Volume Mesh–Based Monte Carlo Particle Transport with Barycentric Particle Tracking

Nuclear reactions generate large temperature differences in materials, causing change in the density of the materials. An uneven density distribution means the macroscopic cross section will change in spatial locations, even within the same material. This scenario makes the neutron transport calculation difficult. However, this issue can be solved by developing an algorithm for neutron transport in volume meshes that stores data about how the medium density changes with space and tracks the neutron in barycentric coordinates.

This study proposes such a novel method by incorporating the barycentric particle tracking algorithm into Monte Carlo transport within volume meshes. The method involves the introduction of face search algorithms, particle-face distance calculation algorithms, and the resolution of compatibility between the distance algorithm and the tracking algorithm. Consequently, the computational results and evaluations performed by our code and the OpenMC code across diverse geometric configurations and enrichments exhibit a noteworthy degree of consistency. The discrepancies in the simulation results between the two codes are all within ±3σ. Therefore, the algorithm’s correctness is affirmed. Moreover, the computational time of the current method displays a logarithmic function–like relationship with the number of meshes, which means the computational performance is highly efficient and desirable.

Finally, the application of the current model in some irregular geometries and geometries with varied temperature distributions is demonstrated. The results prove that the Monte Carlo particle transport method can also be directly applied to these situations. All of this illustrates the future ability of the current method to calculate neutron transport in reactors of extremely nonuniformly distributed physical fields and irregular geometry at relatively tiny geometric scales.