Direct irradiation of long-lived fission products in an ATW system

The feasibility of directly irradiating five long-lived fission products (LLFPs: 79Se, 93Zr, 107Pd, 126Sn, and 135Cs, each with a half-life greater than 10,000 years), by incorporating them into the target of an Accelerator Transmutation of Waste (ATW) system is discussed. The important parameters used to judge the feasibility of a direct irradiation system were the target's neutron spallation yield (given in neutrons produced per incident proton), and the removal rate of the LLFP, with the baseline incineration rate set at two light water reactors (LWRs) worth of the LLFP waste per year. A target was constructed which consisted of a LLFP cylindrical ''plug'' inserted into the top (where the proton beam strikes) of a 30 cm radius, 100 cm length lead target. 126Sn and 79Se were each found to have high enough removal rates to support two LWR's production of the LLFP per year of ATW operation. For the baseline plug geometry (5 cm radius, 30 cm length) containing 126Sn, 3.5 LWRs could be supported per year (at 75% beam availability). Furthermore, the addition of a 126Sn plug had a slightly positive effect on the target's neutron yield. The neutron production was 36.83±.0039 neutrons per proton with a pure lead target having a yield of 36.29±.0038. It was also found that a plug composed of a tin-selenide compound (SnSe) had high enough removal rates to burn two or more reactor years of both LLFPs simultaneously