ANALYSES OF NEUTRON ABSORBER MATERIALS ON THE SAFETY PARAMETERS IN THE RSG-GAS REACTOR

The shutdown system in the core of the RSG-GAS reactor uses a neutron absorber material. Research reactors in the world often use 3 kinds of neutron absorber materials, namely AgInCd, B4C, and Hf. In this research, a neutron absorber analysis was carried out on the neutronic safety parameters for the RSG-GAS reactor core. Neutronic safety parameters for various kinds of neutron absorbing materials in the existing RSG-GAS core have never been carried out. The neutronic safety parameters are keff, neutron flux, core excess reactivity, shutdown margin, control rod total reactivity value, and PPF. A 250 gram silicide fuel was selected as a case study to see the possibility of a better neutron absorber material. In a three-dimensional diffusion model, four groups of neutron energies are selected for the computation of the core. The WIMSD-5B and Batan-3DIFF computer programs were used to perform this calculation. The calculation result shows that the largest shutdown margin value using B4C neutron absorber material; whereas the lowest PPF was obtained using Hf neutron absorbing material. The greatest power density values are in the fuel area around the CIP (center irradiation position), surrounded by the control fuel element, and the standard fuel element beside the berrylium reflector. The largest and smallest fluctuations in power density were obtained using neutron absorber materials B4C and AgInCd, respectively.