Hydride precipitation may impact the integrity of zirconium-based nuclear fuel cladding, both during normal operation and during extended dry storage. To better understand such degradation, a study of hydride precipitation of zirconium hydrides in Zircaloy-4 samples was performed. The samples were submitted to various thermomechanical cycles using both in situ synchrotron X-ray diffraction and differential scanning calorimetry. Results showed that as the hydrided samples were cooled at moderate to fast cooling rates, the hydrogen content in solid solution (CSS) decreased, following the terminal solid solubility for precipitation (TSSP) curve, reflecting hydride precipitation in the matrix. However, when the samples were held for an isothermal anneal at a fixed temperature, the CSS continued to decrease below TSSP and approached the terminal solid solubility for dissolution (TSSD). This result suggests that TSSP is a kinetic limit and that a unique solubility limit TSSD governs zirconium hydride precipitation. Hydride precipitation rate and the degree of precipitation reaction