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This image compares a visible-light photograph (top), an X-ray (center) and a neutron radiograph of a model train. The neutron radiograph shows the model’s interior, including its plastic parts. |
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The core of the neutron radiography reactor. |
Workhorse reactor marks 4,000th startup |
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Argonne-West’s Neutron Radiography Reactor (NRAD) was started for the 4,000th time in 2003, marking another milestone for the workhorse machine. Although the 4,000th run of the reactor involves re-activating a radioactive ytterbium source used in research, the reactor’s main function has been indirect neutron radiography, said Steve Kahn, NRAD Reactor supervisor. Its bread and butter through the years was fuel samples from Experimental Breeder Reactor-II. EBR-II was the backbone of the nation’s breeder reactor research between 1964 and 1994. Neutron radiography was used to analyze EBR-II fuel and cladding for cracks, corrosion and other types of failures. Although EBR-II was shut down in 1994, NRAD is still used several times a year. Routine radiography techniques can’t be used on these kinds of materials. Gamma rays from intensely radioactive specimens would almost instantly fog photographic film. Argonne-West pioneered and refined “indirect” neutron radiography, a technique that sidesteps this problem. The reactor projects a beam of neutrons through a specimen. After passing through the specimen, the neutrons strike a metal foil, activating it. The foil is placed against a sheet of photographic film and left for several hours; radiation from the foil renders an image on the film, which is then developed. “Indirect neutron radiography takes longer than the direct method but can show a lot more detail,” Kahn said. Neutron radiographs also penetrate through metal specimens and can show plastic and other materials. X-rays don’t penetrate metal more than a fraction of a millimeter and can’t be used on radioactive specimens at all. The NRAD facility also provides the ability to neutron-radiograph highly irradiated fuel elements, fuel assemblies and loop experiments—which may react chemically with air—without removing them from the main cell’s argon atmosphere. A second neutron radiography station outside the main cell permits neutron radiography of either unirradiated or irradiated specimens without introducing them into the main cell. Although neutron radiographs are generally taken of irradiated components, such as fuel elements, they can be taken of almost anything. NRAD has been used to check Space Shuttle booster-rocket parts for corrosion. Oysters affected by an oil spill were also radiographed to check for any residual contamination. For more information, please contact David Jacqué. |