A modified predictor-corrector quasi-static method in NECP-X for reactor transient analysis based on the 2D/1D transport method

The 2D/1D transport method is a widely applied method for the whole-core heterogeneous transport calculation. The transient simulation based on the pin-resolved 2D/1D method is implemented in the high-fidelity code NECP-X. The 3D transient fixed source problem (TFSP) is transformed into 2D TFSP and 1D TFSP coupled by leakage, and the pin-based coarse mesh finite difference method (CMFD) is used to accelerate convergence of the 2D/1D TFSP. In this paper, a modified predictor-corrector quasi-static (mPCQS) method is developed to provide better reactivity prediction for PK calculations. Furthermore, the simplified source scaling method (SSSM) is used to accelerate the convergence of the CMFD TFSP iterations. The results of three problems are presented including the 2D C5G7-TD benchmark, a MiniCore-3D rod-ejection problem and a 3D heterogeneous rod-ejection problem. Numerical results reveal that the SSSM method can significantly reduce the number of CMFD iterations without increasing the computational complexity, and the mPCQS method can provide better results than the standard PCQS for step perturbation transient event and rod ejection transient event no matter in the homogeneous case or in the heterogeneous case.