Last Friday at 11 A.M., the operators of the Vermont Yankee nuclear power plant in Vernon, Vt., detected a leak. About 60 gallons (225 liters) of water a minute was escaping from the eastern cooling tower of the 620-megawatt power plant that provides nearly three quarters of the state's electricity needs. By noon, the owners had shut down both the damaged and undamaged cooling towers and had cut the plant's electricity output in half to avoid any harm to the reactor. By Monday, the plant was operating at 23 percent capacity because of limits on the amount of water it could use from the Connecticut River to cool its nuclear core.

But Vermont electric consumers barely noticed—though they might feel it later in their wallets. Despite the shutdown of the state's major power plant, lights, TVs and life's other electrical amenities continued to operate as usual. How is that possible? The company that operates the state's power grid has a contingency plan in case of emergency shutdowns, says Dorothy Schnure, a spokesperson for Green Mountain Power, one of two local utilities that purchase and resell much of the power from Vermont Yankee.

ISO New England, Inc., the independent system operator that ensures juice is flowing in Vermont and the rest of New England, always has spare power sources—courtesy of fossil fuel–fired, so-called "peakers" (units that provide power to the grid only during peak demand)—to compensate if power plants or transmission lines go on the fritz, according Erin O'Brien, an ISO spokeswoman.

Rob Williams, a spokesperson for Entergy Vermont Yankee, the power company that runs the 35-year-old nuclear facility, says it should be back at full capacity by the end of the week, pending a safety inspection by the U.S. Nuclear Regulatory Commission (NRC). The leak was caused by a sagging bracket supporting a cooling pipe in the eastern tower. The problem is worrisome because the bracket—a piece of metal that bolts a support beam in place—was relatively new: All of the brackets in the two towers, which are made of wood, had been replaced after a similar cooling pipe collapse in the western tower last August. The brackets are now being replaced with a new, stronger design, Williams says.

Neither of these problems affected the safety of the nuclear power plant, according to Williams, noting that the towers are primarily used to cool the water before it is put back in the Connecticut River so that it does not scald too many fish.

But they may cause a fiscal twinge. The nuclear power plant provides electricity at slightly more than 4 cents per kilowatt-hour; the power that the utilities must purchase from other power plants to make up for the shortfall costs 8 cents or more. "If Vermont Yankee goes down, it's about $100,000 a day for us," Schnure notes. "But this time it is partially down so it's less than that."

Any increase, however, isn't likely to show up until at least January, Schnure says, because utilities could not raise rates without the permission of the Vermont Public Service Commission.

Costello says the utilities have yet to decide whether to seek a rate increase. "It's too soon to tell," Costello says. "The plant, we hope, will be back online in the not too distant future, and it will not be too large of a significant cost." Meaning Vermont residents may have a reminder of this summertime outage when they pay their electricity bills in the dead of winter.