Investigation of secondary phases formed during long-term aqueous leaching of spent nuclear fuel

For a future deep repository for spent nuclear fuel, the rate and mechanism for dissolution of fission products and actinides from the fuel is a key parameter for the safety assessment of the disposal concept. Although the behavior of spent nuclear fuel under deep repository conditions has been studied extensively, studies of failed fuel are relatively scarce. However, at the Studsvik laboratory, aerated leaching tests of spent fuel started in the 1980s and two of these were finalized only recently. This provides an opportunity to investigate the effects of long-term contact with water under aerated conditions similar to wet interim storage conditions. In this study, surface investigations have been performed on two fuel pellet samples which have been exposed to leaching solutions for over 30 years. Furthermore, the fuel samples have been exposed to carbonate solutions in an effort to dissolve the secondary phases formed during the extended leaching time.