02/15/2012 - 15:32

In hot water: The "other" global warming

Dawn Stover

Dawn Stover

Stover is a science writer based in the Pacific Northwest and is a contributing editor at the Bulletin. Her work has appeared in...

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On January 20, a state engineer with the Utah Division of Water Rights approved two applications that would allow Blue Castle Holdings to take a total of 53,600 acre-feet of water from the Green River annually for a proposed nuclear power plant. That's more than 17 billion gallons a year, enough for a city of 100,000 households.

The Blue Castle Project would be the first new nuclear power plant to go online in the American West since the late 1980s. So you might think it would be a model of modern water-conservation technologies. But you'd be wrong.

Blue Castle proposes to cool its two-unit plant by circulating river water through a closed-cycle system. In such systems, up to 5 percent of the water is typically lost to evaporation on each pass through a cooling tower, and the other 95 percent is recycled. Once the concentration of dissolved solids in the water reaches an unacceptable level, the dirty water -- dubbed "blowdown" -- is discharged to an onsite evaporation basin and replaced with fresh water piped in from the river.

A closed-cycle system has some advantages over the "once-through" cooling systems still used at many older power plants, which dump hot water directly into nearby rivers, lakes, or oceans -- killing fish and altering local ecosystems. Both types of cooling systems will also kill fish by sucking them into equipment or trapping them against intake screens, but the once-through method is more deadly because it diverts more water than does a closed-cycle system. For example, in New York state, Indian Point's once-through nuclear-generating units, which consume about 2.5 billion gallons of water from the Hudson River daily, kill more than one billion aquatic organisms annually.

To be sure, a closed-cycle system such as that proposed by Blue Castle uses less water than a once-through system -- but it's a consumptive use. None of the water withdrawn from the Green River will ever be returned to the river. That means there will be less water for fish. And less water means hotter water.

Meanwhile, climate change is already raising water temperatures. Global warming is usually considered a problem of air pollution: Power plants, vehicles, and other sources are emitting too many greenhouse gases into the atmosphere; that's why the icebergs are melting and why some polar-bear-loving Prius owners are smug about their rides. But what most people don't realize is that global warming is much more complex and that thermal water pollution is itself a very big problem.

Does it really matter if water gets a few degrees warmer? In the case of the oceans, the answer is yes. Water expands as it heats, and this expansion is the main reason why sea level is rising.

At power plants, too, it's a matter of degrees. The lower the temperature of the water used to condense steam, the more efficiently the cooling system works. That's why nuclear power plants tend to have a higher net output in winter than in summer.

The one-two punch of power production and climate change has already made some rivers so hot during the summer that they can no longer provide adequate cooling at power plants without exceeding legal limits on temperature. During the past two summers, the Tennessee Valley Authority had to reduce power production by 50 percent at the Browns Ferry Nuclear Power Plant because the water in the Tennessee River -- where the plant's cooling water is discharged -- was already at 90 degrees. A further complicating factor: At Browns Ferry and many other plants, "uprating" has cranked up the power produced by old reactors. In other words, if climate change and cooling-system impacts weren't already bad enough, now bureaucracy is increasing the temperature allowances of coolant water by a couple of degrees.

The proposed Blue Castle Project will also face water-quality challenges. Kent Jones, the Utah state engineer who approved the water allocation, called it "a significant new diversion from the Green River where efforts are underway to provide habitat for recovery of endangered fish." And regardless of the needs of fish, rivers in the desert have a tendency to dry up now and then. Utah's Department of Natural Resources noted that water-rights approval for Blue Castle "does not guarantee sufficient water will always be available from the river to operate the plant."

Nuclear power is not going to be a panacea. Like every energy sector, nuclear power production must become less thirsty in order to adapt to climate change and increased growth in the 21st century. And, luckily, that goes for the Blue Castle proposal, too. As Michael T. Masnik, water and ecology team leader for the Nuclear Regulatory Commission's Office of New Reactors wrote after an October 2011 pre-application readiness assessment visit to the Blue Castle Project site: "In light of the arid nature of the site and environs, the scarcity of surface waters, and the consumptive nature of the proposed cooling system, the staff expects that a number of alternative cooling systems will be discussed."

One such alternative might be a system like the one used at the Palo Verde Nuclear Generating Station in Arizona, the only nuclear power plant in the world -- so far -- that was not built next to a large body of water. Palo Verde uses treated sewage water from Phoenix, instead of fresh water, to meet its cooling needs. A similar system is proposed for Jordan's Majdal plant.

Blue Castle's proponents say that their project would use a relatively small volume of water compared with the total amount in the Green River or with the amount withdrawn statewide for agricultural irrigation. That's a little like saying, compared with the national debt, Bernie Madoff didn't take that much money. Blue Castle also argues that this water was already approved for use in coal-fired power plants -- plants that were not constructed, but never mind. In any case, none of those arguments really address the question of water quality -- an issue that will only get hotter in the future.