ENVIRONMENTAL SCIENCE

Transcription

1 1 ENVIRONMENTAL SCIENCE A Study of Interrelationships 14 th Edition Chapter 9 Non-Renewable Energy Sources

2 2 Outline 9.1 Major Energy Sources 9.2 Resources and Reserves 9.3 Fossil-Fuel Formation 9.4 Issues Related to the Use of Fossil Fuels 9.5 Nuclear Power

3 3 Outline 9.6 The Nature of Nuclear Energy 9.7 Nuclear Chain Reaction 9.8 Nuclear Fission Reactors 9.9 The Nuclear Fuel Cycle 9.10 Issues Related to the Use of Nuclear Fuels

4 4 9.1 Major Energy Sources Nonrenewable energy sources are those whose resources are being used faster than can be replenished. Coal, oil, and natural gas Renewable energy sources replenish themselves or are continuously present as a feature of the environment. Solar, geothermal, tidal, etc. They currently provide about 12% of the energy used worldwide, primarily from hydroelectricity and firewood.

5 5 9.2 Resources and Reserves A resource is a naturally occurring substance of use to humans that can potentially be extracted using current technology. A reserve is a known deposit that can be economically extracted using current technology, under certain economic conditions. Reserves are smaller than resources. Reserve levels change as technology advances, new discoveries are made, and economic conditions vary.

6 6 9.3 Fossil-Fuel Formation Coal 300 million years ago, plant material began collecting underwater, initiating decay, forming a spongy mass of organic material. Due to geological changes, some of these deposits were covered by seas, and covered with sediment. Pressure and heat over time transformed the organic matter into coal.

7 7 Different Kinds of Coal

8 8 Oil and Natural Gas Oil and natural gas probably originated from microscopic marine organisms that accumulated on the ocean floor and were covered by sediments. Muddy rock gradually formed shale containing dispersed oil. Natural gas often forms on top of oil.

9 9 Crude Oil and Natural Gas Deposits

10 10 World Oil and Natural Gas Reserves 2012 World Oil Reserves 2012 World Natural Gas Reserves 2102

11 Issues Related to the Use of Fossil Fuels Fossil fuels supply 80% of world s commercial energy. Fossil Fuels

12 12 Coal Use Coal is most abundant fossil fuel. Primarily used for generating electricity. There are four categories of coal: Lignite, Sub-bituminous, Bituminous, and Anthracite. Lignite High moisture, low energy, crumbly, least desirable form. Sub-bituminous Lower moisture, higher carbon than lignite. Used as fuel for power plants.

13 13 Coal Use Bituminous Low moisture, high carbon content Used in power plants and other industry such as steel making. Most widely used because it is easiest to mine and the most abundant, supplying 20% of the world s energy requirements. Anthracite Has the highest carbon content, and is relatively rare. It is used primarily in heating buildings and for specialty uses.

14 14 Coal Use: Extraction There are two extraction methods: Surface mining (strip mining), which is the process of removing material on top of a vein, is efficient but destructive. Underground mining minimizes surface disturbance, but is costly and dangerous. Many miners suffer from black lung disease, a respiratory condition that results from the accumulation of fine coal-dust particles in the miners lungs.

15 15 Coal Use: Transportation & Pollution Coal is bulky and causes some transport problems. Mining creates dust pollution. Burning coal releases pollutants (e.g., carbon and sulfur). Millions of tons of material are released into atmosphere annually. Sulfur leads to acid mine drainage and acid deposition. Mercury is released into the air when coal is burned. Increased amounts of atmospheric carbon dioxide are implicated in global warming.

16 16 Coal Mining Methods

17 17 Surface-Mine Reclamation

18 18 Environmental Issues: Subsidence

19 19 Environmental Issues: Acid Mine Drainage

20 20 Oil Use Oil is more concentrated than coal, burns cleaner, and is easily transported through pipelines. These qualities make it ideal for automobile use. It is difficult to find. It causes less environmental damage than coal mining.

21 21 Oil Use Once a source of oil has been located, it must be extracted and transported to the surface. Primary Recovery methods If water or gas pressure associated with the oil is great enough, the oil is forced to the surface when a well is drilled. If water and gas pressure is low, the oil is pumped to the surface. 5 30% of the oil is extracted depending on viscosity and geological characteristics.

22 22 Oil Use Secondary Recovery Water or gas is pumped into a well to drive the oil out of the pores in the rock. This technique allows up to 40% of the oil to be extracted. Tertiary Recovery Steam is pumped into a well to lower the viscosity of the oil. Aggressive pumping of gas or chemicals can be pumped into a well. These methods are expensive and only used with high oil prices.

23 23 Oil Use Processing As it comes from the ground, oil is not in a form suitable for use, and must be refined. Multiple products can be produced from a single barrel of crude oil. Oil Spills Accidental spills only account for about 1/3 of oil pollution resulting from shipping. 60% comes from routine shipping operations.

24 24 Extraction Methods Offshore Drilling Secondary Recovery

25 25 Transportation of Oil

26 26 Environmental Issues Oil Spills From Tankers Sources of Marine Oil Pollution

27 27 Natural Gas Use The drilling operations to obtain natural gas are similar to those used for oil. It is hard to transport and in many places is burned off at oil fields, but new transportation methods are being developed. Liquefaction at -126 o F (1/600 volume of gas) The public is concerned about the safety of LNG loading facilities so they are located off shore. It is the least environmentally damaging fossil fuel. It causes almost no air pollution.

28 Nuclear Power Although nuclear power does not come from a fossil fuel, it is fueled by uranium, which is obtained from mining and is non-renewable. As of 2011, there were 440 nuclear power reactors in operation and 61 nuclear power plants under construction in 13 countries. Of the 158 nuclear power plants currently being planned, most are in Asian countries such as China, India, Japan, and South Korea.

29 29 Nuclear Reactor Statistics

30 30 Distribution of Nuclear Power Plants in North America

31 The Nature of Nuclear Energy The nuclei of certain atoms are unstable and spontaneously decompose. These isotopes are radioactive. Neutrons, electrons, protons, and other larger particles are released during nuclear disintegration, along with a great deal of energy. Radioactive half-life is the time it takes for half the radioactive material to spontaneously decompose.

32 32 Half-Lives and Significance of Some Radioactive Isotopes

33 The Nature of Nuclear Energy Nuclear disintegration releases energy from the nucleus as radiation, of which there are three major types: Alpha radiation consists of moving particles composed of two neutrons and two protons. It can be stopped by the outer layer of skin. Beta radiation consists of electrons from the nucleus. It can be stopped by a layer of clothing, glass, or aluminum. Gamma radiation is a form of electromagnetic radiation. It can pass through your body, several centimeters of lead, or a meter of concrete.

34 Nuclear Chain Reaction Nuclear fission occurs when neutrons impact and split the nuclei of certain other atoms. In a nuclear chain reaction, splitting nuclei release neutrons, which themselves strike more nuclei, in turn releasing even more neutrons.

35 Nuclear Chain Reaction

36 Nuclear Chain Reaction Only certain kinds of atoms are suitable for development of a nuclear chain reaction. The two most common are uranium-235 and plutonium There also must be a certain quantity of nuclear fuel (critical mass) for the chain reaction to occur.

37 Nuclear Fission Reactors A nuclear reactor is a device that permits a controlled fission chain reaction. When the nucleus of a U-235 atom is struck by a slowly moving neutron from another atom, the nucleus splits into smaller particles. More rapidly-moving neutrons are released, which strike more atoms. The chain reaction continues to release energy until the fuel is spent or the neutrons are prevented from striking other nuclei.

38 Nuclear Fission Reactors Control rods made of a non-fissionable material (boron, graphite) are lowered into the reactor to absorb neutrons and control the rate of fission. When they are withdrawn, the rate of fission increases. A moderator is a substance that absorbs energy, which slows neutrons, enabling them to split the nuclei of other atoms more effectively. Water and graphite are the most commonly used. Coolant, usually water, manages the heat produced.

39 Nuclear Fission Reactors In the production of electricity, a nuclear reactor serves the same function as a fossil-fuel boiler: it produces heat, which converts water to steam, which turns a turbine, generating electricity. The 3 most common types of reactors are: Pressurized-Water (60%) Boiling-Water (20%) Heavy-Water (10%) Gas-Cooled Reactors are not popular, and no new plants of this type are being constructed.

40 40 Pressurized-Water Reactor

41 Nuclear Fission Reactors Breeder reactors produce nuclear fuel as they produce electricity. Liquid sodium efficiently moves heat away from the reactor core. Hence they are called Liquid Metal Fast Breeder Reactors. A fast moving neutron is absorbed by Uranium-238 and produces Plutonium-239 P239 is fissionable fuel. Most breeder reactors are considered experimental. Because P239 can be used in nuclear weapons, breeder reactors are politically sensitive.

42 The Nuclear Fuel Cycle The nuclear fuel cycle begins with the mining of low-grade uranium ore primarily from Australia, Kazakhstan, Russia, South Africa, Canada, and the United States. It is milled, and crushed and treated with a solvent to concentrate the uranium. Milling produces yellow-cake, a material containing 70-90% uranium oxide.

43 The Nuclear Fuel Cycle Naturally occurring uranium contains about 99.3% nonfissionable U 238, and.7% fissionable U 235. It must be enriched to 3% U 235 to be concentrated enough for most nuclear reactors. Centrifuges separate the isotopes by their slight differences in mass. Material is fabricated into a powder and then into pellets. The pellets are sealed into metal rods (fuel rods) and lowered into the reactor.

44 The Nuclear Fuel Cycle As fission occurs, U-235 concentration decreases. After about three years of operation, fuel rods don t have enough radioactive material remaining to sustain a chain reaction, thus spent fuel rods are replaced by new ones. Spent rods are still very radioactive, containing about 1% U-235 and 1% plutonium.

45 The Nuclear Fuel Cycle Spent fuel rods are radioactive, and must be managed carefully to prevent health risks and environmental damage. Rods can be reprocessed. U-235 and plutonium are separated from the spent fuel and used to manufacture new fuel rods. Less than half of the world s fuel rods are reprocessed. Rods can undergo long-term storage. At present, India, Japan, Russia, France, and the United Kingdom operate reprocessing plants as an alternative to storing rods as waste.

46 46 Steps in the Nuclear Fuel Cycle

47 The Nuclear Fuel Cycle All of the processes involved in the nuclear fuel cycle have the potential to generate waste. Each step in the nuclear fuel cycle involves the transport of radioactive materials. Each of these links in the fuel cycle presents the possibility of an accident or mishandling that could release radioactive material.

48 9.10 Issues Related to the Use of Nuclear Fuels Most of the concerns about the use of nuclear fuels relate to the danger associated with radiation. The absorbed dose is the amount of energy absorbed by matter. It is measured in grays or rads. The damage caused by alpha particles is 20 times greater than that caused by beta particles or gamma rays. The dose equivalent is the absorbed dose times a quality factor. 48

49 49 The Biological Effects of Ionizing Radiation When alpha or beta particles or gamma radiation interact with atoms, ions are formed. Therefore, it is known as ionizing radiation. Ionizing radiation affects DNA and can cause mutations. Mutations that occur in some tissues of the body may manifest themselves as abnormal tissue growths known as cancers.

50 50 The Biological Effects of Ionizing Radiation Large doses of radiation are clearly lethal. Demonstrating known harmful biological effects from smaller doses is much more difficult. The more radiation a person receives, the more likely it is that there will be biological consequences. Time, distance, and shielding are the basic principles of radiation protection. Water, lead, and concrete are common materials used for shielding from gamma radiation.

51 51 Protective Equipment

52 52 Radiation Effects

53 53 Reactor Safety The Three Mile Island nuclear plant in Pennsylvania experienced a partial core meltdown on March 28, It began with pump and valve malfunction, but operator error compounded the problem. The containment structure prevented the release of radioactive materials from the core, but radioactive steam was vented into the atmosphere. The crippled reactor was defueled in 1990 at a cost of about $1 billion. Placed in monitored storage until its companion reactor reaches the end of its useful life.

54 54 Three Mile Island

55 55 Reactor Safety Chernobyl is a small city in Ukraine, north of Kiev. It is the site of the world s largest nuclear accident, which occurred April 26, Experiments were being conducted on reactor. Operators violated six important safety rules. They shut off all automatic warning systems, automatic shutdown systems, and the emergency core cooling system for the reactor.

56 56 Reactor Safety In 4.5 seconds, the energy level of the reactor increased 2000 times. The cooling water converted to steam and blew the ton concrete roof from the reactor. The reactor core caught fire. It took 10 days to bring the burning reactor under control.

57 57 Reactor Safety There were 37 deaths; 500 people hospitalized (237 with acute radiation sickness); 116,000 people evacuated. 24,000 evacuees received high doses of radiation. Children or fetuses exposed to fallout are showing increased frequency of thyroid cancer because of exposure to radioactive iodine 131 released from Chernobyl.

58 58 The Accident at Chernobyl

59 59 Reactor Safety The Fukushima nuclear power plant was damaged on March 11, 2011 following a magnitude 9 earthquake and tsunami. Heat exchangers were damaged, power to the site was cut off, and the diesel generators designed to provide power in an emergency were flooded and stopped operating. Explosions, fires, and leaks in the cooling system released radiation into the atmosphere and sea water.

60 60 Terrorism After Sept. 11, 2001, fear arose regarding nuclear plants as potential targets for terrorist attacks. Nuclear experts feel aircraft wouldn t significantly damage the containment building or reactor, and normal emergency and containment functions would prevent the release of radioactive materials. Probably the greatest terrorism-related threat is from radiological dispersal devices (RDDs), or dirty bombs. They cause panic, not numerous deaths.

61 61 Decommissioning Nuclear Power Plants The life expectancy of most electrical generating plants (fossil fuel or nuclear) is years. Unlike other plants, nuclear plants are decommissioned, not demolished. Decommissioning is a 2-step process. Stage 1 includes removing, properly disposing of or storing fuel rods and water used in the reactor. Stage 2 is the final disposition of the facility.

62 62 Decommissioning Nuclear Power Plants There are three options to this second stage of the decommissioning process: 1. Decontaminate and dismantle the plant as soon as it is shut down. 2. Secure the plant for many years to allow radioactive materials that have a short half-life to disintegrate and then dismantle the plant. (However, this process should be completed within 60 years.) 3. Entomb the contaminated portions of the plant by covering the reactor with reinforced concrete and placing a barrier around the plant. (Currently this option is only considered suitable for small research facilities.)

63 63 Decommissioning Nuclear Power Plants Today, about 100 commercial nuclear power plants and about 45 experimental reactors in the world have been shut down and are in various stages of being decommissioned. Recent experience indicates that the cost for decommissioning a large plant will be between $200 million and $400 million, about 5 percent of the cost of generating electricity. Although the mechanisms vary among countries, the money for decommissioning is generally collected over the useful life of the plant.

64 64 Summary Resources are naturally occurring substances of use to humans. Reserves are known deposits from which materials can be extracted profitably with existing technology under present economic conditions. Coal is the world s most abundant fossil fuel. The supply of oil, like all fossil fuels, is limited. Natural gas is another major source of fossil-fuel energy, but transport of natural gas to consumers is problematic.

65 65 Summary Nuclear fission is the splitting of the nucleus of an atom. All reactors contain a core with fuel, a moderator to control the rate of the reaction, and a cooling mechanism to prevent the reactor from overheating. The nuclear fuel cycle involves mining and enriching the original uranium ore, fabricating it into fuel rods, using the fuel in reactors, and reprocessing or storing the spent fuel rods. Fuel and wastes must also be transported. Each step in the process presents a danger of exposure.

66 66 Summary Although accidents at Three Mile Island and Chernobyl raised safety concerns for a time, rising energy prices have stimulated increased building of nuclear power plants in many countries. Disposal of waste is expensive and controversial. Long-term storage in geologically stable regions is supported. Russia, Japan, and the UK operate nuclear reprocessing facilities to reduce future long-term storage needs.