The Transient Reactor Test (TREAT) facility was designed and built in the late 1950s. The air-cooled reactor design incorporates fuel composed of highly enriched uranium dispersed in graphite with a 10 000:1 carbon-to-uranium atom ratio to provide a very fast-acting highly negative temperature coefficient of reactivity. The reactor utilizes a forced-air-cooling system for decay heat removal, with a primary function of reducing the time at temperature (oxidation) of the reactor fuel cladding. The simple design with lack of a cooling system pressure boundary provides relatively easy access for instrumentation and experiments. The large thermal mass of the reactor and the simple design allow for high-power transients approaching 18 000 MW in an inherently safe manner. The simple design has allowed TREAT to operate successfully for 35 years before being placed in standby in 1994 and subsequently restarted in 2017 after more than 20 years of standby to continue the transient fuel testing mission in the United States. This technical note addresses the reactor design and experiment capabilities.

The Neutron Radiography Reactor at Idaho National Laboratory (INL) has two beamlines extending radially outward from the east and north faces of the reactor core. The control rod withdrawal procedure has recently been altered, potentially changing power distribution of the reactor and thus the properties of the neutron beams, calling for characterization of the neutron beams. The characterization of the East Radiography Station involved experiments used to measure the following characteristics: Neutron flux, neutron beam uniformity, cadmium ratio, image quality, and the neutron energy spectrum. The ERS is a Category-I neutron radiography facility signifying it has the highest possible rank a radiography station can achieve. The thermal equivalent neutron flux was measured using gold foil activation and determined to be 9.61 × 10⁶ ± 2.47 × 10⁵ n/cm²-s with a relatively uniform profile across the image plane. The cadmium ratio measurement was performed using bare and cadmium-covered gold foils and measured to be 2.05 ± 2.9%, indicating large epithermal and fast neutron content in the beam. The neutron energy spectrum was measured using foil activation coupled with unfolding algorithms provided by the software package Unfolding with MAXED and GRAVEL (UMG). The Monte-Carlo N-Particle (MCNP6) transport code was used to assist with the unfolding process. UMG, MCNP6, and measured foil activities were used to determine a neutron energy spectrum which was implemented into the MCNP6 model of the east neutron beam to contribute to future studies.