Nuclear Energy

Alam Sekitar Dan Manusia (SKL 3201)

Introduction During the 1970’s, interest in different energy alternatives surfaced in this country. Obviously, this increase in public awareness was mainly due to our problems with foreign oil. Energy alternatives, like gas, coal, solar, wind and nuclear have been researched and each of their advantages and disadvantages have been examined and scrutinized. The energy alternative that is the subject of this unit is probably the most controversial, nuclear energy. One reason we discuss this topic is because of the ignorance’s and fears of many people regarding nuclear energy. Our generations will be the adults of tomorrow and should be given the facts on this energy source, its past record and what the possibilities and changes are for the future. Nuclear Energy How does nuclear energy work? This report will explain all about nuclear energy. We will explain the difference between nuclear fission and fusion. We will also explain how a nuclear power plant works. To help you understand this topic better. We will outline the development of nuclear energy. We will discuss the benefits and disadvantage of nuclear energy and where it is used. We will also analyze the problems with nuclear energy.

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What is it? Nuclear energy is a major form of energy made from splitting an atom with a proton. One law of the universe is that energy and matter can't be created or destroyed but can change form. This means that no one can create or destroy energy because another one of the laws is the amount of energy in the universe cannot change. However, matter can be changed into energy. The famous scientist Albert Einstein created the mathematical equation E = mc2 to explain this. This equation says E (energy) = m (mass) times c2 (speed of light squared). Einstein used this famous equation to discover atomic energy and also create atomic bombs. The History of Nuclear Energy in Canada The date was December 2, 1942. Underneath the bleachers of a football field at the University of Chicago, Italian Nobel Prize winners Enrico Fermi with his team of scientists were working on a concealed project. They were attempting to build the world's first nuclear reactor. The nuclear reactor was 400 tons of graphite surrounding 60 tons of uranium. Canadian physicist Walter Zinn was in charge of ZIP. ZIP was the lever that could shutdown the experiment if anything went wrong. As Zinn turned on the machine, Fermi measured the rise in power and in the late afternoon their goal was reached. "The power of the reactor rose to one watt-less than one-hundredth the power of an average light 2

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bulb but nevertheless proof that man had controlled the release of energy from the atom"(Ontario Hydro, 1989 p.4). They sent a coded message to Washington that said, "The Italian navigator has landed in the New World" This meant that nuclear energy had become a reality. "Operational condition reached" were the words dispatched to Ottawa on September 5, 1945 by Dr. Lew Kowarski. The efforts of Canada's scientific team were a success and Canada's and the world's first nuclear reactor was built. On December 12, 1952 an operator's error caused a power surge when the plant was shut down. By the time the authorities could bring the plant under control serious damage had been done to the plant. This day was known as Black Friday. No one was hurt but radioactive particles flew throughout the building and before the reactor was repaired some cleaning up was at hand. Redesigning and rebuilding the plant took 14 months and the groundwork was laid for the CANDU reactor, one of the safest in the world. Fission and Fusion Nuclear fission works by splitting an unstable uranium nucleus making nuclear energy. This produces heat which boils water and creates steam. This steam turns turbines to create energy. The problem is that after the burning is done the leftover material stays radioactive for thousands of years. "Plutonium-239, aby-product of uranium, remains 3

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radioactive for 24,110 years" (Ergon Energy, 1999). Nuclear fusion is supposed to be a very clean form of energy. It works by combining two nuclei to make a bigger nucleus. Fusion gives off energy to boil water and make steam to turn turbines. Unfortunately scientists have not yet been able to use nuclear fusion to make electricity because there are three things required. First, you need an extremely high temperature. Second, you need to have 2 small nuclei that will fuse together and give off energy. Third, you need the ability to capture the energy given off. As you know nuclear fission works on uranium but nuclear fusion uses deuterium and tritium, both isotopes of hydrogen which is an unlimited source of energy. Therefore nuclear fusion could possibly last forever. How Does A Nuclear Reactor Work? A nuclear power plant works like this. First you put in a uranium bundle of about eight rods. Second, you fire a proton at one of the uranium nuclei to split it. This causes a chain reaction splitting all of the other nuclei. The reaction is slowed down by using heavy water. "Chemically, heavy water is called deuterium oxide. Thus the Canadian reactor is named CANDU, for CANada Deuterium Uranium" (Canadian Nuclear Association, 1991). Heavy water, which is also used as a coolant in the nuclear reaction, is heated and travels to heat exchangers to produce

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steam from ordinary water. The steam turns turbines, which makes electricity. This is called nuclear fission.

Advantages One of its best qualities is that it gives off lots of energy from little amounts of uranium. Another advantage to this form of energy is that it doesn't give off greenhouse gases. Greenhouse gases are gases like carbon dioxide, sulfur dioxide and fly ash, which have made the greenhouse affect or global warming. Nuclear energy is cheap too and it helps provide jobs to people. Perhaps the biggest advantage to nuclear energy is the discoveries they have made in nuclear medicine. Such as cancer therapy, CAT scan, MRI machines and the use of irradiation of food. Another advantages nuclear energy is safety. Within the past few years, concern of nuclear power plants has become a public issue and also a political one. In Connecticut, an inspector from the Nuclear Regulatory Commission (NRC) has been assigned to the Connecticut Yankee plant and another to the Millstone plants. These inspectors are responsible for looking over the operations at the plant and that all

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federal regulations are being followed. There are also frequent spot checks to make sure that all regulations are being upheld. As a result, or consequence of the Three Mile Island incident, Northeast Utilities set up a task force in 1979 to work with the NRC to insure that safety regulations are being upheld on a continual basis. Along with the NRC and NE task force was the results of the Kemeny Commission. This commission was set up by former President James Carter to investigate and report back on the situation at Three Mile Island. The main features of a safety inspection include the design, construction and operation of a reactor; accident prevention features, and containment shells to confine or minimize the release of the product of fission reactions. Economic also is an advantages of the nuclear energy. One advantage of nuclear energy that has always keen discussed is its economic value. Uranium is cheaper than oil and coal, and shipments of the fuel for a nuclear plant can be done annually instead of on a constant basis for coal and oil. But uranium is also a non-reusable source and is not immune to inflation, it has risen in cost. The

space

needed

to

accommodate

a

nuclear

plant

is

considerably smaller than other electrical plants with the same output of energy. However, since 1975 there have been no new orders for nuclear plants. The main reasons for this are the uncertainty of governmental involvement, rising construction cost, rising uranium 6

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cost, and delays in licenses and permits. Strict regulations have delayed construction of other plants and new safety measures (since Three Mile Island) are more expensive. In comparison, the construction of a coal plant is much cheaper than that of a nuclear plant. However, nuclear is still cheaper than oil and is more environmentally accepted than coal. Disadvantages One major disadvantage is that it makes variable amounts of radioactive waste. This waste is causing a big problem for the world for its storage and irradiating. The problem with using this nuclear power though is that there is always a chance of a meltdown. A meltdown is when the uranium and nuclear waste are heated to such a level that they melt creating a substance that can supposedly melt through steel, concrete and iron. This is the reason a lot of people don't like nuclear energy but the chance of a meltdown is about a million to one. Environmental Effect Nuclear Power In considering environmental effects, let's look at the effects on air, water, ground, and the biosphere (people, plants, and animals). The type of testing surrounding water and land mass, all life forms and the air.

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The initial sitting important to the environment. The most important concern involved with a sitting is the radiological hazard to the surrounding population. There are now federal laws and regulations for the recording of data near a possible plant site. One law that helps to ensure the safety of the public and surrounding environment is that there must be an area around a plant site that is restricted. There also has to be some structures and dispose of all wastes that occur during normal operations. The obvious advantage to all these regulations is that it ensures the safety of the public and environment. The major disadvantage is the expense,(this will be discussed later under economics).

Air - Gaseous Releases Nuclear plant gaseous releases fall into the following categories: •

Water vapor from cooling towers

•

Ventilation exhaust from those buildings that do not have any processes with radioactivity

•

Diesel generator exhaust

•

Gases and steam from the air ejectors, that are in the main steam system 8

Alam Sekitar Dan Manusia (SKL 3201) •

Ventilation exhaust from those buildings that do have processes with radioactivity

•

Gases removed from systems having radioactive fluids and gases.

The first two release paths are non-radioactive. Often, news photos of nuclear plants tend to focus on the tall (400 foot high) dry cooling towers (e.g. Three Mile Island, Perry). The major effect of these cooling towers is heating of the air around the plant. Warm water vapor is all that

is

released

(unless

chemicals

are

injected

for

biological

treatment). The cooling towers are often required by state and/or federal regulatory agencies to reduce the thermal impact if a river of a lake is the primary cooling source. The second sources-ventilation exhaust from those buildings that do not have any processes with radioactivity-are just like releases from ventilation systems from any office building. Nuclear plants use diesel generators (and some times gas, or combustion,

turbines) for emergency electrical power. These diesels

or turbines are typically started and run at least once a month to ensure they can function as backup power, if required, during a loss of power condition or accident condition. When these diesels or turbines startup, usually black plumes of exhaust gases are released. Operation of these diesels or turbines is the only source of greenhouse gases 9

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(e.g. carbon dioxide, sulfur dioxide, carbon monoxide, nitrous oxides) at a nuclear plant. The air ejector exhaust at PWRs is usually non-radioactive. Only in those cases where there may be leakage through a steam generator tube could that exhaust have any radioactivity. At BWRs, the air ejector exhaust is radioactive, but that exhaust must also pass through delay pipes, storage tanks and a hydrogen recombined before being released to the environment from the very tall stack that you sometimes see at BWRs. Ventilation exhaust from buildings containing radioactive processes have radiation monitors that sample for particles and gases. If unacceptable levels are reached, special fans start, the normal ventilation system is shutdown, and the exhaust is routed through special particulate, high efficiency particulate, and charcoal filters before being exhausted. These systems are designed to reduce the release below acceptable levels.

Radioactive gases may be removed from the systems supporting the reactor cooling system. These gases removed are compressed and stored. The gases are periodically sampled and can only be released when the radioactivity is less than an acceptable level according to the 10CFR20regulation. Releases of this nature are done very infrequently.

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All potential paths where radioactive materials could be released to the environment are monitored by radiation monitors. Water-Liquid Releases Nuclear plant liquid releases fall into the following categories: •

Non-radioactive

•

Slightly radioactive

Water that has been used to cool the condenser, various heat exchangers (e.g. to cool oil, steam, water) used in the turbinegenerator support processes, or that has passed through the cooling towers is non-radioactive. Some or all of this water may be discharged to a river, sea, lake. The thermal discharge of any type of power plant, nuclear or fossil fuel,

using a steam cycle operating under the same

conditions (e.g. steam pressure, inlet condenser water temperature) should be the same. In some cases, a coal plant may operate at higher temperatures and steam pressures than a nuclear plant, thus it may have a slightly higher efficiency, with slightly lower release of thermal discharge to the environment. One way to reduce thermal pollution is to make use of more of the hot water and steam using cogeneration principles. Usually water released from the steam generators (called blow down) is also non-radioactive. Very low levels of leakage (e.g. less than 11

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400 gallons per day) may be allowed from the reactor cooling system to the secondary cooling system of the steam generator. However, in any case where radioactive water may be released to the environment, it must be stored and radioactivity levels reduced through ion exchange processes below levels allowed by the 10CFR20 regulation. Within the nuclear plant, there are a number of systems that may contain radioactive fluids. As noted above, those liquids must be stored, cleaned, sampled, and verified to be below acceptable levels before release may be done-AND-mistakes are not tolerated by the NRC. Effluent requirements are specified in Appendix B Table 2 of 10CFR20. As in the gaseous release case, radiation detectors monitor release paths and isolate (close valves) if radiation levels exceed a preset set point. Some BWR facilities maintain a "Zero Release" management practice to not discharge radioactive liquids.

Solid Releases-Ground Effects Solid radioactive materials only leave the plant by three paths:

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Routine non radioactive office, process, and building material waste via traditional means

•

Radioactive waste (e.g. clothes, rags, wood) is compacted and placed in drums. These drums must be thoroughly de-watered. The drums are often checked at the receiving location by regulatory agencies. Special landfills must be used.

•

Spent resin may be very radioactive and is shipped in specially designed containers.

For introductory information on low level waste, see Low Level Waste and More on Low Level Waste. Currently, the used fuel assemblies are stored underwater in large cooling pools at the plant. In some cases, where storage has become limited, dry cask storage on-site may be used. This storage is covered by the regulation 10CFR72 for Independent Spent Fuel Storage Facilities. For introductory information on high level waste, see High Level Waste and More on High Level Waste.

Ultimate Disposal of Spent Fuel

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Originally, the intent had been that the spent fuel would be reprocessed. The limited amount of highly radioactive waste (also called high level waste) was to be placed in glass rods surrounded by metal with low long term corrosion or degradation properties. The intent was to store those rods in specially designed vaults where the rods could be recovered for the first 50-100 years and then made irretrievable for up to 10000 years. Various underground locations had been considered salt domes, granite formations and basalt formations and finally, Congress designated Yucca Mountain in Nevada. The desire was for a geologically stable location with minimal chance for groundwater intrusion. There is currently some controversy regarding the suitability of Yucca Mountain as a final repository. The intent had been to recover the plutonium and unused uranium fuel, then reuse it in either breeder or thermal reactors as mixed oxide fuel (also called MOX). Currently, France, Great Britain, and Japan are using this process.

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Impact on the Biosphere In the 1960's, the Atomic Energy Commission funded research to investigate effects of radiation on people, plants, and animals. Some of the studies were conducted at the Lawrence Radiation Laboratory in Livermore, California and at various government and university laboratories. A number of studies entitled the BEAR (Biological Effects of Atomic Radiation) and BEIR (Biological Effects of Ionizing Radiation) studies reported on these effects. The most recent, BEIR VII Phase 2, "Health Effects of Exposure to Low Levels of Ionizing Radiation", (see summary) was published by the National Academy Press in 2005. A down to earth discussion of radiation is presented in the University of Wisconsin Graduate School's Why files - Radiation Reassessed.

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Conclusion Nuclear energy is only one of many energy alternatives. What gives nuclear an advantage is its past record, safety features and economical promise for the future. Although we believe that nuclear energy is not the answer-all, we do believe that it is and will continue to be part of our energy future. Energy should be taken seriously and education of our energy sources should not be limited to the school system but be shared with the city or state and the energy facility.

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Bibliography Books Canadian Nuclear Association. (1991). Nuclear Facts: Seeking To Generate A Better Understanding. Canada. Danburg Connecticut. (1992). Encyclopedia Of Knowledge. Grolier Inc. Jack Challoner. (1993). Eyewitness Energy. Dorling Kindersley Limited, London. Judith Hann. Association.

(1991).

How

Science

Works.

Reader's

Digest

Merril Eisenbud. (1987). Environmental Radioactivity from Natural, Industrial and Military Sources. 3rd Edition, Academic Press. Ontario Hydro. (1989). Fifty Years of Fission. Canada. Web Pages www.energyed.ergon.com.au/educatio/nuclear/how.html www.energy.ca.gov/links/nuclear.html www.formal.stanford.edu/jmc/progress/nuclear-faqyhtml/chapter07.html

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