Fast subcritical hybrid reactors for energy production: evolution of physical parameters and induced radiotoxicities

We have performed detailed Monte Carlo simulations of different subcritical fast hybrid reactor fuel configurations leading to the possible use of the se devices as energy generators. The method is based on the coupling betwee n a validated neutron transport code and a mathematical solution of the equ ations describing the time evolution of the neutron spectrum and mean cross -section during the reactor operation. We have optimized the geometrical an d operational characteristics of reactors based on Th-232/U-233 and U-nat/P u oxide fuels and simulated their operation over 20 fuel cycles (200 years of energy generation). Quantitative results are presented for the inventori es. waste production and induced radiotoxicities under alternative scenario s of fuel reprocessing. The possible paths to start a fuel cycle based on t horium are studied. identifying the use of highly enriched uranium or pluto nium from PWR spent fuel as options to start a fuel cycle which tends asymp totically towards Th-232/U-233. The comparison between the simulated hybrid systems and the existing PWR reactors indicate significant reductions of t he total radiotoxicity for fuel cycles based on thorium and fuel reprocessi ng which include the minor actinides. as well as plutonium and uranium sepa ration. (C) 2000 Elsevier Science B.V. All rights reserved.