CORDOVA, Ill. -- Jun 11 - Knight Ridder/Tribune Business News - Mike Hughlett and Robert Manor Chicago Tribune

The Exelon nuclear plant here has suffered damaging vibrations for years, the unintended effect of an industry effort to run reactors harder, longer and faster than ever before.

When Exelon upped power output by nearly 18 percent at its Quad Cities plant in 2002, key components began shaking so badly that vibration monitors were thrown from their mounts and insulation fell from steam lines.

Later, Chicago-based Exelon, the largest U.S. nuclear plant operator, found that vibration in the steam system had caused gaping cracks in heavy metal plates. Steel fragments ended up in places they decidedly shouldn't be, like stuck in a key steam pipe and wedged in the bottom of the reactor. "The plant literally began shaking itself apart at the higher power level," said David Lochbaum, an expert on nuclear energy safety with the Union of Concerned Scientists.

Regulators were concerned, too: Metal chunks should never course haphazardly through a nuclear plant. They concluded, however, that the incident was unlikely to cause an accident.

Further, Exelon, which experienced similar but less severe cracking at another Illinois nuclear plant, believes it finally fixed the problem this spring.

To Lochbaum and nuclear power critics, however, Quad Cities' quaking raises a question: If the big power boost caused such severe vibrations, what other less visible problems might it cause? After all, Quad Cities' damage was relatively easy to spot.

The ratcheting up of power at Quad Cities, one of the nation's oldest nuclear plants, is part of a trend. Utility companies are wringing more from their aging reactor fleet.

Over the last five years, six U.S. plants have boosted power by 15 percent to 20 percent beyond their originally licensed level. Regulators are reviewing plans for 15 percent-plus boosts at two more plants, one in Alabama and one in New York. Similar requests are likely in the next few years.

Federal safety regulators and nuclear experts say power boosts like those at Quad Cities are thoroughly reviewed for safety problems.

The nuclear power surge has been a quiet process with little public debate. It comes at a time when deregulation of the electric utility industry gives power companies the chance to profit by increasing production as cheaply as possible.

New nuclear plants won't be built for years, if ever. So operators, with regulators' blessings, devised ways to get more output from existing plants.

"The incentives are in place to push people and machinery harder," said Mark Sadeghian, a Morningstar utility analyst. "Everyone is doing it."

One way to do it is to increase production beyond the level for which a plant was originally licensed, like at Quad Cities.

In a separate attempt to increase efficiency, nuclear plants are getting more power from reactors by using uranium fuel containing more energy, and then using that fuel for longer stretches of time. Exelon boasted in February that its LaSalle Plant Unit 1 reactor had set a world record of 739 days between refuelings.

As the industry has powered up, most traditional safety measures have improved or at least not eroded. For instance, forced plant shutdowns and safety system failures are rare compared to the 1990s.

But unexpected side effects have appeared, such as Quad Cities' quaking and less severe cracking at Exelon's Dresden plant 60 miles southwest of Chicago. Exelon will spend at least $160 million to fix vibration issues at the plants.

Meanwhile, uranium fuel began failing at an increasing pace four years ago, cracking and leaking radiation into coolant water. Industry observers say stress from increased demand over longer periods of use pushed the fuel past its structural integrity.

Just last month, LaSalle's Unit 1 reactor had to cut power output for several days because a fuel failure could have potentially leaked radioactive material in the reactor. While not an immediate safety problem, it could create problems for Exelon for months to come.

In March, Exelon found it couldn't fully insert a control rod--a key safety component--into LaSalle's Unit 1 reactor. That problem may be linked to the long run between refuelings, some nuclear experts say, though Exelon says otherwise.

Fuel issues like LaSalle's have garnered scrutiny from the Nuclear Regulatory Commission, the nuclear safety regulator. As with Quad Cities' shaking, the NRC says damaged fuel is not a safety problem but can be expensive to fix.

Near-disaster haunts critics

Nuclear power watchdogs are still worried. Critics are haunted by a 2002 incident at FirstEnergy Corp.'s Davis-Besse plant in Ohio.

Workers at Davis-Besse found a pineapple-size cavity at the top of the plant's reactor. Six inches of carbon steel had been eroded by acid, leaving only a thin stainless steel lining. It was bulging and cracking.

Had the lining given way, a disastrous accident could have occurred. It was the most serious nuclear safety problem since the 1979 partial reactor meltdown at Three Mile Island.

It happened at a time when the industry's safety record looked good, and it happened at a plant that regulators considered well run, meaning it received fewer inspections.

Davis-Besse's problems didn't stem from boosting power. Instead, the plant deferred maintenance and therefore missed a brewing problem. FirstEnergy later acknowledged that its managers emphasized production over safety.

The NRC was criticized by its own internal investigative arm for weak oversight that allowed FirstEnergy to put profits above safety. The General Accounting Office, the investigative arm of Congress, agreed.

To critics of nuclear power, Davis-Besse reinforced long-held fears, particularly in an era of deregulation.

"We have long been concerned that the nuclear industry has pitted profit margins against safety margins," said Paul Gunter, of The Nuclear Information and Resource Service, an anti-nuclear group.

But the nuclear power industry says it has a huge incentive to uphold safety: Billions of dollars in assets and revenues are at risk if an accident occurs.

"It is not to our benefit to run any of these billion-dollar assets into the dirt," said Christopher Crane, president of Exelon's nuclear arm. "We are confident of our safety margins."

Exelon has had a solid safety record for years. The company runs 11 nuclear plants, including six in Illinois.

While no new U.S. nuclear plant has been authorized for decades, the industry has quietly boosted power output for years through "uprates" granted by the NRC. Since uprates began in the late 1970s, the industry has added the equivalent generating capacity of about four reactors.

Until 1998, uprates didn't exceed 7 percent of a plant's originally licensed power level. At most plants, equipment tweaks handled those increases, but for larger uprates, regulators require plant modifications.

That's because power boosts add stress to a plant's equipment. An 18 percent increase, for instance, leads to a roughly 18 percent stronger flow of steam through a plant's pipes.

To some uprate critics, that's akin to pushing a 1970s vintage car 18 percent harder. But uprate proponents argue that with plant modifications--like new turbines and reinforced steam lines--that "old car" has had a major makeover.

The industry moved toward larger uprates because smaller boosts, which are those of about 5 percent, had proven successful over the years, said Lochbaum of the Union of Concerned Scientists, which is neutral on nuclear power.

The NRC has no upper limit on uprates. But the larger the uprate, the more costly to equip a plant for the greater stress.

Quad Cities was in the first crop of 15 percent to 20 percent uprates. Quad Cities houses two boiling water reactors. Heat from the nuclear reaction within the reactors creates steam to drive generators that produce electricity.

Exelon sank "tens of millions of dollars" into upgrading the plant to handle the power boost, said Tim Tulon, site vice president at Quad Cities, which opened in 1972.

Excess steam results in hole

The first of its two reactors revved up power in March 2002. Five months later a major problem was discovered.

Workers found a gaping hole in a "steam dryer," a 33-ton piece of equipment the size of a garage that sits above the reactor. The dryer extracts excess moisture from steam heading to a turbine that generates electricity.

The increased steam flow from the power boost had caused vibration that in turn caused the cracking. One dryer fragment was found wedged in a steam line. Another piece was found in a screen in the plant's turbine room. Lochbaum said that given the path the pieces traveled, they could have become jammed in a key safety feature known as a "main steam isolation valve."

In an accident, those valves are supposed to close. If held open by metal fragments, Lochbaum said, radioactive steam could escape into the environment.

The NRC concluded that Lochbaum's scenario was possible but improbable.

"There was a very low likelihood of any issues with the pieces coming off," said Tom Scarborough, the NRC's senior mechanical engineer for component integrity. "That said, we don't want to see loose pieces coming off the dryer."

Exelon made repairs and restarted the reactor. But in May 2003, workers found another large crack. Then, the steam dryer in the plant's other reactor cracked, dislodging a chunk of metal 6 1/2 inches by 9 inches.

The missing piece was never found, but Exelon concluded that the piece posed no safety threat. The NRC agreed.

In December 2003, more cracking was found, this time in a steam dryer at Exelon's Dresden plant.

Dresden won permission in 2001 to raise power 17 percent at its two reactors. Dresden's cracking was also caused by vibration from the power boost.

Questions raised elsewhere

Exelon's problems helped spark the first challenge to a big power uprate: a proposed 20 percent boost at the 33-year-old Vermont Yankee plant in southern Vermont, which is owned by New Orleans-based Entergy.

"Quad Cities confirmed our suspicions," said Raymond Shadis, of the New England Coalition, an anti-nuclear group. The coalition and the state asked the NRC for assurances that Yankee could bear the stress of such a big power boost.

Quad Cities' woes caused the NRC to look hard at vibration issues when it studied Vermont Yankee, significantly lengthening the review process, the commission said.

The New England Coalition never got the assurances it wanted, though the state of Vermont withdrew its concerns in May, a few months after the NRC approved Yankee's uprate.

Vibration problems are limited to Quad Cities and Dresden, the NRC says. So why has Quad Cities shaken so badly?

"We're still looking at that," said the NRC's Scarborough. He thinks the answer involves the layout of the plant's steam system.

Despite repairs, Quad Cities' vibration woes continued. So Exelon decided to replace steam dryers at both Quad Cities and Dresden, an expensive task never done before at a U.S. plant.

Even with new dryers, Quad Cities' problems continued. Last winter, workers found that several safety valves had become worn and needed replacement, apparently because of vibration, according to the NRC.

The valves release pressure in an emergency. Their degradation was of "very low" safety significance, the commission said.

But Quad Cities was fortunate to discover the problem as the valves would have likely degraded further, potentially resulting in the "unavailability of a safety system," the NRC said.

Finally, workers this spring found one of Quad Cities' brand new steam dryers had developed a 5-foot crack. Exelon blames the crack on installation problems.

Quad Cities believes it recently solved the quaking through a complicated $40 million revamp of the plant's steam-line system.

"It works beyond expectations," said Tulon, the site vice president. Vibration levels are less than before the power uprate, he said.

Lochbaum said time will tell if this fix did the trick; Exelon has said before it's solved the problem and "they were equally confident in the past," he said.

Lochbaum worries about less visible problems caused by uprates. Steam dryer cracking, after all, can be easily spotted during maintenance, he said.

"If similar problems are out there in terms of safety systems, these problems may not surface until an accident and they don't do what you want them to do," Lochbaum said.

Exelon's Tulon noted, though, that Quad Cities' steam dryer cracking caused the company to go back and reassess what could go wrong with myriad safety system components.

"That's what good nukes do," he said.

Despite Quad Cities experience, some nuclear experts aren't worried by the uprates.

Neil Todreas, a nuclear engineering professor at the Massachusetts Institute of Technology, is one of them. "The bottom line is I don't think they are pushing us to a dangerous limit or putting us towards the edge in any way. They've been thoroughly reviewed [by the NRC]."

Refueling less frequently

While large uprates are perhaps the most dramatic way of boosting output, the nuclear industry has wrung more production out of its fleet in several other ways, not just running its plants harder but also running them longer and hotter.

Reactors used to refuel annually. Now they refuel every two years, on average, with fuel containing more powerful uranium, reducing the interval when plants produce no electricity.

That has led to its own problems.

Reactors are powered by uranium pellets contained in thousands of zirconium tubes called fuel rods. The zirconium cladding is the first barrier to the release of radioactivity, and it must remain intact.

Beginning in 2002, increasing numbers of fuel rods suffered structural failure.

Under longer use in an environment of intense radioactivity and furiously boiling water, the fuel rods increasingly grew brittle and cracked, the first step toward structural failure.

Too often, cracks expand into holes in the rod and the fuel within spills into the reactor.

"The longer you put [fuel] in the reactor, the likelihood of failure is greater," said Rosa Yang, a fuel expert at the Electric Power Research Institute.

In 2000, the NRC counted 58 fuel failures. In 2003, the number rose to 147. Failures declined to 72 last year, still far above the industry's goal of zero defects.

Nuclear engineers say failing fuel is not a safety issue, as the uranium is contained within the reactor's heavy steel vessel. But failed fuel is expensive to clean up and can force a nuclear plant to shut down. It is a basic principal of nuclear safety that no barrier to radioactive material can be allowed to fail.

NRC Commissioner Jeffrey Merrifield has raised the alarm about fuel failures.

"This is a trend we can neither ignore nor tolerate," Merrifield said at a commission meeting last year.

Merrifield now says the situation may have stabilized, as fuelmakers work to design more durable fuel rods. He said the total amount of failed fuel is very small in comparison with the amount of uranium consumed by the nation's 103 power generating reactors.

Meanwhile, the longer use of nuclear fuel appears to have aggravated a problem involving control rods, a vital reactor safety feature.

The chain reaction within reactor fuel is managed by control rods. Inserting the dozens of control rods through channels into the fuel reduces power output; withdrawing the rods increases power production.

Under bombardment by radiation, the channels can distort, making it more difficult to move the control rods.

That phenomenon appeared in February at Exelon's LaSalle Unit 1 reactor in Seneca, which is about 75 miles southwest of Chicago. During a reactor shutdown there, one control rod failed to fully insert and a distorted channel was found in the fuel.

"We are definitely seeing an increase" in fuel channel problems, said Jim Malone, vice president of nuclear fuels for Exelon, adding that the company is working to reduce the problem.

Malone doesn't believe fuel failures are the fault of nuclear operators. He blames nuclear fuel manufacturers for not making their product more durable.

Areva NP manufactures nuclear fuel and is working to make its product stronger.

"We don't understand how all these effects work together," said John Matheson, senior vice president for fuel at Areva. "Clearly the fuel is being challenged more."

 

 

mhughlett@tribune.com

rmanor@tribune.com

IN BUSINESS Critics warn that safety at nuclear plants could be compromised as workers put in longer hours on the job.