Development of CAD geometry converting and correction method in Monte Carlo code RMC

Abstract

For reactors with complex geometric structures such as fusion reactors, modeling work is relatively complex. The traditional Constructive Solid Geometry (CSG) method in Monte Carlo particle transport simulations shows limitation when constructing the complex geometry accurately. In order to use the CAD models, the Direct Accelerated Geometry Monte Carlo (DAGMC) has been proposed and implemented in many Monte Carlo codes. In the typical workflow of DAGMC method, the commercial mesh generation software Trelis is used. In this work, the DAGMC function was implemented in the Monte Carlo code RMC, and three modifications were also developed in the DAGMC function of RMC. Firstly, a workflow of generating the DAGMC mesh model was proposed using the open-source scripts occ_faceter instead of Trelis. Secondly, a gap correction algorithm was proposed to solve the errors in particle transport process, which is resulted from the existence of gaps between adjacent volumes in the CAD model generated by occ_faceter. Thirdly, the DAG-CSG hybrid geometry method was also developed, which combines the DAG and CSG geometry to construct the geometry more efficiently, and the verification analyses were carried out on the three-dimensional fuel assembly models. Finally, the CAD geometry of the FNG-ITER model was constructed and the developed DAG-RMC was applied to the FNG-ITER benchmark, further verifying the correctness and reliability of the developed DAGMC method.