Fig. 11-4 Concept of Accelerator-driven Transmutation System When a high-energy proton beam from an accelerator is driven into a solid tungsten target, a spallation reaction takes place and a number of neutrons are emitted. The emitted neutrons propagate into a subcritical blanket that surrounds the target. There they induce the fission reaction for transmutation.The proposed system transmutes about 250 kg of transuranic elements yearly. The subcritical blanket is cooled by liquid sodium. The recovered heat is converted into electricity for operation of the system's own accelerator.

A conceptual design study has been performed on a transmutation system driven by an accelerator. A conceptual reference system design was examined to confirm the performance and technical feasibility of the accelerator-driven system. The proposed system consists of the combination of an intense proton accelerator, a spallation target, and a subcritical blanket. When a proton accelerated to a high energy strikes a target nucleus, the resulting reaction tears apart the nucleus and emits a number of neutrons. This reaction is called spallation. Spallation reactions and successive fission reactions induced by neutrons emitted from spallation are used for transmutation. The accelerator- driven system is operated in a subcritical condition, unlike a power reactor. This offers the major advantages of superior criticality safety and high flexibility in design and operation. The figure shows the concept of accelerator-driven transmutation system. The system can transmute transuranic elements discharged from about ten large power reactors. The heat generated in the subcritical blanket is recovered to generate electricity, part of which is supplied to self-sustain the operation of the accelerator. JAERI has proposed the construction of an intense proton accelerator to perform various engineering tests to study accelerator-driven transmutation. For this purpose, accelerator components have been developed and tested. Acceleration of the beam has been successfully demonstrated up to an energy of 2 MeV, a 52-mA peak current, and a 5% duty.

Reference T. Takizuka et al., Conceptual Design Study of an Accelerator-based Actinide Transmutation Plant with Sodium-Cooled Solid Target/Core, Proc. Int. Information Exchange Meeting on Actinide and Fission Product Separation and Transmutation, ANL, (1992). 397.

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