Pandemonium free data for the JEFF-project

Reactor decay heat is due to the decay of both fission products and neutron activated fuel and reactor materials. At relatively short cooling times it is dominated by the beta decay of fission products. The calculation of the decay heat contribution of a particular fission product depends on the proper assignment of the probability of population of each excited state in the daughter nucleus following beta decay. These decay probabilities and the energy distribution of the continuous beta spectra determine both the unrecoverable energy taken away by the neutrinos and the distribution of decay heat between gamma rays and beta particles. The latter is important for further radiation transport modeling, for instance to determine the volume over which the heat is deposited. This paper describes recent advances in measurement and modeling of selected fission products and the impact for JEFF evaluations.