Valve Failure Leads to White Finding at Dresden Nuclear Power Unit

Valve Failure Leads to White Finding at Dresden Nuclear Power Unit

The U.S. Nuclear Regulatory Commission (NRC) issued a white finding of low to moderate safety significance to Unit 2 of the Dresden Nuclear Power Station in Illinois.
In February, one of four valves in the reactor vessel depressurization and overpressure protection safety system failed a required maintenance test. A subsequent review showed that the valve failed because of improper reassembly during the last required test and maintenance in 2013 and increased vibration of plant components resulting from an extended power uprate. The valve failure happened while the plant was shut down and there was no impact on the public’s health or safety.
The safety system controls pressure in the reactor in certain accident conditions. Earlier this year, Exelon (NYSE: EXC) replaced all four valves with a more robust design successfully used at other plants to prevent damage from increased vibration following an uprate project. The uprate project was completed in 2009, and it is known to increase vibration levels on certain plant components, including valves in the depressurization and overpressure protection system. NRC inspectors determined that workers failed to develop effective installation and maintenance procedures and guidance to prevent valve damage in light of the new operating conditions.
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