AbstractThe whole-energy absorption spectrometer (WEAS) was developed to measure decay heat of fusion reactor materials, and the first experimental data of decay heat on Al, Cu and SS304 irradiated by D-T neutrons were obtained. The experiment demonstrated the feasibility of decay heat measurement with WEAS. Validity of decay heat calculations with available codes and data libraries was tested by comparing the calculated results with the measured ones. Some problems were found in the tested codes and data libraries for the decay heat calculation although decay γ-ray calculations with these codes and data have been validated with the existing benchmark experiments. Except for these problems, the decay heat calculations predicted the measured decay heat values mostly within ± 15%.