In 1996, Idaho National Engineering and Environmental Laboratory’s Advanced Test Nuclear Reactor operators manually shut down the reactor after noticing pressure oscillations. A control valve, which was sluggish in responding to input from the pressure control system, caused the fluctuations.
A root-cause investigation revealed that mechanics had adjusted the valve packing gland according to the vendor technical manual during the outage, tightening it because it had a visible leak. The action resulted in higher friction on the valve stem, which caused the valve’s sluggish response.
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