Workers will begin cutting into the unit 3 reactor dome at the San Onofre nuclear plant this month to replace a pair of 640-ton steam generators, the final act in a gargantuan drama spanning a decade.
The $671 million project, including replacement of a second pair of giant generators in the plant’s unit 2 reactor last year, requires ships, cranes, tents, transport vehicles and scaffolds on a scale that makes people look like busy insects.
The replacements will allow San Onofre to continue operating at least until the end of its license, in 2022, and perhaps beyond if the license is one day extended.
While the cost, paid for by Southern California Edison ratepayers, sounds as enormous as the project itself, failing to replace the generators would cost even more, said Joe Sheppard, the nuclear plant’s new chief nuclear officer.
Replacing San Onofre itself, which provides about 20 percent of the Southern California region’s electricity, with new power sources would cost some $1 billion over 12 years, he said.
“You spend $670 million, and you get a billion back,” Sheppard said as he showed the giant steam generators to visitors during a tour on Wednesday.
Until they are ready to be moved, slowly and laboriously, to their new home, the 65-foot-long generators, bearing a slight resemblance to old-time science-fiction rocket ships, are being housed in a tent big enough for a circus on the grounds of the nuclear plant.
The replacement phase begins with the shutdown of unit 3 within the next week. Edison is also using the reactor’s downtime for routine maintenance, such as replacing spent fuel rods.
Once the reactor is safely powered down, the workers – among some 1,000 temporary employees, Sheppard said, in a project that will infuse $300 million into the local economy – begin cutting a hole 28 feet across into the side of the reactor’s containment dome.
Instead of using jackhammer-type tools to cut into the concrete shell, as they did with unit 2, they will use extremely high-pressure water. The pressure is so high, 25,000 pounds per square inch, that it is almost literally ear-splitting; workers in the area will need double ear protection while the pressure pumps are operating.
Once the concrete is washed away, workers will use cutting torches to cut through metal support bars and the steel inner lining of the reactor.
Then, in November, the old generators will be removed and the new ones will be moved slowly into the opening and hoisted into place using massive cranes.
The hole should be plugged and the work finished by early next year. Edison planned the changeout for the winter months intentionally, to avoid having one of its reactors shut down during the summer months of peak power demand.
When moving giant pieces of machinery, Sheppard said, slower is better.
“There is nothing more important to me, and nothing more important to this staff, than to do it safely,” he said. “We’re not going to let anything get in the way — not the schedule, not the cost. Safety is going to trump everything.”
The task the generators perform is fairly simple. Water heated by reactors is piped into the bottom half of the generators through thousands of tubes. The heat is transferred to water circulating through tubes in the tops of the generators, which are never exposed to nuclear radiation.
That water turns to steam, used to power the turbines that generate electricity.
The old generators will be dismembered for disposal. The top, non-radioactive portions will simply become scrap metal. The bottom parts, somewhat radioactive, will be taken to a low-level radioactive-waste storage facility in Utah.
“This project, start to finish, is going to take a decade,” said Mike Wharton, head of the steam generator replacement project. “The last piece is taking the waste material offsite. It took six years to get these generators here. The last few months are just ahead of us.”
Both pairs of generators, built by Mitsubishi in Kobe, Japan, were shipped across the ocean to the Port of Los Angeles, loaded onto a barge, unloaded at a boat dock on the Camp Pendleton Marine base, carried across the beach on a tracked vehicle, and carried up a short stretch of Interstate 5 on a 256-wheeled vehicle called a Goldhofer.
San Onofre is one of 58 nuclear plants around the country that use the same type of steam generators; it is one of 52 of those that has had them replaced.
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