Radiological consequence analysis for hypothetical accidental release from Nigerian Research Reactor-1

Radiological dispersion study is a key element in safety analysis report (SAR) of every nuclear facility for the purpose of emergency response planning. In this work, computational approach was used to determine the total effective dose and ground deposition at critical positions onsite and offsite of the Nigerian Research Reactor-1 (NIRR-1) facility which will be useful in the ongoing development of final SAR for NIRR-1 Low Enriched Uranium (LEU) core. In the methodology used, NIRR-1 LEU core was depleted with TRITON module of SCALE 6.2.3 code and the fission inventory in the core was calculated after a continuous operation at full power of 231.931MWD/MTU for 918 Effective Full Power Days (EFPD) at an operation regime of 3 h per day, 3 days per week and 48 weeks per year. Hot Spot was employed for atmospheric transport and dose calculations with consideration of different accidental scenarios in which 20%, 30%, 60% and 100% gaseous inventory was hypothetically released into the atmosphere. From the results obtained, the total effective dose to maximum exposed workers at 10 m and maximum exposed members of public at 300 m from the reactor were 3.10mSvand0.43mSv respectively for the worst-case scenario with 100% release while the maximum ground deposition was 5.5×10⁶Bq/m² with corresponding maximum ground shine dose rate of 7.5×10^-4mSv/hr. This results are at least one order of magnitude below the dose limits recommended by the International Commission on Radiological Protection (ICRP) and indicate that the present LEU core of NIRR-1 is unlikely to cause any detectable health effect on workers and members of public in the event that 100% of its gaseous inventory is released into air in the environment. Hence it could unequivocally be said that the population is safe from the operation of NIRR-1 in its present location.