The UK has begun to weigh up its options with respect to reprocessing or directly disposing of used nuclear fuel as its main reprocessing plant ages.
An AGR fuel assembly
In a discussion document the Nuclear Decommissioning Authority (NDA) noted its responsibility to manage all the used fuel from the indigenous Advanced Gas-cooled Reactor (AGR) fleet as well as some foreign light-water reactor fuel and a small amount of legacy fuel from early research. At the same time, the primary tool to reprocess these materials, the Thermal Oxide Reprocessing Plant (Thorp) is drawing near to its predicted closure in 2011.
How to go forward is to be the topic of discussion for the NDA and various stakeholders ahead of a 'credible options' paper to be released later in the year. It will not cover plans to manage fuel from future reactors, or that from Sizewell B which is not contracted to NDA to manage.
The UK has completed most of its contracts with overseas utilities with less than 700 tonnes of their used light-water reactor fuel remaining to pass through Thorp. The legacy fuels from the UKAEA amount to only 150 tonnes, leaving some 6600 tonnes of AGR fuel asthe NDA's main concern.
The NDA is responsible for managing these AGR stocks and under current plans it would reprocess some and store the remainder until a geologic disposal facility is available. However, this facility is only assumed to exist from around 2075, meaning a long period of probably wet then dry storage. One pond at Sellafield may be able to tackle this task for as long as 100 years, and work is ongoing to establish this. However, there is no currently proven way of dry-storing AGR fuel for the long term.
To reprocess the stocks does not appear much simpler. AGR fuel will continue to be discharged from reactors until at least about 2023 and reprocessing all this could stretch beyond the predicted lifespan of Thorp. This would require either a major refurbishment, a new domestic reprocessing plant or even politically embarrassing contracts with overseas reprocessors.
Other reprocessing options include using Thorp as long as practicable and leaving an as-yet unknown amount of used fuel for direct disposal. Another is to reprocess only the foreign fuels, leaving AGR fuel to be stored then disposed of as above. It is also possible to reprocess only the fuel for which this would be easier than long-term storage.
Thorp was commissioned in 1994 at about three times the capacity required to treat fuel from the AGR fleet. It was planned to operate until 2011 to meet overseas and AGR contracts and to date it has handled some 6000 tonnes of used nuclear fuel. A problem discovered in 2005 put it out of action for two years and it now operates on reduced throughput due to constraints on evaporator capacity.
While greatly reducing the volume of highly radioactive waste, reprocessing also separates out uranium and plutonium for incorporation into fresh nuclear fuel. There is a plant at Sellafield that does this for foreign customers, but the UK currently has no policy for the future of its own 100 tonnes of separated civil plutonium. This is a matter for government and awaits a decision on whether it should be disposed of, used in mixed-oxide nuclear fuel or kept in storage.
Researched and written
by World Nuclear News