Fast Reactors and Accelerator Driven Systems Knowledge Base

Conference Article: Potential advantages and drawbacks of the thorium fuel cycle in relation to current practice: A BNFL view

Abstract

Thorium could extend the availability of nuclear fuel beyond the necessarily finite reserves of uranium ore, particularly if used in a thermal breeder system with the uranium-233 formed by transmutation serving as fissile content. The cycle produces virtually no plutonium, nor the other transuranic elements that contribute substantially to anxieties about the disposal of nuclear waste. Thorium-based fuels have therefore been proposed as a substitute for uranium, both in existing power reactors and in advanced systems such as the 'energy amplified,' with a sub-critical assembly of fissile and fertile material driven by an independent neutron source. The benefits and drawbacks of thorium need careful evaluation. A self-sustaining, breeding cycle should be possible with good neutron economy, but whether existing modern reactor types meet that condition is questionable, particularly at high fuel ratings where parasitic absorption by 233Pa tends to pre-empt decay to 233U. Radiation from thallium-208, formed in the decay of by-product 232U and 228Th, complicates storage and refabrication. Public perception would favour the cycles producing no transuranic elements and its particular capacity for consuming those already stocked. However, although they contribute largely to the long-lived content of nuclear waste, fission products also do likewise, and since the amounts of these are not greatly changed, any resulting improvement to long-term safety would by no means be decisive. BNFL has recently assessed the outstanding development requirements of the Thorex process. Commercial realisation would require a huge investment with no certainty of success. So far, the potential advantages do not seem likely to justify the risk, but the position is being kept under review in case the balance should be seen to shift.

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Reference:

Proceedings of three IAEA meetings held in Vienna in 1997, 1998 and 1999

International Atomic Energy Agency, Vienna (Austria)

IAEA-TECDOC--1319, pp:305-315