Uncertainties in Kinetics Parameters of Natural-Uranium-fuelled CNDU Cores Introduced by Lattice Homogenization and Group Condensation

Abstract

In the Canadian Nuclear Industry, safety analysis-related reactor kinetics calculations are performed almost exclusively using the Improved Quasistatic (IQS) flux factorization method [1, 2]. The IQS method relies on calculating effective point kinetics parameters using adjoint-weighted integrals. The accuracy of the adjoint representation influences the accuracy of the effective kinetics parameters. The work presented here evaluates the effect of homogenization and group condensation on the calculated effective kinetics parameters of a Natural-Uranium-fuelled CANDU lattice as a function of burnup. Results show that, by using a two-group lattice-homogenized adjoint, the effective delayed neutron fraction is consistently overestimated by approximately 5% over a burnup range between 0 kWd/kg and 8000 kWd/kg. The effective neutron generation time is underestimated by 0.4% at 0 kWd/kg and overestimated by 1.3% at 8000 kWd/kg.