Nuclear is known as the thirstiest power source. Due to high water withdrawals, nuclear power plants are usually located near lakes, rivers, or the ocean. The vast amounts of water are for cooling purposes typically through the use of a direct cooling or closed cycle cooling system. In a direct cooling system, the steam used to turn the turbines is cooled by water that is pumped through the condensers from an outside source and then discharged back into the environment. This differs from the closed cycle cooling system where the water used for cooling is pumped from the steam condenser to a cooling tower or pond and then recycled back to the condenser. While the direct cooling system has a relatively high amount of water usage from the environment, the closed cycle cooling system has higher amounts of water consumption due to losses from evaporation.  In both cases, the water usage and consumption for a conventional nuclear power plant is higher than for the average fossil fuel power plant (Table 1). Nuclear power plants require more cooling water because they operate at thermodynamically lower steam conditions which results in a lower cycle efficiency. Thus a greater steam recirculation rate which contributes to a greater flow of cooling water is needed to produce a given amount of electricity compared to an average fossil fuel plant. 
|Table 1: Comparison of water requirements for fossil fuel and nuclear power plants. Source: EPRI|
As freshwater resources become scarcer, the nexus between water and energy becomes magnified. Thermoelectric power plants, including nuclear plants, make up 40% of freshwater usage in the US. The high water requirements mean that the operations of these power plants are susceptible to heat waves and droughts. If the temperature of a water body is already high, environmental regulations do not allow for further discharges of high temperature water above a certain threshold. Furthermore, if water levels in a body of water drop too low, the power plant may not be able to intake enough water.  In the hot, dry summer of 2006, several nuclear plants across Europe stopped operations due to restricted water availability.  In August 2012, a nuclear reactor at Millstone Nuclear Power Station in Connecticut shut down after the seawater used for cooling became too warm. Other nuclear plants, including the Braidwood Generating Station in Chicago, were only able to continue operations with a high temperature cooling water after receiving special permission from the Nuclear Regulatory Commission. 
Climate change is predicted to have significant impacts on freshwater river flow levels and temperature. Under future climate scenarios for 2031-2060, nuclear and coal power generating capacities during summers are predicted to decrease by 4.4%-16% in the U.S. and 6.3%-19% in Europe due to a lack of cooling water.  To adapt to a warmer climate and scarcer freshwater resources, strategies could focus on siting plants near coasts and increasing the thermal efficiency of power plants.
© Safiyyah Abdul-Khabir. The author grants permission to copy, distribute and display this work in unaltered form, with attribution to the author, for noncommercial purposes only. All other rights, including commercial rights, are reserved to the author.
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