The Nuclear Decommissioning Authority

 

A key area of responsibility for the NDA is managing spent fuel which has been used in reactors across the UK and overseas. Spent fuel management is a commercial Sellafield operation, earning essential revenue for the NDA which can then be used to fund decommissioning activities.

Two fuel reprocessing plants are located at the Sellafield site. One is used to reprocess Magnox fuel from early UK nuclear reactor operations. The other facility is Thorp (Thermal Oxide Reprocessing Plant), which reprocesses fuel from British Advanced Gas Cooled Reactors (AGRs) at British Energy sites, such as Hartlepool and Heysham, plus Light Water Reactor fuel from reactors around the world.

The contracts are overseen by International Nuclear Services (INS), the NDA's commercial sales expert.

Thorp has already reprocessed more than 2,300 (26%) of the estimated 8,800 tonne total of AGR fuel from UK power stations, and has less than 700 tonnes of overseas fuel left to reprocess, plus around 150 tonnes of fuel inherited from historic prototype reactors. At present, Thorp is performing well and, in February, exceeded its output target for 2009-2010. The fuel has a generating life of about four years before being replaced to ensure reactors continue to perform efficiently.

Once removed from the reactor, spent fuel is initially placed in storage ponds at the power stations to cool and allow short-lived radiation to decay. After this cooling period, it is transported to Sellafield either by sea, road or rail using specially designed high-specification shielded flasks.

On arrival at Sellafield, the spent fuel flasks are unloaded by a lifting beam attached to a crane, able to lift up to 150 tonnes. The flasks, usually weighing 40-80 tonnes, are again placed in storage ponds for unloading and further cooling and radioactive decay before the start of reprocessing.

At Thorp, spent fuel is dissolved in acid. This chemically separates the plutonium and uranium from high level waste. The retrieved uranium and plutonium powders are then placed in special containers and stored.

The highly active liquid waste arising from reprocessing operations is treated at the Sellafield Vitrification Plant, where it is subjected to intense heat, evaporation and drying. The resulting calcine powder is mixed with manufactured glass pellets and again heated intensely. The process results in a molten liquid which is poured into a drum to solidify and a lid fitted. Following final checks, the container is moved to the Vitrified Product Store awaiting return to the waste owners.

Reprocessing also generates Intermediate Level Waste and Low Level Waste, for which further treatment may include recycling or compaction.

Remaining Intermediate Level Waste is treated and packaged, then stored on-site in specially engineered product stores. Low Level Waste is packaged and stored off site in the Low Level Waste Repository.

As a result of reprocessing, 97% of spent fuel can be recycled, avoiding large quantities of high level waste which would require storage in the proposed Geological Disposal Facility. Reprocessing also means uranium can be reclaimed and, where appropriate, re-used to make new fuel, helping to conserve finite supplies of natural uranium ore.

The NDA has just published a discussion paper on the development of a strategy for managing spent oxide fuels. See www.nda.gov.uk.