Gamma heating calculations for the HFR

In the design of an irradiation experiment one needs to know the amount of heat generated in it. When photons are the main source of heating, as is the case in experimental positions in a materials test reactor, this poses a problem. The photon source in this case consists of two parts: prompt photons and photons emitted by decaying fission products (delayed photons). The prompt photons are commonly taken into account in particle transport codes, but the photons from fission product decay are not. Here we propose to incorporate the delayed photons by means of a simple engineering correlation, which can easily be implemented in e.g. a Monte Carlo transport code such as MCNP. Our results compare well with data for all experimental positions in the High Flux Reactor (HFR) in Petten, the Netherlands. We also discuss the reduction in heating levels when converting the HFR to LEU. (authors)