An internal coupling method between neutronics and thermal-hydraulics with RMC and CTF

To tackle the high-fidelity multi-physics coupling challenge in nuclear reactors, an internal coupling method was proposed and implemented to closely couple the neutron transport Monte Carlo code RMC and the sub-channel thermal-hydraulics solver COBRA-TF (CTF) using direct memory data transfers. In this coupling system, fixed-point Picard iteration scheme and Gauss-Seidel iteration method were implemented and evaluated. Two accel-eration algorithms were proposed and both proved effective, including the hybrid MPI/OpenMP parallelism scheme and the asymptotic batch coupling method. The coupling system was validated against the VERA benchmarks and compared with literatures. The k eigenvalue differed by 7 pcm and the relative differences in the radial power profiles were less than 0.30%. Moreover, the simulation time was reduced by 48.1% due to quicker convergence with the two acceleration methods. Further analyses also proved the superior precision of this method, especially for asymmetric problems.