Radial Hydride Precipitation in Fuel Cladding During Back-End Cooling Transient Under Decreasing Pressure

During spent fuel assembly transportation or dry cask storage, filling gas and fission gas release pressurize the fuel rods contained in the cask. These rods are heated by fuel assembly residual power resulting in internal pressurization stress increase in the rods. During the subsequent cooling associated to removal of rods from the transportation cask or during the decrease of residual power after a long storage period, the cladding hoop stress is expected to decrease. Concomitant cladding temperature and stress decrease may influence the morphology of precipitated hydrides in corroded claddings. Radial hydride precipitation has a detrimental role on the mechanical resistance of the cladding and is promoted by large hoop stresses during the cooling of the cladding. There is, consequently, a need to predict the radial hydride precipitation in corroded cladding tubes during dry storage or transportation cooling transients. Existing models usually address the radial hydride precipitation conditions under constant stress leading to over-estimated radial hydride content within the cladding.