How safe are aging reactors?

Reformer Staff

This is the seventh in a series of articles that examines the background to the pending sale of Vermont Yankee nuclear power plant.

BRATTLEBORO -- In December 1986, a pipe broke at the 13-year-old Surry nuclear power station in Virginia, killing four workers. The accident made national headlines, especially after it was discovered that the pipe failed because it had been corroded by the simple wear and tear of use.

Two years later, Nuclear Regulatory Commissioner Kenneth Rogers warned that "the aging of nuclear power plants is one of the most important issues facing the nuclear industry worldwide" and likened a reactor with many aged parts to a "loaded gun."

At the time, only three reactors in the nation had run for more than 20 years. Now, many reactors are approaching their third decade of operation. The years following Rogers' speech saw no Chernobyl, no Three Mile Island. In fact, the nation's reactors are now performing more reliably than ever before.

But as Vermont Yankee nuclear power plant closes in on its 30th anniversary, and faces purchase by a corporation that will likely try to run it for another 30 years, some nuclear experts worry: How safe is a 30-year-old nuclear power plant? Or a 60-year-old plant?

Aging: the ongoing debate

Melanie White, spokeswoman for the industry group Nuclear Energy Institute, bristles at the comparison of an aging reactor to an aging car.

"These plants are very well maintained. They have to be maintained like that by law," she says. "Everything is continually updated. If anything is aged or it's not working properly (it's replaced) ... even down to the littlest valve."

Vermont's state nuclear engineer, William Sherman, similarly disagrees with the car analogy.

"Nuclear plants are not like equipment that ... just wears out," he says. "So much of the equipment within the plants has been replaced ... you're not dealing with a 25-to-30-year old plant, you're dealing with a plant that has a lot of new equipment in it."

On the other side of the fence is David Lochbaum, who worked in the nuclear industry for more than 17 years before joining the Washington-based Union of Concerned Scientists. Testifying before a U.S. Senate subcommittee in May, Lochbaum calculated that "since the beginning of the 21st century, at least eight nuclear power plants have been forced to shut down due to equipment failures caused by aging."

An unplanned shutdown, or SCRAM, is not a threat to public health and safety, but Lochbaum and others worry that the faulty equipment triggering SCRAM may indicate that numerous other components are on the edge of failure -- that, despite the industry's claims, old reactors do wear out.

What if all the pipes wear thin?

Nuclear reactors are designed to deal with human mistakes, equipment failure, earthquakes and tornadoes. They have what are called "redundant safety systems," meaning that there are back-ups to everything and back-ups to the back-ups. But the designs generally assume only one human or equipment failure occurs at a time. If, for example, numerous steam generator tubes were worn dangerously thin from decades of use, the results could be disastrous.

"(If that happens), in essence, we have a 'loaded gun,'" Rogers said in 1988. "Under those conditions ... a seismic activity could rupture many tubes simultaneously," causing a failure of containment systems and a release of radiation into the environment.

A decade later, the industry knows a lot more about what goes bad in a reactor and how to find and replace it before there are any adverse effects. But some components are harder to monitor than others. It's relatively easy to periodically test equipment that moves, such as pumps and valves. But it's difficult to measure the thickness of piping, the adequacy of electrical cable insulation, or cracks in the welds that hold the reactor vessel together without taking the plant apart.

"Some of these structures ... may have been inspected only once over the life of the plant," NRC chairwoman Shirley Jackson told a conference in 1998. "Inspection programs for piping have missed fatigue cracking in some cases ... even today we cannot size cracks accurately in certain steam generator tube locations."

Aging at Vermont Yankee

In September 2000, a dead bulb in an indicator light in the control room indirectly triggered an emergency shutdown at Vermont Yankee.

Technicians changing the bulb caused a short circuit which blew a fuse, which in turn caused two valves in another part of the plant to close. The valves were part of the system that maintains a vacuum in the condenser, which cools the steam that turns the plant's turbines and is then sent back to the reactor core as water. Control room operators shut down the reactor within minutes of discovering the condenser problem.

The NRC said there was little or no danger to the public because of the mishap, but a commission spokesman commented that Yankee might have an economic incentive to "alter the design such that a single light bulb being changed and a single fuse blowout would not cause the plant to shut down."

Raymond Shadis, a consultant to the anti-nuclear group New England Coalition on Nuclear Pollution, went further, saying the bizarre chain of events was indicative of faulty or aging wiring.

A definite sign of aging was discovered during the 1995 refueling outage. As in other General Electric boiling water reactors, the shroud inside Vermont Yankee's reactor vessel had begun to crack. The shroud is a 14-by-14-foot open-ended cylinder that directs the flow of water around the reactor core.

In October of the following year, Yankee spent several million dollars to install four top-to-bottom tie rods to reinforce the shroud, a process that was repeated at other reactors of similar design.

"The industry has used this at a number of plants and so far it's been successful," says NRC spokesman Neil Sheehan. "Of course, they still need to go in to check every outage to make sure these bars are holding up properly. (But) the fix seems to work."

"Seems to work" doesn't mean much to the anti-nuclear group Citizens Awareness Network, however. CAN's Paul Gunter describes shroud repair in boiling water reactors as flirting with disaster.

"Operators and their federal regulators are opting for a dangerous, least-cost, piecemeal approach of patching cracking components, with increasing safety risks," he said.

Safer than ever?

Nationwide, reactors are operating more reliably than ever before. No new reactors have been ordered since the Three Mile Island incident in 1979, but the nation's aging fleet has shown increasingly good performance.

In 2000, according to NEI, U.S. nuclear power produced a record 755 billion kilowatt-hours of electricity, and achieved an all-time high average capacity factor (a measurement of the amount of electricity actually produced compared to the maximum output achievable if the plant operated around the clock) of 89.6 percent.

Vermont Yankee had a capacity factor of more than 100 percent and produced power at a record low of 3.9 cents per kilowatt hour. It has not had an unplanned shutdown since September 2000.

Capacity factor and unplanned shutdowns can be indicators of plant safety, because a plant that is having performance or safety problems is more likely to shut down. In the industry's early years, shutdowns were common, occurring several times a year.

But some experts assert that the industry's experience cannot guarantee the safety of aging reactors. In his 1998 paper "Nuclear Safety: Will the luck run out?" Lochbaum cites a 1985 NRC statement that the probability of a severe reactor accident happening in the next 20 years is about 45 percent.

"It is only a matter of time," he wrote, "before the initiating event wheel, the equipment wheel, and the human performance wheel stop in a combination that produces another accident."