With new plants pending, cooling requires serious thought.
William Atkinson is a freelance journalist based in Carterville, Ill.
Thanks to “Blinky,” the three-eyed fish in The Simpsons, nuclear cooling has gotten a bad rap. And these days, as people begin discussing the pros and cons of the nuclear renaissance more frequently, cooling-water issues are emerging as a significant concern—whether enough of it will be available for cooling, and what the environmental consequences might be if new plants are built.
As the Electric Power Research Institute (EPRI) notes, “Growing demand for electric power, coupled with growing water demand in agricultural, municipal, residential, commercial, and industrial sectors, could strain water supplies in the future. … Pressures and associated operating challenges are expected to grow significantly as utilities seek to permit and build new generation facilities to meet growing electricity demand.”
Another organization watching the issue is the Nuclear Energy Institute (NEI). In 2007, for example, NEI noted that, because rainfall in some areas of the country was 15 to 20 inches below normal, energy companies took steps to reduce water consumption and otherwise conserve water supplies.
“Water is a serious issue,” cautions Robert Goldstein, a senior scientist with EPRI. “Every region of the country is vulnerable to shortages. As such, any sector of the economy that uses water is vulnerable to having their activities disrupted.”
And it’s not just a problem in the arid West. “We have already seen the economic and social infrastructures stressed in the Southeast as a result of the recent droughts,” he says.
Joe Turnage, a senior vice president with Unistar Nuclear Energy, the nuclear division of Constellation Energy, agrees with Goldstein. “We are in a water-constrained world,” Turnage says. “Thermoelectric power generation as a whole accounts for about 40 percent of freshwater withdrawal, but only about 3 percent of actual consumption. Going forward, we will have to approach the development of new generation alternatives consistent with the development of available water supply.”
According to Michael Hightower, a member of the technical staff at Sandia National Laboratories, nuclear plants currently use the largest amount of water per megawatt hour of any form of electric generation. He also cites research conducted by the U.S. Geological Survey in 2007, noting that many major groundwater aquifers are experiencing reductions in water quality and yield. In addition, there is little increase in surface-water storage capacity since 1980. “There are also concerns over climate impacts on surface-water supplies,” Hightower says.
According to the Government Accounting Office (GAO), most state water managers expect water shortages over the next decade, even under average conditions. And more to the point: A 2003 heat wave in France caused a water shortage that forced outages at up to 15 percent of the country’s nuclear-generation capacity for five weeks.
“Many of the new nuclear plants being proposed are designed to be built at sites where other plants already exist,” Hightower says. “It may be difficult to license some of these new plants if there are water-availability limitations or thermal limitations.”
Technology to the Rescue
EPRI is conducting research on developing, testing, and deploying efficient advanced water-cooling technologies. Options include power-plant siting, meteorological impacts on air-cooled condensers, indirect dry cooling, hybrid tower designs, water-recovery options, wet surface air coolers, advanced bottoming cycles, and preserving once-through cooling options.
EPRI’s Goldstein sees four options as particularly appealing.
• Implementing a hybrid system that uses a combination of dry (air) cooling and wet cooling.
• Increasing the thermal conversion efficiency of the thermo-electric plant, so more of the heat is used to generate electricity and less is being rejected. “This reduces cooling requirements,” he says.
• Replacing a fresh-water source with a non-traditional water source, such as saline water, sewage treatment effluent, agricultural runoff, water produced in association with the drilling of gas and oil, drainage from mines, etc. “Of course, there are costs associated with this, including pre-treatment and post-treatment,” he points out. “There may also be transport costs.”
• Recycling water within the plant. For example, technologies currently are being explored to capture a certain percentage of the vapor that normally would be leaving wet cooling towers, condensing it, and then recirculating it.
The first option, hybrid cooling, strikes a chord with a number of people in the industry. However, while the technology is quite appealing for coal and gas-fired plants, it presents challenges for nuclear. “Fossil plants can use, and are using, more dry cooling, over hybrid wet-dry cooling,” points out John Maulbetsch, president of Maulbetsch Consulting in Menlo Park, Calif. “It’s unlikely that nuclear plants will be able to use direct-dry cooling, especially nuclear plants using boiling-water reactors.”
Dry cooling might be possible with pressured-water reactors, but even then, it’s unlikely. “Nuclear people don’t want a direct steam path from the turbine exhaust out to a large open structure, so their options are limited to indirect-dry cooling, where the steam is condensed, and then the hot cooling water from the condenser is taken to an air-cooled heat exchanger, rather than an air-cooled condenser,” he explains. It’s cooled, then returned. These systems are more expensive and less efficient than air-cooled condensers, and as a result “going dry” raises costs for nuclear plants.
Costs also are higher for nuclear plants using hybrid systems. These involve air-cooled condensers operating in parallel with wet-cooling towers. “You use dry cooling until the ambient temperature gets high enough that the dry-cooling system can no longer maintain the condenser back pressure at the necessary level,” he says. “At this point, you phase in the wet cooling.”
This works in nuclear plants and fossil plants. However, in nuclear plants, the dry portion probably needs to be an indirect dry system, rather than using an air-cooled condenser, so it will be more costly and less efficient than a comparable hybrid system in a coal plant. “It’s all doable,” Maulbetsch says. “It’s just more expensive.”
Plant siting also might need some serious dialogue in the industry, according to Sandia’s Hightower. “We may end up in a situation where a lot of the new plants have to be located along ocean and large lake shores,” he says. “A lot of people may not like this siting strategy, but it may end up being necessary if the alternative cooling technologies don’t get licensed.”
Would a national policy on water help the situation? No one knows for sure. The only thing experts agree on is that such a policy is not currently on the drawing board.
Doug Houseman, vice president of global energy, utilities and chemicals for Capgemini, has yet to see any policy trends in this direction. “Everyone continues to deal with this issue on a state-by-state, case-by-case basis,” he says. “We don’t have a national water policy, and I don’t think we ever will.”
Unistar’s Turnage is a bit more optimistic. “In terms of policy issues, I think this is just starting to emerge,” he says. “Water is an issue not only for new generation build, but also for existing operating plants. I think this is an idea whose time has come.”
While coordinated legislation on water policy doesn’t seem to be occurring today, Hightower says he’s seeing some activity. “For example, the Nuclear Regulatory Commission is beginning to look at the issue of water availability for power plants and is beginning to understand some of the concerns in their pre-licensing and licensing applications,” he says.
In addition, EPRI realizes the significance of water availability, and has conducted a few workshops on the topic. “EPRI is developing a research program to address some of these concerns,” adds Hightower. In his July 2008 paper, Energy and Water: Issues, Trends and Challenges, Hightower summarizes some of action items being discussed in workshops around the country:
• Better resource planning and management—including integrated regional energy and water-resource planning and decision support tools; infrastructure and regulatory policy changes for improved energy and water efficiency; and improved water supply and demand characterization, monitoring, and modeling;
• Improved water- and energy-use efficiency—including improved water efficiency in thermoelectric power generation, and reduced water intensity for emerging energy resources;
• Development of alternative water resources and supplies—including oil- and gas-produced water treatment for use, and energy efficiency and assessment of impaired water treatment and use;
• Accelerated water resources forecasting and management; and
• New system analysis approaches for co-location of energy and water facilities.
Even though there are a number of new nuclear plants on the drawing board, none of them are being built yet. “This means we have the time now to think about how we are going to deal with water issues,” says Capgemini’s Houseman. “There’s a lot of thinking that needs to be done, and if we start now, we can probably solve this before it becomes a problem.”