San Onofre Nuclear Generating Station Shutdown: "Just the Facts, Ma'am"

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Researched by Industrial Info Resources (Sugar Land, Texas)--At this point, anyone with only a passing interest in the U.S. Power Industry and energy trading markets knows that the 2,200-megawatt (MW) San Onofre Nuclear Generating Station (SONGS) in the northwest corner of San Diego County, California, is down for an unspecified period of time for unplanned inspections and repairs. For those not in the know, on January 31, a leak in one of Unit 3's steam generator tubes allowed a small amount of radioactive water to escape, and the unit was shut down.

The other operating unit, Unit 2, had been brought offline for a planned refueling and maintenance outage only a few weeks before. (The original Unit 1 was decommissioned in 1992.) Inspections of Unit 2 showed unexpected wear on a small number of the 9,727 steam generator tubes in the base of the generator. All of the tube wear in Unit 2 seems to have been caused by tubes rubbing against retainer bars in the plant. Unit 2 required pressure-testing for one steam generator tube; six tubes required plugging; and as a precautionary measure, 186 additional tubes were plugged, which primary plant owner Southern California Edison Company (SCE) (Rosemead, California) said was an amount "well within the extra tube allowance for each steam generator to account for wear and other routine operational developments."

In February, NRC spokesman Victor Dricks told the San Diego Union-Tribune that up to 7% of the generator tubes could be taken out of service without appreciably affecting performance. "We are a long, long, long way away from there," said Dricks . While the wear was unexpectedly premature on the Unit 2 generator, which was replaced in January 2010, the unit might possibly have returned online had the leak in Unit 3 not occurred on January 31, forcing the plant's second reactor offline.

After detecting the steam generator leak in Unit 3, operators performed a rapid shutdown of the unit. Subsequent inspections showed that like Unit 2, premature wear had occurred on the steam generator tubes from rubbing against the retainer bars. In addition, wear was also seen to be occurring by the tubes rubbing against each other, which apparently was not happening in Unit 2. In-situ pressure testing was performed on 129 steam generator tubes in Unit 3 that showed excessive wear. Of these, eight tubes failed these pressure tests. The generator, manufactured by Mitsubishi Heavy Industries (Tokyo, Japan) is even newer than the Unit 2 generator, having been replaced in January 2011.

So what does all of this mean, and what can Southern California's power sector expect in the future? The answer remains uncertain, although much speculation about rolling blackouts and power conservation measures has made its way into the mainstream media.

In a "Confirmatory Action Letter" from the NRC to Southern California Edison, the agency made clear that until the problems with Unit 3 are understood and resolved, neither unit will be restarted. Outlining SCE's necessary course of action, the NRC states: "Southern California Edison Company (SCE) will determine the causes of the tube-to-tube interactions that resulted in steam generator tube wear in Unit 3, and will implement actions to prevent loss of integrity due to these causes in the Unit 2 steam generator tubes. SCE will establish a protocol of inspections and/or operational limits for Unit 2, including plans for a mid-cycle shutdown for further inspections." In other words, SCE will figure out what's happening in Unit 3 to cause the tube-on-tube vibration and wear and take preventative measure for this in Unit 2."

On Unit 3, SCE will have to plug all tubes showing excessive wear and perform preventative plugging for at-risk tubes, as well as taking measures to prevent the progression of the tube wear.

"The media seems to be largely viewing the situation in an all-or-nothing way--as if either both reactors will be running at full capacity or both will be completely offline, but this isn't necessarily the case," said Greg Elliott, Industrial Info's outages products manager. "Both units being offline over the summer is certainly a possibility, but not a definite event. The fact that the NRC mentions 'operational limits' suggests that running the units at partial capacity could provide enough of a solution to prevent the vibration and wear and bring some power online from the plant. Of course, this may not be the case at all."

Officials at the plant have told Industrial Info that they expect Unit 2 to return online in mid-May, followed by Unit 3 in mid-June. Under the circumstances, these dates may still change, but for now this remains their best estimate. SCE remains at the mercy of the NRC, as the company must submit to the NRC its findings and details about the preventative measures taken, and then wait for approval from the agency before starting the reactors. The situation has become quite high-profile, and the NRC will obviously act very cautiously in approving the restart of the reactors.

"California ISO (California Independent System Operator Corporation, the state's grid operator) is making contingency plans if the units fail to return online in the summer. This is a sensible approach. They obviously can't just sit around and not make any plans," said Elliott. "However, making a contingency plan doesn't mean that the plan will be necessary." California ISO's contingency plans include possibly putting gas-fired units that are slated for retirement back into service, the possible fast-tracking of power transmission projects in the area, and conservation campaigns.

"What I find interesting is the request for a 'mid-cycle shutdown' for each of the units," said Elliott. "It will be interesting to see how the scheduling for these inspection outages plays out. In addition, natural gas prices in the area will probably be pushed up. The real issue is why the $670 million generator replacement is already having issues." At this point, the status of the plant remains up in the air, although the restart of the less-damaged Unit 2 by the time severe summer weather hits seems a possibility. Industrial Info's power outages team is consistently tracking the outage situation and will make any further details known as they are confirmed.

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Industrial Info Resources (IIR), with global headquarters in Sugar Land, Texas, and eight offices outside of North America, is the leading provider of global market intelligence specializing in the industrial process, heavy manufacturing and energy markets. Industrial Info's quality-assurance philosophy, the Living Forward Reporting Principle™, provides up-to-the-minute intelligence on what's happening now, while constantly keeping track of future opportunities.