Estimation of the Dose Rate of Nuclear Fuel of Ghana Research Reactor-1 (Gharr-1)

Abstract

Ghana is in the process of converting its fuel from Highly Enriched Uranium (HEU) to Lowly Enriched Uranium (LEU) even though the HEU fuel is not fully spent, thus the handling of the irradiated fuel is in the offing. Irradiated fuel consists of radioactive fission and activation products generated in the nuclear fuel which are hazardous to personnel, environment and the public. As a result, the knowledge of the dose rate will aid in safe guarding the process of core conversion. Two computer codes used to carry out this research work were ORIGEN-S; for computing changes in the isotopic concentrations during neutron irradiation and radioactive decay as well as to determine the source term and MCNP6; which used the source term estimated by the ORIGEN-S code to calculate the dose rate in mrem using point detectors and also to determine the criticality of the core at different heights above the bottom of the core in order to mimic the process of unloading the core. Most of the radionuclides present after the core depletion contributed to the source term of 1.767X1013photons/sec which was observed after thirty days of the cooling period. The dose rates ranged between 3.51x10-25mGy/hr and 4.27x104mGy/hr with the detectors placed at positions above the reactor core, the control room (wall, door and window) and the rabbit room. The criticality (keff) also decreased from 0.99442 to 0.01238 which indicates that the nuclear fuel will remain sub critical. The results proved that the core unloading will be done safely.