- Site: AWE Aldermaston
- IR number: 21-008
- Date: April 2021
- LC numbers: 10, 23, 24, 27, 28, 34
Executive summary
Purpose of Intervention
The Office for Nuclear Regulation (ONR) undertakes all regulatory interaction with the Aldermaston site licensee (AWE plc) against a strategy defined by the ONR Weapons sub-Division. In accordance with that strategy, a planned System Based Inspection (SBI) was carried out on the Main Production Facility in March 2021. The purpose of this inspection was for the ONR to determine the adequacy of the implementation of the extant safety case for a sample of the Primary Containment function in the context of the six Licence Conditions given below.
Interventions Carried Out by ONR
The intervention was performed in line with ONR's guidance requirements (as described in our technical inspection guides) in the areas inspected.
The ONR PTC Facility inspector and an ONR specialist mechanical engineering inspector conducted a SBI of a sample of the main production facility primary containment and their supporting Systems, Structures or Components (SSC’s). The focus of the inspection was on the polymer seals claimed as providing high-integrity containment between gloveboxes and connecting tunnels for the lifetime of the facility. We also examined a cracked glovebox window and discussed how the ongoing primary containment integrity would be assured for the cracked window. The adequacy of the implementation of AWE’s extant safety case for the Primary containment was sampled via compliance inspections against the Licence Conditions (LCs) below.
- LC 10 (training)
- LC 23 (operating rules)
- LC 24 (operating instructions)
- LC 27 (safety mechanisms)
- LC 28 (examination, inspection, maintenance, and testing)
- LC 34 (leakage and escape of radioactive material and radioactive waste).
Explanation of Judgement if Safety System Not Judged to be Adequate
The safety system for the Main Production Facility Primary containment and its associated SSC’s is judged to be adequate.
Key Findings, Inspector's Opinions and Reasons for Judgements Made
The inspection consisted of discussions of the extant safety case documentation for the primary containment. A facility walk down and plant inspection was also carried out, where documented evidence was presented and a number of facility operations staff were questioned to determine their level of understanding of the plant, the process, its hazards and the safety mechanisms and devices in place to prevent and/or mitigate against potential fault scenarios. A few regulatory observations were raised during the plant walk down which were relayed back to MPF staff. No areas of significant nuclear safety concern were identified during this inspection.
Discussions with plant operators and maintenance staff demonstrated an adequate understanding of the limits and conditions of operation required to maintain nuclear safety. Training records were examined for a sample of operational staff and were seen to be completed and in date. We focused on non-routine training for the replacement of a glovebox window and for a press bellows replacement, both of which have a primary containment function. We were satisfied that the procedures in place and the training provided were adequate for these two infrequent processes.
We were assured that the primary containment integrity is maintained despite the cracked window due to the functional moisture monitors in the glovebox, which would alarm in the control room if any moisture ingress via the crack occurred. The Zone 1 ventilation system will also maintain a negative pressure in the box relative to the external pressure, so egress of SNM is prevented should the window fail completely. This is unlikely due to the laminated construction of the window. We were assured that the window would be replaced as soon as possible.
A sample of Safety Mechanisms, Devices and Circuits were observed on the plant and their maintenance records examined. All SMDC’s were seen to have a periodic maintenance regime entry on the Asset Management System (AMS). We were satisfied that the requirements of LC27 and LC28 had been demonstrated by the evidence provided during the inspection.
From the evidence sampled and presented during the inspection we consider AWE to have adequately implemented the claims made within the extant safety case that relate to the primary containment and its supporting Systems, Structures or Components (SSC’s). AWE demonstrated adequate compliance with all LC’s examined during the inspection.
Conclusion of Intervention
Based on the evidence sampled during the inspection the overall ratings for the targeted assessment areas are LC 10 - Green, LC 23 - Green, LC 24 - Green, LC 27 - Green, LC 28 - Green, and LC 34 - Green. No Regulatory Issues were raised during this inspection. Therefore, based on the samples inspected, we are of the opinion that ‘YES’ the system adequately fulfils the requirements of the extant safety case, and therefore the overall SBI rating is ‘Green’ - Adequate.