Experimental Validation of Full Geometry MCNP Model of the UFTR based on NAA

The energy spectrum and spatial distribution of the neutron beam from a reactor is an essential component of designing experimentations utilizing the reactor as a radiation source. Obtaining such information requires the use of detailed MCNP model of the reactor and experimental validation procedures. After updating the MCNP model of the University of Florida Training Reactor (UFTR) to align it with the current core arrangement that uses low enriched uranium (LEU), both the radial neutron flux toward the beam ports and the energy spectrum at the reactor core were generated using the model. This was followed by experimental validations based on neutron activation analysis (NAA) by irradiating multiple activation foils. A constant ratio between MCNP and measured neutron flux values was obtained at multiple locations along the reactor's beam ports, showing that the model captures the spatial distribution of neutron flux profiles without a significant systematic error. The energy spectrum at the core was extracted using the Unfolding with MAXED and GRAVEL (UMG) software. The spectrum unfolded by both MAXED and GRAVEL algorithms display features expected in thermal reactor neutron energy distribution, i.e., thermal, fast or fission, and intermediate or slowing down regions. The thermal and epithermal neutron fluxes at the reactor core calculated from the spectrum unfolded by the MAXED algorithm are 1.56 ± 0.12 × 10
¹²
n/cm
²
s and 1.98 ± 0.01 × 10
¹²
n/cm
²
s, whereas the corresponding values calculated from the spectrum unfolded by the GRAVEL algorithm are 1. 50 ± 0. 12 × 10
¹²
n/cm
²
s and 3.74 ± 0.21 × 10
¹²
n/cm
²
s. Following the n/cm
²
s. experimental validation, the full geometry MCNP model of the reactor has been utilized for a neutron tomography research project and it will continue to benefit future projects using the reactor facility.