CAD-based hierarchical geometry conversion method for modeling of fission reactor cores

The fission reactor core models are usually constructed with abundant nested repeated-structure in several levels. Accordingly, hierarchical descriptions have been adopted in many Monte Carlo (MC) codes to describe fission reactor core efficiently. As the geometry of fission reactor core is more and more complex, modeling for them with some mature Computer-Aided Design (CAD) system becomes more popular. However, the conventional CAD-based MC automatic modeling methods concentrate on decomposing the complex geometries, whereas the hierarchical geometries are neglected. Furthermore, it is time consuming to decompose huge number of geometries in sequence. This paper presents a new method which can generate the hierarchical geometries for MC codes and CAD system in batches. The method can create or gather the hierarchical information as well as other parameters of the models into a dedicated data structure, which can be saved in Geometric Hierarchy Tree (GH-tree). Based on GH-tree, the MC calculation models and CAD models can be generated effectively and accurately. In this paper, the new algorithms were implemented based on the framework of the Super Monte Carlo Simulation Program for Nuclear and Radiation Process (SuperMC), developed by FDS team, and were validated using the models of China Lead-based Research Reactor (CLEAR-I) and IAEA-BN600. The efficiency and accuracy of the new method were demonstrated by the numerical calculation results.