Office for Nuclear Regulation

Barrow - System Based Inspection (SBI) of containment on Boat 4

Executive summary

Purpose of Intervention

The purpose of this intervention was to carry out a System Based Inspection (SBI) at the Barrow nuclear licensed site, operated by BAE Systems Marine Limited (BAESML), in line with the 2018/19 intervention plan and propulsion sub-division strategy.

The aim of the SBI is to inspect the implementation of the safety case with regard to containment on Astute Class Boat 4 (HMS Audacious) in advance of Power Range Testing (PRT).

The relevant systems, structures and components required to deliver containment on Astute Class Boat 4 (HMS Audacious) are primarily within the naval reactor plant safety case. The site safety case identifies a number of key items of plant and/or equipment and explicitly places claims on these to meet specific safety functional requirements. The site safety case references out to, and assumes compliance with, the naval reactor plant safety case, and therefore both the naval reactor plant safety case and the site safety case, are key to this intervention.

Interventions Carried Out by ONR

The inspection considers compliance with a number of licence conditions (LC) to test the adequacy of the implementation of the site and naval reactor plant safety cases. The standard six licence conditions (LC) inspected against are:

The inspection focussed on the systems, structures and components aboard HMS Audacious claimed to provide containment in the event of an accident, to limit the consequences to people and the environment and ensure control of radioactive material is maintained. These systems, structures and components were selected due to the extended build time taken for HMS Audacious, and therefore the requirement for repeat examination, inspection, maintenance and testing prior to Power Range Testing. This includes the:

The intervention was undertaken by the ONR nominated site inspector and an ONR nuclear liabilities specialist inspector. The inspection was conducted jointly with the Defence Nuclear Safety Regulator (DNSR) who are responsible for regulating the through life safety of the naval reactor plant.

Explanation of Judgement if Safety System Not Judged to be Adequate

From the safety systems, structures and components that have been sampled as part of the primary containment boundary and containment automatic isolation system, I judged that overall these are able to fulfil their safety functional requirements, in line with the safety cases. 

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

With respect to the SBI the follow judgements were made;

LC 10 (Training) – I examined the training records for a sample of the personnel involved in the examination, inspection, testing and maintenance of plant which formed part of the containment automatic isolation system.  A well-defined process was found which adequately captured the training requirements and oversight of operations undertaken by BAESML staff. Evidence of its implementation was sampled and found to be in order. . I therefore assign an IIS rating of green for LC10 compliance.

LC 23 (Operating rules) / LC 24 (Operating instructions) – A single operating limit was identified as relevant for this inspection. Based on the evidence sampled, I concluded that an auditable trail of evidence to support how this condition is compiled with could not be identified. The operating limit places requirements on the performance of the safety mechanisms, devices and circuits. For this reason completion of examination, inspection, maintenance and testing activities, as defined by the plant maintenance schedule, infers the operating limit is being complied with. However, specific measureable requirement(s) to provide positive compliance with the operating limit was not explicit within the safety case documentation. This is a shortfall in the regulatory expectation of LC24(2), which requires the licensee to identify adequate instructions to demonstrate compliance with an operating limit.

On this basis a green inspection rating is merited against LC 23, and an amber inspection rating against LC 24. A regulatory issue will be raised to address the finding.

LC 27 (Safety mechanisms, devices and circuits) / LC 28 (Examination, inspection, maintenance and testing) – A number of plant items were selected which were stated as being relevant to the prevention and mitigation of faults identified within the naval reactor plant safety case. In my opinion BAESML presented evidence that relevant safety mechanisms, devices and circuits are adequately implemented and undergo a suitable programme of EIMT. Overall, I judge that an inspection rating of green is merited against both LC 27 and LC 28.

LC 34 (Leak and escape of radioactive material and radioactive waste) – Based upon the evidence sampled on the penetrations and hull volume leak testing, it was judged that an adequate implementation of arrangements to ensure, so far as is reasonably practical, that radioactive material would be adequately controlled and contained within the primary containment boundary structures. On this basis, a green inspection rating is merited against LC34.

Conclusion of Intervention

From the evidence sampled during this SBI; notwithstanding the finding identified, I consider that the primary containment boundary and containment automatic isolation system (CAIS) on Boat 4, HMS Audacious, fulfil the requirements of the safety case.

One regulatory issue is to be raised to address the shortfall relating to the demonstration of positive compliance with the operating limit sampled.