Transmutation of High-level Wastes in a Spherical-tokamak Reactor

抄録

We studied transmutation of high-level wastes in a spherical-tokamak reactor. We examined spent fuel, recovered fuel, natural UO₂ fuel and reprocessed waste, though the natural UO₂ fuel is not a high-level waste. We added a few percent of ²³⁹Pu to the former three fuels to increase the tritium breeding ratio and saw the change in the effective multiplication factor k_eff, number of fissions, multiplication of fusion energy and conversion ratio of ²³⁹Pu. We found that 2.5 and 5.5 fissions are needed to obtain the tritium breeding ratio of 1 and 2, respectively. High amplification of fusion energy occurs. Breeding of ²³⁹Pu is expected for the natural UO₂ fuel even in a subcritical environment. For the reprocessed waste, ⁹³Zr and ⁹⁹Tc are transmuted efficiently by the (n,γ) reaction and so are ²³⁷Np and ²⁴¹Am by the (n,f) reaction. Fusion neutrons of 100MW will transmute half of those nuclides produced from the generation of 1 GW_(e) year in a large pressurized water reactor. However, tritium fuel may not be self-sustained in the reprocessed-waste burner.