NGL), compliance with Licence Condition (LC) 30. The purpose of the intervention was to inspect the adequacy of the licensee’s examinations and inspections of the graphite core and determine compliance with LC 28(1).

Interventions Carried Out by ONR

In relation to the graphite core I carried out the following inspections in order to determine compliance with LC 28:

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

The inspection team had completed 16 of 16 fuel channel inspections and discovered a single fully circumferential crack in a layer 8 brick in channel T71. This is only the second observed crack in a fuel brick in Heysham 2 reactor 8 and more generally, Heysham 2 and Torness power stations contain lower numbers of cracked fuel bricks than other reactors in the fleet. Therefore, these numbers are well below any level that would challenge the safety case and are within NGL’s statistical prediction. I sampled the inspection footage from fuel channel T71 and found it be of sufficient quality for the detection of cracks.

Other inspections, not of the fuelled region of the core but of the graphite peripheral shield wall, were being conducted at the time of the intervention. The peripheral brick inspections utilise different equipment to the fuel channel inspections. NGL had completed 6 out of a targeted 13 sides of inspection and had observed cracking in a small number of bricks as well as small (<10mm) gaps between some bricks. One standpipe, YZ64, which was intended to be used to inspect 3 sides of the peripheral brick wall is currently unavailable due to another piece of inspection equipment becoming stuck in a access standpipe. This potentially means the scope of the inspection may decrease from 13 of 16 sides unless the equipment can be removed in a timely manner. Any reduction in inspection scope will be considered as part of ONR’s return to service consent activities.

In my opinion the video footage of the peripheral shield wall bricks was of reasonable quality but could be improved to provide sharper, more focused images that can be used to accurately measure dimensions such as gaps. Improvement of the peripheral brick imaging capability would aid the assessment of cracks and provide improved insight of the potential cause of the observed cracking and gapping of the peripheral shield wall bricks at Heysham 2 reactor 8 and Torness reactor 2.

My inspection of training records and inspection staff found that the inspections were being performed by suitably qualified and experienced personnel.

I observed a peripheral brick assessment panel meeting whilst they considered some of the peripheral brick inspection findings. The group was quorate in accordance with their terms of reference, complied with their crack sentencing procedures and was composed of suitably qualified and experienced personnel.

Conclusion of Intervention

Overall, from the activities I sampled during my intervention I found that the licensee, EDF Energy Nuclear Generation Limited, were complying with LC 28 in respect of the graphite core inspections and I considered that an inspection rating of ‘Green’ is warranted.

A forthcoming assessment report will consider whether the results from the examinations and inspections are consistent with the graphite safety case in order to support ONR’s return to service consent activities.