Office for Nuclear Regulation

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Hinkley Point B - Fault Studies Specialist Inspection

Executive summary

Purpose of Intervention

The purpose of this intervention was to undertake a planned inspection at EDF Nuclear Generation Limited’s (NGL’s) Hinkley Point B power station in line with the planned inspection programme contained in the Hinkley Point B Integrated Intervention Strategy (IIS) for 2017/2018.

Interventions Carried Out by ONR

We undertook a compliance inspection against the requirements of Licence Condition 23: Operating Rules.  In particular we sampled compliance against the requirement of LC 23(3) for operations to be controlled in accordance with operating rules.  Our attention was focussed on those Operating Rules whose implementation relies wholly or in part on calculations carried out by support staff rather than observation by the reactor desk engineers alone. 

The support staff reside principally in a group termed the ‘Nuclear Safety Group’ (NSG) and hence we reviewed briefly the resourcing and training of the NSG, emergent issues and the group’s future work plans.

We also addressed compliance with LC23 requirements relating to a prolonged loss of alternating current electrical supply from the National Grid, i.e. a loss of off-site power (LOOP) of longer than 24 hours.

Explanation of Judgement if Safety System Not Judged to be Adequate

Not applicable as this was not a System Based Inspection.

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

We made the following observations and judgements based on the sampling undertaken:

The NSG age distribution is heavily weighted to the upper age range. The NSG Head recognised that this distribution poses potentially significant implications to the continuing ability of the group to provide nuclear safety, reactor physics and fuelling advice and compliance work.  These implications are being addressed by focussing on knowledge capture and training of other nuclear safety engineers (NSE) to ensure the station’s future capability.  We noted that the training for Hinkley Point B NSE had recently been awarded a ‘Blue’ exemplar rating by the Training Standards and Accreditation Board (a cross-industry independent body external to EDF NGL).     

The Station Director had clear arrangements for delegating responsibility for compliance with each sub-clause within LC23.  The responsibility for compliance with LC23(3) by ensuring operation remained within the Operating Rules was delegated to the Station Operations Manager.  This responsibility was further delegated to the control room staff as Duly Authorised Persons (DAP) under LC26.  The NSG Head supports the DAPs by ensuring that a Reactor Physicist provides a valid and up-to-date compliance record sheet detailing those Operating Rule limits that cannot be indicated or monitored directly as outputs in the Control Room.  Instead the current values of such parameters or limits, or the remaining margin, are evaluated by Nuclear Safety Engineers within the NSG.  Compliance record sheets were completed, maintained as records and available for examination.

We were aware of the licensee’s on-going work to assess the implications of a loss of National Grid electrical supply (LOOP) for longer than the 24 hour period used a design assumption.  From discussion we judged that resilience against an extended LOOP was adequate based on observations of essential stock levels (kerosene, diesel and water), acceptable storage and distribution plant condition and provision of battery-backed direct current motors and pumps.  ONR noted that the licensee’s estimates of endurance were dependent on management plans to reduce usage rates of essential stocks and thereby prolong the period of adequate post-trip cooling.  ONR concurred with the licensee’s estimates which indicated that for each essential stock a potential endurance of 72 hours (3 days) or longer was achievable.

The intervention was performed in line with ONR’s guidance requirements (as described in our technical inspection guides) in the areas inspected.

Conclusion of Intervention

From the evidence gathered during the inspection, we allocated an inspection rating of ‘Green’ for LC 23. 

There are no findings from this inspection that could significantly undermine nuclear safety.