Construction of the Magnox Swarf Storage Silo (MSSS) first began in the 1960s and since then it has been extended three times. It comprises 22 vertical underwater compartments, storing around 10,000 tonnes of intermediate level waste. It no longer meets modern safety standards and is considered Sellafield’s most hazardous facility.
MSSS was constructed for the underwater storage of Magnox fuel cladding (or swarf) that was removed from used nuclear fuel rods so that fuel could be reprocessed. Over the years other fuel debris and miscellaneous solid waste have also been disposed of in the facility until tipping ceased in 2000.
Investigations have shown that the facility is leaking water into the ground. While we do not consider the leak poses any immediate risk to workers or to public safety, safely removing the waste and placing it into modern storage facilities remains the only long term solution and is one of our highest regulatory priorities.
The task of developing and implementing a programme to safely retrieve the bulk of MSSS waste has proven to be highly complex, but in a major step forward, in 2022 we granted permission for the commencement of retrievals from the facility.
Due to the age of the facility and its position on the Sellafield site, this is difficult and challenging work, with bulk retrievals not expected to be completed before 2060.
Once all of the waste has been successfully removed from MSSS, the facility will be dewatered and eventually demolished.