Module #36

Nuclear Energy Resources

Module Introduction:

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• Because the combustion of fossil fuels releases large quantities of CO₂ into the atmosphere, nuclear energy has received increasing interest.
• Concerns about nuclear energy include radioactivity, the proliferation of radioactive fuels that could be used in weapons, and the potential for accidents.
• Recently, however, nuclear energy has received positive attention, even from self-proclaimed environmentalists, because of its relatively low emissions of CO₂.
• In this module we will examine how nuclear energy works and the advantages and disadvantages of nuclear energy.

Module 36: Nuclear Energy Resources

Essential Knowledge

6.4 Distribution of Natural Energy Resources (Modules 34, 35, 36)

• The global distribution of natural energy resources, such as ores, coal, crude oil, and gas, is not uniform and depends on regions’ geologic history.

6.5 Fossil Fuels (Modules 35, 36)

• The combustion of fossil fuels is a chemical reaction between the fuel and oxygen that yields carbon dioxide and water and releases energy.
• Energy from fossil fuels is produced by burning those fuels to generate heat, which then turns water into steam. That steam turns a turbine, which generates electricity.
• Humans use a variety of methods to extract fossil fuels from the earth for energy generation.
• Hydrologic fracturing (fracking) can cause groundwater contamination and the release of volatile organic compounds.

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Essential Knowledge

6.6 Nuclear Power (Module 36)

• Nuclear power is generated through fission, where atoms of Uranium-235, which are stored in fuel rods, are split into smaller parts after being struck by a neutron. Nuclear fission releases a large amount of heat, which is used to generate steam, which powers a turbine and generates electricity.
• Radioactivity occurs when the nucleus of a radioactive isotope loses energy by emitting radiation.
• Uranium-235 remains radioactive for a long time, which leads to the problems associated with the disposal of nuclear waste.

Essential Knowledge

6.6 Nuclear Power Continued (Module 36)

• Nuclear power generation is a nonrenewable energy source. Nuclear power is considered a cleaner energy source because it does not produce air pollutants, but it does release thermal pollution and hazardous solid waste.
• Three Mile Island, Chernobyl, and Fukushima are three cases where accidents or natural disasters led to the release of radiation. These releases have had short- and long-term impacts on the environment.
• A radioactive element’s half-life can be used to calculate a variety of things, including the rate of decay and the radioactivity level at specific points in time.

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Nuclear Energy

• Nuclear reactors use fission to generate electricity.
• Electricity generation from nuclear fuel uses uranium-235 as a fuel source.
• Fission: A nuclear reaction in which a neutron strikes a relatively large atomic nucleus, which then splits into two or more parts, releasing additional neutrons and energy in the form of heat.

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U-235 is not the only isotope of uranium. U-238 is by far the more common isotope but it is stable and therefore not useful for nuclear fission.

• Energy is released when a neutron strikes a large atomic nucleus (e.g. U-235), which then splits into two or more parts (e.g. Barium and Krypton).

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Nuclear Reactors

• A nuclear power plant uses heat from nuclear fission to boil water. This water produces the steam to turn the turbine, which turns a generator (similar to a coal fired power plant).  
• This schematic shows the basic features of a light water reactor, the type of reactor found in the US.
• Fuel rod: A cylindrical tube that encloses nuclear fuel within a nuclear reactor.
• Control rod: A cylindrical device inserted between the fuel rods in a nuclear reactor to absorb excess neutrons and slow or stop the fission reaction.

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The containment structure is meant to provide shielding and protect the environment from the radiation release during the reaction.

Nuclear Reactor Types

Light Water Reactor (aka. Slow Reactors)

• Cheaper, but less efficient.
• Fuel source = U-235
• Water moderates the reaction, keeping it controlled. Failure to do so results in a meltdown (not unlike a nuclear bomb).
• Not the safest, most efficient (1%) or most advanced type of nuclear reactor, but the most common.
• Produces Barium-142.

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Breeder Reactor (e.g. Fast Reactors)

• Stable isotopes of uranium (U-238) and thorium are converted to fissile materials like Plutonium-239. Breeder reactors (as well as Thorium reactors) help to expand the nuclear fuel supply.
• The reaction “breeds” its own fuel increasing efficiency (70%).
• These are “fast” reactions compared to “slow” reactions like light water reactors.

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This is probably beyond this course and the AP Exam, but still interesting and relevant!

Thorium Power

• The naturally occurring isotope thorium-232 cannot undergo fission, but when irradiated in a reactor, it absorbs neutrons to form uranium-233, which is a fissile material that generates heat.
• A major advantage of thorium over other nuclear fuel sources is that thorium is a waste product of the growing rare-earth mining industry in China, and and currently has little industrial use.
• Additionally, thorium is considered safe because its waste products have less chance of being weaponized than do those of uranium.

Thorium is a weakly radioactive, silvery metal found naturally in rocks.

This is probably beyond this course and the AP Exam, but still interesting and relevant!

Nuclear Energy Use

Advantages

• No air pollution (air pollution kills an estimated 7 million people globally, each year).
• Reduces need to import oil.
• No CO₂ emissions.
• New technologies are emerging that are safer and more efficient.

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Disadvantages

• Possibility of accidents (rare but highly publicized).
• Three Mile Island (1979)
• Chernobyl (1986)
• Fukushima (2011)
• Difficult to dispose of waste.
• Concern about nuclear material being misused.
• Uranium is finite with reserves estimated to last another 100-200 years and mining generates habitat degradation and environmental inequity.

Nuclear Incidents

Three Mile Island

• The Three Mile Island accident was a partial meltdown of the Three Mile Island, Unit 2 reactor in Pennsylvania.
• It began at 4 a.m. on March 28, 1979.
• It is the most significant accident in U.S. commercial nuclear power plant history.
• This was 2 orders of magnitude less severe than the others.

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Chernobyl

• On April 26, 1986, a sudden surge of power during a reactor systems test destroyed Unit 4 of the nuclear power station at Chernobyl, Ukraine, in the former Soviet Union.
• The accident and the fire that followed released massive amounts of radioactive material into the environment.

Fukushima

• The most powerful earthquake ever recorded in Japan struck off the country's eastern coast.
• It triggered a tsunami which swept over the main island of Honshu.
• At the Fukushima nuclear power plant, the gigantic wave flooded the reactors, killing the emergency generators that provided coolant to the reactors.
• Workers rushed to restore power, but in the days that followed the nuclear fuel in three of the reactors overheated and partly melted the cores.

See textbook pages 420-421 for full text and descriptions of each incident.

Nuclear Incidents

Additional Resources:

• Midnight in Chernobyl: The Untold Story of the World's Greatest Nuclear Disaster by Adam Higginbotham
• This is a great video explanation about nuclear incidents.

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• The Three Mile Island Incident (INES Level 5) suffered a partial meltdown and was not nearly as dire of a circumstances as Chernobyl or Fukushima were (INES Level 7). In both of those accidents, the nuclear reactor actually melted down.

Radioactive Waste�

• Radioactive waste: Nuclear fuel that can no longer produce enough heat to be useful in a power plant but continues to emit radioactivity.
• Becquerel (Bq): Unit that measures the rate at which a sample of radioactive material decays; 1 Bq = decay of 1 atom or nucleus per second.
• Curie: A unit of measure for radiation; 1 curie = 37 billion decays per second.
• High-level radioactive waste comes from used fuel rods.
• Low-level radioactive waste is found on the protective clothing, tools, rags, and other items used in routine plant maintenance.
• Uranium mine tailings are the radioactive residue left after uranium ore is mined and enriched.
• In each case, disposal must be handled with great care.

Types of Radioactive Waste

Low-Level

• Low-level waste (LLW) is generated from hospitals and industry
• Low radioactivity level and short half life
• Makes up 90% of the bulk of radioactive waste, but only 1% of the radioactivity.
• No shielding is required, ideal for shallow burial.

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High-Level

• High-level waste (HLW) is generated from the use of uranium in light water nuclear reactors.
• High radioactivity and long half life (tens of thousands of years compared to hundreds of years for LLW)
• Requires cooling and shielding.

The Nuclear Debate

• Is nuclear energy safe?
• What role should nuclear energy play in our future?

The following video series from the Kurzgesagt Youtube Channel explore these issues:

• Nuclear Energy Explained: How Does It Work?
• 3 Reasons Why Nuclear Energy Is Terrible
• 3 Reasons Why Nuclear Energy is Awesome
• Do We Need Nuclear Energy To Stop Climate Change?

Putting Nuclear in Context

“If you got all the electricity for your lifetime from nuclear power, your total share of the waste would weigh two pounds and fit into one Coke can. Of that, only a trace is long-lived. And all that waste is kept out of the biosphere…If an American got all of his or her electricity from coal over a lifespan of seventy-seven years, that person’s mountain of solid waste would weigh 68.5 tons. Picture a soda can next to that” (Cravens, Power to Save the World: The Truth About Nuclear Energy, 9).

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Putting Nuclear in Context

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Putting Nuclear in Context

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Putting Nuclear in Context

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Dealing with Radioactive Waste

• Disposing of nuclear waste can be a challenge; it cannot be incinerated, safely destroyed using chemical, shot into space, dumped in the oceans or buried in an ocean trench.
• Nuclear waste is often stored in metal containers at the power plant where it was produced.
• High-level radioactive wastes require deep burial.
• The site should be isolated from human settlements to prevent contamination and/or exposure to radioactivity and use natural/engineered barriers like clay (impermeable).
• Yucca mountain was to be the site for nuclear storage in US, but was discontinued.
• Vitrification: Nuclear waste is mixed with sugar or slag to form a glass like substance that is safer and easier to store, but expensive to produce.

Fusion Power

• Nuclear fusion: A reaction when lighter nuclei are forced together to produce heavier nuclei.
• Nuclear fusion powers the Sun and other stars.
• Fusion is a promising, unlimited source of energy in the future, but so far scientists have had difficulty containing the heat that is produced.
• Kurzgesagt: Fusion

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Do The Math: Calculating Half-Lives

• See page 422 of the textbook.
• Make sure to review the math problem and make sure you understand the set up, especially the dimensional analysis.
• Your Turn answer =
• 1 half life: 90 g
• 2 half lives: 45 g
• 3 half lives: 22.5 g
• 4 half lives: 11.25 g
• 5 half lives: 5.625 g

If you have questions or need further explanation with ‘Do The Math’, you need to come in for extra help before school.

Module Review:

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• In this module, we have seen that the use of nuclear fuels for generating electricity has significant advantages and disadvantages.
• Nuclear energy is a relatively clean means of electricity generation, although fossil fuels are used in constructing nuclear power plants and mining and processing the uranium fuels.
• The possibility of accidents during plant operation and the difficulty of radioactive nuclear waste disposal are major environmental hazards of nuclear energy used for the generation of electricity.
• Neither of these issues has been satisfactorily resolved at present. Throughout the nuclear electricity generation cycle, carbon dioxide emissions are much less than during electricity generation from fossil fuels.