Magnox Swarf Storage Silos

The Magnox Swarf Storage Silos at Sellafield is one of the site’s four Legacy Pond and Silo facilities. We are focused on safely decommissioning these buildings as part of our hazard and risk reduction programme.

Magnox Swarf Storage Silos
Magnox Swarf Storage Silos


The Magnox type nuclear reactor was the first type to generate nuclear electricity in the UK. Including Calder Hall at Sellafield a total of eleven Magnox power stations were commissioned during the 1950s, 60s and early 70s.

In support of the growing contribution of electricity generated by the Magnox power stations, the Magnox Swarf Storage Silos Facility was built at Sellafield to accommodate the swarf waste produced by the Magnox fuel decanning operations. The cladding swarf was removed from the fuel prior to reprocessing.

The facility became operational in 1964 for the underwater storage of swarf waste.

Following its inception in 1964 with six wet silos, the facility was extended on three further occasions to cater for the increased storage demands; by 1983, a complement of 22 silos had been established.

By the early 1990s, technological developments meant that ‘wet storage’ of Magnox swarf was no longer seen as the best solution. Dry waste, immobilised in discrete containers offered positive advantages: it becomes more passive and much more practical to manage. 

Therefore the Magnox Encapsulation Plant was constructed at Sellafield to receive dry Magnox swarf, encapsulate it in cement and seal it in stainless steel drums.

The Magnox Swarf Storage Silos received Magnox fuel cladding from the First Generation Magnox Storage Pond and the Fuel Handling Plant along with a range of other items of intermediate level waste. The swarf was transported in purpose built flasks and tipped into the silo compartments.

In 1992, swarf received from the Fuel Handling Plant was routed to the Magnox Encapsulation Plant. Various facilities continued to use the Magnox Swarf Storage Silos to aid their own Post Operational Clean Out (POCO). The final receipts were tipped into the compartments in June 2000. 

The Magnox swarf, which is almost 100% magnesium, is stored underwater. The swarf then undergoes a process which results in the release of gaseous hydrogen. The plant design and operations ensure that the heat and hydrogen cannot build up and risk exceeding safe levels within the plant.

Between 1994 and 1999, a significant quantity of metal swarf was retrieved from the facility, by use of the Swarf Retrieval Facility. The waste was exported to the Magnox Encapsulation Plant for encapsulation and storage.