Study on transmutation and storage of llfp using a high-Temperature gas-cooled reactor

There is a need to temporally store high-level radioactive waste (HLW) until the location of final disposal is decided. HLW contains several types of long-lived fission product (LLFP) which stay radioactive for hundreds of thousands of years. In addition, they tend to be chemically mobile when dissolved into ground water thus may not be suited for geological disposal. A facility that is able to store and incinerate LLFP simultaneously is desirable. The high-Temperature gas-cooled reactor (HTGR) is one of the fourth generation nuclear reactors currently under research and it has some favorable characteristics that allow the reactor to destroy LLFP through nuclear transmutation. In this study, the capability of HTGR as LLFP transmuter was evaluated in terms of neutron economy. Considering gas turbine high-Temperature reactor with 300 MWe nominal capacity (GTHTR300) as HTGR, transmutations of four types of LLFP nuclide were estimated using Monte Carlo transport code MVP and ORIGEN. In addition, burn-up simulations for whole-core region were carried out using MVP-BURN. It was numerically shown that the neutron fluxes change significantly depending on the arrangement of LLFP in the core. When 15 t of LLFP is placed in an ideal manner, the GTHTR300 can sustain sufficient reactivity for one year while transmuting up to 30 kg per year. Additionally, there are more space available for storing larger amount of LLFP without affecting the reactivity. These results suggest that there is a possibility of using GTHTR300 as both LLFP storage and transmuter.