Hydrogen is at the source of degradation mechanisms affecting mechanical properties of many structural metal materials. In nuclear power plants, zirconium alloy fuel cladding tubes take up a part of the hydrogen from coolant water due to oxidation. Because of the high mobility of hydrogen interstitial atoms down temperature and concentration gradients and up stress gradients, hydrogen distribution in fuel claddings can often be non-uniform, arising the risk for the integrity of spent fuel rods under mechanical load. At the Laboratory of Nuclear Materials (LNM) in collaboration with the Laboratory of Neutron Scattering and Imaging (LNS), hydrogen redistribution in zirconium alloys was quantified by neutron radiography using the state-of-the-art detector of PSI Neutron Microscope, and the concentration was computed based on thermodynamics, to predict hydrogen diffusion and precipitation for used nuclear fuel.