User:Rails

In nuclear engineering, an assembly is prompt critical if for each nuclear fission event, one or more of the immediate or prompt neutrons released causes an additional fission event.

— Wikipedia

Images I've uploaded

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  Auto Train platform, Lorton VA terminal
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  Auto Train autoracks, front view
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  Auto Train autoracks and loading ramps
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  Auto Train autoracks, rear view
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  Space Shuttle Enterprise left wing
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  Space Shuttle Enterprise left wing
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  Space Shuttle Enterprise left wing