Office for Nuclear Regulation

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Internal Hazards Information Gathering

Executive summary

Purpose of intervention

This intervention was held on the 17 April 2014. This was a specific information gathering meeting but can be viewed as part of a series of regular interactions on the topic of internal hazards. The objective of this meeting was for Nuclear New Build Generation Company (NNB GenCo) to give a more in depth update on some of the deliverables and areas of work currently being progressed in the area of internal hazards with the Office for Nuclear Regulation (ONR). A short teleconference element was also used as an opportunity to discuss the potential venue and agenda for the next regular level 4 meeting.

Interventions Carried Out by ONR

This meeting was held with NNB GenCo at the EDF offices at Barnwood, Gloucestershire.

Discussions during the meeting included:

Explanation of Judgement if Safety System Not Judged to be Adequate

N/A

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

I viewed this meeting to be a useful update of progress and a good exchange of information. I was reassured that internal hazards specialists within the licensees organisation were being involved at the right time and as a result of this changes were being made where necessary. It is important to understand that, due to the volume of design documentation, it is impossible for the licensee's internal hazards specialists to see every document. There is an expectation that suitably qualified and experienced personnel (SQEP) from other disciplines will identify when internal hazards advice is required.

We discussed the turbine disintegration assessment and positioning of plant on a two reactor site. It was agreed that this assessment is not quite completed yet. ONR's view was that the approach may not lead to a degree of plant protection implied by the ONR safety assessment principles (SAPs). NNB GenCo agreed to consider this further as analysis results, expected from a new re-assessment of turbine disintegration, become available

NNB GenCo described the planned approach for the delivery and storage of the hydrogen gas bottles had now been changed from the arrangement in PCSR 2012. Gas bottles will now be delivered by trailer and will remain on the trailer. When the gas bottles are empty, the entire trailer will be replaced. This ensures that connection and disconnection is simple and routine maintenance of the bottles, valves etc. will be carried out by the gas bottle supplier remote from the licensed site.

We discussed the potential for technical gallery collapse due to the erosion of soil caused by the leak of the supply pipework for circulating water filtration system (CRFs). This is large bore pipework linking the circulating water (CW) pump house to the condensers. This has been remedied by piling into the bedrock to ensure that the technical galleries will remain stable in the event of such a leak.

An integrated intervention strategy (IIS) rating of 3 (satisfactory standard) has been assigned to the internal hazards topic stream. This is based on the discussions and behaviours throughout the intervention.

Conclusion of Intervention

I conclude that this was a useful intervention which gave me a more in-depth understanding regarding the work streams currently being completed relating to internal hazards. It is reassuring to be shown evidence of the consideration and if necessary, the changes driven by internal hazards specialists within NNB GenCo. This includes the piling of the technical galleries where necessary and the delivery and storage of the hydrogen supplies.

It is important for NNB GenCo not to be too focussed on risk targets and to ensure that the design of Hinkley Point C (HPC) is hazards tolerant. Consideration also needs to be given to the fact that HPC will be a two reactor site that will require the maintenance of emergency power supplies following a turbine disintegration event within the HPC site.