Office for Nuclear Regulation

Heysham 2 - SBI07 Electrical inspection

Executive summary

Purpose of Intervention

The purpose of this intervention was to conduct a system based inspection (SBI) of key electrical systems that support the safety function of the gas circulators main motors at EDF Energy Nuclear Generation Ltd.’s (NGL’s) Heysham 2 Power Station.

This intervention was undertaken as part of a series of planned interventions that are listed in the Heysham 2 Integrated Intervention Strategy 2019/2020.

Interventions Carried Out by ONR

We performed a safety case informed SBI of the systems that support the safety function of the gas circulators main motors which included examination of the emergency generation system; short break supplies systems; no break systems; transformers; grid and main electrical systems. 

A function of these systems is to provide the infrastructure for electricity supply to Heysham 2 gas circulators under normal operations and in the event of an electrical supply interruption or a grid-derived disturbance.  Through examination of these systems we assessed compliance against the following Licence Conditions (LC):

I judged that LC 34 (Leakage and escape of radioactive material and radioactive waste) was not relevant to this inspection.

The Heysham 2 nominated site inspector also undertook the following regulatory activities on site:

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

Explanation of Judgement if Safety System Not Judged to be Adequate

From the inspection, we judged that the implementation of the arrangements for the combined electrical systems that support the safety function of the gas circulators main motors met the requirements of the safety case and were adequate.

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

LC 10 – Training: we sampled training records for a number of staff who had undertaken maintenance on the electrical systems under question and observed staff undertaking maintenance on related electrical systems.  We also sampled the training materials associated with these activities.  Overall, based on the sample inspected, we were satisfied that staff training records were complete and the standard of training materials met our expectations.

LC 23 – Operating rules: we sampled limits & conditions associated with the various electrical systems supporting the function of the gas circulators. This included limits & conditions identified within technical specifications associated with post trip cooling, nuclear fire boundaries and 3.3KV Auxiliary supplies.  We were broadly satisfied that the limits and conditions were appropriately derived from the safety case and the implementation was suitable and sufficient.

LC 24 - Operating instructions: we sampled a number of operator and station operating instructions related to the systems under inspection.  We also observed instructions being used within the control room and discussed certain scenarios with the operators within the central control room.  Overall, we judged that the licensee’s arrangements for LC 24 associated with electrical systems were adequate.

LC 27 – SMDC: we sampled the system health reviews and visited various relevant plant areas and routes containing the electrical systems under inspection.  Overall, based on our observations, we were satisfied that suitable and sufficient safety mechanisms, devices and circuits were in the expected condition and available in accordance with the safety case.  A number of minor findings associated with housekeeping and plant labelling were identified and accepted by the licensee.

LC 28 - EIM&T: we sampled maintenance and testing records associated with the electrical systems supporting the function of the gas circulators.  Overall, we were satisfied that the maintenance had been undertaken in accordance with the required periodicity as defined by the maintenance schedule, and met with the relevant requirements.  We did, however, identify a number of opportunities for improvement associated with the conduct of maintenance and instruction standards for a small number of activities.  This included completion of ‘as found’ conditions, check sheet completions and approval standards.  The licensee accepted these findings and undertook to address them in a timely manner.

Conclusion of Intervention

From the evidence gathered during the system based inspection of electrical systems that support the safety function of the gas circulators main motors, we assigned inspection ratings of ‘Green’ (no formal action) for LCs 10, 23, 24, 27 and 28.

There are no findings from this inspection that could significantly undermine nuclear safety.  At present, no additional regulatory action is needed over and above the planned interventions at Heysham 2  Power Station as set out in the Integrated Intervention Strategy, which will continue as planned.