A radioactive leak and unprecedented levels of wear on two new steam generator units at the San Onofre Nuclear Generating Station may pose significant health risks and reliability problems, according to nuclear energy experts. The thinning of hundreds of tube walls in one of the new units revealed last week is \u201cextraordinary,\u201d said Arnie Gunderson, chief engineer for consulting firm Fairewinds. The amount of degradation found at San Onofre has not been seen in steam generators younger than 25 years, added Michael Marriotte, Nuclear Information & Resource Service executive director. San Onofre\u2019s unit 2 is shut down for refueling and maintenance. The walls of hundreds of U shaped tubes in the unit thinned by around 20 percent. A leak was found in unit 3\u2019s new steam generator unit as well (Current, Feb. 3, 2012). Gunderson said the leak and tube degradations are \u201csafety and reliability problems.\u201d A leak could cause a \u201ccascading affect,\u201d releasing radioactivity into non-radioactive sections of the unit, he said. The wear of 69 tubes in unit 2 was \u201cin excess of 20 percent and 800 others had more than 10 percent wall thinning but less than 30 percent,\u201d Victor Dricks, Nuclear Regulatory Commission spokesperson, said. \u201cIt\u2019s important to note that it is not unprecedented to find very small areas of accelerated wear during the first couple of years of a steam generator\u2019s life,\u201d Southern California Edison, the primary owner and operator of the nuclear plant, stated. The steam generator units were replaced with an eye toward extending the life of the plants. Edison announced it intended to relicense the plants so they could operate for another two decades after their existing operational licenses expire in the next decade. It put its plans on hold after the Japanese nuclear reactor meltdown. When a leak is found, the offending tube is plugged, taking it out of service. That impacts reliability because the tubes are used to release heat from the plant, and the fewer tubes means less heat expulsion. To keep the unit from overheating, plant output may be ratcheted down. The entire 2,200 MW San Onofre plant has been shut down since last week, producing no power. The original San Onofre units\u2019 steam generators went on line in 1981 and 1982. They were replaced less than two years ago at a cost of $670 million to Southern California ratepayers. In addition to Edison, San Diego Gas & Electric holds a 20 percent interest in the plant. Riverside holds a 2 percent interest. David Lochbaum, Union of Concerned Scientists Nuclear Safety Project director, considered the degree of degradation in the new San Onofre units unusual. He attempted to review nuclear plant start-up reports filed with the Nuclear Regulatory Commission that reveal tube degradation to compare wear rates but the federal agency\u2019s website was down part of this week. Gil Alexander, utility spokesperson, did not address the degree of degradation, stating that testing is in the preliminary stages and the wear characteristics are \u201cnot yet verified.\u201d There are 19,400 tubes, the utility stated. The nuclear industry has reported more wear than in the past in steam unit tube walls that are five to 10 years old, according to Jim Benson, Electric Power Research Institute program manager for the steam generator management program. It may be due to testing methods that are more sensitive than they were 20 years ago, he said. Benson was unable to comment on the tube degradation at San Onfore, but added the trend has seen more tube wear across the nuclear industry. Reports show a range in the numbers of thinning tubes and the degree of wear, according to Benson, though all are at \u201crelatively shallow depths\u201d of less than 20 percent, which he said are not \u201cof any concern.\u201d Edison stated the radioactive readings from the leak at unit 3 \u201cwere still far below the limits that have been established by the Nuclear Regulatory Commission.\u201d Edison is \u201cdownplaying\u201d the problem, according to Marriotte. It is not the utility\u2019s fault if they \u201cbought a lemon,\u201d he added. \u201cIt is their fault for not being open and transparent about the ramifications of the leak.\u201d Edison at first denied any radiation leaked out. In addition to the recent problems with the new steam generator units, an Edison employee fell into one of the pools at San Onofre (see sidebar). U.S. Sen. Barbara Boxer (D-CA) Feb. 8 called on the NRC to investigate and report on its efforts to address the leak, the degradation of tubes, and provide details on the on-site worker accident. The mid-week letter also calls on the agency to detail by Feb. 15 steps needed to resolve unaddressed problems accompanied with a timeline for action. Calls to state ratepayer advocates concerning the $670 million expenditure being paid for by ratepayers were not returned. The cause of the wear of the tubes manufactured by Mitsubishi is unknown. Possible causes range from flawed metallurgy to operating conditions and water chemistry issues. The NRC said an investigation is ongoing. When a leak is discovered at a nuclear plant steam generator, it is shut down for weeks to give the high temperatures time to fall and allow an inspection. After the temperature drops, workers are allowed into the unit to inspect it--but generally for only brief periods of time.