Office for Nuclear Regulation

System Based Inspection (SBI) of Auxiliary Cooling Systems (ACS) and Seawater Systems (SWS)

Executive summary

Purpose of Intervention

This intervention was to undertake compliance inspections at EDF Energy Nuclear Generation Limited’s Hunterston B power station, and formed part of the ONR Hunterston B 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. The licence conditions assessed were: LC 10 (training), LC 23 (Operating Rules), LC 24 (Operating Instructions), LC 27 (Safety Mechanisms, Devices and Circuits), LC 28 (Examination, Inspection, Maintenance and Testing) and LC34 (Leakage and Escape of Radioactive Material and Radioactive Waste).

The ONR nominated Hunterston B site inspector, together with specialist mechanical and chemistry inspectors conducted a Systems Based Inspection (SBI) of System 4, Auxiliary Cooling Systems and System 5, Seawater Systems. For brevity in this intervention report all ONR representatives are referred to as “I” The areas targeted were:

The inspection comprised discussions with the licensee staff, physical viewing and inspection of targeted systems, structures and components and a review of the licensee’s records and other associated safety documentation.

The intervention was informed by ONR technical guidance, which can be found at

Explanation of Judgement if Safety System Not Judged to be Adequate

From the inspection I judged that the safety case supporting the areas of systems 4 & 5 are being implemented adequately. I did however note some areas for improvement as detailed below.

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 PVCW system and DCS. The inspection provided evidence that the areas sampled are inspected, maintained and operated in accordance with the safety case.

LC 10 (Training) – I examined the training records for two individuals involved in the operation, maintenance, inspection and testing of the PVCW system and DCS. 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 LC10 compliance.

LC 23 (Operating Rules) – The technical specification and surveillance schedules adequately specified the limits and conditions of operation (LCO), reflecting those specified in the Living Safetycase Document (LSD).  In addition, the technical specifications and associated technical specification commentaries demonstrated that the limits and conditions of operation specified in the safety case were implemented adequately.  I therefore assigned a rating of Green (No formal action) for LC 23.

LC 24 (Operating Instructions) – I examined the operating instructions used for daily surveillance on nuclear safety significant plant. I confirmed that these had been carried out as stipulated in the Plant Item Operating Instructions (PIOI). I also examined the technical specification Compliance Status Log (TSCSL) and confirmed that completed operating instructions had been logged in accordance with the licensee arrangements. Through our examination of these procedures, I was content that the requirements of the technical specification were adequately confirmed and controlled.  I therefore assigned a rating of Green (No formal action) for LC 24.

LC 27 (Safety Mechanisms, Devices and Circuits) – Through system overview presentations and examination of the LSD, technical specifications and their associated commentaries, the licensee demonstrated compliance with LC27. I sampled the DCS due to its safety function. 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 also physically examined a sample of these SMDC’s and confirmed they were connected and in good working order. I judged therefore, that a rating of Green (No formal action) was appropriate for LC 27.

LC 28 (Examination, Inspection, Maintenance and Testing) – I sampled the licensee’s maintenance arrangements through interrogating the computer based asset management system. I examined the PVCW system and DCS maintenance schedule and confirmed that the licensee’s requirements were being implemented adequately.    

I sampled work order cards and the associated maintenance and inspection procedures and confirmed that these had been completed in accordance with the licensee’s arrangements. From the sample it was noted that one of the Maintenance Schedule tasks had been completed but the associated record of the completed work instruction was incomplete. This indicated a compliance gap on LC28 section 9. As a result a level 4 issue will be raised against LC28.

Although a gap was identified, other records sampled were completed in full with no issues noted. I was content that the evidence presented and examined confirmed that maintenance and inspection was being appropriately undertaken. I considered a rating of Green (No formal action) was merited against this License Condition.

LC34 (Leakage and Escape of Radioactive Material) – The PVCW system was sampled to ensure adequate control and containment of radioactive matter. The PVCW system LSD was found to have shortfalls in identifying and controlling the production of tritium. Given low levels of activity and existence of action levels and surveillance of the PVCW system however, a level 4 regulatory issue was judged to be proportionate. It was therefore judged that a rating of Green was appropriate for LC34.

Station Chemistry

In addition to the SBI, I sampled chemistry related operating rules for the PVCW system and general chemistry compliance. Separately, I sought to understand stations arrangements and their implementation for maintaining off-load chemistry control, given station has experienced prolonged periods in this state.

Based upon my sample, I was content that chemistry was being appropriately controlled at Hunterston B in both the PVCW system and during off-load storage of the boilers. However, I note that station appears to have chosen to not implement certain mandatory company requirements. I have therefore captured this as a new minor regulatory issue, and will seek to understand CTO arrangements for monitoring compliance with this action in my next routine interaction.

Conclusion of Intervention

After considering all the evidence examined during the SBI, I judged based on my sample that the PVCW system (System 4) and the DCS (system 5) met the requirements of the safety case.

The inspection findings were shared and accepted by the licensee in the feedback session.

I considered 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 auxiliary cooling and seawater systems.

I raised two level 4 regulatory issues to track the licensee’s updates to LC28 and LC34 arrangements respectively. Another level 4 regulatory issue related to clarity, consistency and visibility of the chemistry safety case has been raised.