REASON FOUND FOR VIBRATIONS AT NORTH ANNA UNIT 2
RICHMOND, Va., April 28 /PRNewswire/ -- An incorrectly set component caused an air-operated valve in the non-nuclear part of the plant to malfunction, leading to a weekend shutdown of North Anna Unit 2, Virginia Power officials said today.
The valve has been checked, tested and reset, and the pipe and other components have been inspected. Minor damage to pipe supports and insulation has been repaired. Unit 2 is expected to return to service this week.
The valve regulates the flow of high-pressure, high-temperature water in the units' non-radioactive secondary system from the condenser to a steam generator. The valve oscillated -- opened and closed quickly -- starting a strong vibration pattern along the pipe.
An examination revealed that a valve booster, which assists in controlling how fast the valve opens and closes, was set at too sensitive a level by a technician during a refueling outage last April. With the unit operating at about 70 percent power as it was early Saturday, the booster overcompensated, causing the pipe vibration.
Reactor operators, sensing the vibrations, shut down the unit. To ensure that all station employees were safe and to request extra assistance, the operators declared an Alert, which is the second lowest level of emergency in the Nuclear Regulatory Commission's emergency classification system.
"The operators made a prudent decision to declare an Alert," said James P. O'Hanlon, vice president-Nuclear Operations. "The exact problem wasn't clear initially and they wanted to make sure that all of their people were safe. It was a conservative action. At no time was the public in any danger."
Reports of a steam leak early Saturday were erroneous. What observers thought was steam escaping from a pipe suspended between two buildings was actually insulation dust that was caught by the early morning wind.
/CONTACT: James W. Norvelle of Virginia Power, 804-7 KD-IH -- DC021 -- 2020 04/28/93 12:18 EDT