Office for Nuclear Regulation

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Intervention regarding fault studies aspects of the Hinkley Point C (HPC) safety case

Executive summary

Purpose of intervention

The purpose of this intervention was to form a judgement on the adequacy of NNB Generation Company (HPC) Ltd’s (NNB GenCo) and its supporting organisations’ (EDF – the Responsible Designer (RD) and AREVA) arrangements for controlling the codes and methods used in the fault studies aspects of the Hinkley Point C (HPC) safety case.  Furthermore, this intervention provided an opportunity for NNB GenCo, the licensee, to demonstrate how emerging issues relating to codes and methods are identified, documented, controlled and managed.

The intervention was carried out at AREVA’s offices in Paris, to gain confidence in how code development is progressed and monitored within organisations that support the preparation of HPC’s safety case.

This intervention forms the first part of a longer term intervention strategy seeking confidence in the adequacy of NNB GenCo’s arrangements for controlling the codes and methods supporting the major safety submissions for the HPC project. 

Interventions Carried Out by ONR

This intervention was carried out jointly by ONR inspectors and a representative of NNB GenCo’s internal regulator (Safety Directorate – Independent Technical Assessment function) and supported by an ONR technical support contractor.    The relevant ONR Safety Assessment Principles such as those listed under “assurance of validity of data and models” and “fault analysis” were used to inform ONR judgements during this intervention. The intervention included a review of:

The following two areas of analysis were selected for sampling:

Key Findings, Inspector's Opinions and Reasons for Judgements Made

From the information reviewed, AREVA has a well-established set of processes in place to identify and track the need for code developments which may result in code updates.  All relevant code users are informed of the code updates via internal communications.

The requirements for additional or complementary HPC plant performance transients are documented in a ‘kick off’ letter that captures the key parameters, boundary conditions and methodologies to be used, which is agreed between NNB GenCo, the RD and AREVA.  This follows a well-structured approach, using an evolving template and has benefited from the experience gained from its earlier use.

I noted that NNB GenCo’s ‘Generic Acceptance’ document is currently in preparation requiring further development by NNB GenCo.  Whilst this intervention highlighted a number of good practices in this area, the following observations were recorded for NNB GenCo’s further consideration during the development of its review and acceptance arrangements:

There is a long chain of activities that cover the initial identification of a requirement (parameters to be used for transient analysis), production of analysis, verification leading to final acceptance using multiple specification and guidance documents, which is further complicated as some documents are in French.  NNB GenCo should therefore consider producing an overarching interface arrangements document to increase visibility of the framework that defines the working relationship between the various stakeholders supporting the HPC project in this area.

Conclusion of Intervention

During this intervention, the main evidence was provided by AREVA, concerning its processes for managing codes and methods supporting the relevant aspects of the design. The arrangements employed within the RD were summarised along with NNB GenCo’s plans for generic acceptance of the code and methods used by its suppliers.  Future interventions on this topic will consider NNB GenCo’s and the RD’s arrangements in more detail.

Based on the evidence gathered, a number of good practices in the codes and methods area were observed demonstrating that adequate arrangements are in place. However, a number of observations were noted for further consideration by NNB GenCo during the development of its review and acceptance arrangements.

The following recommendations resulted from this intervention, which will be taken forward as part of routine interactions in the fault studies topic stream and future planned interventions: