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On the basis of numerous rough calculations it has generally been assumed that if the water flow to a tube were to stops while pile operation continued. The tube central temperature would increase in a matter of seconds to dangerously high values. In several seconds the water around the central slugs would flash to steam, shortly thereafter the aluminum cans would melt and this would give good contact between the slug and the tube which would quickly melt. The bare uranium would react with the steam and possibly the pile gas atmosphere. Radioactive Xenon and fission products would be spread through the gas system, and the molten aluminum and uranium would fill up all of the cracks in the graphite and the tube would be impossible to discharge by all normal methods after the pile is shut down. If the pile were operated with this tube blocked off there would still be the problem of exceedingly high graphite temperatures around it, and the spread of contamination in the gas system. Because these problems are expected with an undetected water failure in a pile, where the operation is maintained, a program is underway to ensure proper and sufficient tube instrumentation to …