Office for Nuclear Regulation

System Based Inspection of Chemical Plant Glove Box Ventilation System

Executive summary

Purpose of Intervention

The Office for Nuclear Regulation (ONR) undertakes all regulatory interaction with the Nuclear Fuel Production Plant site licensee (Rolls Royce Submarines Limited (RRSL)) against a strategy defined by the propulsion sites sub-division. In accordance with that Strategy, a System Based Inspection (SBI) of the Chemical Plant glove box ventilation system was planned and undertaken in February 2020.

The purpose of this inspection is for ONR to examine whether the licensee’s safety case claims in respect of this system important to safety have been adequately implemented.

The scope of this inspection was limited to sampling the glove boxes, the inlet and extract ductwork and associated fans, filters and instrumentation of the Chemical Plant glove box ventilation system. This also included the common discharge stack and stack monitoring equipment. The glove box ventilation system is important to nuclear safety as it confines pyrophoric radioactive material within the system, and mitigates the risks to workers and the public’s safety from the activities conducted in the Chemical Plant glove boxes.

ONR’s SBI process examines evidence to determine compliance against six key licence conditions (LCs). These LCs have been selected in view of their relevance to ensuring nuclear safety, and in providing a structured approach to determining whether the safety case has been implemented adequately through the system being inspected.

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.

As part of my preparation for the delivery of this intervention, the following ONR guidance documentation was used:

LC10 requires RRSL to make and implement adequate arrangements for suitable training of those who have responsibility for any operations that may affect safety.

LC23 requires RRSL to produce adequate safety cases to demonstrate the safety of its operations, and to identify and implement operating conditions and limits necessary in the interests of safety.

LC24 requires RRSL to make and implement adequate arrangements for the provision of suitable written instructions for undertaking any operation that may affect safety.

LC27 requires RRSL to ensure that, before a system is operated, inspected, maintained or tested, all safety mechanisms, devices and circuits are properly connected and in good working order.

LC28 requires RRSL to make and implement adequate arrangements for the regular and systematic examination, inspection, maintenance and testing of all plant which may affect safety.

LC34 requires RRSL to ensure that its radioactive material and radioactive waste is at all times adequately controlled and contained, and that no leak or escape of that material or waste can take place without being detected.

I carried out this SBI over the course of two days. I was assisted by ONR specialist inspectors with expertise in the field of mechanical engineering, fault studies internal hazards and human factors respectively. The inspection comprised discussions with RRSL staff, physical viewing and inspections of targeted structures, systems and components, and review of RRSL’s records and other safety documentation.

Explanation of Judgement if Safety System Not Judged to be Adequate

I judge the safety case supporting this system to be adequately implemented.

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

From the areas I targeted and the evidence I examined during this inspection, I consider that RRSL has adequately implemented those safety case claims that relate to the Chemical Plant glove box ventilation system. RRSL has undertaken work to improve their written instructions and has put in place an adequate inspection and maintenance regime of the glove box ventilation system to ensure its continued safe operation with suitably qualified and experienced personnel. In general, I found evidence of adequate operating procedures that identified the actions required in the event of a loss of the glove box ventilation systems, as well as regular and systematic examination inspection, maintenance and testing to ensure that a pressure differential sufficient to protect workers from a leak or escape in the event of a reasonable foreseeable breach of containment. RRSL also has in place a detailed inspection and surveillance regime targeted at specific locations of potential containment weaknesses. As such I award inspection ratings of Green (No Formal Action) for LCs 10, 24, 27, 28 and 34.

I also identified two specific areas for improvement. The first related to operating rules. Although RRSL presented some examples of good practice, I identified a significant shortfall in that RRSL failed to ensure that the glove box ventilation system is ascribed a suitable safety function.   I judged that this was a significant shortfall in the implementation of RRSL’s arrangements. As such I awarded an inspection rating of AMBER (seek improvement) for LC 23.

The second related to operating instructions. Although RRSL presented some examples of good practice, I identified a minor shortfall in that RRSL failed to consistently ensure that all maintenance instructions are completed correctly.

In the course of my inspection I did not identify any significant concerns with the adequacy of the licensee’s safety case for this system that would necessitate an earlier than planned assessment by ONR.

Conclusion of Intervention

I consider that the licensee has a good knowledge of the physical condition of the structures, systems and components reviewed during this inspection and has in place appropriate management controls to ensure on-going safety.

I have, however, identified two specific areas for improvement, which requires appropriate attention from the licensee. I have therefore raised two ONR Regulatory Issues, one at Level 3 and one at Level 4, to ensure a timely response from RRSL to address these.

Overall, on balance, I consider the safety case supporting this system to be adequately implemented.