Evaluation of nuclear heating of small samples in a research reactor core

A simple analytical model is presented which indicates that the ratio of heating power densities of two different materials, irradiated under the same conditions inside a reactor core, can be estimated from material properties only. The developed approximate method allows simplifying the measurement technique of a number of samples from different materials by performing measurement of only one sample. The latter is a primary result of the proportionality between the heating and the thermal neutron flux for samples irradiated under the same conditions. This is confirmed by measurements in the Greek Research Reactor (GRR1) showing that the temperature of materials irradiated at various positions of a vertical core channel due to all heating mechanisms follows the spatial variation of thermal neutron flux. Validation by the numerical 3D gamma heating code GHRRC developed in NCSR Demokritos shows that the conclusions of the simple analytical method apply also for the total heating by all gammas in the core. A model is also presented for the estimation of heating by elastic neutron scattering. Furthermore, a methodology is suggested for the estimation of the temperature and the heat power deposited on materials irradiated during normal reactor operation, based on in-pile temperature measurements performed at low reactor power levels.