The purpose of this intervention was to form a judgement on the adequacy of NNB Generation Company (HPC) Ltd’s (NNB GenCo) arrangements for controlling development of the fuel building Fault and Protection Schedule (F&PS). The F&PS is an important part of the safety case that links initiating events, fault sequences and the safety measures designed to prevent faults or mitigate the consequences. This intervention provided an opportunity for NNB GenCo to demonstrate the way the fuel building F&PS has been produced and developed; explaining the processes employed for fault identification, screening, bounding and the substantiation provided for the safety measures identified as lines of defence.
This intervention forms the second part of a longer term intervention strategy, seeking confidence in the adequacy of NNB GenCo’s arrangements for controlling the production and development of the F&PS. As such, progress against a set of observations made in the first intervention of this series was also reviewed.
This intervention was carried out collaboratively by ONR and representatives of NNB GenCo’s Safety Directorate (Independent Technical Assessment (ITA)). The intervention sampled a selection of faults from the fuel building F&PS in order to determine the adequacy of:
During this intervention, evidence concerning the processes for managing the development of the F&PS was provided by the Responsible Designer, on NNB GenCo’s behalf. The arrangements adopted for identification, screening and bounding of design basis initiating events were tested via sampling of specific entries in the schedule. Furthermore, the next stages of fault analysis production, for further development of the schedule, were explained. Future planned interventions will consider NNB GenCo’s, Areva’s and the Responsible Designer’s arrangements for the incorporation of updated supporting analysis in more detail.
Based on the information reviewed, I judge that NNB GenCo (by way of the Responsible Designer) has established an adequate set of processes to identify and capture the faults and safety measures presented in the fuel building F&PS.
Progress is being made against observations from the previous intervention into the reactor building F&PS; and where work is not yet underway plans are in place to address those observations.
While no significant issues were identified during this intervention, observations were made relating to the documentation sampled and are recorded for NNB GenCo’s further consideration.
Based on evidence provided, several good practices in the production and development of the F&PS were observed during this intervention, and further improvements in the processes have also been achieved since the previous intervention. Therefore, based on the progress made and plan of activities presented, the outcome of this intervention has been rated as GREEN.
The observations arising from this intervention will be followed up as part of routine regulatory interactions with NNB GenCo