In this 1961 historical photo from the U.S. space agency, two technicians clad in anti-contamination clothing manipulate a shim safety control rod in a water canal in the hot laboratory. The twenty-five foot deep water provided shielding from the radiation, yet still enabled visible contact with the research experiments. The water also allowed the underwater transfer of irradiated materials from the reactor to the hot laboratory for inspection. Moving materials by canal reduced the need for lead transfer casks, though they were still needed when the radioactive materials were taken out of the water.
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Each weekday, SPACE.com looks back at the history of spaceflight through photos (archive).