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JAEA Reports

Study on dissolution of UO $_{2}$ to obtain the high U solution

Sano, Yuichi; *; Sakurai, Koji*; ; Nomura, Kazunori; *

JNC TN8400 2000-032, 98 Pages, 2000/12

JNC-TN8400-2000-032.pdf:1.94MB

Concerning the preparation of high U solution for the crystallization process and the application of UO $_{2}$ powder dissolution to that, the effects of final U concentration, dissolution temperature, nitric acid concentration and powder size on the dissolution of UO $_{2}$ powder in the nitric acid where the final U concentration was 800g/L were investigated. The experimental results showed that the solubility of UO $_{2}$ decreased with the increase of final UO $_{2}$ concentration and powder size, and with the decrease of dissolution temperature and nitric acid concentration. It was also confirmed that in the condition where the final U concentration was sufficiently lower than the solubility of U, UO $_{2}$ dissolution behavior in the high U solution could be estimated with the equation based on the fragmentation model which we had already reported. Based on these experimental results, the dissolution behavior of irradiated MOX fuel in high U solution was estimated and the possibility of supplying high U solution to the crystallization process was discussed. In the preparation of high U solution for the crystallization process, it was estimated that the present dissolution process (dissolution for fuel pieces of about 3cm long) needed a lot of time to obtain a high dissolution yield, but it was shorted drastically by the pulverization of fuel pieces. The burst of off-gas at the early in the dissolution of fuel powder seems to be avoidable with setting the appropriate dissolution condition, and it is important to optimize the dissolution condition with considering the capacity of off-gas treatment process.

JAEA Reports

Behavior of fine particle originated from cement

Tanaka, Satoru*

JNC TJ8400 2000-003, 62 Pages, 2000/02

JNC-TJ8400-2000-003.pdf:11.88MB

For the safety assessment of radioactive waste disposal, it is important to elucidate the effect of colloids on radionuclide migration, which are released with dissolution of cementitious materials composing engineered barricr. In the previous work, we identified and characterized the colloidal particles in the solutions contacting cement hydrates, OPC and low-alkaline cement paste, and observed the release of the colloid particle. In the present work, we performed same experiments as the last year to confirm the reproducibility of the colloid release. We studied the leaching behavior of the colloid when OPC and low-alkaline cement past contact water flow. Furthermore, the effect of an alumina particle was studied, which is used as a barrier material for colloid migration. The following conclusions were derived: (1)In the solution contacting cement paste, the small amount of particles, which are considered as CaCO $_{3}$ or silicate colloids were observed. Thus, the reproducibility of the last work was confirmed. (2)The leaching of colloid in the solution was confirmed by water flow through the cement paste. The concentration of particle was as low as 10 $^{3}$ 10 $^{5}$ mL $^{-1}$ . (3)Al $_{2}$ 0 $_{3}$ powder, with the diameter of 200150m, was found to be effective to some extent as a barrier for a colloid migration from low-alkaline cement paste.