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Nuclear Power Struggle

San Onofre's big promises and big failure


(page 4 of 5)

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San Onofre’s upgrade went smoother, even if not perfectly. Flaws were found in two generators before they left Japan, where they were manufactured by Mitsubishi Heavy Industries. Inspectors discovered a 5-inch-long crack in one. Both had welding defects. But the generators were fixed before making the long trip across the Pacific.

Once installed, the gigantic new generators, which weigh 640 tons apiece, began their essential function: Helping the plant produce electricity.

Here’s how it works. After nuclear fission heats water in the plant’s reactor core, that super-hot, radioactive water leaves the reactor and passes through thousands of thin tubes in the steam generators, before eventually returning to the reactor. It’s a closed cycle. Radioactive water doesn’t get out.

As the water passes through, those thin metal tubes conduct heat, warming water inside the generator. That turns into steam, which turns turbines that make electricity.

The tubes are purposely thin, so they transfer heat efficiently. But they’re not supposed to break or leak. If they fray and radioactive water leaks into the rest of the steam generator, it can escape into the environment.

That’s what happened when the high-radiation alarm sounded at San Onofre on January 31. One of the thin metal tubes sprung a leak.

The generators hadn’t been operating a full year. But tests showed those thin tubes were prematurely wearing out. Since the January shutdown, Edison has closed more than 1,300 of the almost 39,000 steam tubes in San Onofre’s generators.

While Edison said one of San Onofre’s reactors could start again in late August, no timeline has been announced for the other. First, the problems will have to be fixed to assure federal regulators and the public that the tubes won’t continue wearing out early.

Even if the plant is able to run again, Edison may reduce its output to prevent the tubes from deteriorating further. But producing less power could complicate the plant’s economics. Other nuclear plants confronted with the same problem have opted to replace their generators or close altogether. In June, Edison CEO Ted Craver allowed for the possibility that San Onofre would need new generators. He told the Los Angeles Times the decision to restart the plant would be one of the toughest calls of his career.

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