Determination of Reactor Parameters for Different Subcritical Configurations of the Philippine Research Reactor-1 TRIGA Nuclear Fuel

The Philippine Research Reactor-1 (PRR-1) will be revived as a subcritical assembly for training, education, and research (SATER) in the field of nuclear science and technology. SATER will utilize the existing slightly irradiated nuclear fuel rods that have been maintained in the PRR-1 facility for more than 30 years. A subcritical arrangement for the fuel rods was chosen considering the inherent safety of this configuration. In this paper, we calculate relevant reactor parameters that characterize different annular and hexagonal subcritical configurations of 44 PRR-1 fuel rods. These parameters include the neutron multiplication factor k_eff the effective delayed neutron fraction β_eff and the mean neutron generation time λ, which are essential quantities to describe reactor behavior. Calculations were performed using the well-validated Monte Carlo radiation transport code MCNP5 v.1.6 together with the ENDF/BVII. 1 evaluated nuclear data library. The maximum k_eff value is 0.96735 ± 0.0003 at 4.3 cm pitch for the chosen hexagonal arrangement. For these configurations, the reactor kinetic parameters were β_eff=756 ± 4pcm and λ = 41 μs for the annular arrangement, while β_eff = 460 ± pcm and λ = 40 μs for the hexagonal arrangement. Results demonstrate that with 44 fuel rods, different fuel arrangements remain subcritical with a subcriticality margin that is at least 3% Δk/k or maximum k_eff of 0.97. The key reactor performance characteristics determined in this study can aid in the analysis of transient behavior and safety assessment of subcritical core configurations with TRIGA fuel rods. Our results provide support in expanding the utilization options for irradiated TRIGA fuel rods, even for other TRIGA facilities. (authors)