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

Area of Science:

• Nuclear Engineering
• Radiological Safety
• Environmental Science

Background:

• Radiological dispersion studies are crucial for nuclear facility safety analysis reports (SAR) and emergency planning.
• The Nigerian Research Reactor-1 (NIRR-1) is undergoing development of its final SAR, necessitating a comprehensive safety assessment.

Purpose of the Study:

• To computationally determine the total effective dose and ground deposition at critical onsite and offsite locations for the NIRR-1 Low Enriched Uranium (LEU) core.
• To assess the potential radiological impact on workers and the public under various accidental release scenarios.

Main Methods:

• Depletion of the NIRR-1 LEU core using the TRITON module of the SCALE 6.2.3 code.
• Calculation of fission inventory after 918 Effective Full Power Days (EFPD) of operation.
• Atmospheric transport and dose calculations using Hot Spot code for hypothetical gaseous inventory releases (20% to 100%).

Main Results:

• Maximum effective doses for workers (10m) and public (300m) were 3.10mSv and 0.43mSv, respectively, under a 100% release scenario.
• Maximum ground deposition was 5.5×10^6 Bq/m², with a corresponding maximum ground shine dose rate of 7.5×10^-4 mSv/hr.
• All calculated doses are at least one order of magnitude below the International Commission on Radiological Protection (ICRP) recommended dose limits.

Conclusions:

• The current LEU core of NIRR-1 is unlikely to cause detectable health effects on workers or the public, even in a worst-case 100% gaseous inventory release.
• The study concludes that the population is safe from the operation of NIRR-1 in its current location.
• The findings support the ongoing development of the final SAR for NIRR-1.