Transmutation of minor actinides (MA) with pebble bed type HTGRs

摘要

It has been proposed to transmute minor actinides (MA) in LWRs, FBRs or actinide burning reactors. In FBRs and actinide burning reactor, MA is transmuted only about 10%. In LWRs, MA could not transmuted because MA is produce more than that of transmuted. Therefore, the large number of reprocessing process has to be carried out for further transmutation of MA repeatedly.rnHTGRs can achieve higher burnup with its coated fuel particles. We have found a reactor system that can transmuted more of MA in fuel for one burnup cycle. This system is a pebble bed type HTGR using MA balls and Pu balls. The Pu is obtained from reprocessing LWR fuel. The criticality maintains with the Pu. MA is converted to fissile nuclides by neutron absorption reaction, then transmuted by fission reaction.rnThe fuels are loaded and removed from the core continuously. The burnups of the fuel ball are evaluated by measuring the strength of γ-rays when they are exhausted from the core. They are reloaded again if the burnups are still under the expected burnups. They are discharged form the reactor system as spent fuels if the expected burnups are achieved.rnSo for, the achievable burnup of the fuel is about 600GWd/t. The ratio of the residual MA to initially loaded MA is about 40%. The MA transmutation ratio is five times higher than that of reactors above mentioned. As the same time, about 50% of plutonium is also transmuted.rnMoreover, it is expected that the MA will transmuted nearly 100% by many improvements. For example, MA balls are reloaded into the core more times than Pu balls, low outlet coolant temperature, diluted fuel kernel, and so on.rnWe think that the reactor system is one of the most promising options with which the transmutation of MA can be carried out effectively.