neutron chiller exhibit

This area is for discussions involving any fusion related radiation metrology issues. Neutrons are the key signature of fusion, but other radiations are of interest to the amateur fusioneer as well.
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Rich Feldman
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Real name: Rich Feldman
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neutron chiller exhibit

Post by Rich Feldman » Wed Oct 10, 2018 12:02 am

Today I had the good fortune to visit NIST in Gaithersburg, MD, for a technical seminar. It would have taken a lot more advance planning, maybe even a letter of recommendation, to be allowed into NIST Center for Neutron Research. But there are some cool places open to badged but otherwise unescorted visitors, including cafeteria and museum in the administration building.

This eye-catching exhibit in the corridor is a spare neutron chiller (made of aluminum) and a preliminary glass mock-up. The latter has a spiral-shaped heating element between the inner and outer spheres. The real metal chiller is identical to the spare, except it's too radioactive to be on display.
The annular space between inner and outer spheres is for 5 liters of liquid hydrogen at 20 K. When placed inside a roomy research reactor, neutrons are moderated down to 5 milli-eV of kinetic energy. Concurrently, the LH2 is boiled off by up to 1200 watts of absorbed neutron and gamma energy, and replenished by "thermo siphon" circulation from an overhead reservoir. The glass mock-up was to study the mixed-phase hydrogen flow, including things like the volume fraction occupied by vapor bubbles. Result was a couple of changes to hardware design and operating procedure.
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