The Nuclear Decommissioning Authority

 

The boxes might be square or cylindrical, but they're definitely yellow and definitely pioneering in terms of storing the UK's Intermediate level radioactive waste. 

Square versions of the MiniStores were successfully tested at the Dungeness A site last year while trials of the smaller, cylinder-shaped Mosaik containers are currently under way. Each has different qualities and is used for different types of waste.

The hope is that the MiniStores, which provide shielding from radiation, will provide an alternative to the construction of purpose-built on-site stores across the Magnox sites. Current plans assume that all sites will build stores over the coming years – some are already complete - but using the MiniStores could provide a much more affordable and flexible decommissioning solution.

The boxes would store the material until a geological disposal facility is developed, and, ideally, simply be transferred at the appropriate time.

The MiniStores concept has been used extensively in Europe for more than 20 years, where the boxes are used for interim storage, transportation and final disposal. Their introduction in the UK, however, needs to be comprehensively assessed and approved by the nuclear regulators.

Weighing 18 tonnes each and holding up to about 2.85m³ of waste, the Dungeness MiniStores contain spent resin from existing storage tanks, freeing valuable space and allowing an additional 10 years' capacity, adequate for the projected life of the cooling ponds.

Regulatory approval from the Nuclear Installations Inspectorate was received last year for three Dungeness MiniStores to be used for 13 years storage, though not for final disposal in a repository. The approval was preceded by rigorous testing over a period of 20 weeks.

However, the project has provided valuable data to support a case for longer-term storage.

Mosaik containers weigh 7.6 tonnes when empty and 8.6 tonnes when full, and are being tested for the storage of highly irradiated debris from the fuel elements, in the form of springs, coupling wires and caps. Inside the container is an internal pot which contains the waste and was designed by the Dungeness team, with 75mm thick lead walls and an outer stainless steel frame.

Magnox intermediate level waste (ILW) management director Mike Gull said: "The outcome of the Dungeness pathfinder projects and our wider MiniStores assessment will hugely influence the future strategy for managing ILW and potentially save millions of pounds in decommissioning costs."

Last autumn, more than 40 local community representatives from Magnox North and Magnox South sites attended a workshop, aimed at giving them the opportunity to participate in the decision-making process.

Magnox North and Magnox South Nuclear Safety Committees have now agreed that the MiniStores approach can be included in their decommissioning strategies following a detailed analysis of technical issues. This has been endorsed by the NDA's Expenditure Review Panel (ERP), which has approved proposals to develop Lifetime Plan changes, reflecting the MiniStores approach, at eight Magnox sites.