Puncture rigs were used to measure pressure during irradiation.
In this historical photo from the U.S. space agency, puncture rig is shown. Puncture rigs were used to penetrate the outer capsule of each experiment and measure the pressure increase in the system due to released gases during irradiation. The plastic vial on the left was used to determine the isotope content of fission product gases, xenon and krypton, using gamma ray spectrometry; the tubular sample container below it was used to measure the volume percent of the two gases.
The entire puncture operation and collection of gas samples was done inside the hot cells using the remote manipulators. The sample containers were then removed from the puncture rig and transferred to the radiochemistry laboratory for analysis.
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