Implementation and Analysis of Thermal Hydraulics Feedback in High-Fidelity Neutron Transport Program HNET

With the growing requirement of predicting reactor behavior in high-fidelity detail at practical conditions, it is urgent to accomplish thermal hydraulics (T-H) feedback in the high-fidelity neutron transport program HNET. For better convergence behaviors than Picard iteration, the Matrix Free Newton/Krylov (MFNK) method was employed to resolve neutronics and thermal-hydraulics coupling system. MFNK treats each subsystem as a black box within the Newton method framework, so it can facilitate the coupling procedure without surrendering efficiency or robustness. For the T-H feedback effects, a simplified internal thermal hydraulics model was adopted to provide T-H conditions for neutronics. The convergence behaviors of MFNK and Picard iteration were assessed through simple typical cases. Finally, the effectiveness of the coupling system was verified by the VERA problem #6. Numerical results demonstrate the efficiency and stability of MFNK compared with Picard iteration. Moreover, it turns out that the coupling system has a good performance in realistic cases.