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Corrosion Cracking Shuts Nuke Reactor

Monday, May 20, 2013

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Stress corrosion cracking in a North Carolina nuclear reactor has forced operator Duke Energy to take the plant offline, officials said.

The company also says it will suspend its application for two proposed new nuclear units at the Shearon Harris plant in Wake County, NC.

The new shutdown is the result of a recent review of ultrasonic tests taken a year ago at the reactor, when the plant was taken offline for refueling, Duke told the Nuclear Regulatory Commission in a new filing.

No Indications of Leak

The new review revealed “primary water stress corrosion cracking” on a nozzle that overlaps a weld on the reactor head at the plant, 20 miles south of Raleigh.

Harris Nuclear Plant
Smith College

The plant was originally licensed in 1986, and its current license runs through 2046. Duke Energy has withdrawn an expansion application submitted in 2008 by its predecessor, Progress Energy.

No radioactive material leaked from the plant, and public health and safety is not in danger, Duke spokeswoman Kim Crawford told reporters.

For now, Duke considers the crack superficial.

“Initial evaluation indicates that the flaw is not through the wall, and there is no evidence of leakage based on inspections performed on the top of the reactor vessel head during the spring 2012 refueling outage,” according to information Duke filed with the NRC.

The vessel wall is a protective barrier made of carbon steel that measures about six inches thick.

"There are no indications that there was any leakage," Crawford said. "We made the conservative decision to take the unit offline and make the repair."

Without repairs, a small crack could widen and allow water that keeps the reactor cool to escape, putting the plant at risk of a meltdown and possible release of radiation, reports said.

Out of Commission

Crawford said she couldn't say how long the reactor would be out of commission, but she said the utility had plenty of capacity and would not need to purchase electricity from outside sources to meet demand.

"We're not anticipating any issues," she said. "While our plant is offline, we'll continue to serve our customers."

Repairs will take place in a highly radioactive area and will require the use of robotics, NRC spokesman Roger Hannah told the News Observer.

Shearon Harris provides power to about 550,000 customers, and industry sources said the shutdown could cost Duke about $1 million a day.

The NRC will hold an annual public meeting and question-and-answer session today (May 20) to discuss the NRC review and take questions from the public. The meeting was already scheduled to review the plant’s 2012 performance.

Common Problem

Corrosion cracking is common in aging nuclear plants, David Lochbaum of the Union of Concerned Scientists, told the News Observer. The plant was originally licensed in 1986; in 2008, its license was renewed through 2046.

Harris Nuclear Plant
NRC

Experts call the cracking a common problem caused by corrosion. But they question why the issue was not spotted a year ago, during an initial review while the plant was offline.

“Impurities in the water can collect in tiny cracks formed in metal by stress,” said Lochbaum, a former NRC employee. “These impurities, called corrosion, exacerbate stress factors accelerating the propagation of tiny cracks.”

However, critics expressed concern, particularly over the time lag in addressing the problem.

"To have a crack in a reactor vessel head that went undetected for at least a year, that's very troubling," Jim Warren, executive director of utility watchdog NC WARN, told WRAL.com.

"My concern is the industry hasn't solved this particular problem. We've known about this (issue) for well over 10 years," Warren told the news site.

He attributed the delay in repairing the Shearon Harris crack to "some sort of breakdown in procedures."

"What they're going to find when they're able to get in there and look more closely will be of great interest to the public," he said.

The Harris plant was previously operated by Progress Energy, which Duke acquired in July 2012.

FL Cracks...

In February, Duke was forced to mothball a nuclear plant in Crystal River, FL, that Progress Energy closed in the fall of 2009 after finding a crack in the outer layer of the containment building's concrete wall.

While trying to repair the problem in 2011, crews cracked other portions of the wall, and officials said repairing the damage might have cost more than $3 billion, reports said.

Crystal River Nuclear Plant
NRC

Duke Energy decided in February not to reopen the Crystal River Nuclear Plant in Florida, which was closed because of cracks in the fall of 2009.

Duke also announced this month that it was suspending a 2008 application originally submitted by Progress Energy to add two units at Harris. The announcement cited “slower growth” as the reason for its decision, but said the plant “has not been eliminated from our long-term consideration as a site to expand our nuclear fleet.”

...And Others

The NRC is confronting infrastructure-related issues at several other nuclear plants.

In 2011, FirstEnergy Nuclear Operating Co. reported "extensive cracking" in an uncoated shield structure at the Davis-Besse Nuclear Power Station near Toledo, OH. Repairs to the 2.5-foot-thick reinforced concrete building will cost millions.

In New Hampshire, discovery of cracking in multiple structures at the Seabrook Station Nuclear Plant led the NRC to issue a general alert to all of its facilities and applicants regarding the risk of the same problem elsewhere.

Davis-Besse Nuclear Plant
NRC

In Ohio, officials are trying to repair extensive cracking in a shield structure that was never coated. Plant operator FirstEnergy Nuclear Operating Co. is coating the structure with a waterproofing material.

The problem is known as Alkali-Silica Reaction-induced (ASR) concrete degradation, a slow chemical degradation process that occurs when alkalis—usually from cement—react with certain types of silica in the aggregate when moisture is present.

The reaction produces an alkali-silica gel that can absorb water and expand to cause micro-cracking of the concrete. Excessive expansion of the gel can lead to significant cracking.

   

Tagged categories: Concrete repair; Corrosion protection; Cracks; Enforcement; Government; Health and safety; Nuclear Power Plants; Waterproofing

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