Dissolution Behavior Of (U,Zr)O-2-Based Simulated Fuel Debris In Nitric Acid

To explore the possibility of dissolving fuel debris into nitric acid as a potential pre-treatment for waste treatment in which the U and Pu are removed from the inventory, dissolution tests of U1-xZrxO2 and (U,Pu)(1-x)ZrxO2 were carried out in 6 M HNO3 at 353 K. At the end of the dissolution test (after 4 h), the ratio of dissolved uranium decreased with an increase in the Zr contents, x. While the dissolution of U-rich samples was congruent, a preferential leaching of U was observed with Zr-rich samples. Taking into account these different dissolution phenomena, the dissolution rate analysis was carried out using surface-area model to calculate the instantaneous dissolution rate (IDR). The IDR decreased from 10(-5) down to 10(-10) mol cm(-2) min(-1) as x increased from 0 to 0.95. From these findings, dissolution with HNO3 is expected to be only applicable in U-rich part of fuel debris (x < 0.3) if the dissolution in 6M HNO3 at 353K is assumed. Application of complexing acids, such as mixture of HNO3 and HF, should be considered to increase the dissolution rate of the Zr-rich part.