Davis-Besse's pressure-pump problems have hit what plant officials are calling another “tiny” snag.
In theory, a tear the size of a fingertip could overheat the two high-pressure emergency injection pumps that flush the plant's reactor core with water during emergencies.
Davis-Besse is being refurbished after a football-sized hole was found in the carbon steel of the reactor head while the reactor was shut down for routine refueling in February, 2002. The corrosion left only a stainless-steel lining less than three-eighths of an inch thick to prevent a high-pressure rupture.
Davis-Besse has had problems with the emergency pumps before.
FirstEnergy Corp., the plant's owner, is spending a little over $3 million to fix a prior flaw relating to the possibility that the pumps' bearings could be damaged by debris during high-pressure usage. A pair of extremely fine “strainers” are being installed to filter debris and keep the bearings protected.
Now there's another hitch. According a report by an NRC inspection team that FirstEnergy reviewed and agreed with, the emergency pumps could overheat if one of the pipes carrying water to the core - pipes the pumps are responsible for servicing - were to tear to a very small degree: a half-inch or less.
The difference in temperature between the heated reactor core and cool water coming through the tear could create a counter-pressure that could cause the pumps to overheat. “It's a very unlikely scenario; we're not sure it would ever actually happen, even in extreme situations,” said FirstEnergy spokesman Richard Wilkins. “But we're fixing it.”
To correct the problem, engineers at the plant will connect two-inch-wide emergency valves to the core ends of the pipes serviced by the emergency pumps - in effect, a set of emergency valves for the emergency pumps.
If one of the emergency pumps has the type of pressure plant officials fear would make it overheat, the valve on the bottom end of the line would open to relieve the counter-pressure on the pump.
Fixing the new design flaw should “only cost a couple of thousand dollars” and “only take a couple of weeks,” Mr. Wilkins said.
“The big test will be our `full-pressure test' in mid-July,” Mr. Wilkins said. During that test, plant engineers will increase water pressure in the pump system to its operational capacity of over 2,000 pounds per square inch for several days, then shut it down for final inspections. “That's when we'll know how we really stand,” he said.
But Viktoria Mitlyng, an NCR spokesman, said regardless of FirstEnergy's hopes, the NRC's emphasis is on safety, not schedules. “In addition to the pump system, there are other major issues that need to be addressed before the plant goes online,” she said.
Of primary concern to the NRC are issues connected with a “safety-conscious work environment” - in other words, workers feeling free to bring up problems at the plant and having their concerns heard.
“The problem with the plant's safety culture is one of the things that brought about the reactor head degradation in the first place,” Ms. Mitlyng said. Still, she said FirstEnergy has made some progress and is heading in the right direction.