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

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 Am-241 on both radiotoxicity and decay heat is significant. However, the effect of 239Pu and 240Pu, which are produced as daughter nuclides of Am-243 and Cm-244 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 Am-241 alone. When TRU generation reduction fuel is adopted, the production rate of Am-243 and Cm-244 is reduced by more than 90% when the enrichment is increased from 3.8 wt% to 20 wt%, and the generation of Pu-239 and Pu-240 as daughter nuclides are also reduced almost correspondingly. As a result, increasing the initial U-235 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.