Office for Nuclear Regulation

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Planned System Based Inspection (SBI) - Vaults - AWE (A) Main Production Facility

Executive summary

Purpose of Intervention

This intervention, conducted at the Atomic Weapons Establishment (AWE) Aldermaston licensed site, was undertaken as part of the 2019/2020 intervention plan and weapons sub-division strategy.

Interventions Carried Out by ONR

The ONR site inspector for PTC and ONR specialist inspectors in mechanical engineering conducted a planned System Based Inspection (SBI) of the Vaults in the AWE Aldermaston Main Production Facility. Implementation of AWE’s safety case for the Vaults was sampled via compliance inspections against a number of Licence Conditions (LCs).

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

Not applicable.

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

Conduct of the Main Production Facility Vaults SBI was via examination of work instruction documentation and records, discussion with key plant personnel and inspection of the relevant plant areas. The key findings against each LC are recorded below:

LC 10 (Training) – Rating = Green

The training for both the Fissile Movement Control System (FMCS) staff who operate the Vaults and maintenance staff working on the Vault systems were considered.

The training arrangements sampled for the FMCS resources were judged to be robust and comprehensive and application of these arrangements was demonstrated.

Gaps were identified in the resilience and succession planning of the maintenance resources and it was observed that only two individuals (one Mechanical and one Electrical Engineer) were in post. AWE recognise the shortfall in relation to maintenance staff training and an extant Regulatory Issue (RI 6541) already provides oversight to monitor improvements on a wider scale than the Main Production Facility Vaults.

Therefore, given the considerations above, we were satisfied that the overall inspection rating against LC 10 was ‘Green’.

LC 23 (Operating rules) – Rating = Green

The floor area of the Secure Transit Bay/Secure Packing Bay (serving the Vault operations) has a transport index restriction limiting the number of packages stored there. Whilst the licensee was able to demonstrate adequate control over this key safety parameter we observed that no independent compliance audits are undertaken. We advised that this provision could be implemented and the licensee accepted this advice. 

The total number of package moves per annum has an upper limit in the safety case. The number of package moves is not monitored although it is recognised that the total moves per annum is significantly below the safety case limit. The licensee accepted that a routine report from the FMCS development team would assist in closing this gap.

During the inspection it was stated by the AWE Safety Case Manager that an investigation into the maximum ‘skew’ is being evaluated as part of the safety case development. We advised that timely resolution of this investigation is required to determine whether a new operating rule is required. The licensee accepted this advice.

From the evidence presented during the inspection we considered there to be relatively minor deficiencies in compliance of arrangements for LC23, and the licensee readily accepted our advice regarding closure of the gaps. Therefore we were satisfied with a ‘Green’ rating.

LC 24 (Operating instructions) – Rating = Green

The sampled documents identified that four packages on the Secure Packing Bay (SPB) floor should have been unpacked some time ago however remain resident. AWE accepted that no meaningful progress has been made to make and implement adequate arrangements to deal with these packages. We advised that this be addressed in a timely manner which was accepted by the licensee.

Two operating instructions were sampled relating to weight gain of the Special Nuclear Material (SNM) and Vault Retrieval Mechanism (VRM) skewing limits. Evidence of adequate review and amendment of the instructions regarding the SNM weight gain was demonstrated. Amendment of the VRM instructions to account for skewing limits could not be demonstrated by the licensee. We advised that the gap in the VRM operating instruction was to be addressed in a timely manner which was accepted by the licensee.

Although the inspection identified gaps in the implementation of changes to some of the sampled operating instructions, and licensee work to address the safe unpacking of a number of historic packages in the SPB, we considered these to be minor shortfalls. The licensee accepted its obligation to provide timely resolution of the gaps. The licensee also demonstrated adequate implementation of change control to operating instructions relating to SNM weight monitoring. Therefore we were satisfied that the overall rating for LC24 was ‘Green’. 

LC 27 (Safety Mechanisms, Devices and Circuits – SMDC) – Rating = Amber

AWE’s compliance with LC27 is delivered through its implementation of LC28 arrangements. The inspection rating for LC27 can therefore be considered as that for LC28.

LC 28 (Examination, Inspection, maintenance and Testing – EIM&T) – Rating = Amber

Two aspects of AWE’s LC28 arrangements were sampled relating to the Vault fume cupboard ventilation and the Vault Retrieval Mechanism (VRM). The sampled documents for Vault fume cupboard ventilation were considered adequate although minor deviations were identified regarding pass/fail criteria and missing annotation of document steps.

Shortfalls against Relevant Good Practice (RGP) were identified in the application of statutory examinations. We identified gaps in communication of structures, systems or components that may affect safety to inform the scope of inspection. AWE recognised the shortfall and an extant Regulatory Issue (RI 4171) already provides oversight to monitor improvements on a wider scale than the Main Production Facility Vaults. In addition AWE could not demonstrate that adequate arrangements were in place to manage defects identified during statutory examinations and to ensure corrective actions are effectively implemented.

Overall, although relevant good practice was generally met with the ventilation arrangements, the shortfalls in the implementation of VRM EIM&T justified an ‘Amber’ rating for LC28.

LC 34 (Leakage and Escape of Radioactive Material and radioactive Waste) – Rating = Green

Continuous Activity in Air Monitors (CAMs) are required to detect potential airborne activity release and have been tested to ensure they respond in an appropriate timescale. The CAMs are routinely maintained and tested verses their original specification however, recognising ageing and obsolescence issues, work is in progress to develop and test replacement CAMs.

The sampled documents included the Vault fume cupboard ventilation and filtration arrangements and identified a minor shortfall in the adequacy and implementation which is being addressed by AWE. Consideration of differential pressure indication of the fume cupboard filter was proposed by AWE as a means of providing ‘real time’ performance indication and is recognised as RGP.

We were satisfied that RGP was being met and judged that the appropriate rating for LC34 was ‘Green’.

Conclusion of Intervention

LCs 10, 23, 24, and 34 were rated as ‘Green’ (although noting that in all cases minor recommendations were communicated to the licensee).

In the case of LC 27 and LC 28 it was judged that the shortfalls identified were significant enough to merit ONR oversight of actions designed to monitor effective remedy by the licensee. LCs 27 & 28 were therefore rated Amber and ONR issues are required to agree and track to closure appropriate actions with the licensee.

Overall a Green rating was awarded as it was acknowledged that the shortfalls against RGP identified against LC28 are mitigated by extant Regulatory issues (6541 and 4171) which are being progressed.