## PREDICTIONS OF THE DECAY HEAT OF NUCLEAR REACTORS BY MICROSCOPIC BETA DECAY CALCULATIONSMax-Planck-Institut für Kernphysik, Heidelberg, GermanyA new procedure for calculating the decay heat power of nuclear reactors is presented. Basis is a new program, THOR-I ( Theory of Heat Of Reactor -I), which calculates the isotopic inventory of a reactor as function of time during reactor operation and after shutdown by the analytical method and which uses a new set of β decay data, in which β decay of experimentally unknown nuclei has been calculated for the first time by microscopic nuclear structure calculations. The decay heat power for short time irradiation of ^{232}Th, ^{233}U, ^{235}U, ^{238}U, ^{239}Pu, ^{241}Pu by thermal and fast neutrons, as well as for realistic light water reactor (LWR) operation cycles, have been calculated as function of time after irradiation (or operation) and shutdown, respectively. The effect of neutron capture is explicitly taken into account. Comparison of the results with the ANS (DIN) standard shows that the current standards systematically overestimate the decay heat of LWRs by about 6-8% in the first 10^{4} sec after shutdown. Similar results are found for other reactor types such as boiling water reactors, advanced pressurized water reactors and CANDU. It is shown that the accuracy of the new procedure is such that a) summation calculations of this type could be considered as basis of new standards, b) might lead directly to economic benefit.KEYWORDS: Nuclear Reactors, Decay Heat Prediction, Standards of Decay Heat |