Inspection: A search for flaws deep in the heart of Surry reactor
Posted on 07.12.2004 - 13:35 UTC in INSPECTION NEWS (Topside) by Rons_ROV_Links
SURRY — Deep inside the water-filled nuclear reactor, a robotic inspector poked its sensor-tipped arm into a pipe to scan for cracks thinner than a human hair.
Meanwhile, a tiny remote-controlled submarine left its post in the reactor and rose to the surface, its headlights glowing like the eyes of a sea creature. In a trailer about 100 feet outside the reactor building, engineers watched computer screens as they adjusted the robotic arm, moving it by fractions of an inch and crunching the streams of data it collected.
|A remote-controlled submarine surveys one of Surry Nuclear Power Station’s water-filled reactors, which was shut down for inspection to search for flaws as small as microscopic cracks.|
These tools step in for humans in the dangerous environment of a nuclear reactor, and they find flaws that the human eye could not. They are among the instruments of the 21st century that Dominion Resources Inc. uses to run and maintain the 32-year-old Surry Nuclear Power Station.
The nuclear power industry has combined human experience and high technology to reach an era of relative safety 25 years after the accident at the Three Mile Island plant in Pennsylvania.
Dominion prides itself on taking stringent measures to detect and head off problems and to keep its plants running as efficiently and competitively as possible.
“If we’re not generating electricity, we’re not making money, which is not good business sense,” said Richard Zuercher, spokesman for Dominion’s nuclear operations.
The robot, or ROSA, for “remotely operated service arm,” came to work at Surry’s Unit 1 reactor last month during a scheduled five-week outage of the plant. Every 18 months, routine maintenance is performed on each of the two reactor units and spent fuel is replaced. But the ROSA visit was part of an intense inspection that’s done every 10 years to check welds on the pipes that carry water into and out of the reactor core.
The core is where the radioactive process of nuclear fission takes place, heating water to create steam that runs turbines to generate electricity. Leaks in the pipes that carry that water could be disastrous.
The robotic arm used highly precise sensors to find and measure nearly invisible cracks or signs of corrosion where the massive pipes are welded to the reactor.
In the trailer near the reactor, computer screens displayed various images of the ROSA and the pipe’s cross-section to help the technicians position the robot.
The ROSA recorded a profile of each weld and sent back its readings through fiber optic cable. A crack would show up as a disruption in the image.
Two technicians from WesDyne International, the subsidiary of Westinghouse Electric Co. that created the inspection system, collected the data. One image looked like an asphalt road with a bump of bright orange down the center where the weld is.
In the 10 years since the last inspection, WesDyne has tweaked the system for greater accuracy and detail. It now takes 5½ days to cover all the welds, down from about 10 days in the past, said Ron Thomas, project manager of the inspection. “We can collect a lot more data in a lot less time.” Surry completed its maintenance and restarted Unit 1 on Thursday. The inspection revealed no immediate issues, Surry officials said, but they will continue to study the data.
During the routine reactor shutdowns, which occur at each of the plant’s two units every 18 months, Surry employees take apart every piece of the power generator and inspect various spots in the reactor. Operators want to catch warning signs, such as those hairline cracks. If they catch them early enough, they could have as much as 20 years to react before any leakage would have occurred to disrupt the reactor cooling system.
Dominion, the Richmond-based parent of electricity utility Dominion Virginia Power, wants to keep its nuclear plants running 24 hours, seven days a week. Any problem that leads to an unexpected shutdown can cost the company as much as $100 million a day to replace the power, said Kenny Sloane, Surry’s director of nuclear operations and maintenance.
Surry and the company’s two other nuclear units at the North Anna station north of Richmond are among the largest and most-efficient generators in the state. Surry produces more than 1,600 megawatts of electricity, enough to serve about 400,000 average Virginia homes.
Surry’s reactors opened in 1972 and 1973, each with a 40-year operating license. They were beset by safety problems for about 15 years, undergoing frequent shutdowns because of weak or blocked pipes, damaged turbines, water leaks, fires and even earthquake concerns. Employee sabotage at the plant in 1979 prompted an FBI investigation, and four workers were killed in an accident at Surry in 1986.
“We were not an excellent operator in that period,” Zuercher acknowledged. “We learned a lot from those hard times. The industry as a whole had not evolved to the industry it is today. It was not efficient.”
Dominion has since boosted the plant’s safety record, instituting a policy for nuclear safety and professionalism in 1989.
In the past year, both units have been cited by the Nuclear Regulatory Commission for minor safety concerns during regular inspections. This has kept the plant out of the commission’s best-performance group, but the findings are considered far from serious, requiring only a slight increase in oversight, said Roger Hannah, a nuclear commission spokesman.
The Nuclear Regulatory Commission granted approval to extend Surry’s operating licenses for 20 more years, which means that with the 10 years left on the original license, the plant’s aging parts must last three more decades. Surry replaces $2 million to $4 million worth of pipes and other components every year, Sloane said.
Hannah compared a nuclear station to an old-model car that has mostly new parts. “You can almost run that car forever,” he said. “That’s one of the things they do with nuclear plants.”
Dominion also recently spent $175 million to replace the reactor heads on all four units at Surry and North Anna. It was a pre-emptive measure to address tiny cracks where water had seeped through the heads, which are steel lids covering the reactor vessels.
Similar early indicators went unchecked at the Davis-Besse nuclear plant near Toledo, Ohio, where corrosion turned cracks in the reactor cap into a large hole. A subsequent two-year shutdown, which ended in March, and federal investigation of plant owner FirstEnergy Corp. brought scrutiny to the entire industry’s safety measures.
Davis-Besse notwithstanding, the industry has taken steps since the 1980s to share information and police itself.
“We have to operate safely if we want to continue to operate and have the public trust,” Zuercher said.
All over the Surry plant, signs on walls stress Dominion’s need for safety, responsibility and housekeeping.
Workers undergo a pain-staking process to protect themselves and outsiders from radioactivity. Those who enter the “containment” area of the reactor building must wear radiation monitors called dosimeters.
Employees working inside the reactor first must strip out of regular clothes and change into the aqua-colored “scrubs” that surgeons wear. Over that, they cover themselves head to toe in white, lightweight, throwaway jumpsuits and hoods, with double layers of rubber gloves and boots. Around the reactor core, deemed the “foreign material exclusion area,” they must attach every loose item – including pens, ID badges and eyeglasses – to their suits with duct tape.
When they leave the reactor, they carefully remove each outer layer of clothing, one piece at a time, standing in a specific spot on the floor, careful not to touch an unexposed foot in an exposed area. Then, they step into a full-body scanning machine that detects any radioactive contaminants.
Technology has improved these longtime safety practices as well. A surveillance room holds a bank of screens with video cameras where radioactivity levels in each area of the plant can be monitored.
Some of the industry’s modern safety methods are not so much high-tech as practical. In the computerized control room, where every aspect of the plant is managed, Surry uses “distinctive dress.”
Each supervisor wears a specific color of shirt, such as red or green, so employees can readily identify who is making decisions. Sloane said this started after the Three Mile Island accident in 1979, when a leakage caused a near meltdown at the plant and threw the operation into such chaos that no one knew who was in charge.
6 December 2004