Modeling and Simulation Optimization and Feasibility Studies for the Neutron Detection without Helium-3 Project.

摘要

This report details the results of the modeling and simulation work accomplished for the Neutron Detection without Helium-3 project during the 2011 and 2012 fiscal years. The primary focus of the project is to investigate commercially available technologies that might be used in safeguards applications in the relatively near term. Other technologies that are being developed may be more applicable in the future, but are outside the scope of this study. During the last two years the primary focus was to develop models and perform simulations using alternatives to helium-3 to investigate the possibilities and optimizations for multiplicity counters in safeguards applications. The high capability helium-3 multiplicity counter, the Epithermal Neutron Multiplicity Counter (ENMC), was used as the baseline requirement for alternative technologies, which, if a suitable alternative can be found, should also satisfy systems with less stringent requirements, including coincidence counters. The project is in collaboration with Los Alamos National Laboratory (LANL), and the baseline model of the ENMC that had been developed and validated at LANL was used as a starting point. The model was modified to support optimization investigations, and verified with the LANL model for the helium-3 baseline material. The model was then modified to incorporate boron-trifluoride (BF3) gas, which can be used as a proportional gas similar to helium-3. The BF3 gas however, cannot be operated at very high pressure. Therefore, optimizations were performed with lower pressures consistent with available detectors and the optimization involved changing the tube size and number, as well as the moderator material. The simulation of this model is very similar in approach to the model with helium-3 where the simulation ends when the neutron is captured in the boron. The reaction products are easily detected in the proportional gas, and the simulation results of counting the number of reactions matches well with experimental data without any correction factors.