Design of an ultra-compact imaging chamber and radiation beamstop for a neutron radiography system employing particle transport

Abstract

A new neutron radiography facility for the University of Utah TRIGA Reactor (UUTR) is computationally designed to support a multi-purpose irradiation and imaging chamber with a terminal beamstop. Previous efforts from a 3-D MCNP6 UUTR neutron beamport simulation reveals an available neutron flux of 2.5 × 107 ± 1.4 × 105n/cm2/s with an associated dose rate of 5.0 × 105 ± 2.8 × 103 mrem/hr at the end of the beamline system. The shielding required to attenuate the neutron beam and other secondary radiation from reaching the surrounding environment during radiography experiments has been assessed and implemented into MCNP6 Monte Carlo and PENTRAN SN transport code models to assess shield performance and directly compare response solutions between the two methods. In addition, the neutron importance function obtained from adjoint-SN transport is utilized to optimize calculation efficiency in a weight window accelerated PENTRAN-CADIS-MCNP6 model of the irradiation chamber beamstop. Good agreement between adjoint-SN and PENTRAN-CADIS-MCNP6 dose rate calculations is achieved, yielding predicted detector responses within an 8% difference in tally regions of importance. The total neutron dose rate is estimated throughout the entirety of the beamstop prototype, where recommended dimensions and material compositions of the shielding apparatus are provided with supporting analysis.