The U.S. Nuclear Regulatory Commission (NRC) staff said the failure of a low pressure coolant injection valve last fall at the three-unit 3,440 MW Browns Ferry nuclear plant was of “high safety significance” and will result in increased NRC inspection and oversight of the facility. The plant is operated by the Tennessee Valley Authority (TVA).
On Oct. 23 2010, the valve failed to open when operators attempted to use the residual heat removal shutdown cooling loop during Unit 1 refueling. TVA later determined that the last time the valve had worked as required was on March 12, 2009 when the loop was placed in service.
NRC said the system is counted on for core cooling during certain accident scenarios. The valve failure left the system inoperable, which potentially could have led to core damage had an accident involving a series of unlikely events occurred.
A regulatory conference was held on April 4 to discuss the issue. TVA said the failed valve was the result of defective manufacturing, but that it still would have opened and supplied the necessary cooling water. The NRC review disagreed and concluded the violation of “high safety significance.”
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