Implementation of Hydrogen Solid Solubility Data and Precipitation Threshold Stresses in the Fuel Rod Code TESPA-ROD

During operation of light water reactors, the Zircaloy fuel rod cladding is susceptible for hydrogen uptake. When the local solubility limit of hydrogen in Zircaloy is reached, additional hydrogen precipitates as zirconium hydride, which affects the ductility of the fuel rod cladding. Especially, the radially aligned hydrides enhance embrittlement, while circumferential (azimuthal) hydrides have a less detrimental effect. In this work, the influence of high temperatures during the dry storage period on hydride dissolution and precipitation is demonstrated. Therefore, in a descriptive example scenario being discussed, the simulation of a limited heat removal from the cask will heat up the dry storage cask for days and causes dissolution of hydrides in the cladding. Depending on the threshold stress for reorientation, the following cooldown results on different hydride precipitation behavior. The threshold stress leads to an enhanced or delayed precipitation of radial hydrides. The GRS fuel rod code TESPA-ROD is equipped with a new model for hydrogen solubility and applied to long-term storage transients. In this article, hydride refers to zirconium hydrides formed inside the fuel rod cladding.