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

The proliferation hardening of the 233U fuel in a thorium fusion breeder has been realised successfully with a homogenous mixture of ThO2, natural-UO2 and CANDU spent nuclear fuel in the form of a triple mixed oxide (TMOX) fuel. The new 233U component will be suc- cessfully hardened against proliferation with the help of the 238U component in the natural- UO2 and spent fuel. The plutonium component remains non-proli®c through the presence of the 240Pu isotope in the spent CANDU fuel due to its high spontaneous ®ssion rate. A (D,T) fusion reactor acts as an external high energetic (14.1 MeV) neutron source. The ®ssile fuel zone, containing 10 fuel rod rows in the radial direction, covers the cylindrical fusion plasma chamber. A quasi-constant power density in the ®ssile zone has been achieved by reducing the ThO2 component in the rods continuously in the radial direction (from 91 down to 64%). Three di€erent coolants (pressurised helium, natural lithium and Li17Pb83 eutectic) are selec- ted for the nuclear heat transfer out of the ®ssile fuel breeding zone with a volume ratio of Vcoolant=Vfuel ˆ 1 in the ®ssile zone. The ®ssile fuel breeding occurs through the neutron cap- ture reaction in the 232Th (ThO2), in the 238U (natural-UO2 and CANDU spent fuel) isotopes. The fusion breeder increases the nuclear quality of the spent fuel, which can be de®ned with the help of the cumulative ®ssile fuel enrichment (CFFE) grade of the nuclear fuel calculated as the sum of the isotopic ratios of all ®ssile materials (233U+235U+239Pu+241Pu) in the TMOX fuel. Under a ®rst-wall fusion neutron current load of 1014 (14.1 MeV n/cm2 s),