The San Onofre Nuclear Generating Station (SONGS), a nuclear power plant set into the seaside bluffs in northern San Diego County, is closing after the high cost of repairs and a Nuclear Regulatory Commission board ruling prompted its owner, Southern California Edison, to pull the plug on the 45-year-old facility.
The announcement Friday that San Onofre’s two functioning reactors were being shut down brings to four the number of reactors that nuclear utilities have slated for closure since last November. Meanwhile, nuclear utilities have three new reactors on the drawing boards.
At least for now, "we're losing them faster than we're building them," quips David Lochbaum, a nuclear engineer by training who focuses on nuclear-energy issues at the Union of Concerned Scientists in Washington.
In February, Duke Energy announced it was shutting down the reactor at its Crystal River power station in Florida after workers discovered a crack in the containment dome. The crack was created during efforts to replace a critical component of the reactor system that transfers heat to water in order to generate steam for the plant's turbines.
In early May, the utility Dominion shuttered its single-reactor Kewaunee nuclear plant in Carleton, Wis., a casualty of cheaper sources of electricity and an inability to build additional reactors to take advantage of what the company called economies of scale.
"Nuclear economics is tenuous at best," Mr. Lochbaum says. "If you do everything right, you can make money at this. But if you stumble, there's a big price to pay, and not just from a Fukushima-type tragedy."
Financial setbacks can take their toll as well, he says, whether a setback comes from lost business or from hardware failures or human error that sets the stage for costly repairs.
In announcing San Onofre's closure Friday, Ted Craver, Southern California Edison's chairman and chief executive officer, noted that the station has been generating electricity for more than 40 years, "but we have concluded that the continuing uncertainty about when or if SONGS might return to service was not good for our customers, our investors, or the need to plan for our region's long-term electricity needs."
The utility first broke ground on SONGS in 1964. The plant initially hosted one nuclear reactor. Two more were added and came on line in 1983 and '84. Since then, the plant's first reactor was decomissioned, leaving units 2 and 3 to help power southern California's voracious demand for energy.
Both units sported relatively new sets of steam generators – components that along with the reactor sit inside a concrete containment building. The steam generator houses bundles of tubes through which high-pressure, superheated steam from the nuclear reactor flows. Pumps force water past the searingly hot tubes to produce the steam that drives the plant's generators.
In early January 2012, the utility took Unit 2 down for a routine refueling outage. At the end of the month, operators running Unit 3 detected a small leak in a steam generator tube that allowed radioactive steam to mix with the steam sent outside the containment building to the generators.
The utility shut down Unit 3 and began an exhaustive inspection of the steam generators for both reactors. The inspections revealed unexpected wear and tear on a significant proportion of the tubes.
The ultimate cause of the excessive damage to the tubes came from an attempt to make the tubes more resistant to cracking than were the tubes in the original designs, Lochbaum says. In the past, tubes have been subject to damage because they were too vulnerable to vibrations caused by instabilities in the superheated steam flowing through them. These instabilities cause the tightly packed tubes to vibrate and knock into one another.
The new tubes were stiffer. But tubes can vibrate in two directions, Lochbaum explains. The computer simulations designed to model the performance of the new design failed to take into account one of those two directions. The modelers assumed that the supports for the tubes that dampened one set of vibrations would dampen the other as well – which also happened to be the mode that inflicts the most damage.
Engineering studies indicated that the company could restart Unit 2, but it would have to run at 70 percent of its rated output, at least for the first five months, according to the company's statement. Lochbaum adds that the assessments also indicated that the plant would have to shut down every 15 months, rather than every 18, to perform the inspections needed to ensure tubes were not being damaged.
What looked to the utility to be a sensible $780 million investment in 2009 and '10 to extend the lifetime of the two reactors turned into an economic albatross, Lochbaum suggests.
In addition, the Nuclear Regulatory Commission's Atomic Reactor Safety and Licensing Board recently ruled that prior to any reactor restart, groups that have opposed restarting SONGS were entitled to present their case against restart.
Southern California Edison's announcement noted that the additional delays this process would impose could last more than a year.
Opposition has been fueled by increased NRC scrutiny the plant reportedly has received in recent years over safety concerns. Meanwhile, in April, the ABC News affiliate in San Diego reported that an unnamed nuclear-safety engineer at the plant had come forward to highlight the danger from the defective steam-generator tubes.
Environmental groups that had opposed restart were quick to applaud the decision.
“Shutting down San Onofre is the right thing to do,” said Michelle Kinman, with Environment California, in a prepared statement. “Shutting down this nuclear plant will best protect public safety and the environment.”
The announcement also drew support from Sen. Barbara Boxer (D) of California.
"I am greatly relieved that the San Onofre nuclear plant will be closed permanently. This nuclear plant had a defective redesign and could no longer operate as intended. Modifications to the San Onofre nuclear plant were unsafe and posed a danger to the eight million people living within 50 miles of the plant," she said in a statement released Friday.
With SONGS not only down, but now out, California still has enough generating capacity to get it through the summer, according to the California Independent System Operator, a group that runs much of the state's electrical grid.
The two SONGS reactors represent a combined generating capacity of about 2,200 megawatts. Over the past year, the state has added generating capacity of about 2,500 megawatts, with another 891 megawatt expected to have come on line between April and June, according to the group.
Still, managing the loads during the summer will remain challenging, the group says, especially if high-voltage lines fail due to a fire or some other event, some localized blackouts could occur. In addition, population growth in the L.A. basin could lead to "marginally more challenging" conditions than last summer in ensuring that Orange and San Diego Counties receive reliable service.