Instrument Description
The HFEF TRIGA reactor is known as NRAD. It is used for neutron radiography. Both dysprosium and cadmium-covered indium foils are used as neutron detector foils; these are irradiated in the neutron beam, then transferred to a film cassette and allowed to decay for three to four half-lives against ordinary X-ray film to form the image. The dysprosium foils, used for thermal neutron radiographs of low-enriched fuels and thin structural materials, produce excellent detail, but specimen thickness and fuel enrichment is limited. The indium foils are used for epithermal neutron radiographs of highly enriched fuels and thicker structural materials. These do not show as much specimen detail, but they can be used for thicker specimens and more highly enriched fuel. In many cases, both foils are used to gain an outline of the fuel as well as its internal structure.
NRAD is capable of performing small-scale material activation in one of two irradiation locations within the reactor core. Irradiation/activation experiments may be placed in either the dry irradiation tube, positioned at the edge of the reactor core, or in the wet tube located in the center of the reactor core.
Applications
NRAD enables neutron-radiography irradiations to verify materials behaviors such as:
Fuel pellet separations
Fuel central-void formation
Pellet cracking
Evidence of fuel melting
Material integrity under normal and extreme conditions
The NRAD beam tubes were designed for examination of fuel elements to identify areas of interest, such as location of fuel for disassembly, identification of cracking, density variations, and hydrides in cladding. NRAD is equipped with two beam tubes and two separate radiography stations. Neutron radiography of elements, capsules and loops is performed in the main cell at workstation 4M. Specimens are placed into a radiograph holder that is lowered into the NRAD neutron beam located below the floor. The holders optimally position the specimen for radiography without excessive neutron scattering. The north beam connects to a shielded radiography cell capable of accepting a shielded cask directly. This allows for larger radiography specimens to be brought to HFEF, lowered directly from the cask into the neutron beam for radiography, and then returned to the cask without having to be transferred into the HFEF main cell.
Specifications
Maximum specimen length: 152 in
Maximum specimen diameter: 6.5 in (round) or 4.5 X 8.5 in (rectangular)
Specimen weight: 600 lb