Office for Nuclear Regulation

Intervention to inspect work conducted following discovery of cracking in the main steam system

Executive summary

Purpose of Intervention

This is a summary of a reactive unplanned intervention by the Office for Nuclear Regulation (ONR) at Dungeness B (DNB) Power Station on the 8th of November 2018, both reactors were shutdown at the time of my inspection. The purpose was to inspect work by the licensee, EDF Energy Nuclear Generation Limited, carried out in response to the discovery of cracking in the main steam line of boiler 27.

Interventions carried out by ONR

I met with members of the licensee staff and a contractor. I concentrated on aspects of structural integrity that I judged important to nuclear safety, in particular the method, conduct and outcome of inspections of the main steam system.

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

I have reviewed the scope of the inspection programme, prompted by the discovery of cracking in the main steam system of boiler 27. I have inspected the methods applied, quality control arrangements, record keeping and sentencing of results. The licensee has provided evidence of to justify scope, techniques and treatment of inspection data. In each respect I have found that evidence to be adequate.


I have found each aspect I have inspected to be satisfactory and, based on ONR inspection rating guidance, award an inspection rating of green.

However, the inspection programme is not finished and has so far resulted in the discovery of a number of significant defects within the main steam lines of boilers associated with both reactors. I will address their treatment and the findings of the completed inspection programme in a future assessment report that will consider the justification for return to service of both reactors. In the mean time I will continue to engage with the licensee and monitor progress of the recovery operation.