Fade-out time shortening on radiotoxicity and decay heat using TRU generation reduction fuel

Abstract

We analyzed the possibility of TRU generation reduction fuel using HALEU as the initial enrichment to reduce the radiotoxicity and decay heat of TRU when using the LWR fuels that can suppress radiotoxicity and decay heat in HLW. Fade-out time was defined as the period required to decay to the level of natural uranium ore, focusing on the radiotoxicity, and decay heat up to one million years, which is generated from the reduced TRU generation type fuel (FORSETI) consisting of uranium fuel of HALEU enrichment. The decay characteristics of TRU nuclides in HLW after plutonium removal by reprocessing and the effect of shortening the fade-out time were mainly discussed. The level of 241 Am on both radiotoxicity and decay heat is significant. However, the effect of 239 Pu and 240 Pu, which are produced as daughter nuclides of 243 Am and 244 Cm after reprocessing, significantly lengthens the fade-out time to 100,000 years for radiotoxicity and to 40,000 years for decay heat, compared to several thousand years for 241 Am alone. When TRU generation reduction fuel is adopted, the production rate of 243 Am and 244 Cm is reduced by more than 90% when the enrichment is increased from 3.8 wt% to 20 wt%, and the generation of 239 Pu and 240 Pu as daughter nuclides are also reduced almost correspondingly. As a result, increasing the initial 235 U enrichment from 3.8 wt% to 20 wt% reduces the fade-out time of radiotoxicity from 100,000 to 3,000 years and the fade-out time of decay heat from 40,000 to 2,000 years for HLW, respectively by FORSETI-type TRU generation reduction fuel. As described above, it is shown that using TRU generation reduction fuel can significantly accelerate the decay of TRU radiotoxicity and decay heat in HLW without transmutation of TRU.