Dissolution of uranium oxide TBP-HNO complex

Mori, Yukihide*; Shimada, Takashi*; Kosaka, Yuji*; Mizuno, Mineo*

As a head end process for the pulverization of the spent fuel, the mechanical method (the shredder method) and the pyro-chemical method (oxidization heat-treatment) have been examined. UO is a main ingredient of Uranium oxide powder by the mechaical method, and UO is that by the pyro-chemical method. Moreover, the particle size of the pulverized powder depend on the conditions of the pulverizing process. As it was considered that the difference of dissolution rates of samples was caused by the difference of sample chemical forms and dissolution temperature, parametric surveys on chemical form and particle size of powder and dissolution temperature were carried out, and the following results were obtained. (1)The remarkable difference of dissolution rate between U3O powder(average particle size 3.7m) and UO powder (average particle size 2.4m) which have comparatively similar particle size was not observed. (2)It was confirmed that the dissolution rate became lower according to the particle size increase (average particle size 2.4m1mm) And it was considered that dissolution rate had strong dependency on particle size, according to the results that the powder with 1mm particle size did not dissolute completely after 5 hours test. (3)The temperature dependency of the dissolution rate was confirmed by dissolution test with UO powder (average particle size 2.4m 1mm). The higher dissolution rate was obtained in the higher dissolution temperature, and 11 kcal/mol was obtained as activation energy of dissolution. (4)In the dissolution test of UO powder, the nitric acid concentration started to change earlier than that of UO powder and concentration change range became larger compared with that in the dissolution test of UO powder. It was considered that those differences were caused by difference in mole ratio of Uranium and nitric acid which are consumed in the ...