Development of a neutron space-time kinetics solver with improved quasi-static method based on OpenFOAM

To analyze the transient problems for neutronics and make the preparation for high-fidelity multi-physics simulation. In this study, a neutron space-time kinetics solver called "KaiyangIQS" with the improved quasistatic method based on OpenFOAM is developed. The basic principles of improved quasi-static method, numerical method, and solver strategy are derived and discussed in detail. Separate validations for the modules of solving amplitude function and adjoint scalar flux diffusion equation are carried out. The results show that OpenFOAM can effectively handle the stiff matrix of amplitude equations with high accuracy and robustness. The adjoint scalar flux diffusion equation solver is also validated by the IAEA 3D benchmark. For the improved quasistatic method solver, unidimensional rod ejection problem, TWIGL benchmark problem, and three-dimensional rod ejection problem are carried out for calculation and validation. Normalized power prediction, reactivity prediction, effect of adopting different discretization schemes of transient terms, rod cusping effect, and lag effect of delayed neutron precursors are analyzed in detail. The numerical results of the solver with improved quasistatic method that developed in this study are in good agreement with references, and this solver can be considered a promising tool to simulate the transient neutron kinetics problems.