Water is a constraint on coal-fired power generation, and most of these areas are located in water-scarce regions. 

Each of the different cooling methods has local environmental and social impacts, as well as being regulated.

1. The situation in China

Water is a limiting factor for coal-fired power generation in China's inland regions, which are mostly located in water-scarce regions.

Air-cooling retrofits reduce efficiency by 3-10% and reportedly cost around $200 million per 1000 MWe of capacity—about 2.5 C/kWh.

The World Energy Outlook 2015 reported that more than 100 GWe of coal-fired power plants in northern China (12% of the entire

coal-fired fleet) use dry cooling, and demand for dry cooling is expected to continue to increase.

In particular, the coal-fired capacity of about 175 GWe requires a dry cooling retrofit.

Due to the high cost of transporting coal, the cost of mining from Xinjiang to the east coast has more than tripled, so many new power

plants are being built near coal mines in the north, and high-voltage direct current transmission lines are used to send power south.

The cost increment for dry cooling is about $0.7/MWh, which is the same cost as HVDC.

China plans to use small modular molten salt reactors as an energy solution in northwestern China, where water is scarce and population

density is low.

In the late 2020s, the use of TMSR-SF reactors for waterless cooling in arid regions is envisaged. In addition to the solid-fuel design, a 168

MWe liquid-fueled MSR is planned to be built primarily through cavity cooling, with passive removal of waste heat.

2. Environmental and social impacts

Each of the different cooling methods has local environmental and social impacts, as well as being regulated.

Direct cooling effects, including the amount of water extracted and effects on organisms in the aquatic environment, especially fish

and crustaceans.

These include deaths from impingement (catching larger fish on screens) and entrainment (attracting smaller fish, eggs and larvae

through cooling systems), as well as changes in ecosystem conditions caused by elevated temperatures in discharge water.

Effects of wet cooling towers, including water consumption (as opposed to pure extraction) and visible steam plumes from cooling

tower emissions.

Such plumes are considered by many to be a disturbance, and in colder conditions some tower designs allow for icing that can cover

the ground or nearby surfaces.

Another possible problem is steam carryover, where salts and other contaminants may be present in the steam droplets.

Over time, understanding of these effects has increased, cooling environmental effects have been quantified, and many solutions

have been developed.

Technical solutions such as fishing nets and plume eliminators can effectively mitigate many of these impacts, but the associated

costs increase with complexity.

In a nuclear power plant, aside from some slight chlorination, the cooling water is not contaminated by use - it never comes into

contact with the nuclear part of the nuclear power plant and only cools the condensers in the turbine room.

On a regional and global scale, less efficient cooling, especially dry cooling, will lead to an increase in associated emissions per

unit of output electricity.

This is a greater concern for fossil fuel power plants, but arguably also has implications for waste from nuclear power.

3. State supervision

DOE report

On the policy side, a DOE report noted that a major purpose of the Clean Water Act in the United States is to regulate the impact

of cooling water use on aquatic organisms, which has prompted the choice of recirculating systems over once-through systems

for fresh water.

This will increase water consumption unless more expensive and less efficient dry cooling systems are used.

This will be disadvantageous for nuclear energy compared to supercritical coal, although coal-fired flue gas desulfurization (FGD)

demand will balance the water balance to at least some extent, and future carbon capture and storage (CCS) will be further

disadvantageous for coal.

An August 2010 report by DOE's National Energy Technology Laboratory (NETL) analyzed the impact of new environmental

regulations for U.S. coal-fired power plants.

Upcoming environmental protection regulations expected in February 2011 will mandate the use of cooling towers as "best available

technology" to minimize the environmental impact of polluting water intakes.

Site-specific assessments and cost-benefit analyses are no longer allowed to determine the best options for protecting aquatic

species from a range of proven technologies.

This could mean that all new plants, and perhaps many existing units, will need to install cooling towers and not use direct cooling,

as direct cooling does require a lot of water, but about 96% of the water is returned, which is slightly warmer high.

Not only are cooling towers more expensive, they also work by evaporating large amounts of water, putting a strain on the fresh

water supply - according to reports, cooling towers consume 1.8 L/kWh of water compared to less than 0.4 L/kWh for once-through

cooling towers .

The NETL report states that coal-fired power plants are expected to increase water use over the next two decades if new plants no

longer allow direct cooling, but this does not affect the potential for many coal-fired power plants to add carbon capture and storage

(CCS) technology to limit U.S. carbon emissions. properties, thereby further increasing water consumption by 30-40%.

EPRI study

A 2010 study by the Electric Power Research Institute (EPRI) found that the total cost of installing cooling towers at U.S. power plants

would exceed $95 billion.

The cost of just 39 nuclear power plants (63 reactors) is close to $32 billion.

The EPRI study covered 428 U.S. power plants with once-through cooling systems that may be subject to revised regulations by the U.S.

Environmental Protection Agency (EPRI) to protect aquatic organisms from becoming trapped in cooling water intake structures.

As noted above, under proposed amendments to the Clean Water Act, the EPA could mandate that closed-loop cooling be a "best available

technology" to minimize adverse environmental effects on aquatic life.

The EPRI study considered capital costs, lost revenue due to prolonged downtime required to replace the system, and costs associated with

loss of plant efficiency, including increased energy use for fans and pumps in closed-cycle cooling systems.

Such a change would cost each of the 311 million U.S. citizens $305 to retrofit all once-through cooling power plants, "to remedy a nearly

non-existent environmental impact, according to scientific studies of the plant's aquatic populations."

In May 2014, the EPA issued a final rule regulating water intakes at 1,065 plants and plants, allowing existing plants to use various options

for protecting aquatic life, although new options require closed-loop systems.

Compared to once-through cooling systems, cooling towers consume twice as much water from the aquatic habitat we want to protect. 

This fact is important in light of the forecasted future in which much of the United States will face water scarcity.

The structure of the cooling water intake of the power plant, a technology-based solution, in the protection of fish, can be adapted to

the ecological diversity of different locations.

As the EPA has previously noted, solutions such as moving screens with collection and return systems are comparable to cooling towers

in protecting aquatic organisms in water bodies used to cool power plants.

France and Australia

In France, all but the four EdF nuclear power plants (14 reactors) are located inland and require fresh water for cooling.

Eleven of the 15 inland nuclear power plants (32 reactors) have cooling towers and use evaporative cooling, and the other 4 (12 reactors)

use river or lake water directly.

Regulatory limits on increasing the temperature of the receiving water mean that power generation may be limited during the sweltering

summer months.

For example, in Bugey, the maximum increase in water temperature is typically 7.5°C in summer, 5.5°C in summer, 30°C maximum discharge

temperature (34°C in summer), and 24°C maximum downstream temperature (35°C maximum allowed in summer) .

For power plants using direct ocean cooling, the allowable temperature rise at sea is 15°C.

In the United States, power plants using direct river cooling must reduce power in hot weather.

TVA's three Browns Ferry nuclear power units are operating at 50% speed with river temperatures exceeding 32°C.

With one exception, all nuclear power plants in the UK are located on the coast and use direct cooling.

In the 2009 UK siting study for new nuclear power plants, all recommendations were for locations within 2km of rich waters - oceans or estuaries.

An Australian study recommending the use of renewable energy sources (wind and solar) at one site in South Australia shows that the CSP

plant uses 0.74 GL/yr of water to clean mirrors (heliostats), totaling 540 MW, 2810 GWh/year, so 0.26 L/kWh.

In addition to cooling, water use needs to be considered when comparing the water requirements of nuclear and coal-fired power plants.

Coal-fired ash removal is often used for water treatment, which can easily cause pollution, as is runoff from coal storage.

Fresh water is a valuable resource in most of the world.

Where water is scarce, public opinion supports government policies to minimize water waste.

Other than being close to major load centers, there's no reason to build nuclear plants far from the coast, where they can use once

-through seawater cooling.

The location of coal-fired power plants requires consideration of the logistics (and associated aesthetics) of the fuel supply, as each

1000 MWe power plant requires more than 3 million tonnes of coal per year.

"Nuclear power plants use a lot of water, but only slightly more than coal-fired power plants.

Nuclear power plants operate at relatively low steam temperatures and pressures, so the cycle is less efficient, which in turn requires

higher cooling water flows.

A more efficient coal-fired power plant can cool the water by slightly lowering the steam temperature and pressure.

If any thermal power plant - coal or nuclear - needs to be located inland, the availability of cooling water is a key factor in location selection.

Where cooling water is limited, the importance of high heat load efficiency is high, but any advantage of supercritical coal over nuclear

energy may be greatly diminished due to the water requirements for flue gas desulfurization (FGD).

Even if water is very limited to be used for cooling, the plant can be kept away from the load demand and have enough water for efficient

cooling (accepting some losses and additional transmission costs).

Gen III+ nuclear power plants have higher thermal efficiency compared to older plants and should not be disadvantaged relative to coal

due to water usage considerations.

Of course, considerations to limit greenhouse gas emissions will be superimposed on the above factors.

CO2 capture will increase water use by 50-90% in coal-fired and gas-fired power plants, making the former more water-intensive than

nuclear power plants, according to DOE.

Another implication involves cogeneration, the use of waste heat from shoreline nuclear power plants for desalination.

In the Middle East and North Africa, a large amount of desalination already uses waste heat from oil and gas power plants, and in the

future many countries hope to use nuclear energy to achieve this combined heat and power role.

2. Environmental and social impacts