NRC ISSUES FINDING OF LOW TO MODERATE SAFETY SIGNIFICANCE
TO LIMERICK UNIT 2 NUCLEAR POWER PLANT
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The Nuclear Regulatory Commission staff has issued a "white" finding for an issue involving a valve at the Limerick Unit 2 nuclear power plant. The NRC considers the issue to be of low to moderate importance to safety but one which may require additional NRC inspections. The plant, which is located in Montgomery County, Pa., is operated by Exelon Nuclear Corp.

The finding was identified during an NRC inspection conducted from September 30, 2001, through November 10, 2001. It pertains to a failure to have adequate measures in place to identify that one of the plant's safety/relief valves was in a degraded condition and vulnerable to not reclosing after opening. (Safety/relief valves are used to control temperatures and pressures in nuclear power plants' reactor coolant systems.)

Specifically, Limerick personnel had been tracking the temperature of the valve in question, with a plan to repair or replace it if the component's temperature dropped below 497 degrees Fahrenheit. An analysis had shown that the valve might not reclose if it opened below that temperature. However, in August 2000, the temperature threshold was reduced to 475 degrees Fahrenheit.

Subsequently, beginning on December 5, 2000, the temperature did drop below 492 degrees, resulting in what the NRC describes as an "actual condition adverse to quality." But the condition was not identified until February 23, 2001, when the valve opened and did not immediately reclose. The NRC issued a Notice of Violation to Exelon for not having adequate measures in place to identify the adverse conditions.

Using the agency's significance determination process, NRC officials classify certain conditions at nuclear power plants as being one of four colors which delineate increasing levels of safety significance, beginning with green and progressing to white, yellow or red.

In the case of this finding, the company declined an opportunity for a regulatory conference to discuss this issue or to respond in writing.

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Monday, December 08, 2008