The Office for Nuclear Regulation (ONR) undertakes all regulator interaction with the Sellafield site licensee (Sellafield Limited, SL) against a strategy defined by the ONR Sellafield, Decommissioning, Fuel and Waste Division. The inspection plan PP5 for the Operational Waste Facilities (OWF) details a strategic programme of regulatory inspections which includes a System Based Inspection (SBI) of the Electrical System in the Highly Active Liquor Evaporation and Storage (HALES) facility.
The purpose of this inspection is for ONR to examine whether the licensee's safety case claims in respect of the HALES electrical system have been adequately implemented. The electrical systems targeted in HALES were those responsible for supporting a number of structures, systems and components (SSCs) important to safety. These SSCs provide key safety case claimed functions including removal of the decay heat and hydrogen generated by the highly active liquors processed and stored in the facility.
ONR's SBI process examines evidence to determine compliance against six licence conditions (LC). These LC's (listed below) have been selected in view of their relevance to ensuring nuclear safety and provide a structured approach to determining whether the safety case has been implemented adequately through the system being inspected.
LC 10 requires SL to make and implement adequate arrangements for suitable training for those who have responsibility for any operation which may affect safety.
LC 23 requires SL to produce an adequate safety case to demonstrate the safety of its operations, and to identify the conditions and limits necessary in the interests of safety.
LC 24 requires SL to ensure that all operations which may affect safety are carried out in accordance with written instructions.
LC 27 requires SL 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.
LC 28 requires SL to make and implement adequate arrangements for the regular and systematic examination, inspection, maintenance and testing of all plant which may affect safety.
LC 34 requires SL to ensure, so far as is reasonably practicable, that radioactive material and radioactive waste on the site is at all times adequately controlled or contained so that it cannot leak or otherwise escape. On this occasion LC 34 (leakage and escape of radioactive materials) was not included in the System Based Inspection as we judged that it was not sufficiently applicable to the systems under considerations.
I, the ONR lead electrical engineering specialist, conducted the System Based Inspection of the HALES facility normal duty and backup electrical system over the course of two days. I was assisted by the ONR Site Inspector for the facility and an ONR Electrical, Control and Instrumentation Specialist Inspector. A trainee on the industry nuclear graduates scheme was also a member of the inspection team, acting as an observer to assist in her professional development. This inspection was also attended by a member of SL staff from the internal regulatory function. The inspection comprised discussions with SL staff, physical viewing and inspection of targeted structures, systems and components (SSC) through a plant walk-down and examination of a sample of operational documents and records.
The System Based Inspection was preceded by a planning meeting to assist ONR to determine an efficient and effective inspection sampling strategy.
The ONR site inspector also conducted follow up enquiries in the Waste Vitrification Plant facility following a recently failure of a power supply which resulted in a process trip. This was reported to ONR under INF1 2017/679.
The intervention was performed in line with ONR’s guidance requirements (as described in our technical inspection guides) in the areas inspected.
The safety case supporting this system was judged to be adequately implemented.
Based on the areas I targeted and the related evidence I examined during this inspection, I consider that SL has adequately implemented those safety case claims that relate to the HALES Electrical System. As such, I judged that in general Sellafield met the legal requirements and therefore awarded inspection ratings of Green (No Formal Action) for LCs 10, 23, 24, 27, and 28.
Licence Condition 34 was not judged relevant for this system based inspection.
I judge that the facility's implementation of the site's arrangements for the five applicable Licence Conditions is good in many areas. For example, the staff interviewed had a good knowledge of the existing arrangements and the state of the plant and equipment provided good evidence to this effect.
The SL personnel involved in the inspection were knowledgeable, professional and demonstrated good situational awareness throughout. However, I raised two minor regulatory issues, 5914 and 5920, as a result of this inspection, although this does not detract from my overall inspection conclusions. The first relates to improvements in the maintenance recording and approval process and the second to ensuring electrical maintenance is completed on one switchboard in a timely manner. These issues will be followed up during ONR's future routine regulatory engagements.
I consider that the pre-inspection planning meeting assisted in providing the ONR inspection team with a clear understanding of the role of the electrical power system to support the HALES safety case. The meeting also provided clarified expectations regarding SL's actions needed to address HALES electrical-related regulatory issues 4164 and 4777.
The site inspector judged that the loss of power event did not meet the ONR formal investigation criteria and the remedial actions identified by Sellafield ltd would be monitored under the existing ONR issue 5204.
The findings of this System Based Inspection was shared and accepted by the licensee as part of normal inspection feedback.
I concluded that the HALES electrical system fulfils the requirements specified in SL's safety case and it is my opinion that an inspection rating of Green (No formal action) is appropriate for compliance against the Licence Conditions 10, 23, 24, 27 and 28.
From the evidence gathered during this intervention, I do not consider there to be any matters that have the potential to impact significantly on nuclear safety.
At present, no additional regulatory action is needed over and above the planned interventions within the Operational Waste Facilities Operating Unit at the Sellafield Nuclear Site as set out in the Integrated Intervention Strategy, which will continue as planned.