The importance of the cooling water to the successful operation and safety of the pile cannot be overstressed. An active process tube running dry would not be a minor problem. Even if it didn’t destroy the pile, it could do serious damage to the tube and its surrounding graphite, while compromising safety. Of course, while the pile was being repaired, the production of plutonium would come to a halt. That’s why the vast majority of all the instruments were dedicated to monitoring the pile’s cooling water. These instruments could scram the pile or alert the operators, but actual control of the water system was handled in the various water-supply buildings in the 100-B Area.
The water pressure in each process tube was monitored continuously, for a total of 2,004 gauges and associated hardware. If the pressure in any gauge exceed the specified range, a scram would be triggered via the No. 2 safety circuit. The sheer number of gauges was a significant factor in itself, because normalsized gauges might have filled the entire control room. The Panellit gauges that were ultimately used were notable at the time for their petite size. Even so, the Panellit board measured some 24 ft long by 9 ft high.
A sensing line ran from the inlet end of each process tube, just downstream of the orifice that controlled the flow of water, to the Panellit pressure gauges and switches in the control room. A bourdon tube in each gauge rotated a disk to reflect pressure changes. Two magnets on the dial were positioned for high and low trips.
During initial use, small variations in pressure caused a number of accidental scrams via the No. 2 safety circuit, most often because the gauges were not properly dampened. In fact, a worker just bumping against the Panellit board might cause any one of the gauges to trigger a scram.