Theory and Performance of the Fast-Running Multidimensional Pressurized Water Reactor Kinetics Code, SPNOVA-K

A New Precursor Integral Method for Solving Space-Dependent Kinetic Equations in Neutronic and Thermal-Hydraulic Coupling System

The accurate prediction of the neutronic and thermal-hydraulic coupling system transient behavior is important in nuclear reactor safety analysis, where a large-scale nonlinear coupling system with strong stiffness should be solved efficiently. In order to reduce the stiffness and huge computational cost in the coupling system, the high-performance numerical techniques for solving delayed neutron precursor equation are a key issue. In this work, a new precursor integral method with an exponential approximation is proposed and compared with widely used Taylor approximation-based precursor integral methods. The truncation errors of exponential approximation and Taylor approximation are analyzed and compared. Moreover, a time control technique is put forward which is based on flux exponential approximation. The procedure is tested in a 2D neutron kinetic benchmark and a simplified high-temperature gas-cooled reactor-pebble bed module (HTR-PM) multiphysics problem utilizing the efficient Jacobian-free Newton–Krylov method. Results show that selecting appropriate flux approximation in the precursor integral method can improve the efficiency and precision compared with the traditional method. The computation time is reduced to one-ninth in the HTR-PM model under the same accuracy when applying the exponential integral method with the time adaptive technique.

Application of Stiffness Confinement Method in Transient Transport Calculation

Stiffness confinement method (SCM) can effectively alleviate the stiffness in the neutron kinetics equation and can use larger time steps to obtain the same calculation accuracy and improve the computational efficiency. However, the existing SCM is mainly used to solve two group transient diffusion equations. In this paper, the SCM is employed to solve the multigroup transient transport calculation. On the basis of the original method of characteristics (MOC) code PEACH, the transient function is added, and the PEACH-K program is developed. Based on the numerical results of the latest published OECD/NEA C5G7-TD benchmark, it shows that the PEACH-K program developed in this paper has both high computing precision and good numerical stability.