Estimation of the dose rate of nuclear fuel of Ghana Research Reactor-1 (GHARR-1) using ORIGEN-S and MCNP 6

Ghana is in the process of converting its fuel from Highly Enriched Uranium (HEU) to Lowly Enriched Uranium (LEU). Radioactive fission and activation products generated in the irradiated nuclear fuel are hazardous to personnel, environment and the public. Investigation into the levels of radiation dose will help in a safe and efficient core conversion process. Two computer codes used 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 ORIGEN-S code to calculate the dose rate. The criticality of the core at different heights above the bottom of the core was also obtained. Most of the radionuclides present after the core depletion contributed to the source term of 1.767 × 1013 ± 0.0008 photons/sec which was observed after thirty days of the cooling period. The dose rates ranged between 3.51 × 10−25 ± 0.0003 mGy/h and 4.27 × 104 ± 0.0006 mGy/h at different positions above the reactor core, the control room (wall, door and window) and the rabbit room. The criticality (keff) also decreased from 0.99442 ± 0.00006 to 0.01238 ± 0.00002 as the core moved from the bottom of the reactor vessel to the top.