Proposal of Direct Calculation of Kinetic Parameters .BETA.eff and .LAMBDA. Based on Continuous Energy Monte Carlo Method

Abstract

Direct calculation methods of kinetic parameters are proposed based on the continuous energy Monte Carlo method. In the proposed methods, the effective delayed neutron fraction eff and the neutron generation time à are estimated using eigenvalue calculations. The expected number of fission neutrons in the next generation is newly applied to the proposed methods instead of the adjoint flux that has been conventionally used. The algorithms to estimate the kinetic parameters are established and incorporated into the continuous energy Monte Carlo transport calculation code MCNP-4C, which is versatile for eigenvalue calculations of nuclear reactor cores with various types of neutron energy spectrum and geometry. The proposed methods were validated since the calculated values agreed with the experimental data of eff and eff =à for the critical cores within accuracies of 4.5% and 10%, respectively.KEYWORDS: kinetic parameter, effective delayed neutron fraction eff , neutron generation time Ã, continuous energy Monte Carlo Method, expected number of fission neutrons in the next generation

Reactor physics analysis of the SPERT III E-core with Tripoli-4®

“…The kinetics parameters for the core loading with 32 elements are not reported in the original documents. We have nonetheless computed the adjoint-weighted kinetics parameters with T-4 R by resorting to the Iterated Fission Probability (IFP) method (Nauchi and Kameyama, 2010;Kiedrowski, 2011;Leppanen, 2014;Truchet et al, 2015), which yields β eff = 778 ± 4.6 pcm for the effective delayed neutron fraction and Λ eff = 22.2 ± 0.02 µs for the effective mean generation time. For comparison, the typical values for a commercial 1000 MW PWR at ∼ 3.25 % enrichment and moderator to non-moderator ratio equal to ∼ 2 are β eff 700 pcm and Λ eff 25 µs (Duderstadt and Hamilton, 1976).…”

“…For comparison, the typical values for a commercial 1000 MW PWR at ∼ 3.25 % enrichment and moderator to non-moderator ratio equal to ∼ 2 are β eff 700 pcm and Λ eff 25 µs (Duderstadt and Hamilton, 1976). In order to evaluate the impact of the IFP method on the assessment of the kinetics parameters, we have also computed the adjointweighted kinetics parameters by resorting to the IFP 0 approximated method, based on the expected number of fission neutrons in the next generation (Nauchi and Kameyama, 2005), which yields β 0 eff = 768 ± 1.2 pcm for the effective delayed neutron fraction and Λ 0 eff = 25.8 ± 0.007 µs for the effective mean generation time. The computed (un-weighted) delayed neutron fraction reads β 0 = 724 ± 0.8 and the (un-weighted) mean generation time Λ 0 = 45.8 ± 0.02 µs.…”

Calculation of Effective Delayed Neutron Fraction Using a Modified k-Ratio Method

“…1) On the other hand, Meulekamp et al assume that eff is the ratio of the average number of fissions generated by delayed neutrons to the average number of fissions generated by all neutrons. 2) In these methods, the number of fission neutrons or the number of fissions are counted at each neutron generation in continuous-energy Monte Carlo calculations.…”