High Burn-Up UO2 Fuel Corrosion under Reducing Conditions

A fission product and Pu rich porous structure forms at the radial periphery of LWR fuel pellet at a local burnup of ~70 GWd/tHM. This restructured fuel region, usually referred to as rim, will be the first part of the spent fuel to be exposed to groundwater in the event of failure of all the containment barriers. The corrosion behavior of rim-structured high burn-up UO2 fuel under conditions expected in a deep geologic repository is not fully understood today. To address this issue, a corrosion experiment on rim-containing fragments of high burnup UO2 fuel has been performed in a titanium autoclave. To simulate deep bedrock repository conditions, the autoclave was filled with a dilute carbonate groundwater, and pressurized to 4 MPa with H2. The results obtained during the first year of corrosion showed that the concentration of 238U in the leachate decreased below 5·10-10 M, the plutonium concentration fell below 6·10-12 M while the 137Cs concentration remained constant. Removal of the instant release fraction gave new insight of the chemical behavior of U, Pu and Cs under such conditions. Altogether, it was shown that the radiolytic oxidants produced by the intense a-, ß-, and ¿-radiation field of the high burn-up fuel were consumed in the system under study.

FORS Patrick;  CARBOL Paul;  VAN WINCKEL Stefaan;  SPAHIU K.; 

2010-01-19

American Nuclear Society (ANS)

JRC56329