Abstract
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 keff, 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.
