Office for Nuclear Regulation

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Wylfa Power Station

Executive summary

Purpose of intervention

This report covers the nuclear safety related inspection of Wylfa power station undertaken as part of a series of interventions including those listed in the Integrated Intervention Strategy (IIS) plan, inspections deemed necessary to cover emergent work, and follow-up of matters carried forward from previous visits.

Interventions Carried Out by ONR

This intervention included planned compliance inspections against the following Licence Conditions (LCs):

Licence Conditions 10, 23, 24, 27, 28 & 34 were covered as part of a safety system inspection of the Emergency Plume Gamma Monitoring System (EPGMS).

An incident on the site notified to ONR under the arrangements made for LC7 was followed-up during the visit.

Other matters of a routine nature that are deemed unlikely to have a significant effect on nuclear safety, and which are being addressed routinely under the licensee's arrangements, were also covered during the inspections.

Explanation of Judgement if Safety System Not Judged to be Adequate

From the inspection, I judge that overall the EPGMS safety system provisions meet the requirements of the safety case and are adequate.

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

A safety system inspection of the EPGMS was carried out as part of the programme of safety system inspections included on the Wylfa site intervention plan for 2014/15, to identify the adequacy of the station arrangements made to ensure the system will perform its safety function. In deciding if suitable and sufficient measures have been put in place for the safety system, these inspections consider compliance with a number of licence conditions to test the adequacy of the arrangements implemented. The standard consideration of licence conditions during safety system inspections includes LCs 10, 23, 24, 27, 28 & 34, with conditions added or excluded depending on their applicability.

The system inspection found that station has made arrangements to ensure that the EPGMS is maintained and operated in accordance with its safety case, and that on the basis of the inspection sample the arrangements are deemed to be implemented in an adequate manner. Therefore, I have given an inspection rating 3 (adequate) in respect of the LCs inspected, and also judged that overall the system meets the requirements of its safety case and is adequate. During the inspection, opportunities for improvement were identified that station has agreed to address, and ONR will monitor the action they take during routine inspections at the site.

Station notified ONR of an event under the arrangements for reporting incidents on the site, where it was necessary for them to manually shutdown reactor 1 during return to service of the reactor, following the extended periodic shutdown. The event concerned a steam leak that emerged on Turbine No 1, which could not be resolved with the turbine remaining on-load. The reactor was safely shutdown to allow remedial work to be performed, and they have taken suitable corrective action in readiness for re-starting the reactor. They are continuing to investigate this matter to help prevent a re-occurrence. While the licensee's response to the incident was appropriate under the incident reporting arrangements, the event involved an unanticipated challenge to the station safety systems and introduced an unscheduled plant load cycle that may affect safety. Therefore, I have given an inspection rating 4 (below standard) in respect of LC28, from this component of my inspection.

During the intervention visit, opportunity was taken to inspect station's response to incidents on the site, including those notified to ONR, and I consider that the inspections carried-out confirm that they have responded adequately to emergent plant conditions. On the basis of the sample inspections, I judge that they have complied with licence condition arrangements in relation to emergent work, which has arisen since the previous inspection.

The licence conditions were inspected against ONR's published guidance requirements (as described in our technical inspection guides).

Conclusion of Intervention

From the information gathered and evidence obtained during this intervention, no matters have been identified that are likely to have an adverse impact on nuclear safety on the station that are not being addressed. Therefore, I consider that no additional regulatory action arising from this visit is necessary currently, and the interventions for Wylfa power station should continue to be implemented as set out in the Integrated Intervention Strategy. I judge the corrective action taken by station in response to emergent matters to be appropriate in the prevailing circumstances. The outcome from the inspections has been captured within the station event and action tracking arrangements, in the actions recorded in this intervention report, and in the ONR issues database, as appropriate.