Office for Nuclear Regulation

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Hunterston B - Compliance inspection - High wind and aircraft impact

Executive summary

Purpose of Intervention

This was a planned inspection of EDF Energy Nuclear Generation Ltd.’s (NGL’s) Hunterston B Power Station, undertaken as part of the planned intervention strategy for the Operating Facilities Division (OFD) of the Office for Nuclear Regulation (ONR).

The work was carried out in accord with the planned inspection programme contained in the Hunterston B Integrated Intervention Strategy (IIS) for 2018/19.

Interventions Carried Out by ONR

On 27-28 November 2018 as an ONR specialist inspector, external hazards, I carried out an on-site licence condition (LC) compliance inspection, in relation to high wind hazard and accidental aircraft impact, accompanied by a specialist inspector colleague. The inspection addressed the following:

The inspections were based on sampling the implementation of the licensee’s arrangements at Hunterston B Power Station against the LCs. The objective of the inspection was to determine whether the licensee’s arrangements were adequately implemented and in accordance with the high wind and accidental aircraft impact safety case requirements.

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

Explanation of Judgement if Safety System Not Judged to be Adequate

No system based inspection was undertaken hence, this is not applicable for this intervention.

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

Licence Condition 23 (Operating rules) – the Licensee’s approach in providing guidance via Station Operating Instructions (SOIs) and Symptom Based Emergency Response Guidelines (SBERGs) etc., rather than using rigid Operating Rules for every possible scenario is realistic, reasonable and was judged to be adequate. On this basis, I judged that compliance with LC23 met ONR’s expectations, taking account of compliance with LC24 (see below), I therefore assigned a rating of Green (no formal action) for LC23.

Licence Condition 24 (Operating instructions) – I inspected a sample of operating instructions including: a SOI for actions relating to high wind hazard; the emergency handbook, and; severe accident scenario for inadequate heat removal. The SOI for high wind did not explicitly state what the wind speed referred to – whether it is a wind gust, mean wind speed over given period etc. – which would lead to certain operator actions but the Nuclear Safety Engineer clarified that unless otherwise stated it is the 3 second wind gust. I therefore assigned a rating of Green (no formal action) for LC24.

Licence Condition 27 (Safety mechanisms, devices and circuits, SMDCs) – I examined the potential for simultaneous failure of diverse and redundant SMDCs due to aircraft impacts or extreme winds. I concluded that due to low target areas and adequate redundancy, diversity, segregation, surrounding structures and maintenance, the simultaneous loss of diverse or redundant SMDCs is extremely improbable. I therefore assigned a rating of Green (no formal action) for LC27.

Licence Condition 28 (Examination, inspection, maintenance and testing) – on the basis of the sampled documentation, including Maintenance Inspection and Test Schedule (MITS) and Work Order Cards relating to the examination, inspection, maintenance and testing of high wind hazard or accidental aircraft impact related structures, systems and components (SSCs), I judge that Hunterston B has adequate arrangements in place for compliance with LC28. I therefore assigned a rating of Green (no formal action) for LC28.

Conclusion of Intervention

There were no findings identified from this inspection that could significantly undermine nuclear safety. At present, no additional regulatory action is needed over and above the planned interventions at Hunterston B Power Station as set out in the Integrated Intervention Strategy, which will continue as planned.