Xcel Energy still making big investments in nuclear power

  • Article by: DAVID SHAFFER , Star Tribune
  • Updated: June 16, 2013 - 2:08 PM

Three U.S. utilities are closing older nuclear reactors, but Xcel Energy is investing $1.8 billion to keep its two Minnesota plants operating for another two decades.

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Terry Pickens, Xcel Energy's director of nuclear regulatory policy, stood in front of two steam generators that will be installed at the Prairie Island nuclear plant in Red Wing, Minn.

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As some U.S. utilities are abandoning old nuclear power plants, Xcel Energy says it’s investing $1.8 billion to extend the life of its 40-year-old Minnesota reactors.

At the company’s Prairie Island nuclear plant in Red Wing, Minn., 1,550 contract workers this fall will replace two massive steam generators — at $280 million, its single most costly improvement project. The plant was completed in 1974 at a cost of $350 million.

The Minneapolis-based utility’s other reactor, in Monticello, Minn., also is getting a $600 million upgrade that aims to keep it running safely and boost its output by nearly 13 percent.

“What we are facing here is a lot of spending to extend life another 20 years,” Laura McCarten, Xcel’s regional vice president, said last Thursday as she invited community members to see the new seven-story-tall steam generators to be installed at Prairie Island Unit 2.

Xcel’s investments come at a time when some utilities are retreating from nuclear power.

Just 10 days ago, Southern California Edison said it would permanently retire both reactors at its San Onofre Nuclear Generating Station between Los Angeles and San Diego. The decision came three years after spending $600 million to replace its steam generators. That project went badly. Leaks in the massive equipment triggered an emergency shutdown in January 2012. The plant never reopened.

Two other utilities this year have said they will shut down, or decommission, nuclear power plants, including one in Wisconsin. But Xcel executives say nuclear power remains a critical part of its power generation, which also relies on coal, wind, natural gas and other sources to serve its 1.2 million Minnesota electric customers.

Generating steam, and risk

At pressurized-water reactors like those at Prairie Island, steam generators are a key component, and a long-standing maintenance challenge.

The new, 330-ton steam generators for the Prairie Island plant were assembled in France, arrived by ship and barge, and this fall are to be hoisted through a hatch in the containment building with only inches of clearance.

Like the original steam generators, which will go to an unspecified out-of-state disposal site, the new units perform a crucial task — transferring heat from the reactor and creating steam that runs turbines to generate power.

The technology relies on thousands of tubes that separate radioactive reactor water from the steam entering the turbines. Over time, the tubes have been known to deteriorate, leaking radioactive water into the turbine steam, and forcing utilities to plug or repair failed tubes and filter out radioactive contaminants from the steam. Most of the 69 U.S. reactors with steam generators have already replaced them with models having corrosion-resistant steel tubes.

Xcel engineers say good maintenance at Prairie Island has allowed the original Unit 2 steam generators to run longer than any others in the U.S. industry. They are confident the replacement units, which are similar to those installed in Unit 1 in 2004, won’t suffer from the problems that shuttered the San Onofre reactors.

“We paid a lot of attention to it,” said Terry Pickens, Xcel’s director of nuclear regulatory policy, who noted that the San Onofre equipment has a different design and manufacturer than Prairie Island’s equipment. “We knew we better understand what is going on there.”

Scott Marty, director of Xcel’s steam generator replacement project, said he visited the San Onofre reactors to assess that problem, which has been attributed to unexpected vibration and deterioration of the tubes.

San Onofre is the only U.S. nuclear power plant to shut down because of problems related to a steam generator replacement, said Randy Stark, who manages the steam generator program at the utility-supported Electric Power Research Institute.

“The reason for doing these steam generator replacements is to improve safety,” Stark said.

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  • Inside these concrete containment buildings are two steam generators that, in pressurized-water reactors, convert hot, radioactive fluid from the reactor core into nonradioactive steam to drive turbines.

  • Red Wing residents viewed the replacement heat-conversion units. Xcel officials say they have learned from the San Onofre plant in California, which closed when replacement steam generators leaked.

  • The twin 330-ton replacement units, built in France, rely on nearly 3,400 tubes — perhaps the weakest link in the technology — to transfer heat.

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