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May 31. 2011 10:13PM

Seabrook tunnel raises questions

SEABROOK — Water is leaking into a large tunnel beneath the Seabrook nuclear power plant, according to a report released this month, raising concerns about the vital electrical cables within.

The water is likely to become a larger issue as Seabrook proceeds with relicensing, a two-year or longer process that was begun last fall to extend the plant’s operating permit another 20 years, from 2030 to 2050.

Officials at the plant have known about groundwater seepage into the tunnel for years, apparently the result of a waterproof membrane that never worked, and elected to test five sections last year to look for further problems.

Their results, published in a Nuclear Regulatory Commission report dated May 23, found the concrete in one section of tunnel had lost about 20 percent of its strength since it was built in 1979 because of an alkali-silica reaction, a common effect of water slowly degrading the aggregate within concrete, making it weaker. The other sections all tested fine.

The weakened tunnel section carries cable that provides electricity to equipment needed to run the plant safely, like cooling systems.

The NRC and NextEra, which owns and operates Seabrook, said none of those cables are in danger and officials have already increased existing efforts to drain water from the tunnel.

Alan Griffith, a NextEra spokesman, noted that even at its highest point, water had accumulated to just two inches deep within the tunnel, where the cables run along the ceiling, five feet or more off the ground.

The tunnels are enormous, constructed with two-foot-thick concrete, with ceilings beyond reach in some instances, Griffith said. He said the cables are not in danger of being submerged under water.

“What’s most important is that none of these safety systems or structures, as the NRC report clearly states, have been impacted,” he said.

But those who have lined up against the plant’s relicensing say that the tunnel’s weakened concrete could lead to problems in the future, whereby the electrical cables would be submerged in water, setting off a cascade of trouble.

Two environmental groups, the Vermont-based New England Coalition and the Maine-based Friends of the Coast, both raised the issue of possible submerged cables early on when they petitioned to intervene in Seabrook’s relicensing, essentially earning a seat at the table to comment on the proceeding going forward.

The groups want Seabrook, and other nuclear plants, to switch all their underground cable to ones that can be submerged, a process that would cost millions.

“The condition of the concrete is not the core problem,” said Raymond Shadis, a spokesman for both groups. “The core problem is that if there is a chance where the safety-related cable can become wet or flooded, then you must put in cable that is designed to withstand flooding or moisture.”

Shadis said the groups plan to raise the issue in Seabrook’s relicensing process, but it’s unclear whether the NRC will order any substantive changes.

In the meantime, NextEra plans to retest the one section of tunnel with weakened concrete to try to verify the earlier results, Griffith said. Officials are unclear why that section, and none of the others, was affected more by groundwater seeping in.

“We’re confident we’re going to be able to demonstrate our ability to operate beyond 20 years,” Griffith said of how NextEra expects to be relicensed.


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