Work continues on San Onofre Nuclear Generating Station

Two giant holes will be cut into the side of the landmark domes at the San Onofre Nuclear Generating Station beginning next fall as engineers install a pair of 65-foot long, 22-foot wide steam generator, it was reported Sunday.

The twin nuclear reactors will be shut down, and holes cut in the domed containment structures, to swap out massive generators, the North County Times reported Sunday.

In an e-mail to the Del Mar Times, a spokesman for Southern California Edison - San Onofre’s operators and majority owner - wrote that “although preparations have been underway for years, the actual steam generator replacement construction project ... does not begin until this fall.

Gil Alexander also said that the work on the two domes will not be done simultaneously.

“This fall we will remove and replace the two steam generators in Unit 2 (the northern most dome),” he wrote. “We will then work on the Unit 3 replacement during the fall of 2010.”

Southern California Edison, San Onofre’s operators and majority owner, commissioned the generators - and two more just like them that have not yet arrived - in 2005 at a cost of $680 million, the North County Times reported.

The massive steel structures will eventually transfer extreme heat from water that circulates in the nuclear pile. That superheated water is forced through millions of tiny pipes, where heat is moved from that water to a separate body of water carried by a second set of tiny pipes.

The paper reported that the existing generators have become brittle over the three decades that they have been in service, and that the new generators have been fabricated out of a more-robust type of steel alloy.

The generators contain thousands of thin metal tubes and function like a car’s radiator. According to previous Edison statements, the plants existing steam generators must be replaced because their internal tubes are cracking, and the new generators are made of a tougher alloy that is more resistant to the extreme heat generated by San Onofre’s controlled nuclear fission.

They were built by Mitsubishi Heavy Industries in Kobe, Japan were carried across the Pacific Ocean by the heavy-lift ship Happy Ranger, and arrived at a dock in Long Beach Harbor in late December, the North County Times said.

From there they were loaded onto a barge for the trip south to the Del Mar Boat Basin at Camp Pendleton, and they were transferred ashore during a 7-foot high tide Saturday morning.

The generators will apparently be hauled up the beach through Camp Pendleton this winter, although details are confidential.

Slicing into the concrete containment vessels is no small matter, Edison engineers have said. The cement structures are reinforced and held together by massive steel cables that are held under tension.

Each of the two domes contains a latticework of tensioned steel cables called tendons, which give the domes extra rigidity. San Onofre was built with extra tendons in order to make it more resistant to earthquakes. Ross Ridenoure, the company’s chief nuclear officer, said.

And it will be necessary to “de-tension’’ and remove about 100 of the tendons in order to cut an access hole into the concrete reactor domes, a move that worries some anti-nuclear activist groups who fear something could go wrong as those cables are cut and the tension is released.

Edison is confidant it can pull the job off with no ill effects.

“This is the biggest project we’ve undertaken since construction took place in the 1970s and early 1980s,’' Ridenoure told the North County Times. The replaced components will extend the plant’s life by decades.

According to a draft environmental impact report filed with the California Public Utilities Commission in 2005, the operation will be somewhat unique.

“De-tensioning tendons of the type at (San Onofre) has never been attempted at another operating nuclear plant,’' the report states. “Most of the tendons are not designed to be de-tensioned or removed.’'

Since the report was written, the North County Times reported, generators have been replaced at the Diablo Canyon plant in Central California. The containment domes are designed to keep radioactivity contained should an accident occur as radioactive uranium heats water to generate electricity - about 20 percent of the electricity used by the 15 million people served by Southern California Edison.

“This operation has been performed at, I believe at 28 other plants across the country,’' Ridenoure told the North County Times. “We are confident that it will go smoothly.’'