Executive summary
Date(s) of inspection: May 2024
Aim of inspection
The aim of the inspection was to sample NNB Generation Company (HPC) Ltd's (NNB GenCo) arrangements for compliance against Licence Condition (LC) 21 (commissioning). The licensee has developed key documentation to ensure that all nuclear safety related requirements on structures, systems and components (SSCs) that need evidence generated during the commissioning phase are identified. This documentation includes:
- Commissioning Test Packages (CTPs): CTPs define the scope of plant to be handed over from the other delivery programmes to the Commissioning Programme.
- Basis of Commissioning (BoCs):the BoC captures all the peripheral information for a system such as assumptions, operational experience (OPEX), the grade of the systems (graded approach), and how the intelligent customer role is discharged, etc.
- Sufficiency Analysis Notes (SANs): SANs identify the functional safety requirements to be tested during commissioning and the appropriate acceptance criterion.
- System Commissioning Programme (SCP): in the SCP, the tests are organised into an executable test programme.
- Commissioning Procedures (CPs): the CPs provide detailed information on how to execute the test and identify measures to protect against latent faults. The CPs also include information on the temporary means and devices (TMDs).
- Commissioning Instructions (CIs): CIs are stepwise instructions on how to deliver a test on-site and support the implementation of measures to protect against latent faults. CIs include the instructions to connect and disconnect the TMDs. The CIs capture the test grade.
The main objective of the inspection was to test if the above approach ensures the traceability of requirements from the design documentation into the commissioning phase tests and their acceptance criteria. This was done through sampling the above documentation for specific systems, but limited to systems to be commissioned up to the auxiliary transformer energisation (TAE). ONR sought evidence of intelligent customer (IC) oversight during the production of SANs, SCPs and CPs by the Responsible Designer (RD).
As part of this inspection, ONR sampled the suitably qualified and experienced persons (SQEP) competency compliance checks against the NNB GenCo personnel undertaking and managing commissioning activities up to TAE. This included the following specialisms: electrical engineering and control and instrumentation (C&I).
Subject(s) of inspection
- LC21 - Commissioning - Rating: Amber
Key findings, inspector's opinions and reasons for judgement made
The aim of commissioning is to demonstrate that the safety functional requirements (SFRs) meet the required acceptance criteria defined in the safety case. Consequently, identifying the scope of SFRs to be tested during commissioning and providing traceability to the safety case is fundamental for all commissioning tests. The purpose of this inspection was to sample SFRs to establish whether there was adequate evidence to support a demonstration of the golden thread in the safety case to underpin the commissioning requirements for the systems to be commissioned in 2024. Electrical and C&I systems are the first systems to be commissioned (in 2024) by the NNB GenCo commissioning team, therefore the inspection focused on the low voltage (LVL) boards (electrical system) and the KCM system (C&I system). Ahead of the inspection, ONR reviewed the relevant technical documentation related to these two systems.
The main focus of this inspection was to test whether there was adequate traceability of SFRs throughout the safety case and commissioning documentation. In addition, the licensee presented the arrangements in place to ensure that NNB GenCo’s commissioning team are SQEP to undertake the activities.
The inspection team found that the traceability of the sampled SFRs was adequate for the LVL boards as they could be traced through the commissioning documentation and back to the safety case. The inspection highlighted an area of good practice in the Commissioning Instructions where conventional health and safety was considered within the test conditions, but also identified a shortfall on the traceability of electrical statutory requirements. The C&I inspectors found significant shortfalls in the traceability of SFRs from their origin in the safety case through to the commissioning documentation. There were shortfalls in deviating from the documented process for developing commissioning documentation (for example, use of a Requirements Traceability Matrix (RTM) instead of SANs) and in evidence of implementation which led to a lack of clear traceability of requirements during the inspection. In addition, there was a lack of clarity on the plan and scope for updating the documented process, which meant that there is a deviation from the approach presented in the Summary Safety Case Document#2.
Conclusion
Overall, ONR found the traceability of the electrical requirements to be adequate.
However, significant shortfalls were identified with the process for developing the C&I commissioning documentation that led to a lack of clear traceability of requirements during the inspection for a key C&I system to support TAE. ONR considered this shortfall to be significant as the KCM system will be commissioned soon after the LVL boards, and currently the C&I commissioning documentation is being developed outside the extant process and without an up-to-date SAN or RTM, and there is a lack of clear traceability of evidence. Therefore, given the significance of the shortfall and considering that the commissioning of the system sampled will take place this year, the inspection was rated amber against LC21.
ONR raised a level 3 regulatory issue that captures the C&I shortfalls. A level 4 regulatory issue has been raised to capture the identified electrical shortfall.