In a memo issued today, the U. S. Nuclear Regulatory Commission (NRC) said that the failure of a low pressure coolant injection valve last fall at the Browns Ferry nuclear plant, located near Athens in north Alabama, was of “high safety significance”
NRC inspection findings are evaluated using a safety significance scale with four levels, ranging from “green” for minor significance, through “white” and “yellow” to “red” for high significance. On Oct. 23, 2010, a valve failed to open when operators attempted to use a shutdown cooling loop during refueling. Tennessee Valley Authority (TVA), the plant operator, later determined that the last time the valve had definitely worked as required was on March 12, 2009 when the loop was placed in service. At the time, the public was not endangered because no actual event occurred. However, the system is counted on for core cooling during certain accident scenarios and the valve failure left it inoperable, which potentially could have led to core damage had an accident involving a series of unlikely events occurred.
An accident such as the one that occurred on April 27th when the town of Tuscaloosa, Alabama, only 100 miles south of the Browns Ferry nuclear plant, was devastated by an estimated EF-4 tornado over a mile wide that stayed on the ground for 2 hours, leaving behind a shocking landscape of twisted wreckage for seven miles. That same storm cell took out transmission lines to the plant causing it to lose offsite power and triggering the three units at the plant to shut down automatically.
A regulatory conference to discuss the issue was held on April 4, just weeks before the massive tornado cell swept through the southeast. TVA stated that the failed valve was the result of defective manufacturing but still would have opened and supplied the necessary cooling water. The NRC review disagreed and concluded the violation was “red” or of “high safety significance.” The valve was repaired after its failure was discovered last October and prior to returning the unit to service, however the NRC has determined that significant problems involving key safety systems warrant more extensive NRC inspection and oversight.
Had the problem not been discovered and repaired six months before the the tornados shut down the plant, would the outcome have been different? More Fukashima-like? The increased scrutiny of the nation’s aging nuclear industry, due in large part to the disaster in Japan, is uncovering some disquieting issues. Will the NRC’s return to being a regulatory agency instead of a shill for the industry, and their heightened oversight prevent another nuclear disaster – or is it only a matter of time before an undetected problem at a plant, coupled with unforeseen events, has the US coping with its own disaster?
