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How San Onofre's new steam generators sealed nuclear plant's fate

San Onofre's replacement generators were supposed to extend the nuclear plant's life and save money. The opposite ensued.

July 13, 2013|By Abby Sewell and Ken Bensinger
  • Aerial view of the San Onofre Nuclear Generating Station in the northwestern corner of San Diego County. Problems with replacement steam generators led to the plant's permanent shutdown.
Aerial view of the San Onofre Nuclear Generating Station in the northwestern… (Don Kelsen / Los Angeles…)

In March 2004, an attorney for Southern California Edison sat before state utility regulators to propose what seemed like a great deal.

The San Onofre nuclear plant was approaching the end of its life span. But Edison wanted to invest $680 million in new steam generators, attorney Carol Schmid-Frazee told a judge presiding over a hearing at the California Public Utilities Commission's San Francisco headquarters. The new equipment, she said, would give the 2,200-megawatt plant a new lease on life, providing cheap, reliable energy in Southern California for decades to come while also saving ratepayers nearly $2 billion.

Edison's lawyer also issued an ominous warning: If regulators did not approve the upgrade, the plant would close, provoking "very serious problems with the California electric grid."

The commission was persuaded, and Edison began remaking San Onofre.

But less than a year after the new steam generators came online, a tube in one of them sprang a radioactive leak, setting off a chain of events that ultimately led Edison to close the plant permanently. The generators that were supposed to save San Onofre ended up killing it, and today the atomic behemoth sits idle, never again to produce a watt of power.

Instead of a boon to California, the steam generator replacement became a billion-dollar debacle, leaving 1,100 workers facing layoff and the plant's owners, suppliers, regulators and customers wrangling over who is to blame, how to replace the plant's power — and who will pay for the mess.


The affair began with good intentions.

The nuclear plant, one of only two in the state, had been an eye-catching fixture on San Diego County's north coast since 1968, powering about 1.4 million homes. But by 2001, one of its reactors had permanently shut down and the other two were showing their age. Edison believed modernizing San Onofre would provide cheaper electricity than building new natural gas plants or purchasing imported power.

That year, Edison began a formal study of the plant's biggest problem: cracking and wear on the tubes in its original steam generators, which produce power and help cool the reactor core. Thousands of narrow tubes carry superheated water from the reactor that is used to create the steam that turns electricity-producing turbines.

The four generators, each as long as an 18-wheeler, were supposed to last through the end of San Onofre's operating license in 2022. But, like most steam generators of the era, their tubes had corroded, and Edison feared it might have to close the plant more than a decade early if it didn't replace them.

Doing so was expected to aid its chances of getting a 20-year license renewal from the U.S. Nuclear Regulatory Commission. It was a big job, but a routine one: By 2004, nearly three dozen other plants in the U.S. had already swapped out their steam generators.

Not everyone was on board. The plant's minority co-owners — San Diego Gas & Electric and the cities of Anaheim and Riverside — protested that Edison had embarked on the project without their input. Filings with the PUC spoke of "acrimony" between the parties.

SDG&E President Mike Niggli said his company "had serious questions about whether it would be the right investment."

Anaheim pulled out, dropping its 3% ownership stake. SDG&E, which initially refused to participate, finally agreed to contribute 20% of the cost, and Riverside — which owns less than 2% of the plant — also went along.

In September 2004, Edison selected Japanese company Mitsubishi Heavy Industries to design and build the generators. Mitsubishi had made more than 30 nuclear steam generators in other countries and was replacing the ones at Nebraska's Fort Calhoun plant, which were similar to San Onofre's.

In fact, though, Mitsubishi's engineers had never made steam generators as large as San Onofre's, each of which stood more than 65 feet tall, weighed 620 tons and contained more than 9,000 tubes.

From the outset, Edison was worried about the design of the generators' anti-vibration bars — support structures that are supposed to prevent the tubes from shaking.

"I am concerned that there is the potential that design flaws could be inadvertently introduced" in the large generators, wrote Edison's then-vice president in a November 2004 letter to Mitsubishi. He worried, he added, about "unacceptable consequences."

Edison and Mitsubishi formed a special committee to deal with the issue, which met for more than a year to debate possible solutions.

The final design incorporated significant changes. The companies swapped out the alloy used in the tubes for one less susceptible to corrosion. Because the new alloy conducts less heat, they also added 377 more tubes in each steam generator. Other plants, including Fort Calhoun, had made similar changes and experienced no problems.

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