Proliferation Hardening of Thorium Fusion Breeders with CANDO Spent Fuel

Abstract

The denaturation of the ²³³U fuel can be realised with a homogenous mixture of ThO₂ and CANDU spent nuclear fuel. The new ²³³U component will be successfully hardened against proliferation with the help of ²³⁸U component in the spent fuel. The plutonium component remains non-prolific through the ²⁴⁰Pu isotope in the spent CANDU fuel.

In this work, a thorium fusion breeder is presented. 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 radial direction, covers the cylindrical fusion plasma chamber. The rods contain a mixed oxide (MOX) fuel consisting of 25 % spent nuclear fuel of CANDU reactors and 75 % ThO₂. The fissile zone is cooled with pressurised helium gas with volume ratios of V_coolant/V_fuel = 1 and 2 in the fissile zone.

The fissile fuel breeding occurs through the neutron capture reaction in the ²³²Th(ThO₂) and in the ²³⁸U (CANDU spent fuel) isotopes. The fusion breeder increases the nuclear quality of the spent fuel. It can be defined with the help of the cumulative fissile fuel enrichment (CFFE) grade of the nuclear fuel which is the sum of the isotopic ratios of all fissile material (²³³U+²³⁵U+²³⁹Pu+²⁴¹Pu) fuel.

Under a first-wall fusion neutron current load of 10¹⁴ (14.1-MeV n/cm².s), corresponding to 2.25 MW/m² and by a plant factor of 100 %, the MOX fuel can achieve an enrichment degree of ~1 % after ~12 to 15 months. A longer rejuvenation period (~30 months) increases the fissile fuel enrichment levels of the MOX to much higher degrees (~2 %), opening new possibilities for diverse purposes, such as utilization in advanced CANDU thorium breeders.