Influence of geometry in TRIGA reactor criticality calculation and reactivity determination using Serpent 2 and MCNPX codes

The IPR-R1 TRIGA Mark I research reactor is located at the Nuclear Technology Development Centre (CDTN), in Belo Horizonte, Brazil. It is operating for more than 50 years and was successfully simulated before. However, new techniques and methods used in nuclear reactors analysis make a further simulation inevitable. In this manuscript, the computational model of an initial core of the IPR-R1 TRIGA reactor was developed employing two different Monte Carlo codes, MCNPX and Serpent 2, to simulate the neutronics behaviour. A new model is suggested, more complete, to improve the simulations results making the model more close the experimental data. This work explores how changes could be inserted in order to make the model closer to reality and if such participation would be noticeable in both codes used. The neutronic parameters obtained from these simulations performed in Serpent 2 are compared to MCNPX simulation results at the same conditions, and the results are compared with previous experimental data.