Nuclear characteristic analyses of TRU burner reactors

To study conceptual design of TRU burner reactors, nuclear characteristic analyses have been performed. Two kind of reactors for Na-cooled alloy fuel assembly and He-cooled particle fuel assembly have been proposed as potential transmutation system for TRU waste nuclides. To perform neutronic calculations for these reactor cores, group constant library and burnup calculation code for TRU nuclides have been produced. In the Na-cooled TRU alloy fuel burner reactor, the fuel and core specifications in which the maximum temperature limited for fuel and cladding are satisfied were obtained by the parametric calculations for fuel elements, core geometry, power distribution and reactor power. Furthermore, power flattening and burnup reactivity swing reduction have been studied. As the result, two-region core was obtained, in which the fuel compositions were 58Np-22Pu-20Zr for inner core and 60AmCm-35Pu-5Y for outer core. The presently designed core is the thermal power of 170 MW and can transmute TRU of 47 kg per year. A reactor system of six-modular-cores can transmute TRU of 260 kg which are generated from ten PWRs per year. In the He-cooled particle fuel burner reactor, the fuel particles are packed between two concentric porous cylinders of HT-9 with a multitude of small holes to make annular fuel elements (frits). The reactor core was designed by considering the maximum temperature (1000deg K) of central fuel particle and fast neutron fluence of 3.5 x 1023 (n/cm2) during each burnup cycle. This reactor with thermal power of 1200 MW can obtain high transmutation rate of 17 % per 300 days. TRU nuclides have large uncertainties for nuclear and physics data, and then the effect of the uncertainties on the nuclear characteristics were studied. (author)