Diablo Canyon unit closing for 35 days of refueling, repairs

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Nuclear plant cutting back as spring energy demand rises

Diablo Canyon unit closing for 35 days of refueling, repairs

Christian Berthelsen, Chronicle Staff Writer Tuesday, April 24, 2001


California will be entering a phase of extremely tight energy supply beginning Sunday, when a major power-producing unit of PG&E's Diablo Canyon nuclear plant goes out of service for more than a month of refueling and repairs.

The resulting loss of 1,100 megawatts -- about 3 percent of the state's power demands at the moment -- will leave very little breathing room between electricity generation and consumption for about two weeks, until about mid- May, according to the California Independent System Operator, the agency that operates California's electricity grid.

"The next two weeks are going to be very tight, because we do have anywhere from 10,000 to 13,000 megawatts offline," said ISO spokeswoman, Stephanie McCorkle. A megawatt is enough power to supply 1,000 homes simultaneously.

She declined to comment yesterday on whether the agency anticipates another round of blackouts or extreme shortage warnings, which often lead to astronomical energy prices.

The Diablo Canyon repair work had been planned five years in advance with the federal Nuclear Regulatory Commission and scheduled with the ISO for one year.

But the shutdown comes at a time when up to 13,000 megawatts of generation is unavailable this spring because of both scheduled and unplanned outages. Moreover, there is a growing debate over how much control state agencies should have over power plants going offline. At the moment, the ISO has authority only over transmission outages and so-called "required-must-run" units, but not all generation units.

Shortage warnings have gone away for the moment, as available electricity supply has been running roughly 4,000 megawatts ahead of demand. But in the coming weeks, electricity usage is expected to spike as summer returns to California and residents begin turning on their air conditioners.

An increase in average heat by 10 degrees translates into about 2,000 more megawatts of demand, McCorkle said, which would further narrow the spread between supply and demand. While the difference will at least partly be made up with electricity imports from the northwest and southwest and increased power from hydro units because of increased spring water flow, the loss will still be significant.

The Diablo unit is scheduled to be out of commission for 35 days. But the loss is expected to be less serious after the first two weeks of May, as other units that have been down for repairs come back on line.

Unplanned outages, which usually occur when a company is forced to take a unit offline to repair an unexpected malfunction, are running high above historical norms and are more than double what was anticipated for summer months by the grid operators.

Two bills are in the works in the legislature to give state regulators greater authority to require power plants to run if outages are determined to be a way of withholding electricity needlessly.

PG&E said the work on the Diablo Canyon's second unit was originally scheduled to begin May 6 but had been moved up a week to take advantage of as much low-demand period as possible. Jeff Lewis, a spokesman for the utility, said the work is necessary to replace about a third of the fuel rods that no longer produce sufficient heat to generate the same amount of electricity. Delaying the work would only result in decreased electricity supply in the deep demand period of summer, he said.

E-mail Christian Berthelsen at cberthelsen@sfchronicle.com.


-- Martin Thompson (mthom1927@aol.com), April 24, 2001


Power plants require preventive maintenance and repair, so "planned" outages have to come sometime, to hopefully reduce non-Y2K overstress related breakdown unplanned outages, at the worst possible times. The best time for these planned outages is when grid load is lowest, which is when air conditioning and heat demand is lowest, in spring and fall.

However, it is unfortunate that these planned outages have been moved forward too close to the summer high demand period. The low demand period is already almost over. The ISO projected grid load chart for today, April 24, has a "summer" shape, for the first time, with peak demand projected for midafternoon. The typical "winter" shape shows demand peaking in the 5pm - 8pm time frame.

Also, why have there been so many unplanned outages? Very likely, some are directly Y2K related. Others are due to overstress and overwork, due to the Y2K caused outages. These are thus indirectly Y2K caused "cascading effect" outages. When will the dominoes stop falling?

-- Robert Riggs (rxr.999@worldnet.att.net), April 24, 2001.

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