Concerns about safety and the durability of components at San Onofre Nuclear Generating Station are continuing to surface as the plant approaches a full week of complete shutdown. The plant’s Unit 3 reactor was taken out of commission after a radioactive water leak was discovered on January 31, while Unit 2 was already down for scheduled maintenance. The Unit 1 reactor was taken offline permanently in 1992.

In the immediate aftermath of the detection of a leak in the piping of a recently installed steam generator, officials downplayed any potential threat, noting that the amount of radiation leaked was so small that Nuclear Regulatory Commission rules did not call for a mandatory shutdown. Later it was disclosed that radioactive gas from the leak had been vented to an auxiliary building that did not have the same safety seals to prevent radiation from being released into the atmosphere as are found on the reactor.

Once the Unit 2 reactor was shut down, it was discovered that hundreds of tubes on the generator, replaced in 2009 as part of a $670 million-plus overhaul using components supplied by Japan-based Mitsubishi Heavy Industries, had suffered significant deterioration over their relatively short service lives. Aside from the one tube known to have failed at Unit 3, two tubes at Unit 2 were found to have more than a third of their thickness worn away, requiring them to be plugged and incrementally increasing the burden on the remainder of the 9,700 tubes in the system. While only these two were worn to the point of needing to be taken offline as a safety precaution, 69 other tubes showed deterioration of at least 20 percent, and more than 800 had thinned by 10 percent or more.

“I’ve never heard of anything like that over so short a period of time,” retired Nuclear Regulatory Commission engineer and researcher Joram Hopenfeld told the Associated Press about the level of damage discovered.

Edison spokesman Gil Alexander disagreed, countering that “It’s not unprecedented in the industry for there to be accelerated wear in small sections of tubes in early years of usage.”

The new generators were installed because the originals, designed to last the full life of the reactors they cooled, were failing after only 20 years. Majority plant owner Southern California Edison successfully argued at that time that replacing the steam generators would be cheaper than monitoring and inspecting the old ones for damage. Utility customers bore the full cost of replacement through increased rates.

The California Public Utilities Commission, in granting Edison the right to charge ratepayers for the original retrofit, capped costs associated with the project at $782 million. The Public Utilities Commission’s decision means that further costs, including repairs to the new system, should be charged against the profits of shareholders in the company, rather than once again billed to utility customers.

Watchdog group Alliance for Nuclear Responsibility intervened in the 2004/2005 hearings that granted the money for the generator replacement and is calling on the utility to allay fears that customers will be forced to pay for premature failure of the new systems they’d been billed hundreds of millions to install.

“[Edison] should make it clear that the vendor pays or its shareholders pay. The ratepayers did not pay for defective parts, materials, or maintenance,” asserts Alliance director Rochelle Becker.

Beyond the late January leak, an ammonia leak in November 2011 led to an emergency being declared that required a partial evacuation of the facility. And the week prior to the Unit 3 shutdown, it was reported that an employee fell into a reactor pool where highly radioactive fuel rods are stored and whose water regularly cycles through the reactor’s core. The pool had been cleared of fuel, however, and the employee returned to work the same day, allegedly receiving a dose of radiation only slightly higher than that experienced during a chest x-ray.

The Unit 2 reactor had cooled to the point last night that it was safe for crews to enter and begin assessing damage, the U-T San Diego reports. The paper states that “a small portion of the nearly 20,000 tubes within two generators at the northern reactor” are of concern to Edison, per Alexander. According to the Nuclear Regulatory Commission’s finding that a minimum 871 of 19,400 tubes have thinned by 10 percent or more, a total of 4.5 percent of the tubes have been compromised to some extent, almost one in twenty.

Meanwhile, the Public Utilities Commission last week denied a request by Pacific Gas & Electric to bill customers $85 million for its attempt to extend the license of Diablo Canyon, California’s other active nuclear plant. Rulings concerning the central coast facility are closely watched in Southern California, as San Onofre faces a parallel road on its quest to extend the plant’s operating license for 20 years beyond its current expiration in 2022.