Office for Nuclear Regulation

Sizewell B - System Based Inspection - SBI 9 - Reserve Ultimate Heat Sink

Executive summary

Purpose of intervention

The purpose of this intervention was to undertake licence condition (LC) compliance inspections at EDF Energy Nuclear Generation Limited (NGL) Sizewell B power station in line with the inspection programme contained in the Sizewell B integrated intervention strategy (IIS) for 2015/16.

Interventions Carried Out by ONR

As part of this intervention, I carried out a system based inspection (SBI) of the reserve ultimate heat sink (RUHS) supported by an ONR specialist civil engineering inspector.  Through examination of this system I performed compliance inspections against licence conditions LC 10: Training; LC23: Operating rules; LC24: Operating instructions; LC27: Safety mechanisms, devices and circuits; LC28: Examination, inspection, maintenance and testing; LC34: Leakage and escape of radioactive material. The inspection was based on sampling the implementation of the arrangements in place at the station against each licence condition.

This intervention also included a number of information gathering meetings with station personnel.  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 this inspection, I judge that overall the safety provisions applicable to the RUHS meet the requirements of the safety case and are adequate. Further details are provided below.

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

A SBI of the reserve ultimate heat sink was carried out to judge the adequacy of the implementation of station arrangements to ensure that the system can perform its requisite safety function. In deciding if suitable and sufficient measures have been put in place for this system, the inspection considers compliance with a number of licence conditions to test the adequacy of the arrangements implemented. The standard consideration of LCs during SBIs include LCs 10, 23, 24, 27, 28 & 34, with some added or excluded depending on their applicability.

The SBI inspection did not raise any significant shortfalls in regulatory compliance.  However the maintenance arrangements were rated as being below standard due to the current material condition of the RUHS support structure.  This had already previously been recognised by the Licensee as part of its own periodic safety review carried out under their LC15 arrangements, and its findings are being addressed by an on-going investment programme of material condition improvement. The condition of the structure does not currently threaten the adequate operation of the RUHS system, and the implementation of the expected remedial works will be monitored by ONR as part of PSR2 close-out.

In summary, the outcome from the safety inspection of the RUHS system is that the arrangements and their implementation are deemed to be adequate overall, and therefore we have given IIS ratings of 3 (adequate) in respect of LCs 10, 23, 24, 27 and 34.  LC28: Examination, inspection, maintenance and testing attracted a rating of 4 (below standard) due to the current material condition of the structure, which is subject to remedial works that will be monitored by ONR.

The intervention was performed in line with ONR’s guidance requirements (as described in our technical inspection guides) in the areas inspected.

Conclusion of Intervention

After considering all the evidence examined during the sample inspections undertaken against LCs 10, 23, 24, 27, 28 and 34, we considered that the RUHS system met the requirements of the safety case.

From the information gathered and evidence obtained during this intervention, no matters have been identified that are likely to have significant impact on nuclear safety on the station at this time. Therefore we consider that no additional regulatory action arising from this visit is necessary currently, and the interventions for Sizewell B power station, set out in the integrated intervention strategy, should continue to be implemented as planned.