Dissolution of UO2 by photochemical reaction

In this study, photodissolution tests of UO2 powder, green pellet and sintered pellet were carried out in a nitric acid solution and at about 40 degrees C under UV irradiation. Light source is Hg-lamp emitting 254 nm wavelength. Nitric acid concentration ranged from 2 M to 4 M. As results, UO2 powder and green pellet were rapidly dissolved within 2 h at 2 M HNO3 while UO2 sintered pellet was hardly dissolved. This was attributed to surface characteristics of the sintered pellet: UO2 sintered pellet is very dense and has extremely low specific surface area. Accordingly, oxidizing species such as *NO3-, NO2- produced from NO3- during photolysis have great difficulty to penetrate into the core of UO2 sintered pellet. However, this was considerably improved by adding small amounts of H2O2, which could increase the surface area by etching the surface of UO2 sintered pellet. Additionally, an increase in the number of pellets resulted in a rapid increase of uranium concentration in the solution even at 2 M nitric acid concentration and low temperature under irradiation.