Design of an in-core fission-spectrum neutron irradiation facility with pneumatic sample transfer at a research reactor

摘要

The primary objective of the work being presented is to design and optimize a fast neutron irradiation facility with pneumatic sample transfer for use in fast neutron activation analysis. The facility will be used to improve uncertainties in the yields of fission products induced by fission neutrons. Various materials and geometric designs were researched and modeled in MCNP for the filtration of thermal neutrons from a research reactor core. These models yielded the finalized design of a layered cylindrical system to be placed in the 3-EL irradiation position in the core of the TRIGA MARK-II reactor at The University of Texas at Austin. The design balances the need to maintain high total neutron flux with the careful shaping of a neutron spectrum to be as close to the Watt fission spectrum as possible. The models indicate that thermal neutron flux may be reduced by at least five orders of magnitude while only reducing the overall fast neutron flux by less than an order of magnitude. The fast:(thermal+epithcrmal) fission ratio should exceed 100:1 with an integrated fast flux value (defined > 0.001 MeV) of at least 7.8x10~(11) n cm~(-2) s~(-1).