At the time, it was just a minor release of radioactive gas at San Onofre Nuclear Generating Station, prompting the power-down of one reactor.

That was Jan. 31, 2012. No one understood at the time that the reactor would never power up again.

Almost exactly eight years after that fateful day, the tear-down of San Onofre Units 2 and 3 will finally, formally begin. Operator Southern California Edison mailed notices to 12,000 residents in a 5-mile radius of the plant on Wednesday, Jan. 22, saying it expects to launch “deconstruction” work about Feb. 22. Those notices should be arriving in South County mailboxes shortly.

One of the first orders of business will be to upgrade the rail spur at the north end of the site. Rather than trucking debris out, Edison will move as much as possible by rail to minimize traffic disruptions, spokesman John Dobken said.

Office trailers will be set up in parking lot areas, and the permanent office buildings will be torn down.

Twin domes will stay awhile

Work also will begin on the twin domes themselves, though they won’t disappear for quite some time. Edison must create access so workers eventually can dismantle the reactors and other structures inside the containment domes, which will involve removing asbestos-containing materials.

These tasks are expected to be complete by the end of this year, and site-wide preparation work should be finished by early 2022.

“I’m happy to see progress being made because, in part, removal of the facility is one of the big expectations of the community, alongside safe stewardship of the fuel and active efforts to move the fuel out of here,” said David Victor, an international law professor at UC San Diego and chairman of San Onofre’s volunteer Community Engagement Panel.

The tear-down is expected to last through 2028 and remove above-grade structures on land, as well as much of the offshore conduits, those giant pipes that sucked in ocean water to cool the plant and spit it back out again, quite a bit warmer. Offshore buoys and anchors will be removed as well.

“We’re going to be a good neighbor throughout the decommissioning process, and that means providingtimely, usable information to the community and to the people who use the recreational resources next doorto us,” said Doug Bauder, Edison vice president and chief nuclear officer for San Onofre, in a prepared statement. “We will be providing quarterly updates going forward, so folks are aware of the work that is happening on site.”

Residents can reach Edison’s “deconstruction liaison” with questions or comments at nuccomm@songs.sce.com, or by calling 800-332-3612. Plans and progress will be posted at SONGScommunity.com.

Fuel pools, too

In October, impassioned activists beseeched officials to spare San Onofre’s spent fuel pools from destruction, raising the specter of an “apocalyptic nightmare” — crippled canisters stuffed with dangerous radioactive waste, stranded on an abandoned beach because the pools that could have helped repair or repackage them no longer exist.

Edison countered that such pools are, indeed, available for emergencies as spent fuel is moved from wet to dry storage, where experts say it’s safer. That’s when canister damage can occur — as evidenced by the near-drop of a canister in an underground bunker in 2018 — but once all the canisters are inside the “concrete monolith,” the pools will be unnecessary.

All spent fuel is expected to be in dry storage this year.

In October, Edison unveiled a video showing a cutting-edge technology to repair damaged nuclear waste canisters while they’re still in vaults. In the video, robots crawl into crevices and seal cracks by applying new layers of metal over damaged areas — a revelation meant to refute critics who say the canisters are not retrievable or repairable, and to underscore the company’s assertion that fuel pools are unnecessary and outmoded technology.

“Rather than removing the fuel from the canister and repackaging it, you repair the canister itself,” said Tom Palmisano, recently retired from Edison but pressed back into service to explain the system last fall. “If you can repair from the outside, that’s preferable. You don’t want to open them up and take the fuel out.”

Cost of tear-down: $4.4 billion

The decommissioning budget for work over the next eight to 10 years is roughly $1.9 billion, Dobken said. All told, the tear-down is slated to cost $4.4 billion. That money has already been set aside in a decommissioning fund, which customers paid into while the plant was generating electricity.

The problem began with a faulty redesign of San Onofre’s steam generators, which cost $671 million and were supposed to give the plant new life. The new generators were installed by 2011, and premature wear of the heat transfer tubes inside them was discovered in 2012 after that small radiation leak.

Blame was placed on Mitsubishi, the manufacturer, for “faulty computer modeling” during the design of the steam generators. Those modeling flaws caused excessive vibrations among thousands of tubes in each of the steam generators. The vibrations then caused unexpected wear in some of the tubes.

The iconic twin domes have been a fixture off Interstate 5 south of San Clemente for 40 years. Eventually, the site will be returned to the Navy in close-to-original condition, but the dry storage systems for nuclear waste may remain for decades.