Office for Nuclear Regulation

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Hunterston B planned Intervention

Executive summary

Purpose of intervention

This intervention was to investigate the actions taken that resulted from EDF Energy Nuclear Generation Limited (NGL’s) own investigation of Local Exhaust Ventilation (LEV) adverse conditions that arose during vessel entry work during Hunterston B Reactor 4 statutory outage in 2014. It follows on from a previous ONR intervention in April 2015 where a review of NGL’s own investigation confirmed a number of actions to be carried out prior to the Reactor 3 outage due in October 2015.

The intervention also sought to achieve confidence in the overall radiological protection arrangements planned for the Reactor 3 outage due in October 2015. This was achieved by a review of the LEV issue described above, a review of the overall planned vessel entry campaign, and inspections of the vessel-entry complex, pile-cap/ charge hall area and gas circulation hall.

Interventions Carried Out by ONR

This intervention sought to establish NGL’s on-going compliance with the Ionising Radiations Regulations 1999 in relation to the matters investigated and in its Adverse Condition Investigation (ACIN).

Explanation of Judgement if Safety System Not Judged to be Adequate

No system inspection was undertaken during this intervention.

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

NGL’s investigation was effective in identifying the causes of the LEV efficacy failures which had led to a number of low-level personal contamination events involving vessel entry workers (i.e. low personal doses) in 2014. The investigation was also conclusive on the improvements that needed to be made to LEV operation and maintenance and on the need for better training and operational oversight of the ventilation systems that contribute to the establishment of effective LEV during vessel entry work programmes at the Station.

Overall, I was satisfied with the corrective actions that NGL are undertaking and with the urgency it is being given; principally that most of it should be completed prior to, and the remainder immediately upon, commencement of the Hunterston B Reactor 3 2015 statutory outage.

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

NGL have completed their review of the LEV systems and have made various improvements to processes, systems and plant. They also have a plan to complete this work soon after commencement of the Reactor 3 outage. No other issues were identified that would question confidence in the overall radiological protection arrangements planned for the Reactor 3 outage due in October 2015.