Calculation of kinetic parameters for mixed TRIGA cores with Monte Carlo

Modern Monte Carlo transport codes in combination with fast computer clusters enable very accurate calculations of the most important reactor kinetic parameters. Such are the effective delayed neutron fraction, βeff, and mean neutron generation time, Λ. We calculate βeff and Λ for various realistic and hypothetical annular TRIGA Mark II cores with different types and amount of fuel. It is observed that the effective delayed neutron fraction strongly depends on the number of fuel elements in the core or on the core size. βeff varies for 12 wt.% uranium standard fuel with 20% enrichment from 0.0080 for a small core (43 fuel rods) to 0.0070 for a full core (90 fuel rods). It is found that calculated value of βeff strongly depends also on the nuclear data set used in calculations. The prompt neutron lifetime mainly depends on the amount (due to either content or enrichment) of 235U in the fuel as it is approximately inversely proportional to the average absorption cross-section. It varies from 28 μs for 30 wt.% uranium content fuelled core to 48 μs for 8.5 wt.% uranium content LEU fuelled core. Description of the calculation method and detailed results are presented in the paper.