Experimentally Validated Neutron Flux Simulation for TRIGA Large Irradiation Cell
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The one megawatt TRIGA reactor at Texas A&M has various methods of irradiating samples, but one of the most unique dose positions is severely underutilized. This irradiation cell is a large space where samples may be placed for activation by moving the reactor bridge to a window on the wall of the cell and operating the reactor. Due to the cell's large size, neutron flux for experiments is difficult to resolve spatially, giving predictions of dose to samples a high level of uncertainty. To this end, Parallel Deterministic Transport (PDT), a rapidly maturing radiation transport code, is used to simulate the neutron flux distribution for reactor experiments in the cell. By utilizing PDT, a model for the cell is created, and experiments are performed to validate the computational results benefitting both the Nuclear Science Center (NSC) and PDT development. To construct the PDT model, the cell's geometry, material properties, and boundary conditions are necessary. By measuring the cell, identifying construction materials, and performing experiments to measure flux at various cell locations, input to the computational model is developed by constructing a mesh reflecting cell geometry, processing neutron interaction cross sections for cell materials, and fitting a surface to flux collected on the boundary, then discretizing flux in angle. After the model is constructed, it is validated by perturbing the boundary condition using error from the surface fit in an attempt to generate model results that bound the experimental data. While the model results in the epithermal region would benefit from inclusion of higher energy groups, the thermal model results bound almost half of the experiment data, giving confidence in the method's increased accuracy in future work.
Tompkins, James Brandon (2016). Experimentally Validated Neutron Flux Simulation for TRIGA Large Irradiation Cell. Master's thesis, Texas A & M University. Available electronically from