Office for Nuclear Regulation

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System Based Inspection - SBI 09 - Main Electrical System

Executive summary

Purpose of intervention

This report covers a nuclear system based inspection of Torness Power Station, undertaken as part of a series of planned interventions that are listed in the Integrated Intervention Strategy (IIS) 2014/15 plan for the station; to cover any emergent work; and, to follow-up any matters raised during previous visits, as deemed necessary.

Interventions Carried Out by ONR

As part of this intervention, we carried out a system based inspection of the Main Electrical System. Through examination of this system we 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. The inspections were based on sampling the implementation of the arrangements in place at the station against each licence condition.

Explanation of Judgement if Safety System Not Judged to be Adequate

From this inspection, we judge that overall the safety provisions applicable to the Main Electrical System 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 system based inspection of the Main Electrical System, including main supplies, transformers and grid connection apparatus, was carried out as part of the programme of safety system inspections included on the Torness IIS plan for 2014/15, to identify the adequacy of the station arrangements made to ensure that this system can perform its safety function. In deciding if suitable and sufficient measures have been put in place for this 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 system based inspections includes LCs 10, 23, 24, 27, 28 & 34, with conditions added or excluded depending on their applicability. In this case, LC34 that relates to leakage and escape of radioactive material and waste is not applicable to the Main Electrical System and therefore has been deemed not applicable to the inspection.

During the course of this system based inspection it was found that station has made arrangements to ensure that the main electrical supplies system is maintained and operated in accordance with its safety case and the arrangements are deemed to be implemented in an adequate manner, on the basis of those areas sampled by the inspection. The inspection identified a number of areas for potential improvement, and although none gave rise to significant concern, the station has agreed to take action to address them.

In summary, the outcome from the safety inspection of the main electrical supplies system is that the arrangements and their implementation are deemed to be adequate, and therefore we have given IIS ratings of 2 (good standard) for LC23, 3 (adequate) in respect of LCs 10, 24, and 28, and 4 (below standard) for LC27. The IIS rating of 4 for LC27 reflects an apparent omission within the stations arrangements for functional testing of an interlock associated with the main electrical supplies, which station has subsequently agreed to rectify.

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

Conclusion of Intervention

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

There are no findings from this inspection that could significantly undermine nuclear safety.