Analysis of Loss of Water Inventory at the Philippine Research Reactor-1 Fuel Storage Facility

Abstract

The Philippine Research Reactor-1 (PRR-1) fuel storage facility is a wet storage for irradiated nuclear fuel. The behavior of the facility in case of accidental loss of water is currently unknown. Safety analysis of a repository of fissile material involves criticality safety assessment and radiation dose estimation for normal and accident scenarios. To determine the radiological consequences of loss of water inventory in the fuel storage facility, we calculated the effective multiplication factor (keff) and gamma dose rate distribution in the system using Monte Carlo N-particle (MCNP) radiation transport code. Results show that keff will decrease from a maximum of 0.61424 ± 0.00013 when the water level is decreased from its fully moderated condition. In contrast, keff will increase to a maximum of 0.7468 ± 0.0002 when voids are introduced in the water. These results indicate that the system will remain subcritical (keff<1) and a runaway supercritical fission chain reaction cannot result from any moderating conditions. Furthermore, the dose assessment for the case of complete loss of water revealed a maximum dose rate of 5.52 ± 0.045 mSv/h and 288 ± 4.65 𝛍Sv/h at the tank surface and tank platform, respectively. These values are significantly above background radiation levels; however, the calculated spatial distribution is highly asymmetric and the dose rate falls off rapidly with increasing distance. These results suggest that a facility-level emergency response is sufficient to address the accident. Our findings can augment the existing facility emergency procedures, thereby contributing to the improvement of radiological safety.

Radiological Characterization of the Philippine Research Reactor-1 Legacy Neutron Sources via Monte Carlo Simulation

“…The storage rack is an aluminum structure that measures an 8 x 4 rectangular array of holes where 30 TRIGA fuel clusters were accommodated. A detailed description of the computational modeling performed for the storage tank is provided in previous work (Gatchalian et al, 2021). For the calculation of the dose distribution, a rectangular mesh centered at the tank with mesh element dimensions of 1 x 1 x 50.8 cm was used to calculate the x-y plane distribution of the dose rate.…”