Utilization of two-dimensional deterministic transport methods for analysis of pebble-bed reactors

This paper presents an overview of the investigations on the need for deterministic transport methods for the analysis of pebble-bed reactors. To account for the transport effects present in the PBMR design that cannot be modeled accurately with the diffusion theory, a two-dimensional neutronics solver based on transport theory is implemented in the Penn State NEM-THERMIX code system.The necessity of equipping neutronics analysis codes with neutron transport theory capability is investigated along with the challenge to accomplish this in an efficient and versatile manner. For this purpose a time-dependent two-dimensional neutron transport code DORT is utilized as a first step. The developed benchmark test cases, based on the PBMR 268 MW design, are used for this work and results from the comparative analyzes of these test cases are presented. The results show clearly that even in steady-state calculations, the differences between diffusion and transport-based methods in analyzing the PBMR are observed and need to be addressed.