Office for Nuclear Regulation

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Balance of Nuclear Island (BNI) Safety Functional Requirements Note (SFRN) Cross-Cutting Intervention

Executive summary

Purpose of intervention

As part of a planned cross-cutting intervention relating to NNB Generation Company Ltd's (NNB GenCo) balance of nuclear island safety functional requirement note (BNI SFRN), a team of six Office for Nuclear Regulation (ONR) specialist inspectors examined (by sampling) the adequacy of the substantiation of the safety classification results presented in the BNI SFRN. SFRNs are key design documents, providing the classification of safety features and will be part of the substantiation process supporting the next revision of the Hinkley Point C pre-construction safety report (PCSR).

The BNI SFRN was produced early in the engineering phase of the project with plans, previously outlined to ONR, to revise the SFRN ahead of the next revision of the Hinkley Point C PCSR. Previous questions had been raised within level 4 meetings on whether adequate substantiation to support the BNI SFRN would also be available to support these timelines.

The purpose of my intervention was to:

Interventions carried out by ONR

A team of six ONR specialist inspectors considered the adequacy of the substantiation through review of relevant NNB GenCo and Responsible Designer documentation and discussion with NNB GenCo. This intervention is part of a planned series of interventions outlined in the ONR project task sheet for safety categorisation and classification.

The adequacy of the substantiation of the safety classification will inform ONR's judgement on NNB GenCo's acceptance of reference configuration (RC) 1/1.1 and its progress with preparations for proceeding with construction of Hinkley Point C.

Explanation of judgement if safety system not judged to be adequate

Not applicable as a safety system inspection was not carried out.

Key findings, inspector's opinions and reasons for judgements made

The BNI SFRN has been subjected to primary surveillance by NNB GenCo with a significant number of comments raised. The adequacy of the surveillance was not considered during this intervention, but will be considered at a later date.

The intervention was intended to consider a selection of systems, however focused on the safety features associated with the containment heat removal system. Out of 11 safety features of the containment heat removal system, identified in the BNI SFRN, adequate substantiation of the safety classification was only provided during the intervention for one safety feature.

NNB GenCo was unable to provide any documentary evidence during the intervention as to why one of the safety features, identified in earlier documentation produced to define the Generic Design Assessment (GDA) EPR reference configuration, is not considered in the BNI SFRN.

NNB GenCo was unable to provide evidence during the intervention of adequate substantiation to support the classification of most of the frontline safety features and supporting safety features of the containment heat removal system. Due to difficulties in NNB GenCo providing adequate substantiation and documentary evidence, further systems planned to be sampled were not considered during the intervention.

Given that the BNI SFRN has undergone primary surveillance, I consider it is of concern that NNB GenCo was unable to provide evidence of adequate substantiation to the ONR team. This may be indicative of inadequate NNB GenCo intelligent customer capability, inadequate review and acceptance of the BNI SFRN, and/or inadequate preparation for the intervention. Further engagement with NNB GenCo is required before an appropriate assessment of the adequacy of NNB GenCo's surveillance of the BNI SFRN and its supporting material can be reached.

It is not clear whether there is inadequate substantiation of the classification of the BNI systems' safety features, or whether there is adequate substantiation and NNB GenCo was unable to present this during the course of the intervention. Furthermore, it is not clear whether NNB GenCo convinced itself, as part of its primary surveillance of the BNI SFRN, whether the substantiation is adequate.

No representative from the Safety Directorate attended this intervention. I note from previous level 4 meetings that the Safety Directorate is also planning to consider the adequacy of the substantiation of the SFRNs as part of its ongoing interventions.

Conclusion of intervention

Based on the information provided during the intervention, NNB GenCo did not provide adequate evidence of sufficient substantiation of the safety classification that is presented in the first version of the BNI SFRN. Previous interactions have identified the production of additional BNI classification substantiation; however the timescales for production of this additional justification was not in line with my expectation. I consider that this is of considerable concern as the BNI SFRN (along with two other SFRNs) will underpin the next revision of the Hinkley Point C PCSR. If adequate substantiation does not exist or evidence of it cannot be presented to ONR, this will be a risk to ONR consenting to the start of construction (first safety related concrete).

Given the gap to ONR's expectation, a level 3 issue has been raised on ONR's issues database for NNB GenCo to ensure that adequate substantiation is documented. Furthermore, I will arrange a follow-up intervention once NNB GenCo has provided sufficient assurance that the concerns raised during the intervention have been addressed.