Simulation of gamma dose from shielded TRIGA fuel using OpenMC
The nuclear commissioning of the Philippine Research Reactor-1 (PRR-1) Subcritical Assembly for Training, Education, and Research (SATER) involved loading slightly irradiated TRIGA nuclear fuel in the reactor core. The previous irradiation of the fuel rendered them with Cs-137 fission products that emit 0.662 MeV gamma rays. Hence, radiation shielding should be provided during the movement of the fuel rods to ensure that personnel handling the fuel are sufficiently protected from radiation. This is accomplished by employing a lead transfer cask that can accommodate four fuel rods at a time. Monte Carlo simulations were performed to investigate the effectiveness of the transfer cask in reducing the dose from the fuel rods. The OpenMC code was used to simulate four TRIGA fuel rods in bare and shielded conditions and to calculate the gamma dose distribution for both cases. Results show that the transfer cask reduced the dose rate by 200%. Calculated dose maps showed that the largest contributor for the reduction of the dose rates were the Pb content of the transfer cask. Regions wherein Pb is present showed the largest amount of reduction. The dose maps also showed regions outside the transfer cask where the calculated dose rate is minimal. These results were used as basis by the reactor team in verifying that sufficient radiation protection measures are in place during the commissioning of the facility.