Office for Nuclear Regulation

System Based Inspection (SBI) of Shutdown Systems

Executive summary

Purpose of Intervention

The purpose of this intervention was to undertake compliance inspections at EDF Energy Nuclear Generation Limited’s Hunterston B power station, in line with the planned inspection programme contained in Hunterston B’s Integrated Intervention Strategy (IIS) for 2019/20.

Interventions Carried Out by ONR

Systems based inspections examine evidence to determine compliance against six key Licence Conditions (LCs), selected to help determine whether the safety case requirements of the system concerned are adequately implemented, and safety systems and structures are fit for purpose and will fulfil their safety functional requirements . The licence conditions assessed were: Licence Condition 10 (Training), Licence Condition 23 (Operating Rules), Licence Condition 24 (Operating Instructions), Licence Condition 27 (Safety Mechanisms, Devices and Circuits), Licence Condition 28 (Examination, Inspection, Maintenance and Testing) and Licence Condition 34 (Leakage and Escape of Radioactive Material and Radioactive Waste).

A specialist mechanical engineering inspector, mechanical nuclear associate and specialist structural integrity inspector conducted a remote system based inspection (SBI) of system 28, shutdown systems. For brevity in this intervention report all ONR representatives are referred to as “I”. The areas targeted were:

The Diverse Shutdown System comprises two sub-systems; the Nitrogen Injection System and the Enhanced Shutdown System.

The inspection comprised discussions with the licensee staff remotely via teleconference, and a desktop review of the licensee’s records and other associated safety documentation. This inspection was carried out remotely due to government advice regarding the Covid-19 restrictions at the time of the inspection.

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

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

From the areas targeted and the evidence I examined during this inspection, I consider that the licensee has adequately implemented the safety case claims relating to the Diverse Shutdown System and Control Rod System. I am content that the areas of the system I sampled are inspected, maintained and operated in accordance with the safety case. I did however identify a number of shortfalls, however I do not consider that these shortfalls prevent the system from fulfilling its nuclear safety function. The ratings I have assigned for each of the Licence Conditions and any shortfalls are detailed below.

LC 10 (Training) – I examined the training records for three individuals involved in the operation, maintenance, inspection and testing of the Diverse Shutdown System and Control Rod System. I judged that the personnel undertaking and supervising these activities were suitably qualified and experienced.  I therefore assigned a rating of Green (No formal action) for License Condition 10 compliance.

LC 23 (Operating Rules) – I sampledthe system to ensure operating rules identified in the safety case were clearly identified in the technical specifications and complied with at all times via the surveillance schedules or similar.

From my sample, I judge that the Licensee has an adequate process in place for identifying the operating rules to demonstrate the safety of an operation for the Nitrogen injection system.  However, I consider that for the control rod system, the Licensee has shortfalls in the adequacy of the system based view, and in the visibility of the operating rules within operational documentation. I consider these shortfalls to be a significant failure in the technical quality of the safety case, and I therefore intend to raise a regulatory issue to resolve this shortfall.

Although a significant shortfall was identified, I sampled other areas of the Nitrogen System and Control Rod System and noted no further issues, therefore I do not consider that this shortfall prejudices overall nuclear safety. I consider a rating of Amber (seek improvement) to be appropriate.

LC 24 (Operating Instructions) – I examined the operating instructions used for surveillance on nuclear safety significant plant. I confirmed that operations had been carried out as stipulated in the Operating Instructions. I consider that the Licensee has adequate arrangements in place for the production and implementation of Operating Instructions. The requirement to carry out the operating instruction is clearly stated and the licensee clearly demonstrated the link between these requirements and the safety case. Overall, I judge that a rating of Green (no formal action) is appropriate for this licence condition, License Condition 24.

LC 27 (Safety Mechanisms, Devices and Circuits) – I reviewedsystem overview presentations, maintenance records  safety case documentation, technical specifications and their associated commentaries, and I consider that the licensee demonstrated that Safety Devices Mechanisms and Circuits were connected and in good working order. The key safety mechanisms devices and circuits were clearly identified, and adequate surveillance to confirm plant condition and availability was being undertaken in accordance with the licensee’s arrangements. I judged therefore, that a rating of Green (No formal action) was appropriate for License Condition 27.

LC 28 (Examination, Inspection, Maintenance and Testing) – I sampled the licensee’s maintenance arrangements through reviewing records and discussion with the system engineer. I examined the Nitrogen Injection System and Control Rod System maintenance schedule, completed work order cards and the associated maintenance and inspection procedures and confirmed that the licensee’s requirements were being implemented adequately.           

I did however note a number of shortfalls with the completion of records across the Control Rod System and Nitrogen Injection System. I consider this to be a systematic shortfall in maintaining a full and accurate record of the maintenance undertaken. I have therefore raised a regulatory issue to resolve this shortfall.

I judge that the licensee is undertaking examination, inspection, maintenance and testing in accordance with the specified arrangements and frequencies.  Overall, I am content that there was evidence of adequate implementation of arrangements in the majority of the evidence sampled. I did identify systematic shortfalls with the completion of records; however I do not consider that these shortfalls significantly affect nuclear safety. Therefore, I judge that a rating of Green (no formal action) to be appropriate for licence condition 28.

LC 34 (Leakage and Escape of Radioactive Material) – The Nitrogen Injection System was sampled to ensure adequate control and containment of radioactive matter. From discussions with the licensee and sampling of system drawings, I am content that the licensee has adequate arrangements for monitoring the leakage and escape of radioactive material.

I therefore judge that a rating of Green was appropriate for License Condition 34.

Conclusion of Intervention

Based on my sample, I consider that the shutdown system (System 28) met the requirements of the safety case, with some shortfalls as noted above. The inspection findings were shared and accepted by the licensee during the feedback session. I have raised two regulatory issues to resolve the shortfalls I have identified.

I consider that the licensee adequately demonstrated ownership and implementation of its safety case.  In addition, it demonstrated an adequate understanding of its arrangements to ensure and maintain the safety of its shutdown systems.