Waterford — Last month’s unprecedented 12-day shutdown of part of the Millstone Nuclear Power Station sent a shudder through the nuclear energy world.
Caused when the seawater used to cool the plant’s generating Unit 2 became too warm, it was the first time any U.S. nuclear plant was shut down because of intake water temperature problems.
Nuclear energy officials were concerned, but “I don’t know if we would say ‘surprised,'” said Richard MacManus, Millstone’s director of nuclear safety and licensing. He spoke as he stood alongside Niantic Bay, taking in the panoramic view of the massive Millstone facility and Long Island Sound, its source of water.
The shutdown capped a season of power reductions and other difficulties at several of the nation’s power plants — including non-nuclear ones — caused when summer heat and drought compromised the vast amounts of water needed to cool them. It has also set in motion a cascade of other potentially debilitating effects, all of which point to the likelihood that climate change has placed part of the U.S. power grid at risk.
Curiously, the industry and its watchers had seen it coming — for decades.
The water intakes at the Millstone Nuclear Power Station. Unit 3’s is the bunker-like structure at the water line on the left; Unit 2 on the right.
Dave Lochbaum, director of the Union of Concerned Scientists‘ nuclear safety project, has documented nuclear plant water usage incidents since the 1970s — 29 pages worth even without this summer’s problems. While many stem from clogs caused by everything from jellyfish to seaweed to microbial infestations, a number were because intake or discharge water was too warm or water levels were too low, occurrences he said have increased in recent years.
“It’s not an every-year-is-worse-than-the-previous-year thing,” he said; “2009 was pretty bad; 2010 wasn’t so bad. The overall trend is warming water or longer droughts.”
Initially Lochbaum was surprised that an ocean-sited plant would have intake temperature problems. But on second thought he realized that since plants use historical water temperature data when setting their design parameters, Millstone is just as vulnerable as a plant that uses inland fresh-water sources that are typically more sensitive to summer conditions.
“With global warming, what the history has been over the last 20 or 50 years is nice, but it may not be bounding,” he said. “If we don’t also couple our past with our best estimate of what future conditions may be, we’re going to be facing more and more of these, quote, surprises.”
There was no surprise at Millstone though. Since Unit 2 went online in 1975, plant scientists have watched the Sound’s temperature rise about 0.7 degrees a decade — 2.8 degrees total.
Under their licenses, Millstone 2 and 3’s intake water temperatures — measured in three locations for Unit 2 and six locations for Unit 3 — cannot exceed 75 degrees as averaged over a 24-hour period, or 77 degrees at any point. The plants had used the highest reading among the locations to make their calculations. If water temperatures at either plant exceed the limit, the licenses do not permit a power cutback. The plant must be shut down.
By mid-July, Dominion, Millstone’s owner, knew there was trouble at Unit 2. On July 17, it sent a letter to the Nuclear Regulatory Commission requesting a license amendment that would allow it to average the three temperature readings instead of using the highest one. On Aug. 9, it sent another letter asking that the July 17 request be considered an emergency.
“Water temperatures in Long Island Sound have been averaging 1.7 degrees higher than normal,” the company wrote. “Current trending projections of the water temperature, wind direction, and tidal conditions indicate the maximum allowed Technical Specification (TS) UHS temperature limit will be exceeded on August 10, 2012 at approximately five o’clock in the evening.”
On Aug. 10, the NRC approved the emergency request. Millstone was wrong about the Aug. 10 prediction, but only by two days. On Aug. 12 it reached the 75-degree threshold and Unit 2 was shut down. Its 880 megawatts of generating potential was idled until Aug. 24, when the unit began powering back up. It reached full power the next day.
In fact, the temperature actually hit a high of 77 degrees for a short period of time a day or two into the shutdown. Unreported, however, was that the temperature of Unit 3’s intake water, which comes from a deeper and therefore colder area, was also creeping up.
“I don’t know that ‘worry’ would be the word that we would use,” MacManus said. “We were close, but still we had margin within that.”
A spokesperson for the Independent System Operator that manages the power grid for New England said the loss of Unit 2 did not cause power distribution problems. PSE&G‘s coal-burning power plant in Bridgeport was brought online, and no emergency procedures were needed.
But the ISO declined to comment on what adding a shutdown of the considerably larger Unit 3 might have meant. Together both units typically supply nearly half of Connecticut’s power. The spokesperson said there had been other “generator reductions due to water conditions” this year, but declined to elaborate.
“It’s really a very big problem for the state of Connecticut that the largest power generation source in the entire state would be shut down for several weeks in the hottest summer days with the greatest air-conditioning demand,” said Department of Energy and Environmental Protection Commissioner Dan Esty, who was kept informed of the situation prior to the shutdown.
But that’s only the beginning of Esty’s concerns. He said he is also worried about pollution from the older, dirtier fossil-fuel plants that have to operate when Millstone is unavailable, and about the environmental effects as hot discharge water mixes with warmer-than-usual Sound water. Unknown is whether that could trigger more dead sea life or enhanced marine growth — either of which could mean more debris clogs at the power plant, which Millstone has already experienced.
As a solution to the water temperature problem, Dominion has initiated an engineering analysis to determine whether the plant can operate safely with higher intake water temperatures. It aims to have a license revision request into the NRC in time for a ruling before a potential repeat performance next summer. A Millstone spokesman all but rejected as too expensive other solutions such as installing larger pumps that can handle higher temperatures, or redesigning the intake system to use Unit 3’s deeper intake location.
“We want to make sure that power is available. Of course we want that power to be generated under conditions that are safe,” Esty said. “There is a balancing act here.”
Water consumption
But some view raising the plant’s operating temperature as a Band-Aid for the real problem — the amount of water the nation’s 19,000 power generating units, including 104 nuclear ones, use. They consume 100 billion gallons a day — three times what cascades over Niagara Falls in the same time frame.
This chart shows how nuclear, coal and gas-fired generators compare in their use of water.
“U.S. power plants are at risk from not enough water due to situations like drought, too much water because of sea level rise and flooding, or water that is simply too warm,” said Steve Fleischli, acting director of the Natural Resources Defense Council‘s water and climate program. “From our perspective, what power plants can do to protect the grid is not rely so much on water.”
Most of the cooling water is returned to its source and then re-used, according to the U.S. Geological Survey, which documents fresh- and saltwater use every five years. Since 1965 most water withdrawals have gone for thermo-electric power generation. In 2005 (2010 data is not available yet), that figure was 40 percent nationally.
But in Connecticut it’s 82 percent. Among freshwater withdrawals, 24 percent goes to power plants. Of the saltwater withdrawals here, 99 percent goes to power plants.
At Millstone, Unit 2 uses 450,000 gallons of water per minute, and Unit 3 uses twice that amount. Coal plants like that in Bridgeport, which also takes its water from Long Island Sound, withdraw nearly the same amount of water as nuclear plants per megawatt hour. Gas and oil plants — similar in their water needs — require less than nuclear and coal. Conventional plants, however, generally can use warmer water than nuclear plants because without radiation concerns, their safety systems are less critical.
EquiPower‘s natural gas-fired plant in Milford, for example, uses more than 2.5 million gallons of water each day, pulling 90 percent from the Housatonic River and the rest from the public water supply. It has no intake temperature cap, a spokesman said.
But the water use at EquiPower’s Lake Road natural gas plant in Killingly is zero. It’s air-cooled.
That’s one of the solutions environmental groups and others envision to limit water use. But it’s more expensive, as are other options including using reclaimed water such as wastewater. The groups also favor more stringent regulations for water intake as part of new cooling water standards the Environmental Protection Agency is formulating now.
“Optimizing the consumption, use and discharge of water represents a significant challenge for power generation facilities,” said Richard Breckenridge, a senior project manager with the Electric Power Research Institute. “It’s more than just changing one cooling source to another. It’s redesigning the entire power plant, so it becomes very cost prohibitive.”
To help find less expensive and less water-dependent power plant systems, this summer EPRI and Georgia Power opened a Water Research Center that is looking at solutions like wet and dry cooling hybrids and moisture recovery technology.
Other risks, too
As if warm water and lack of water haven’t produced enough hand-wringing at power plants this summer, scientists also are mindful that climate change includes sea level rise and increasingly violent storms. Millstone, literally at the water’s edge, has suffered storm-related power reductions over the years. MacManus said waves came over the seawall during Tropical Storm Irene, but water did not enter any buildings.
The NRC’s new chairwoman, Allison Macfarlane, has asked her staff to examine the effects of climate change on nuclear power plant operation.
But the industry bristles at the notion that it has ignored water issues. “It would be wrong to think that this is a sudden thing no one has ever thought about, no one has ever talked about,” said William Skaff, director of policy analysis at the Nuclear Energy Institute, the industry’s policy organization.
But others like John Rogers, co-manager of the energy and water project for the Union of Concerned Scientists, saw the Millstone shutdown and other incidents as wake-up calls.
“It’s clear that past energy choices in numerous instances are colliding with available water resources,” he said. “What this summer did was really underscore the potential for collision. In a lot of cases power plants got the water they needed. What we don’t know is who didn’t get the water.”