Office for Nuclear Regulation

Sellafield progress case studies

Sludge removal from the First Generation Magnox Storage Pond

ONR recently agreed to the commissioning of a new facility to receive radioactive sludge from the First Generation Magnox Storage Pond (FGMSP). The new Sludge Packing Plant (SPP1) was constructed specifically to handle legacy waste from the pond, which is transferred by robust pipework in to three enormous stainless steel buffer storage vessels. The FGMSP is an open-air pond and was constructed in the 1950s and 1960s to store, cool and prepare Magnox fuel for reprocessing. It now contains used nuclear fuel, sludge, intermediate level waste and pond water, each of which needs to be safely removed and processed through separate routes.

The new plant SPP1 is now ready to receive its first batch of sludge from the pond, expected in February, which is a significant milestone in reducing hazard and risk on site. There were some regulatory challenges along the way, including non-compliance with fire regulations, but ONR worked through these issues with the licensee to ensure that safety improvements were met and timescales were not compromised.

Plutonium wastes moved to safer storage

A project to transfer highly hazardous plutonium wastes from a fragile aging structure to more robust storage facilities was completed a week ahead of schedule in December 2014, significantly reducing the hazard and risk associated with the facility and the overall site. The old storage facility was built in the 1950s and the plutonium waste had been stored in small ' plastic bottles for more than 20 years.

The waste presented a high hazard and was identified as one of ONR's key regulatory priorities on site. In August ONR permissioned the start of the work and the bottles were recovered by Sellafield Ltd, handled by operators in air-fed suits, who decanted the waste into new robust containers for transfer to a more modern storage facility. This work had the effect of reducing the overall size of the off-site planning zone for Sellafield.

Canned fuel removed from Pile Fuel Storage Pond

Emptying canned fuel from the oldest pond at Sellafield, the Pile Fuel Storage Pond (PFSP) restarted over three months ahead of schedule. Decommissioning the pond is a significant challenge as it contains nuclear fuel, sludge, intermediate level waste and pond water, which all need to be removed and processed through separate routes. ONR applied its new strategy and through effective regulation working with Sellafield Ltd and the NDA, resolved emerging issues quicker than would have been previously possible. This resulted in the acceleration of fuel removal, and 10 flasks of fuel have now been removed from the pond for re-canning and storage in modern fuel facilities.

Potential acceleration of new facility by three-and-a-half years

The PFSP Drum Filling Plant is an enabler for the export of sludge from PFSP to the Waste Encapsulation Plant. It is a key work stream associated with the decommissioning of the legacy pond. Sellafield Ltd has worked with ONR and the NDA to ensure that when the project reached the detailed design phase, approvals could be granted in a timely manner to expedite the work. This will potentially provide a three-and-a-half year acceleration to the construction phase of the facility from the original baseline date of January 2019 to July 2015.

Reduction in Highly Active Liquor (HAL) stocks

HAL stocks at Sellafield represent a significant fraction of the radioactivity stored on the site. Sellafield Ltd take liquid waste from the reprocessing of spent fuel and concentrate it by evaporation to produce HAL. HAL is self-heating and is stored in special, cooled tanks, before it is reduced by vitrification into glass blocks in the waste vitrification plant (WVP) at Sellafield. This latter process immobilises the waste.

In 2001, ONR introduced a Specification which required Sellafield to reduce HAL stocks over time and they are now less than a third of their peak levels. An extended outage of one of the WVP facilities has resulted in a position where the demands of the specification will now not be met, posing a threat to continued Thermal Oxide Reprocessing Plant (THORP) reprocessing. ONR has considered the overall picture, and has engaged in discussions to determine whether operation of THORP could continue, whilst maintaining effective regulatory control of HAL stocks. ONR has now agreed that operating with HAL stock level above the specification will result in minimal hazard increase and negligible increase in risk but will provide overall benefits in safety in the longer term.

Standard approach to use of mobile cranes

As part of the process to reduce hazard and risk on site, mobile cranes are used across the Sellafield site to undertake decommissioning work and ensure safe access to facilities. ONR has agreed a standardised methodology for the use of mobile cranes on site, which means that instead of permissioning the use of cranes on a case-by-case basis, the standard approach represents acceptable practice, saving time and reducing bureaucracy.