Photoproduction data for heating calculations

For irradiations in a materials test reactor, the prediction of the amount of gamma heating in the reactor is important. Only a good predictive calculation will lead to an irradiation in which the specified temperatures are reached. The photons produced by fission product decay are often missing in spectrum calculations for a reactor, but the contribution of the photons can be computed effectively using engineering correlations for the amount of fission product decay and the ensuing photon spectrum. The prompt photons are usually calculated by a spectrum code based on the underlying nuclear data libraries. For most of the important nuclides, the nuclear data libraries contain data for the photon productions rates. However, there are still many nuclides for which the photon production data are missing, and some of these nuclides contribute to gamma heating. In this paper it is estimated what the contributions to heating are from photon production on nuclides such as 236U, 238Pu, 135I, 135Xe, 147Pm, 148Pm, 148mPm, and 149Sm. Also, simple arguments are given to judge the effect from photon production on all other (lumped) fission products, and from 28Al decay. For all these calculations the High Flux Reactor is used as an example. (authors)