This Post is UPDATED Here As of February 4nd, 2012 – 5:50 P.M. EST
NRC – San Onofre Corrosion Damage Seen In Multiple Nuclear Reactors Across United States
Southern California Edison (SCE), operator of the San Onofre Nuclear Generating Station, continues to plan for the repair of the steam generator tube leak in Unit 3 following a precautionary shutdown Tuesday. Some locals reported seeing a steam cloud rising from the plant after the event as they contacted local news stations worried about potential leaks and odors as the lingering haze lifted up into the sky.
The generators siphon heat from a reactor’s core and convert it into steam, which in turn spins turbines and produces power. The failure occurred despite a recent multi-million dollar project to replace the generators on both reactors. The water leak occurred in the thousands of tubes that carry heated water from the reactor core through the steam generator, a 65-foot-tall, 640-ton piece of equipment that boils water used to drive the unit’s turbines.
The NRC said sensors showed a tiny amount of radioactive gas leaked out of the containment dome before the reactor was shut down late Tuesday. The steam system, which is supposed to be shielded from exposure to radiation, was replaced in December 2010.
The company said it believes at least some of the thousands of thin tubes inside the generator burst, allowing radioactive reactor coolant to mix with nonradioactive water used to make the steam that generates power at the plant.
The facts remain unclear and will stay that way until engineers can cool down the reactor and enter the Unit 3 structure to begin probing each individual tube, they won’t know how extensive the damage is, officials said. The leak in the reactor’s primary radioactive steam system appears to have contaminated the secondary non-radioactive steam system that drives the plant’s turbines.
In addition to the leak, other tubes appear to be damaged, an NRC spokesman said. The development is extra vexing as Edison recently spent millions of dollars replacing both reactors’ steam generators.
A steam generator functions like a car’s radiator, removing heat from a nuclear reactor‘s core and converting it into steam that spins the plant’s turbines, generating electricity. Hot, slightly radioactive water pumps through the tubes day and night. Cool, nonradioactive water is pumped around these tubes, and flashes quickly to steam, which travels out of the plant’s massive concrete containment domes to the electricity-generating turbines.
A leak in one of these thin tubes would allow radioactive water to mix with the nonradioactive water that gets turned into steam.
Alexander said radiation monitors at the plant did detect an increase in the radioactivity of the steam water that pumps through the generator. But he said that the amount of radioactivity is small. “We detected a slight increase in radioactivity, but it’s still within acceptable levels,” Alexander said.
Each steam generator can contain as many as 16,000 tubes, each about 0.75 inch in diameter. The hot, pressurized water flowing through the tubes heats non-radioactive water outside the tubes. The resulting steam is used to turn turbines to make electricity. According to the NRC, the tubes have an important safety role because they represent one of the primary barriers between the radioactive and non-radioactive sides of the plant. If a tube breaks, there is the potential that radioactivity from the system that pumps water through the reactor could escape into the atmosphere. Edison did not respond to a question Wednesday about who will be financially responsible for fixing the break, since the units steam generators are nearly brand new.
The Unit 3 reactor returned to full power in February 2011 after it was refueled and its two aging steam generators were replaced. The plant’s other reactor, Unit 2, had similar work.
The total retrofit cost more than $670 million.
A spokesman for the Nuclear Regulatory Commission said there were also signs of damage to multiple tubes in a second reactor, which is offline for maintenance.
“They found indications of excess wear of 30 percent of the thickness of that metal tube in only a year and a half, which is very unusual, and they are attempting to identify the reason.” said NRC spokesman Victor Dricks.
Alexander was unable to confirm early Thursday that damage had been found in unit 2’s steam generator tubes. He also was working to confirm that alarms were tripped in the auxiliary building near unit 3, indicating a release of a small amount of radioactive gas.
One of the most concerning aspects was that “many” tubes that carry pressurized radioactive water were damaged, according to a spokesman for the Nuclear Regulatory Commission. It’s not clear what caused the pipe to fail, or whether the company was facing an isolated break in a single alloy tube or a manufacturing defect that might be at issue elsewhere in the massive plant tube system.
This might mean there is a now a worry about the possibility that San Onofre has purchased 4 faulty steam generators from Mitsubishi, and the financial costs to replace them might prevent the plant from restarting. Southern California Edison said a manufacturing defect was reported by Mitsubishi before delivery of two generators from Japan — but that the equipment was retested by the manufacturer and plant operator and determined to be fine before installation at the southern reactor.
The potential leak was detected about 4:30 p.m., Southern California Edison said. Operators shut the plant down and isolated the component that contained the leaking tube within four hours of detecting the indications.
NRC Spokesman Dricks said radioactive gas that leaked from that tube in the plant’s steam generator was vented into the auxiliary building. The radiation was detected by monitors in that building, which is separate from the sealed structure that houses the reactor.
This lack of information is not a new phenomenon for SCE. The company has not always been transparent about discussing the problems at their plants, according to Daniel Hirsch, who lectures on nuclear policy at the University of California, Santa Cruz.
Hirsch said he was concerned that the problem occurred with recently installed equipment. “Edison has historically not been candid about the problems at San Onofre. That lack of transparency causes tremendous distrust and increases risk.”
“It makes one wonder about the quality assurance for the replacement equipment,” he added. “This is not due to old equipment breaking but new equipment that wasn’t up to snuff in the first place.”
An alarm alerted station personnel to the presence of radioactivity in the ancillary structure, and they immediately began shutting down the reactor, according to Nuclear Regulatory Commission spokesman Victor Dricks. Dricks said that sensitive alarms were tripped in an auxiliary building near San Onofre’s unit 3 reactor after the leak was detected about 5:30 p.m. Tuesday, indicating that at least some radioactive gas escaped unit 3’s containment dome.
A Plant spokesmen said Wednesday that radioactive water was passing through a crack inside the generator at a rate of 80 to 100 gallons per day when Edison began shutdown procedures. He said engineers spent Wednesday drawing up plans on how they would pinpoint the leak while they waited for the reactor to cool enough to enter the Unit 3 containment dome.
The commission has cited the plant for a series of safety violations over the past four years, and many of those lapses were blamed on human error. “The feeling is that they’re not making the kind of improvement that we want to see. so we want to take a deeper look at what could be contributing to that,” commission spokesman Victor Dricks – November 2009
Public frustrated by downplay over details approach
Victor Dricks, a spokesman for the NRC, said a small release could have occurred because the leaking component at San Onofre’s Unit 3 reactor vents into a building outside the reactor’s towering containment dome. That building is not sealed or pressurized, he said. “We know that it vented some radioactive gases into the auxiliary building because that’s what triggered the radiation alarm that told them they had a leak,” Dricks said.
This was in contrast to the original statement from Edison on Wednesday saying, “There has been no release to the atmostphere”. When asked, Southern California Edison spokesman Gil Alexander did not directly address why the plant used the language it did. He emphasized the relatively minor nature of the incident.
“I can’t speak for the NRC but we would agree that there might have been an insignificant or extremely small release,” Alexander said. He said the amount might not be detectable by monitors. Neither the NRC nor Edison were able to supply the amount of radiation detected in the auxiliary building. The NRC is continuing to investigate Edison’s response to the incident.
Contract Worker Work Incident
New findings also emerged about an unrelated accident on Friday, when a contract worker slipped into a pool above the unit 2 reactor, now offline for maintenance, while trying to retrieve a flashlight. The man, whose name Edison declined to release, was not injured from the fall, but might have ingested the mildly radioactive water, Alexander said. No internal contamination was found.
U.S. Rep. Ken Calvert, whose district includes the San Onofre plant, said his office was notified about the leak about three hours after the precautionary shutdown. The first word came from federal regulators through email, followed by the company five minutes later. The plant’s Unit 2 reactor has been offline since mid-January for maintenance, and Unit 1 was decommissioned in 1992. Thus, the plant is currently not contributing any power generation to the grid.
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This was not the first time a leak-scare has occurred at the San Onofre plant. In November 2011, a level 1 alert was issued at the plants but the appropriate alarms did not go off. San Onofre just finished replacing both steam generators attached to Unit 2 and 3. Many other plants of similar design have conducted similar upgrades, but none, according to the NRC, has had a rupture after being installed. The leak is not Edison’s first problem with the new steam generators. In September 2009, Edison met with NRC officials to discuss weld defects that were detected in both of the 640-ton crucibles. The utility notified the NRC in August 2009 that the replacement generators for Unit 3 had developed cracks in a weld that connects a 5-inch-thick steel plate that supports each generator’s innards. Inspections found that use of a special metal-gouging tool caused the welds to become brittle and crack. Mitsubishi Heavy Industry, the company that built the generators for Edison, fixed the cracked welds, and they passed NRC inspection.
|Power Reactor||Event Number: 47628|
|Facility: SAN ONOFRE Region: 4 State: CA Unit: [ ] [ ]  RX Type:  W-3-LP, CE, CE NRC Notified By: DOUG FOOTE HQ OPS Officer: JOHN KNOKE||Notification Date: 01/31/2012 Notification Time: 22:58 [ET] Event Date: 01/31/2012 Event Time: 17:30 [PST] Last Update Date: 01/31/2012|
|Emergency Class: NON EMERGENCY 10 CFR Section: 50.72(b)(2)(iv)(B) – RPS ACTUATION – CRITICAL||Person (Organization): JEFF CLARK (R4DO) SCOTT MORRIS (IRD) LOUISE LUND (NRR)|
|Unit||SCRAM Code||RX CRIT||Initial PWR||Initial RX Mode||Current PWR||Current RX Mode|
|3||M/R||Y||100||Power Operation||0||Hot Standby|
|MANUAL TRIP DUE TO A PRIMARY TO SECONDARY LEAK GREATER THAN 30 GAL/HR”At 1505 PST, Unit 3 entered Abnormal Operation Instruction S023-13-14 ‘Reactor Coolant Leak’ for a steam generator leak exceeding 5 gallons per day.”At 1549 PST, the leak rate was determined to be 82 gallons per day. At 1610 PST, a leak rate greater than 75 gallons per day with an increasing rate of leakage exceeding 30 gallons per hour was established and entry into S023-13-28 ‘Rapid Power Reduction’ was performed.”At 1630 PST, commenced rapid power reduction per S023-13-28 ‘Rapid Power Reduction’. At 1731 PST, with reactor power at 35% the Unit was manually tripped. At 1738 PST, Unit 3 entered Emergency Operation Instruction S023-12-4 ‘Steam Generator Tube Rupture’.”At 1800 PST the affected steam generator was isolated.”All control rods fully inserted on the trip. Decay heat is being removed thru the main steam bypass valves into the main condenser. Main feedwater is maintaining steam generator level. No relief valves lifted during the manual trip. The plant is in normal shutdown electrical lineup.Unit 2 is presently in a refueling outage and was not affected by this event.The licensee has notified the NRC Resident Inspector. The licensee has issued a press release.|
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- Radioactive release possible at California nuke plant: “We can’t make a black and white statement that absolutely none escaped” – Workers unable to enter to check if leaking (enenews.com)
- LA Times: Small leak at San Onofre nuclear power plant investigated (ex-skf.blogspot.com)
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- *Just In* AP: Many tubes found damaged at San Diego-area nuke plant – “Unusual” says NRC – Cause unknown – Radiation could have escaped… Developing (enenews.com)
- Nuclear News Update – February 2nd, 2011 (enformable.com)