Environment

Introduction

The environmental effects of nuclear power exploitation have been a central point of the debate over the feasibility of nuclear power in the near future. Green house gas emissions are considered to be one of the key contributors to global climate change. Nuclear power plants release close to zero green house gasses directly. It is their biggest advantage over conventional coal power plants. However, indirect emissions associated with power plant operations are significant. Costs of transportation of fuel and nuclear waste, waste storage, and other factors contribute to the overall emissions associated with nuclear power. In addition, nuclear power plants still release heat into the environment, leading directly to global warming.

Among the greatest disadvantages of nuclear power plants is the issue of nuclear waste. We will discuss problems of transportation and storage in this segment of our website, along with ways to resolve them. 

Briefly on Global Warming

In this section, global climate change will be mentioned multiple times. Although it is a controversial subject, it has become a widely accepted phenomenon among scientists and engineers.  It is currently held that CO2 emissions are the chief contributor to global warming, and although the direct correlation is uncertain, the risk mitigation of potential climate change has become a primary objective for many engineering projects. Low carbon emissions are a key advantage that nuclear power holds over other energy sources. We believe carbon emissions are a good way to gauge the feasibility of a particular power source from the environmental point of view.

Health Risks

When operated properly, nuclear power plants release virtually no radioactive material to the surrounding environment. In the United States, annual emissions for nuclear power plants are limited to 1 mSv (miliSievert) per person per year. Such exposure is estimated to increase the risk of cancer individual by 0.005% per person per year. For comparison, an average person receives around 3.6 mSv per year, and approximately 80% of this number comes from natural background radiation and cosmic radiation. The other 20% are contributed by the effects of nuclear weapons testing in the early Cold War period (1940-60s).11

The maximum allowable exposure to radiation is 50 mSv per year and 100 mSv per five years to people who work with radioactive materials directly, as mandated by the US as well as international regulatory commissions. Studies are currently under way to determine effects of such exposures. Scientists suspect higher risks of leukemia and cancer, but no direct correlation has been established yet.

Interestingly enough, coal power plants release more radiation into the surrounding environment than nuclear reactors. Although nuclear processes are inherently more radioactive, they are better isolated in a nuclear power plant. Coal power plants are not isolated and the ore itself contains small amounts of Uranium and Thorium. As a result, a coal power plant will release a radioactive dose approximately 100 times greater than a nuclear power plant over the course of one year.5

In the case of an accident, effects of radiation exposure can be catastrophic to humans as well as the surrounding environment. After the Chernobyl accident in 1986, an increased number of cases of thyroid cancers and leukemia were recorded, particularly among children and rescue workers. Psychological and social impacts of the catastrophe were also tremendous. Although another accident of such magnitude is highly unlikely, it is important to acknowledge the dangers nuclear technology can possess if not treated with utmost respect. Find out more about the Chernobyl Disaster.

Power Plant Impact

Although nuclear power plants do not burn fossil fuels, they still release a small amount of greenhouse gasses. In the United States, two reactor systems are currently utilized: the Pressurized Water Reactor and the Boiling Water Reactor. Find out more about how these systems differ. Below is the full list of on-site emissions of a typical nuclear power plant:

Direct Emissions

Air-Gaseous releases: gasses released by nuclear power plants into the atmosphere directly are never radioactive.
 
• Water vapor from cooling towers – non-radioactive water vapor can be seen rising from the cooling towers built on site.

• Ventilation of non-radioactive exhaust from buildings – air ventilated from buildings not associated with radioactive processes.
 
• Diesel generator exhaust – power plants have a diesel generator or turbines on site that are used for emergency power productions. These generators are run periodically for testing. Backup generators are the only source of greenhouse gas emissions at a nuclear power plant.
  
• Gases and steam from the air ejectors – gasses and steam coming from a Pressurized Water Reactor (PWR) are non-radioactive, and are released directly into the atmosphere. Boiling Water Reactors (BWR) release slightly radioactive gasses which are passed through a system of delay pipes, storage tanks and hydrogen recombiner before they are released into the atmosphere. The source of release is a very tall stack that can be found onsite of a BWR power plant.
 
• Ventilation of from buildings that have processes with radioactivity – gasses ventilated from these buildings are monitored with radiation sensors. In case an unacceptable level of radioactivity is reached, the ventilation system is shut down and rerouted through a system of filters specifically designed to lower radioactive emissions below acceptable levels.
 
• Gases removed from systems having radioactive fluids and gases – these gasses are collected and stored in pressured tanks. They are closely monitored and sampled periodically. When the level of radioactivity in the gas reaches a sufficiently low level, these gases may be released into the atmosphere. Releases of this kind are very rare.

Water-liquid releases: Water that comes out of a nuclear power plant can be divided into two sub categories: nonradioactive and slightly radioactive. Most nuclear power plants use water as coolant, and also for steam in the power generation turbine cycle. Water discharged by Pressurized Water Reactors is not radioactive, and is released into the environment via steam on the cooling towers, as well as directly into the surrounding bodies of water.

In a Boiling Water Reactor, some water may come into contact with radioactive elements. In these cases, radioactive water is channeled and stored. Many BWR equipped power plants practice a “Zero Release” policy, and do not release any radioactive fluids into the environment.
 
Solid releases: Solid releases of a power plant are the “elephant in the room” when it comes to nuclear power, and is perhaps its greatest disadvantage. The debate over disposal of nuclear waste has been raging in the United States for decades, and it is unlikely to be resolved in the near future.6 Broadly speaking, there are two types of nuclear waste released by a typical power plant: High Level Waste (HLW) and Low Level Waste (LLW). High level waste is highly radioactive, and accounts for approximately 99% of all waste radioactivity. Low level waste is less radioactive but the most voluminous, taking up around 85% of all waste volume.13 Nuclear waste cannot be reprocessed all the way, although its radioactivity can be reduced. We will discuss the details of nuclear waste storage and reduction methods later in this article.

Thermal Emissions

Although we know that nuclear power plants produce almost no greenhouse gasses, they still contribute to global warming. From thermodynamics, we know that any work producing process also releases heat. This principle is universal, and applies to nuclear power plants as well. Heat released by a nuclear plant is known as thermal pollution, and is a source of some concern.
Effects of Thermal Emissions

Typically, power plants are cooled by a “once through” water cooling system. In effect, water is collected from the nearby river or lake and sent through the power plant as coolant. Then, the water is released back into the environment. The temperature of the coolant water rises by as much as 20 - 30oF, and can have a serious effect on the water habitats surrounding the power plant.

Water that is significantly warmer may affect the migration patterns of fish, and in the worst case scenario kill them. Often times, the cooling systems undergo “heat treatments,” in which the direction of water through the cooling system is reversed to clear intake pipes. In such cases, hot water is pumped quickly into areas of low ambient temperature around the intakes, leading to thermal shock.4 The effects of ambient temperature change are not all one sided, however. The Turkey Point Plant in Florida, for example, has helped sustain the American Crocodile population in its cooling canals.

Reduction Options
The thermal pollution of the surrounding bodies of water can be reduced by using cooling towers or cooling canals. A cooling canal essentially delays returning heated water into the surrounding water systems by slowly running exhausted hot water through a certain distance. During the delay, the water is cooled by ambient air.

In a cooling tower, the hot water is circulated inside the tower while being cooled by surrounding air. Most state governments require nuclear power plants to employ a cooling tower in order to minimize the thermal emissions in the nearby water systems. However, excess heat is then released directly into the air.
Side Effects
According to the First Law of Thermodynamics, whenever work is generated, heat will be produced. Work can be anything: from walking to eating, to power generation. No matter how small or efficient the process, heat will always be produced. Generally, heat released as a byproduct of work generation is vented into outer space through natural processes. As a result, the global temperature remains relatively constant. As we know, it doesn’t grow continuously.

The rate at which heat can leave the atmosphere is limited by the greenhouse gasses. At equilibrium, heat will dissipate into outer space as fast as it is produced. At the current rate of heat production worldwide, the global temperature would have to rise by approximately 1.8oC before equilibrium can be reached again.9 In that sense, nuclear power plants as well as any other power generating systems contribute to global warming directly. However, because they help reduce green house gas emissions, nuclear power plants have a tremendous benefit in the long term: as power consumption across the globe rises in the future, green house gas emissions will be reduced and thus the global temperature rise will be slowed.
 

What about coal?

Coal power plants also release heat during the power generation process. Conventional coal plants convert around 33% of the energy in coal into useful energy. The rest is lost as heat. Combined cycle power plants, also known as cogeneration plants, are approximately 50% efficient. In a combined cycle plant, excess heat produced during power generation is channeled to create steam, which is sold to the nearby industries and homes.

Nuclear power plants, on average, have thermal efficiencies of 33% or higher. However, combined cycle processes are not utilized in nuclear power plants in the United States. Following Chernobyl and Three Mile Island incidents, nuclear power plants have been built away from population centers. In addition, the public has not been receptive to steam generated by nuclear power plants in fear of radiation.

Water Consumption

According to the US Geological Survey, electricity accounts generation accounts for 3.3% of all water consumption in the United States. For comparison, residential consumption accounts for 6.7%, and irrigation makes up for 81.3% of all water consumed. A typical power plant will consume between 6 and 16 gallons per household per day, if the said power plant does not operate a cooling tower. With a cooling tower, water consumption rises to 20-26 gallons per household per day. A typical power plant will supply approximately 740,000 households with electricity around the clock. A typical household, consisting of three people, consumes an estimated 300 gallons of water per day.  

Indirect Emissions

Nuclear power plants emit very small quantities of radiation and greenhouse gasses. However, the logistics associated with providing a nuclear power plant with fuel, as well as the disposal of waste, have a significant contribution to the overall environmental impact of a nuclear power plant.

Logistics Emission Costs

Logistics costs associated with nuclear power plant operation come from several major sources. Mining of fuel, uranium enrichment and transportation of fuel and waste are the major contributors. Carbon Dioxide (CO2) emissions due to logistics operations in the extreme case fall between 1.4 and 200 g CO2 per KWh of power generated. The low end estimate assumes high very high quality ore, while the high end estimate assumes low quality. Realistically, uranium of such low quality is unlikely to be used due to impractically high costs. At the same time, high quality uranium is not common. A more recent and more realistic estimate suggests a range of 16-60 g of CO2 released per KWh generated. This number is expected to decrease further as centrifuge technology replaces gaseous diffusion for uranium enrichment. To learn more about uranium enrichment, go here. For comparison, CO2 emissions by power sources are listed below:11
 
Coal –   790-1020 g CO2 per KWh

Nuclear -  16-60 g CO2 per KWh

Hydroelectric- 17-22 g CO2 per KWh

Wind-  4.2-11.1 g CO2 per KWh

Uranium Mining Costs

Nuclear power plants require fuel in the form of enriched uranium. Before uranium can be enriched, it has to be mined from the ground. Uranium mining is a hazardous occupation with significant potential health risks. Inhalation and ingestion with food or water are the most common forms of uranium penetration into the human body. Uranium ingestion may cause heavy metal poisoning, bone and lung cancer, and leukemia. A number of studies have been recently undertaken to determine effects of uranium mining on workers and surrounding environments.

A 2001 study in Lagos Real, Brazil, found no increase in heavy metal content in the area surrounding the mine. The lack of results can be attributed to the short time of the study, however, as it spanned only two years. Mining in Lagos Real began in 2000.3

One of the waste products of Uranium mining is the uranium tailings that are produced during the process. Uranium tailings are lightly radioactive, and in the past were left on the surface near the mines. When left to dry out, the tailings release Radon gas, which is also radioactive. In addition, sand particles can be carried great distances by water or wind, expanding the affected area. A recent study on mines in Spain determined a higher risk of leukemia mortality among people living in the vicinity of the uranium mills. However, the data could not be tied to the facility operations directly, and the effects remain uncertain.7 Enclosed storage of uranium tailings can reduce potential health hazards.

Nuclear Waste

As we mentioned before, nuclear waste is one of the greatest disadvantages of nuclear power generation. At this point in time, there are no technologies that would allow for nuclear waste to be fully reprocessed. For the foreseeable future, any waste generated by the power plants will have to be stored.
 
There are four major types of nuclear waste:

High Level Waste (HLW) – high level waste includes highly radioactive material, for the most part spent fuel. It is very radioactive, and accounts for 99% of all nuclear waste radioactivity.

Low Level Waste (LLW) – low level waste includes any components that have come into contact with radioactive elements and become irradiated. It can range from clothing to mechanical components, to water and gasses passing through the reactor system. Low level waste accounts for 85% of all nuclear waste by volume.

Transuranic Waste – waste which has been contaminated with alpha-particle emitting radio nuclides. This waste category is unique to the United States classification system.

Uranium Mill Tailings – byproduct of uranium mining. 
 

Storage Methods

In the United States and around the world, nuclear waste produced by power plants is stored on site. Although there have been attempts at constructing a nuclear storage waste facility at Yucca Mountain, that project has been put on halt due to lack of public and political support. For the time being, temporary storage will be employed until a more permanent solution can be found.2 To learn about nuclear waste storage methods in greater detail, click here.

Reduction Options

Reduction options:
Currently, nuclear waste produced by power plants will remain radioactive for thousands of years. A table with typical isotope lifetimes is show below.12
 
You may notice that radioactivity for some isotopes starts low, then increases before decreasing again. As radioactive isotopes break down, they release other radioactive isotopes. The biggest risk associated with nuclear waste storage is predicted to happen within tens of thousands of years, when waste canisters would degrade from external water exposure, and release radioactive materials into the ground.10 However, the lifetime of nuclear waste produced by power plants can be reduced from tens of thousands of years to several centuries.

A Breeder Reactor generates more fissile material than it consumes per fuel cycle, resulting in greater fuel economy. In addition, it does not use a once-through fuel cycle, and consumes a much greater portion of the initial fissionable material. However, breeder reactors produce plutonium as a byproduct of the power generation process. In 1977, due to concerns over terrorism and nuclear proliferation, President Carter banned civilian reprocessing of nuclear fuel. As a result, breeder reactors were effectively banned in the United States. Many countries abroad continue to operate them, including France, Japan, Korea and Russia.

An additional benefit of breeder reactors is their high fuel efficiency which may indirectly benefit the environment due to a reduced need for uranium mining. However, a 2009 MIT study on the future feasibility of nuclear power concluded that breeder reactors are unnecessary. According to the report, fuel limitations will not be a concern in the foreseeable future, and known uranium sites are capable of providing the world with the necessary uranium fuel. The authors of the study believe that nuclear proliferation will be a much greater concern in the near future.1 

Concluding Remarks

Having said all that, what is the final verdict? Is nuclear power an environmental hazard or a savior for our ever increasing energy needs? In truth, it is neither. Today, nuclear power remains one of several viable alternate energy sources. It is a well explored technology that is continuing to develop, and can reliably provide power independent of local climate or geography. When managed properly, nuclear power plants are safe to operate and environmentally friendly. However, nuclear power, as any other source of energy, is not without its faults. Political and social issues surrounding nuclear waste are unlikely to be resolved in the near future.

The MIT study mentioned previously concluded that for most Americans, halting nuclear proliferation in the developing countries is more important than global reduction of carbon emissions. With nuclear power, it seems, short term goals overshadow the long term benefits. 

Sources

1. "The Future of Nuclear Power: An Interdisciplinary MIT Study." The Future of Nuclear Power.   MIT, 2009 <http://web.mit.edu/nuclearpower/>.

2. Brongers, Michiel P.H. United States. Corrosion Costs and Preventive Strategies in the United   States: Nuclear Waste Storage, Apendix CC . Dublin, Ohion: CC Technologies, 2001.   Web. 18 Sep 2010.

3. Carvalho, Ilson G., Rosa Cidu, Luca Fanfani, Helmut Pitsch, Catherine  Beaucaire and    Pierpaolo Zuddas. "Environmental Impact of Uranium Mining and Ore Processing in   the Lagoa Real District, Bahia, Brazil." Environmental Science and Technology. 39.   (2005): 8646-52.

4. Deysher, Larry. "Thermal Pollution." Pollution Issues. N.p., n.d. Web.      <
http://www.pollutionissues.com/Te-Un/Thermal-Pollution.html>.

5. Gabbard, Alex. "Coal Combustion: Nuclear Resource or Danger." Oak Ridge National    Laboratory. ORNL, n.d. Web.  <
http://www.ornl.gov/info/ornlreview/rev26-  34/text/colmain.html>.

6. Gonyeau, Joseph. "Environmental Effects of Nuclear Power." The Nuclear Tourist. N.p.,    21.12.2005. Web. 25 Oct 2010. <
http://www.nucleartourist.com/basics/environ1.htm>.

7. Lopez-Abente, Gonzalo, Nuria Aragones, Maria Pollan, Maria Ruiz, and Ana Gandarillas.   "Leukemia, Lymphomas, and Myeloma Mortality in the Vicinity of Nuclear Power   Plants and Nuclear Fuel Facilities in Spain." Cancer Epidemiology, Biomarkers and   Prevention. 8. (1999): 925-34.

8. Morland, Martin. "Climate Change and Nuclear Energy." International Relations. 15.4 (2001):   53-64.

9. Nordell, Bo. "Thermal Pollution Causes Global Warming." Global and Planetary Change. 38.   (2003): 305-12.

10. Peterson, Per F., William E. Kastenberg, and Michael Corradini. "Nuclear Waste and the    Distant Future." Issues in Science and Technology. 22.4 (2006): 47-50.

11. Ramana, M. V. "Nuclear Power: Economic, Safety, Health Environmental Issues of Near Term   Technologies." Annual Review of Environment and Resources. 34 (2009): 127-52.

12. Warf, James C., All Things Nuclear, First Edition, Southern California Federation of Scientists,   Los Angeles, 1989, p. 85.

13. Yim, Man-Sung, and K. Linga Murty. "Materials and Issues in Nuclear Waste Management."   JOM 52.9 (2000): 26-29.