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Researchers at Sandia National Laboratories are working with the nation’s largest nuclear power plant to reduce water use and costs to generate electric power.
The researchers have developed a model to track the water and gauge water quality at the Palo Verde Nuclear Generating Station, near Phoenix, which converts heat from nuclear reactions into electricity.
“We are looking at how much water they are using, the chemicals being used in the treatment and the cost,” said Bobby Middleton, a nuclear engineer at Sandia. “We are trying to help them make adjustments to save money and water.”
Reducing water use is important because more than 40% of all the water used in the country’s power plants is for cooling. It’s even more critical at Palo Verde, which is in an area where water is scarce. The Arizona Legislature adopted a drought contingency plan last year that trimmed the state’s annual allotment of Colorado River water by about 7% to maintain levels in river reservoirs, and lawmakers have expressed concern about overpumping of water and depletion of aquifers.
Palo Verde’s cooling water is treated wastewater, which is becoming increasingly expensive as other customers – who are willing to pay higher prices for water – emerge. To curb rising costs, operators want to reduce the plant’s water use by about 9 million gallons a day, the researchers said.
To evaluate different emerging technologies, Middleton developed software that combines the physics of the cooling process – such as fluid flow, heat transfer, atmospheric evaporation and water treatment – with the financial impact of different solutions. Sometimes, a certain technology saves a plant money through increased efficiency; other times, reductions in water use deliver overall cost savings, they said.
The wastewater that arrives at Palo Verde contains silica, calcium, magnesium and phosphate ions. These salts concentrate as the cooling water evaporates in the cooling system, possibly forming new minerals that might clog the cooling towers.
Currently, operators add lime, soda ash and acid to the wastewater before it enters the cooling tower to reduce mineral formation.
The model is being used to identify less expensive ways to remove ions at different points in the cooling cycle.
Middleton and Sandia chemist Patrick Brady believe their analysis can also be applied at nuclear plants across the country.
“Palo Verde is in the hottest, driest part of the U.S.,” Middleton said. “If we can be successful there, it can be successful in other places. It’s a great test place.”
Brady said that even though power plants in the East have more access to water through rivers and lakes, “water usage is still an issue there.”
“The Environmental Protection Agency has regulations that restrict the water they can use,” he said.
The researchers believe that analysis could be used to save water at these power plants, too, whether they run on coal, natural gas or nuclear energy. Middleton and Brady said they intend to consult with other power plants during the process.
The researchers have also redesigned and patented an air cooling system to make waterless cooling more energy-efficient and possible over a wider range of operating conditions, and believe that can be part of the solution at Palo Verde. Palo Verde is committed to providing part of the funding, Middleton said. If the Department of Energy approves funding, Brady said, the prototype could be operational in a little more than two years, and the system itself by the mid-2020s.
New Mexico has a significant stake in Palo Verde. Public Service Company of New Mexico owns 288 megawatts of the electricity generated by the plant, and it leases another 114 MW.
El Paso Electric also owns 15.8% of Palo Verde’s generation.