Office for Nuclear Regulation

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Hunterston B - Pre-Stressed Concrete Pressure Vessels - LC28 Inspection

Executive summary

Purpose of intervention

The purpose of this intervention was to undertake Licence Condition (LC) compliance inspections at EDF Energy Nuclear Generation Ltd.’s (NGL’s) Hunterston B power station. This intervention was planned to coincide with examination, inspection, maintenance and testing operations being carried out on the Reactor 4 pre-stressed concrete pressure vessel under the station’s Licence Condition 28 arrangements.

Interventions Carried Out by ONR

This intervention included compliance inspections against the following Licence Conditions:

The intervention sampled matters related to the periodic testing of the pre-stressing tendons for the Reactor 4 pre-stressed concrete pressure vessel.  NGL carries out a range of inspections and tests on the pre-stressing system every two years in accordance with the station’s LC 28 arrangements and as part of their demonstration of compliance with the Pressure Systems Safety Regulations (PSSR) 2000. The purpose of the inspections and tests is to provide evidence in support of the Appointed Examiner’s judgement on whether the pre-stressed concrete pressure vessel remains fit for continuing operation. I also carried out an inspection of the concrete surfaces local to the superheater outlet headers for R3 and R4, where the Appointed Examiner has identified elevated concrete surface temperatures.

I also held discussions with EDF-NGL’s pre-stressed concrete pressure vessel Appointed Examiner regarding ONR’s recommendations following return to service of Reactor 3 and Reactor 4 after their last Licence Condition 30 periodic shutdowns.

Explanation of Judgement if Safety System Not Judged to be Adequate

The current inspection was not a system based inspection, and therefore this section is not applicable.

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

Overall I judged from the sampled activities and the records provided that:

Conclusion of Intervention

I have allocated an IIS rating of ‘3 – Adequate’ for LC 28 – Examination, inspection, maintenance and testing, in light of the appropriate standard of documents and demonstrable compliance with company arrangements. A higher rating was not awarded because I judged there is a need for improved alignment between the job instructions and the Appointed Examiner’s Branch Instructions and I also found minor anomalies in the job instructions and identified improvements to tendon cleaning facilities.

There are no findings from this inspection that could significantly undermine nuclear safety and, at present, no additional regulatory action is needed over and above the planned interventions of Hunterston B power station as set out in the Integrated Intervention Strategy. The actions from the inspection have been captured in the ONR issues database as appropriate and will be tracked as part of normal regulatory business.