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Partitioning and transmutation
When spent fuel is unloaded from a nuclear power reactor, only around 4% by weight is ‘ultimate’ radioactive waste (i.e. fission products). The rest is made up of unused uranium – most of the initial uranium is still present – and a small amount (1%) of plutonium, which was formed in the reactor. The uranium and plutonium can be recycled and re-used in fresh fuel, an industrial practice carried out in a number of reprocessing plants around the world.
Plutonium is particularly radiotoxic (it is an alpha-particle emitter) for very long periods of time. However, to further reduce the long-term toxicity of the ‘ultimate’ waste, the small quantities of other hazardous isotopes such as americium, neptunium, caesium, technetium and iodine can also be chemically separated (or partitioned) from the remaining waste before vitrification. The most toxic isotopes can then be converted into stable or short-lived isotopes by nuclear transmutation in fast-neutron reactors or accelerator-driven sub-critical systems.
This is collectively referred to as partitioning and transmutation (P&T). Because P&T aims to reduce the inventories of long-lived radionuclides in radioactive waste, the techniques could alleviate the problems linked to disposal of high-level radioactive waste in deep geological formations and enable optimal use to be made of these disposal facilities.
The primary objective is to provide a basis for the development of pilot facilities and demonstration systems for the most advanced partitioning processes and transmutations systems, with a view to reducing the volumes and hazard of high-level long-lived radioactive waste issuing from the treatment of spent nuclear fuel.
Apart from ways to reduce the volume and long-term toxicity of radioactive waste, research in this field will also explore the potential for new reactor concepts and fuel cycles to produce less waste during the operation of nuclear power plants. This is linked with generation-IV systems research.
Partitioning processes for viable recycling strategies will need to be developed to full demonstration at pilot plant level. Initially, work may concentrate on extending the technically mature aqueous chemical separation processes that are compatible with both fuel fabrication and future fuel recycling strategies.
In parallel, the development of pyrochemical techniques for partitioning will continue in line with the roadmaps outlined for this technology under the Sixth Euratom Framework Programme (Euratom FP6).
This research will lay the groundwork for future sustainable nuclear fuel-cycle strategies, whether involving transmutation in a dedicated waste-burning accelerator-driven system (i.e. a sub-critical reactor) or in future generation-IV power plants.
These techniques may allow the period over which high-level radioactive waste remains hazardous to be reduced from hundreds of thousands of years down to a few hundred years.