Improved Approach to Multiregion Supercritical Transient Analysis Based on the Integral Kinetic Model and Monte Carlo Method

An approach to multiregion supercritical transient analysis based on the integral kinetic model (IKM) and Monte Carlo method is further developed with new features. The IKM describes the region-dependent fission rate during the transient in a system of arbitrary geometry using a secondary fission probability density function, which takes the explicit neutron transport time between successive fissions across the regions into account. The new features of the improved approach include treatment of the multiregion transient using repeated multidimensional linear interpolation between pre-obtained kinetic functions (i.e., secondary probability density function), a new method for calculating the kinetic functions using the continuous-energy Monte Carlo code MVP2.0, and utilization of kinetic functions directly in the IKM without the fitting function that introduces a fitting error. The improved approach is verified by applying it to the supercritical transient in simple Godiva systems of different region combinations without feedback. In addition, we attempt to validate the improved approach by applying it to the supercritical transient in a simplified Godiva system with thermal expansion feedback and compare the obtained and experimental results. The verification results indicate the improved approach works well with different combinations of regions while the validation results show promising agreement with the experimental results. This study is part of an ongoing research activity on the development of Multi-region Integral Kinetic (MIK) code for general space- and time-dependent kinetic analyses.