Office for Nuclear Regulation

Sizewell B – Inspection ID: 52158

Executive summary

Date(s) of inspection:

  • March 2023

Aim of inspection


To support ONR’s permissioning of Sizewell B return to service from RO18, ONR chemistry inspectors are seeking to conduct an inspection of significant chemistry related outage activities and off-load chemistry control.


The inspection will seek to sample safety relevant systems where there is a requirement to apply chemistry controls off-load. The inspection will start from the safety case claims and follow the “control and management” trail through operating instructions, monitoring results and maintenance. The main Licence Conditions will therefore be relevant aspects of LC 28 (examination, inspection, maintenance and testing) and LC 23 (operating rules).

Subject(s) of inspection

LC 23 – Operating rules – Rating: GREEN

LC 28 – Examination, inspection, maintenance and testing – Rating: GREEN

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

This was a planned chemistry inspection of the Refuelling Outage 18 (RO18) at Sizewell B (SXB), taking place over 8 and 9 March 2023. The primary purpose of the inspection was to rate LC 23 (Operating Rules) and LC 28 (Examination, Inspection, Maintenance and Testing) relevant to chemistry limits and conditions, required plant to maintain compliance with these limits and significant chemistry outage activities. This will support ONR’s overall judgement for adequacy for return to service in PR-01033.


Licence Condition 23 – Operating Rules

Based on my sample, I was content that chemistry-relevant limits and conditions (operating rules) for outages were captured in SXB’s suite of technical chemistry techincal standards (TCTS) documents and implemented through station operating instructions (SOIs). Further, I was content on the basis of my sample that SXB was demonstrating effective control with these limits and conditions. I judge however that the importance of chemistry in outages (and steam generator lancing activity) is not adequately reflected in the current safety case user guide (SCUG) for chemistry. While I do not judge this presents a return to service issue, I consider this represents a gap with the standards of a modern standards safety case and will be an area of focus for ONR assessment in PSR3. Station has therefore raised CR1310890 to capture these observations. Overall, I was content with the implementation of chemistry operating rules however and therefore judge a rating of GREEN to be appropriate for LC 23.

Licence Condition 28 – Examination, Maintenance, Inspection and Testing

In respect of LC 28 and following my sample thread from LC 23, I sought confidence that plant important for maintaining effective chemistry control was in an adequate condition to maintain the safe operating envelope. This focused on secondary side chemistry noting a recent system based inspection of the chemical volume control system (IR-52027). Based on my sample of the steam generator blowdown system, condensate chemical addition and condensate polishing plant, I was content that these systems were in suitable condition to maintain compliance with chemistry operating rules. Further, I was content with progress of steam generator lancing activities and welcomed recommendations raised within maintenance strategy review reports. I was therefore content that the requirements of LC 28 had been met, and judged a rating of GREEN to be warranted for LC 28.

Overall I rated both LC 23 and LC 28 GREEN. From from the perspective of chemistry therefore, I have no objections for the return to service of SXB from RO18.