Nuclear stations generate electricity by heating water to create steam to turn turbines, which turn a generator. As part of electricity production, these stations need a way to cool this steam back to water for reuse. Because of this water need, nuclear plants are typically located near lakes, rivers or the ocean. However, because these lakes and rivers are used for other purposes, such as drinking water, irrigation and industrial uses, Duke Energy established environmental programs decades ago to protect aquatic life.
The cooling water, drawn through large pipes by pumps, never touches the steam. Cool lake or river water circulates through pipes, cooling, or condensing, steam back to water when the steam falls on the pipes (similar to how a car radiator works). In the process, the cooling water picks up a little heat from the steam and is warmer when it is returned to the lake. However, to ensure water quality of the water used, the U.S. Environmental Protection Agency and state agencies regulate the temperature of the water that is discharged. The state sets discharge temperature limits for each plant. These limits are established using scientific data and research. Compliance with these limits is ensured through regular data collection and reporting by the utility.
Duke Energy teammates Linda Hickok (Water Resources Manager) and Bill Foris (Lead Scientist) put things in perspective through the following Q&A.
Q: Why are lake temperature limits in place for power plants?
A: Temperature limits are in place to protect the aquatic ecosystem of the water body receiving the heated discharge. The limits are set at levels that allow integration of the heat into the ecosystem without disrupting fish, plant and other aquatic organisms in the lake.
Q: What lake discharge temperature limits must nuclear plants adhere to?
A: Temperature limits are established during a permitting process based on site-specific conditions. The site permit contains these specific limits.
Q: Who regulates the limits and how are they regulated?
A: Typically, permits are issued by the state as the designated agency to implement federal and state laws and regulations governing wastewater and thermal discharges. The permitting agency reviews monitoring data and conducts inspections to assess permit compliance.
Q: Why is it important for stations to stay within permitted limits?
A: To ensure protection of the aquatic life and water quality within the water body (lake, river, etc.).
Q: How does Duke Energy ensure temperature limits are not exceeded?
A: In most instances, water temperature of the thermal discharge is measured at least hourly year-round to assure the site-specific limit is met. This data is reported to the state on a regular basis, and is readily accessible by nuclear station personnel for reviewing and making operational decisions .
Q: How does Duke Energy maintain healthy aquatic life?
A: Duke Energy actively monitors the water quality, plankton and fishery of reservoirs throughout the year, and submits annual reports to the state summarizing these important environmental attributes.
Q: Is there any type of special permit requirement for nuclear stations?
A: The National Pollutant Discharge Elimination System (NPDES) permit includes requirements for discharge quality (limits on chemicals or heat in the discharge water), monitoring and reporting. NPDES is a program created by the federal Clean Water Act to regulate wastewater and thermal discharges from industrial and municipal facilities.