Reactor Simulation with Coupled Monte Carlo and Computational Fluid Dynamics

This paper demonstrates the applicability of Monte Carlo analysis to perform nuclear reactor core simulations with thermofluid feedback from a computational fluid dynamics code. An interface program, McSTAR, was written to couple MCNP5 to the commercial computational fluid dynamics code STAR-CD. McStar is a Perl script which alternately executes MCNP5, STAR-CD and cross section update routines on multiprocessor Linux clusters. It also performs the necessary manipulations in the MCNP5 input and data files. Cross section libraries are generated using the sub-pin level temperature distribution calculated by STAR-CD, and MCNP input files are manipulated to reflect the moderator density distribution provided by STAR-CD. Using this feedback data, the MCNP simulation proceeds and determines the next approximation for the eigenvalue as well as the heat source distribution for the next CFD calculation. Several methods to update cross section library were investigated and are described in the paper. The coupled codes were tested using a single PWR pin-cell problem and 3x3 array of PWR fuel pins. The preliminary results are compared with those obtained from a STAR-CD calculation coupled with the deterministic transport code DeCART. Ongoing research is described to investigate more efficient acceleration and convergence methods, as well as more robust methods to validate the coupled calculation.