Research on the stability of fuel debris consisting of oxides and alloys, 5; Leaching behavior of nuclides from simulated fuel debris in the UO-SS system; Irradiation or addition method

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

Fuel debris generated in the 1F severe accident remains in direct contact with water and leaching of nuclides from the debris is anticipated to continue. Therefore, in order to comprehend the leaching behavior, we have investigated the leaching of fission-product (FP) elements. We employed two methods for the synthesis of simulated fuel debris containing FP elements, that is (1) irradiation method: generating radioactive FPs in the simulated debris by irradiation of thermal neutron and (2) addition method: adding stable isotopes of FP elements into the starting materials of the simulated debris. In the early stage of leaching to water, Cs dissolved from these simulated debris ahead of U. But Cs/U ratio in water decreased with time, suggesting that water-soluble elements at the surface promptly dissolved. Divalent elements, Ba and Sr, dissolved similarly to Cs, whereas the leaching of Nd and Eu proceeded concomitantly with the U dissolution.