Thermal stability test and analyses for irradiated nitride fuel; Nifti-1 results and analyses

Sato, Isamu; Hirosawa, Takashi  ; Ishida, Takashi*; Miwa, Shuhei  ; Tanaka, Kenya

Thermal stability test for irradiated mixed nitride fuel by the low heating rate was performed with the FP release behavior device. The decomposition behavior and the release behavior of fission gas and radioactive FPs of the nitride fuel were evaluated for the thermal stability and the source term, based on the behavior of nitride decomposition and FP release observed in the test. The findings for these behavior are as follows; (1)The practical decomposition of the irradiated nitride fuel occurred over 1900C. In the region of lower temperature than 1000C, nitrogen could be released along with the decomposition of FP nitrides such as BaN. (2)Fission gas release started from 1400C, and then was terminated. After the temperature reached to 1700C, the burst-like release of fission gas occurred again. The former was slightly related to the decomposition, but the latter was hardly dependent on it as well as the release of Cs. (3)The swelling of fuel by the heating test occurred and then the porosity reached to approximately 40%. The porosity is equal to the maximum value obtained in the evaluation of post irradiation examination, which indicated that the porosity is saturated by the heating. (4)Most of Cs and Sb were released from the fuel after the heating. The chemical form of released Cs could be mainly elemental Cs and somewhat CsI. The form of released Sb could be elemental. (5)Ru could be hardly released, nevertheless most of Eu was released from the fuel. (6)On the basis of these results and discussions, we proposed the test plan of Nifti-2 (Thermal stability test for irradiated nitride fuel under transient thermal condition).