A Novel Hybrid Deterministic and Monte Carlo Neutron Transport Formulation and Algorithm (tRAPID) for Accurate and Fast 3-D Reactor Kinetics

The available three-dimensional (3-D), time-dependent neutron transport algorithms and codes (deterministic or Monte Carlo) are very computationally intensive and are impractical for the simulation of real-world reactors. Henceforth, commonly approximate forms of the transport equation (e.g., diffusion or SPn) are used with expected loss of accuracy. We have developed a hybrid deterministic and Monte Carlo algorithm that not only preserve a Monte Carlo-level accuracy but can achieve a solution in seconds or minutes. This algorithm has been incorporated into the RAPID code system and tested for a number of benchmark problems. This novel time-dependent algorithm, referred to as tRAPID, utilizes a transient fission matrix methodology and allows for fast and accurate simulation of 3-D time-dependent neutron transport problems. The tRAPID algorithm is used to calculate neutron kinetics parameters (such as l(eff) and Rossi-a) and 3-D time-dependent prompt and delayed fission source distributions for two reference models: the Flattop-Pu critical assembly and the Jozef Stefan Institute TRIGA Mark-II benchmark core. Results are compared to experiments reported in the International Criticality Safety Benchmark Evaluation Project Handbook as well as to a reference Serpent Monte Carlo calculation. The tRAPID results are in excellent agreement with both the experimental data and Serpent predictions, while requiring minimal computing resources.