The unusually hot summer across much of the country has not only taken a toll on our lawns and plants, it’s also slowly raised the temperature of some of our lakes and rivers. Many nuclear power plants rely on lakes or rivers for water to cool the plant. So, what is the effect of slowly-rising water temperatures?
If the temperature of the water used to cool the plant rises too high, a plant may have to reduce the amount of electricity it generates. Reducing electrical output reduces the heat generated by the plant, so that the plant can be safely cooled even with higher-than-normal temperatures of intake water.
The NRC requires that intake water temperature be continuously monitored to make sure that appropriate action is taken before any safety limits are exceeded. This year, a few plants have had to either reduce power or seek special NRC approval in order to temporarily operate with higher-than-normal cooling water temperatures. Unit 2 of the Millstone plant in Connecticut has had to temporarily shut down because of warm water temperatures.
What about water that is discharged from a plant after it has been used to for cooling? If the temperature of that water is too high, it can harm aquatic life or have other impacts on water quality. So, a plant may need to reduce electrical output to keep the discharged water sufficiently cool, or request special permission to exceed permissible temperature limits, which are set by other federal and state regulators with responsibility for water quality.
With autumn approaching, the temperatures will fall. Even after the summer heat passes, the NRC will continue to ensure plants closely monitor the temperature of their cooling systems. Whatever the season, safety remains the agency’s top priority.
Jared K. Heck Regional Counsel NRC Region III
U.S. NRC Blog 
Thermal discharge i.e. hot water is a “nonradiological pollutant” regulated by U.S. Environmental Protection Agency or the states, in accordance with section 511(c)(2) of the Federal Water Pollution Control Act (86 Stat. 893, 33 U.S.C 1371(c)(2)). The NRC may set technical specifications on a plant-by-plant basis about the temperature of the water coming into the plant to cool the reactor, but that is not your question..
Hi,
I’m curious about what the regulations are regarding thermal discharges from nuclear power plants in the U.S., particularly those in southern waters (e.g., Crystal River 3, Turkey Point, Diablo Canyon, etc.) Can you point me to information about thermal discharge regulations?
Also, I assume that whatever regulations were developed were based on some sort of analysis of the effects of thermal discharges on aquatic life. Could you point me to any literature on that subject?
Thanks,
Mark Bahner