Despite safety advances, the public - and utilities - remain wary of nuclear power

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WASHINGTON - At 4 a.m. on March 28, 1979, a pump malfunction set off an alarm at the Three Mile Island Unit 2 nuclear-power plant outside Harrisburg, Pa. Within nine seconds, equipment failures and human error caused a dramatic drop in the reactor-core water level, setting off the worst nuclear accident in U.S. history.

No one was injured, but the partial meltdown at Three Mile Island, and the far worse meltdown and explosion at Chernobyl seven years later, left deep scars on the American psyche about the dangers of nuclear power. Not a single plant has been ordered since 1973.

Now, however, the Bush administration's plan to increase energy supplies - including nuclear generation - has focused attention on whether the United States again might turn to the atom to fulfill its electricity needs.

The nuclear-power industry thinks it's ready. Since Chernobyl, engineers have designed a new generation of nuclear plants they believe will reduce the risk of another Three Mile Island sharply.

Three simpler - and therefore cheaper and safer - versions of the power plants currently in use have been approved by the Nuclear Regulatory Commission (NRC), a crucial vote of confidence for any interested utility.

Moreover, an international consortium has designed a new type of plant that uses hundreds of thousands of billiard-ball-sized "pebbles" of nuclear material instead of a conventional reactor core. It does not have enough radioactive fuel in a confined space to generate temperatures necessary for the pebbles to explode. In theory, it is meltdown-proof.

But none of these advances has enticed a U.S. utility to order a nuclear plant, and many obstacles persist.

Polls show that public dread endures. About 40,000 tons of radioactive waste from existing reactors are piling up across the country because the Energy Department has not found a permanent repository.

Critics still skeptical

Critics of nuclear power remain skeptical of the new plants' safety. And although the economics are good today, who's to say how long that will last? Even if a utility decided to build a reactor tomorrow, it would take a snag-free minimum of six to 10 years to bring it on line.

"There's renewed interest, but people are still skeptical that the public will allow nuclear (plants) to be built again," said Stephen Lee of the Electric Power Research Institute, the utility industry's research and development arm. "Also, the financial risk is quite large. The private investor will always take the lowest-risk, highest-return option, which, for now, is still gas generation."

U.S. utilities in 31 states operate 103 commercial reactors, which provide about 20 percent of the nation's electricity.

All U.S. plants are either "boiling water reactors" or "pressurized water reactors" that use uranium-rich fuel rods in a reactor core to create a controlled nuclear chain reaction. Resulting heat changes water into steam that drives the turbo-generators. "Control rods," usually made of boron, are inserted or withdrawn from the core to regulate the pace of the reaction by soaking up excess neutrons.

As with any boiler, the integrity of a nuclear core depends on operators and instruments to prevent overheating. But while a conventional boiler may blow up in a cloud of fire and soot when it becomes too hot, a nuclear core can spew deadly radioactivity.

The keys to avoiding trouble are many: adequate operator training, fail-safe shutdown measures and careful monitoring of valves, gauges and instruments. This can be difficult, partly because of the machinery's intrinsic complexity, but mostly because U.S. plants are all one-of-a-kind designs with modifications added along the way. Washington state's lone operating nuclear plant, the Columbia Generating Station on the Hanford nuclear reservation, had a spotty record after its construction in 1984, with numerous safety shutdowns until a management overhaul and major renovation greatly improved its performance.

Energy planners now are studying the viability of finishing construction of the dead plant next door to Columbia, WNP-1, and firing it up. The debate will kick off in earnest this summer when the study is completed and open to public consideration.

In recent years, utilities markedly have improved safety records with better training and upgrades. Between 1987 and 1999, the number of automatic shutdowns per plant dropped from 3.6 per year to 0.6 per year, according to the NRC. The number of safety-system failures per plant was cut in half, to 0.8 per year.

In the meantime, the industry prepared three new reactor designs and obtained NRC certification for them. The object was standardization: "Right now there's a lot of highly skilled construction - it's like airports," said James Lake, president of the American Nuclear Society. "We're looking for a way to change to building airplanes. If you can build in one place on an assembly line, it's much, much cheaper."

The three designs - one by General Electric and two by Westinghouse - are based on traditional technology. GE simplified safety systems, reduced the amount of hardware and made the plant easier to operate.

"It's still concrete, steel, welding, pumps and valves," said Steven Hucik, GE's general manager for nuclear-plant projects. "But when you simplify the design, there's much less of it. You can reduce the size of the building, and that means savings."

GE has built two 1,350-megawatt "advanced boiling-water reactors" in Japan and has six under construction: four in Japan and two in Taiwan. The two operating plants took 4 years, 3 months to build, and "we're predicting 54 months (4-1/2 years) in the United States," Hucik said.

Neither of Westinghouse's two designs, both pressurized-water reactors, has been built. The System 80-plus, also 1,350 megawatts, is projected to be South Korea's next-generation reactor. The Westinghouse 600-megawatt "AP600" departs more from tradition because it incorporates "passive" safety features based on gravity and other natural forces. Many safety devices are activated without human intervention.

Off-site construction

Obtaining certification for the passive safety system was "a fundamental issue" for Westinghouse, said Howard Bruschi, the company's chief technology officer, because the system will allow off-site, modular construction that can be finished in three years.

Critics acknowledge that standardization and simplicity make new-generation plants safer, but reactors "are inherently dangerous, so while it's a question of properly managing the risk, you can't make it zero," said David Lochbaum, a nuclear-safety engineer with the Union of Concerned Scientists.

The only truly innovative design on the horizon for the U.S. market is the pebble-bed reactor. Instead of fuel rods, the pebble-bed reactor uses tiny particles of uranium dioxide encased in layers of graphite and silicon carbide and shaped into spheres. These pebbles - 320,000 of them - are poured into a 65-foot cylindrical hopper that is lined with graphite bricks and has a hollow column in the middle.

Helium, not steam

Once in place, the pebbles initiate a chain reaction. But instead of making steam, the plant pumps helium into the top of the hopper and extracts the heated gas at the bottom, where it drives the turbines.

To shut down the reactor, control rods are inserted through conduits in the graphite bricks. Because the rods cannot run straight through the pebble bed, the reactor must be small - 110 to 130 megawatts, vs. 1,000 megawatts or more for a water reactor. But proponents see small size as a plus.

"You can build it in a modular fashion and locate it close to transmission lines where you need generation," said Oliver Kingsley, president and chief nuclear officer of the U.S. utility Exelon. Small size also should make the reactor virtually accident-proof. Computer modeling shows that the plant can't generate enough heat to melt the pebbles - even if helium flow is stopped and the control rods are withdrawn.

"You can't have a runaway accident, and that's one thing that's very attractive," Lochbaum said. "But the jury's still out. Graphite can catch on fire, like it did at Chernobyl."

Seattle Times staff reporter Lynda V. Mapes contributed to this report.