New optical fiber remains transparent under extreme gamma radiation

Engineers at AFO Research (Glendale, CA) have developed a new type of fluorophosphate-glass optical fiber (179 µm fiber diameter, 284 µm acrylate-coating diameter) that has been recently been radiated in a high-intensity gamma-ray environment at a level of 1.8 × 106 rad per hour for 30 days at the Idaho National Laboratory (INL; Idaho Falls, ID) in its cobalt-60 irradiator; total gamma-radiation dosage was 1.29 × 109 rad. After withstanding such high levels of radiation, the optical fiber—made of glass that contains no hydrogen or oxygen—remains transparent with no solarization having occurred (the dark area on the fiber in the figure is only the acrylate protective coating, which does turn brown).

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AFO plans to do further testing in conjunction with INL with the goal of creating a fiber-optic-based monitoring system that can visually inspect highly irradiated places—such as the core of a nuclear reactor, which is in operation on a continual basis. Currently, nuclear power plants must shut down for inspections every 12 to 14 months, says Jack Illare III, AFO’s president and chairman. “Each shutdown costs something like $50 million,” he notes. The fiber-optic inspection system will consist of a 150-m-long fiber-optic cable terminated with a sensor system on a robot that is able to continuously crawl around inside the reactor, says Illare. Contact Illare at jackillare@AFOResearch.com.