The Nuclear Regulatory Commission has launched a special inspection to figure out why a pair of safety valves failed to close last month at the Shearon Harris nuclear plant when the Wake County facility was shut down for refueling.
Four NRC inspectors will spend the week reviewing the mechanical malfunction at the nuclear plant, which is operated by Progress Energy and located less than 25 miles from downtown Raleigh.
The problem at Shearon Harris did not cause a safety hazard but could have jeopardized lives and equipment if the plant’s pipes had burst and blasted scalding steam onto equipment and plant workers, as has happened at other U.S. nuclear plants.
Because of the potential seriousness of the problem, the NRC launched the special inspection, which is more involved than a routine review.
Raleigh-based Progress has its own team investigating the mishap to determine if the enormous industrial valves can be repaired or if they will have to be replaced.
“There was no release of radiation, and the issue posed no threat to public health and safety,” said Progress spokesman Mike Hughes.
The Harris plant has three steam isolation valves that are designed to shut off the flow of high-pressure steam within 5 seconds.
Plant operators attempted to close the valves when they shut down the plant April 21 for a planned refueling. One of the valves took a half hour, and the other required three hours to close fully.
The steam isolation valves are designed to cut off the flow of steam in 32-inch pipes pressurized at 1,000 pounds per square inch, more than 100 times higher than household plumbing.
The Harris plant has several hundred feet of high-pressure steam pipes. The valves are essential safety equipment but too large to close manually and dependent on mechanized shut-downs, said Randy Musser, the NRC’s branch chief in the division of reactor projects.
“These are big valves, bigger than a person,” Musser said. “It wouldn’t be a pretty picture if one of those lines breaks.”
Pipe blowouts are rare but not unheard of. In 1996, seven plant workers at Duke Energy’s Oconee’s nuclear plant in South Carolina were burned when a pipe ruptured as they were working on equipment.
A decade earlier, the NRC investigated “a catastrophic failure” of a feedwater pipe when a valve failure did not stop a rupture that injured and killed workers at the Surry nuclear plant in Virginia.
The NRC’s special inspections team for Shearon Harris includes the NRC’s resident inspector at the plant as well as personnel from the NRC’s Region II office in Atlanta and NRC headquarters in Rockville, Md.
They will review Progress Energy’s actions leading up to the event to determine if the company committed any violations, and they will also examine the performance history of the valves to determine if they have a potential design flaw.
The final results of the review will be issued within 45 days of the completion of the inspection.