Office for Nuclear Regulation

Sizewell B – Inspection ID: 52057

Executive summary

Date(s) of inspection:

  • December 2022

Aim of inspection

System based inspections (SBIs) are an essential element of ONR’s overall interventions on nuclear licensed sites. They are intended to establish that the basic elements of a site/facility safety case as implemented in safety systems and structures are fit for purpose and that they will fulfil their safety functional requirements. This inspection will focus on the CVCS (BG) and ECS (BP).


To evaluate, on a sample basis with focus on nuclear safety significance, that the CVCS and ECS meet the requirements, claims and arguments made within the safety case.

Subject(s) of inspection

  • LC10 – Training – Rating: Green
  • LC12 – Duly authorised and other suitably qualified and experienced persons – Not rated
  • LC23 – Operating rules – Rating: Green
  • LC24 – Operating instructions – Rating: Green
  • LC27 – Safety mechanisms, devices and circuits – Rating: Not rated
  • LC28 – Examination, inspection, maintenance and testing – Rating: Green
  • LC34 – Leakage and escape of radioactive material and radioactive waste – Not rated

Key findings, inspector’s opinions and reasons for judgement made

The main purpose of this intervention was to undertake a system based inspection (SBI) at EDF Energy Nuclear Generation Ltd’s (NGL) Sizewell B (SZB) power station.  The system inspected was the Chemical and Volume Control System (CVCS) and Emergency Charging System (ECS). The inspection was conducted in line with the inspection programme contained in the SZB integrated intervention strategy for 2022/23.

The inspection was carried out by chemistry and fault studies specialist inspectors, supported by the nominated SZB site inspector. For the purposes of brevity, all inspectors are referred to as “I” in this report. Compliance inspections were completed against the standard SBI licence conditions: LC 10: Training; LC23: Operating Rules; LC24: Operating Instructions; LC27: Safety Mechanisms, Devices and Circuits; LC28: Examination, Inspection, Maintenance and Testing and LC34: Leakage and Escape of Radioactive Material.

  • LC 10 (Training) – For this part of the inspection I sampled training records for CVCS and ECS system engineers. Based on my sample, I was content that all “essential” role requirement training was completed for the ECS System Engineer, and was content with handover arrangements for the incoming CVCS system engineer. I observed some difficulty however in EDF NGL navigating the newly implemented electronic training records platform. I therefore recommend that ONR’s nominated site inspector follow up implementation of this platform in six months to ensure this has been adequately implemented. I therefore judge a rating of GREEN to be appropriate for LC 10.
  • LC 23 (Operating Rules) – Relevant to LC 23, Station provided a comprehensive overview of CVCS and ECS safety functions. I opted to sample inventory control, chemical control and ECS operability safety functions. Based on my sample, I was content appropriate limits and conditions were evident for each of these functions in technical specifications or equivalent documentation. I therefore judge a rating of GREEN to be appropriate for LC 23.
  • LC 24 (Operating Instructions)  Following the thread from LC 23, I sampled implementation of limits and conditions in written instructions. This included routine reactor inventory balance and leak response in the event of a fault. For both routine and fault conditions, I was content adequate instructions were in place to deliver compliance with limits and conditions. Of minor note however, I identified that instructions for initiation of a second CVCS charging pump  referenced instruction to initiate a pump change over. Station however raised a document update to rectify this. I therefore judge a rating of GREEN to be appropriate for LC 24.
  • LC 27 (Safety Mechanisms, Devices and Circuits) – While no explicit list of safety mechanisms was evident, based on discussions I was content that safety mechanisms devices and circuits were captured by technical specifications, maintenance strategy reports and system descriptions. I therefore judge a rating of GREEN to be appropriate for LC 27.
  • LC 28 (Examination, Inspection, Maintenance and Testing) – For LC 28, I sampled high level system health metrics and individual maintenance records for CVCS pumps and valves and ECS charging pumps. Regarding high level plant health metrics, I identified good practices at SZB related to inclusion of a chemistry metric and sensitivity to underlying plant condition and numbers of plant defects. For specific CVCS and ECS pumps and valves, I was content maintenance records were complete and adequate. I therefore judge a rating of GREEN to be appropriate for LC 28.
  • LC 34 (Leakage and Escape of Radioactive Materials and Radioactive Waste) – Based on discussions, for general arrangements for leaks inside containment and auxiliary building, I was content that adequate arrangements were in place to identify and manage leaks through monitoring or planned remediation in upcoming outages. I welcomed enhancement of leak detection arrangements in inaccessible areas of the CVCS. While I observed a minor uncontrolled edit to a procedure, this was accepted by station and self-corrected alongside a number of other documents. I therefore judge a rating of GREEN to be appropriate for LC 34

Based on the evidence I sampled during the inspection, I judge that the CVCS and ECS systems met the requirements of the safety case. While minor issues were identified, I was satisfied these were rectified with appropriate document update requests raised during the intervention. I was therefore content there were no matters that are likely to have significant impact on nuclear safety. I observed some difficulty however in EDF NGL demonstrating completion of all essential training for relevant system engineers. This was exacerbated by implementation of a new training records platform, which had been in use for approximately two weeks. While I was able to ascertain that essential training had indeed been completed, I judge the system to be convoluted and unclear. I therefore recommend that ONR’s nominated site inspector should follow this up in subsequent interventions to ensure initial challenges have been abated.


Based on my sample, I was content that station was adequately implementing  the CVCS and ECS safety case, and that both systems were available to perform their safety functions. I therefore judge an overall rating of GREEN (no formal action) to be appropriate for this system based inspection.