Leaching behavior of simulated fuel debris in the UO-SUS system prepared by irradiation or tracer doping method

Sasaki, Takayuki*; Tonna, Ryutaro*; Kobayashi, Taishi*; Akiyama, Daisuke*; Kirishima, Akira*; Sato, Nobuaki*; Kumagai, Yuta   ; Kusaka, Ryoji  ; Watanabe, Masayuki   

Under the high-temperature conditions in the reactor cores of Fukushima Daiichi Nuclear Power Station (FDNPS) during the accident, UO, zircaloy, and structural materials such as stainless steel are thought to be reacted. Since it will take a long time to retrieve the fuel debris, it is essential to accumulate basic knowledge for anticipating the secular change of chemical properties. In this study, to examine the dissolution behavior to water, the simulated alloy-based debris samples were prepared by two methods, and the dissolution behavior was analyzed; 1) Irradiation method: the simulated debris was irradiated by thermal neutrons to introduce FP, 2) Doping method: non-radioactive elements (cold FPs) simulating FPs were doped to the sample. Based on the concentration of the nuclide M in the sample, the leaching ratio was evaluated from the relationship of / . The leaching ratio which was normalized by was also discussed. In samples of UO, UZrO and UCr(Fe)O, Cs leached preferentially to U immediately after immersion ( ) in both the irradiation and the doping methods, and then the value decreased with time, suggesting U dissolution would be a rate-limiting reaction thereafter. Divalent Ba (FP) and Sr (cold FP) also leached preferentially to U, while trivalent Nd (FP) and Eu (cold FP) showed a harmonious dissolution with U. The value was in the order of pure water (PW) and 0.1 M NaClO (Na) artificial seawater (SW), and the effect of complex formation with anions in the solution on the order was observed. The values depended on the valence of ions; PW and Na SW for and , while PW Na and SWfor . The leaching behavior will be discussed in relation to the existing state in the solid phase and the chemical state in the aqueous phase.