Concrete Plan at NH Nuke

Friday, March 30, 2012 @ 05:03 PM gHale

While Seabrook’s nuclear power plant in New Hampshire is safe, it committed two “very low significance violations” in its evaluation of its decaying concrete problem, a new report said.

The report on the concrete degradation caused by water that is infiltrating subterranean walls in five areas at Seabrook Station came out earlier this week by the Nuclear Regulatory Commission’s (NRC) Region 1, which has jurisdiction over nuclear power plants in this area.

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The 20-page document discusses the findings of six NRC inspectors who spent eight days during two separate visits last year to Seabrook Station, as well as an additional inspection of the laboratory in Illinois that is conducting tests on core samples of the concrete in question.

The inspectors determined the concrete areas affected by the deterioration are “operable but degraded,” said Neil Sheehan, spokesman for NRC’s Region 1. Basically, that means the NRC believes the structural integrity of the affected walls is not an immediate concern, due to the safety margins inherent in their design and construction.

“(The NRC does) believe that Seabrook is safe,” Sheehan said.

Sheehan said there are three reasons behind that determination. The first reason is referred to as the plant’s “conservative load factors,” meaning they built it stronger than it needed to be, with thick concrete walls reinforced with a lattice of steel reinforced bars.

Second, during their inspection, the commission’s concrete experts found the degradation is limited to localized areas at the plant.

The third reason is the concrete degradation is progressing slowly, he said.

The bulk of the concrete problem is in a roughly 40-foot-long section of a wall in an electrical tunnel about 40 feet below ground level. The 100-yard-long tunnel contains wires connecting the plant’s controls to machinery throughout the sprawling plant. There are two such tunnels in the plant, identical in design and function. At any given time, one is in use, and the other serves as a backup.

The two violations discussed in the report, both considered to be “of very low safety significance,” relate to the extent of the evaluation into the problem done by the plant’s owners. The highly technical report said in one violation, NextEra “failed to fully evaluate potential structural and seismic response impacts in accordance with the requirements” in the company’s own procedures. The second violation was similar to the first, citing the plant for not following certain test guidelines laid out in federal regulations.

Both are considered by the NRC to be “non-cited violations,” which means Seabrook Station will add the issues to their action program for remedy, with the NRC following up to ensure the proper action results, Sheehan said.

Officials at the plant are pleased the NRC has made clear it has no immediate safety concerns at Seabrook Station, said NextEra Energy Seabrook spokesman Alan Griffith.

“The NRC is doing exactly what it’s supposed to do,” Griffith said. “All the testing and evaluation is to make sure we have a strategy in place for the long term. Our intent is to leave no stone unturned on this. That’s why there’s so much information going back and forth and so many questions that continued to be asked and answered.”

Alkali-silica reaction happens when moisture seeps into concrete structures and interacts with some of the materials used to make concrete, such as Portland cement. When the reactive silica is in a high-alkali environment — like Portland cement’s high pH level — the potassium and sodium hydroxide present in the cement paste combine to form alkali-silica gel. The gel expands within the concrete and causes micro-cracks.

Characteristics are pattern cracks in the concrete, with secondary deposits of calcium oxide showing, along with a dark staining on the concrete representing the alkali-silica gel. Not uncommon in highways and bridges where it has been successful patches, this is the first time ASR was at a nuclear power plant.

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