The Office for Nuclear Regulation (ONR) undertakes all regulatory interaction with the Sellafield site licensee, Sellafield Limited (SL), against a strategy defined by the ONR Sellafield, Decommissioning, Fuel and Waste Division (SDFW). The inspection plan for the Spent Fuel Management (SFM) outlines a programme of regulatory inspections which includes a System Based Inspection (SBI) of the cooling system in the Waste Vitrification Plant (WVP).
The purpose of this inspection was for ONR to examine whether the licensee’s safety case claims in respect of the WVP cooling system are being adequately implemented. The cooling systems targeted were those in WVP Line 3 and the Vitrified Product Store (VPS) responsible for supporting a number of structures, systems and components (SSCs) important to safety. These SSCs provide key safety case claimed functions including the removal of the decay heat generated by the highly active liquors stored and processed in the facility and maintaining the structural integrity of the store.
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 all those on site who have responsibility for any operations which may affect safety.
LC23 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.
LC24 requires SL to ensure that all operations which may affect safety are carried out in accordance with written instructions.
LC27 requires SL to ensure that a plant is not operated, inspected, maintained or tested unless suitable safety mechanisms, devices and circuits are properly connected and in good working order.
LC28 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.
LC34 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 from such control or containment.
On this occasion, LC 34 (leakage and escape of radioactive materials) was not included in the System Based Inspection as ONR judged that it was not directly applicable to the system under consideration.
ONR carried out a two day SBI of the WVP cooling systems. Sellafield’s Nuclear Intelligence and Independent Oversight (NI&IO) participated in part of the inspection. The inspection comprised discussions with SL staff, a targeted plant walkdown and a review of plant records and other documentation.
The intervention was performed in line with ONR's guidance requirements (as described in our technical inspection guides) in the areas inspected.
ONR judged the implementation of the safety case supporting WVP cooling systems to be adequate.
From the evidence made available during the inspection, ONR consider that SL has adequately implemented the claims made in the safety case which relate to the WVP cooling systems.
As part of the scope of this SBI, ONR considered whether it may be required to assess the safety case in a timeframe shorter than otherwise planned. Based on the information gathered during this SBI, ONR has no reason to recommend an early assessment of the safety case.
The loss of cooling represents the hazard with the highest potential consequences in WVP, owing to the nature of the material stored and processed. The heat loading of the inventory currently stored and processed in WVP is significantly lower than the historic inventory and the plant design basis. As a result the burden on the cooling system is currently less onerous, and the facility has more time to respond to a loss of cooling before any adverse consequences would occur.
Throughout the inspection, the SL staff encountered were considered to be knowledgeable and professional; and provided open and honest responses to ONRs questions.
SL demonstrated a good understanding of how the facility would react to the loss of cooling, and how long this could be tolerated before there would be any radiological consequences. ONR were satisfied that contingencies are in place to ensure that cooling is maintained.
ONR judged that all of the safety measures sampled were in good working order and appropriately controlled and maintained. However, in some instances we sampled SL was not able to provide records demonstrating that maintenance had been conducted in accordance with the appropriate maintenance instructions. A Level 4 Regulatory Issue was raised to address this minor shortfall.
Based on the evidence sampled during this inspection, I judge that SL has adequately implemented the claims made in its safety case. I therefore consider that inspection ratings of Green (no formal action) are appropriate against LC 10, LC 23, LC24, LC27 and LC28 in accordance with ONR assessment rating guidance. Licence condition LC 34 was judged not relevant for this system based inspection.