Progress Energy now knows why layers of concrete separated in a wall at its Crystal River nuclear plant, but it has yet to put a final price tag on repairs.
The gap formed last fall as workers prepared to cut a hole in the wall of the plant's reactor containment building, according to a nine-month investigation by the utility. Fortunately, the problem was limited to the area where the work was taking place.
Also, the company's assessment of the containment dome concluded that it can handle normal and emergency operations.
Repairs had cost $25 million and replacement fuel had cost $95 million as of March 31.
Progress Energy plans to use insurance and other means, perhaps including trying to recover costs from its contractors, to "minimize the impact on customers," Progress Energy spokesman Mike Hughes said Wednesday.
Still, the outage comes at a bad time. Energy use in Florida so far this year is running more than 5 percent above normal. The Crystal River nuclear plant typically generates about 20 percent of the power Progress Energy's customers use in Florida.
With the plant offline, Progress Energy has turned to its own peak-usage generation plants and bought electricity from neighboring utilities to meet demand.
Work is under way to replace the separated concrete. The company is expected to discuss when the plant could return to service during an earnings conference call next week.
In a presentation to the Nuclear Regulatory Commission on June 30, Progress Energy said the separation, known as a delamination, formed last fall. The company powered down the plant in September for a $310 million job to replace two huge steam generators inside the reactor building.
At the time, workers were easing the tension in a series of steel reinforcing tendons embedded in the building's outer wall and were cutting a large hole in the wall.
"Those activities resulted in an additional stress that was beyond the original containment building design," Hughes said.
That means the gap didn't form before the start of the job. Progress Energy also found no other areas of separated concrete in the building.
The utility cut the 25- by 27-foot hole because the reactor building's regular equipment hatch is too small for the generators, which weigh 550 tons each. The separation inside the wall was up to 2 inches wide, and it formed about 9 inches below the outer surface of the wall, which is 42 inches thick.
The team that delved into the possible causes of the separation included experts in root cause investigation techniques, nuclear operations and maintenance, material science, computer analysis and concrete standards, testing and construction.
Refuted as possible causes were concrete shrinkage or settlement, chemical or environmentally induced stress, external events and things that happened during plant operations.
In November, the director of the NRC's Office of Nuclear Reactor Regulation said Crystal River's problem raised concerns because other nuclear plants around the country had cut into their containment walls 26 times before, but no one ever saw concrete separate like this.
NRC inspectors monitoring the repair job are looking for whether there was something about the design or construction of the reactor building that could have contributed to the formation of the gap, agency spokesman Roger Hannah said.
So far, he said, nothing presented by the company or turned up by inspectors indicates a design or construction flaw played a role.
Reach Richard Danielson at email@example.com or (813) 226-3403.