AbstractWith the intention of developing the decomposition process of tritiated compounds, ZrNi alloy was taken up as one of proper materials and its methane decomposition properties were experimentally investigated in a laboratory-scale flowing gas system. Methane was selected as a typical tritiated compound because of being known to be hardly decomposed and little data. The performance tests of methane decomposition using ZrNi alloy under various process conditions of gas flow rates (20, 35, 70 and 100 cc min−1), granular sizes (70–200, 200–400 and <400 mesh) and reaction temperatures (823, 848 and 873 K), have been carried out. As a result, the methane and hydrogen concentrations after undergoing decomposition process showed qualitatively similar four-stage-time change profiles for all of the independent experimental conditions. However, the definite dependence of decomposition properties on the decomposition conditions was recognized by observing a duration time of a briskest decomposition rate of more than 70%, volumes of decomposed methane and generated hydrogen.