UCD McClellan Nuclear Radiation Center

The UCD/ MNRC research reactor of the TRIGA type is designed to be operated at a nominal 2 .0 MW steady state power as well as pulse and square wave operation. It is cooled and moderated by light water and reflected by graphite. The reactor core is located near the bottom of a water-filled aluminum vessel 7.0 ft in diameter and 24.5 ft in height. It went first critical in 1990 and has since become the highest power TRIGA reactor in the U.S. Radiation hardness testing of materials is made possible through the so-called “neutron irradiator” which provides fast neutron exposure to samples with minimal contamination from thermal neutrons and gamma rays. This neutron irradiator has three primary components; conditioning well, exposure vessel, and detachable upper shield for the exposure vessel. The conditioning well is installed adjacent to the annular graphite reflector inside the reactor tank. It is held vertically in place and rests at the bottom of the tank. The well-structure is shielded with sufficient boron nitride and lead encased in aluminum to remove thermal neutrons and gamma rays, respectively. The removable and water-tight exposure vessel has a usable inner space of approximately 7” in diameter and 9” in height. There are six removable titanium plates with holes arranged in a hexagonal shape which can hold the components to be irradiated. It also contains a valve at the bottom to purge and pressurize an assembled unit with helium in order to reduce Argon-41 production during irradiation. The exposure vessel is lined with boral and gadolinium paint to insure minimal leakage of thermal neutrons. The detachable upper shield contains boron nitride and lead encased in aluminum to complete the upper shield for the exposure vessel before it is lowered into the conditioning well for irradiation. Monte Carlo code simulation is benchmarked with multiple threshold neutron flux measurements. The converted 1 MeV equivalent silicon neutron flux at 1.5 MW operating power is 2.3 x 10^10 n/cm2.sec. Among others, materials such as silicon based devices, coatings for metals, superconducting magnets which are susceptible to fast neutron exposure and damage in their working environments are examined. This unique irradiation facility enables us to provide credible information regarding fast neutron radiation tolerance of materials used in crucial applications.