Proliferation hardening and power flattening of a thorium fusion breeder with triple mixed oxide fuel

The proliferation hardening of the U-233 fuel in a thorium fusion breeder h as been realised successfully with a homogenous mixture of ThO2, natural-UO 2 and CANDU spent nuclear fuel in the form of a triple mixed oxide (TMOX) f uel. The new U-233 component will be successfully hardened against prolifer ation with the help of the U-238 component in the natural-UO2 and spent fue l. The plutonium component remains non-prolific through the presence of the Pu-240 isotope in the spent CANDU fuel due to its high spontaneous fission rate. A (D,T) fusion reactor acts as an external high energetic (14.1 MeV) neutron source. The fissile fuel zone, containing 10 fuel rod rows in the radial direction, covers the cylindrical fusion plasma chamber. A quasi-con stant power density in the fissile zone has been achieved by reducing the T hO2 component in the rods continuously in the radial direction (from 91 dow n to 64%). Three different coolants (pressurised helium, natural lithium an d Li17Pb83 eutectic) are selected for the nuclear heat transfer out of the fissile fuel breeding zone with a volume ratio of V-coolant/V-fuel = 1 in t he fissile zone. The fissile fuel breeding occurs through the neutron captu re reaction in the Th-232 (ThO2), in the U-238 (natural-UO2 and CANDU spent fuel) isotopes. The fusion breeder increases the nuclear quality of the sp ent fuel, which can be defined with the help of the cumulative fissile fuel enrichment (CFFE) grade of the nuclear fuel calculated as the sum of the i sotopic ratios of all fissile materials (U-233+U-235+Pu-239+Pu-241) in the TMOX fuel. Under a first-wall fusion neutron current load of 10(14) (14.1 M eVn/cm(2) s), corresponding to 2.25 MW/m(2) and by a plant factor of 100%, the TMOX fuel can achieve an enrichment degree of similar to1% after simila r to 12-15 months. A longer irradiation period (similar to 30 months) incre ases the fissile fuel enrichment levels of the TMOX towards much higher deg rees (similar to2%), opening new possibilities for utilisation in advanced CANDU thorium breeders. The selected TMOX fuel remains non-prolific over th e entire period for both uranium and plutonium components. This is an impor tant factor with regard to international safeguarding. (C) 2000 Elsevier Sc ience Ltd. All rights reserved.