Nuclear PoweR “The discovery of nuclear reactions need not bring about the destruction of mankind...

Nuclear PoweR

Nuclear PoweR “The discovery of nuclear reactions need not bring about the destruction of mankind any more than the discovery of matches”

-Albert Einstein

I. Using Nuclear Reactions to I. Using Nuclear Reactions to Generate PowerGenerate Power


A. Nuclear Fission – the splitting of a nucleus into smaller fragments (the splitting is caused by bombarding the nucleus with neutrons). This process releases enormous amounts of energy.

A nuclear chain reaction is a reaction in which the material that starts the reaction (neutron) is also one of the products and can be used to start another reaction.

B. Nuclear Reactors use controlled – fission chain reactions to produce energy.



C. A radioisotope is a radioactive isotope (remember different number of neutrons). Uranium-235 is the radioisotope used in nuclear reactors to produce energy.

D. Nuclear fission produces much more energy than coal or natural gas. 2.2 pounds of uranium produces the same amount of heat energy as 32,000 pounds of coal.



E. A nuclear reactor is just a complex device used to boil water, generate steam, and use that steam to turn a turbine.

F. Four critical components to any nuclear reactor are shielding, fuel, control rods, and coolant.



1) shielding – radiation absorbing material that is used to decrease exposure to radiation.



2) fuel – uranium is most often used



3) control rods – neutron absorbing rods that help control the reaction by limiting the number of free neutrons

Steam



4) coolant – water acts as a coolant and transports heat between the reaction and the steam turbines to produce electric current

G. A light water reactor is the type of reactor used most in the world (85% worldwide, 100% in the U.S.).

H. Light-water reactors are very inefficient, losing about 83% of the energy in their nuclear fuel as waste heat to the environment. Nuclear reactors cause huge amounts of thermal pollution in the lake or river with which they are associated.

Coal vs. Nuclear Coal vs. Nuclear Coal vs. Nuclear Coal vs. Nuclear

Coal Nuclear

Ample Supply Ample supply of uranium

High net energy yield Low net energy yield

Very high air pollution No air pollution

High carbon dioxide emissions No carbon dioxide emissions

High land disruption from surface mining

Much lower land disruption from surface mining

High land use Moderate land use

Low cost (with huge subsidies) High cost (even with huge subsidies)

Long term waste storage issues

II. Radioactive WasteII. Radioactive WasteII. Radioactive WasteII. Radioactive Waste

A. Radioactive waste is the huge long-term problem with nuclear reactors.

B. There are two types of radioactive wastes, low-level and high-level wastes.

C. Low-level wastes contains low levels of radiation, and remains dangerous for a relatively short period (has a half-life of a few hundred years or less).


D. Low level wastes includes most medical and university research.

E. Low level waste can be stored on-site, for a few hundred years at most, and just needs to be stored in barrels, with shielding not required.

F. Applications that F. Applications that Produce Low-Level Produce Low-Level

WasteWaste

F. Applications that F. Applications that Produce Low-Level Produce Low-Level

WasteWaste1) Carbon-14 dating –

Used to determine the age of historical artifacts

2) Radioactive Tracers In medicine:

absorbed by specific organs and used to diagnose disease (Iodine-131)

3. Nuclear MedicineRadiation Treatment

larger doses are used to kill cancerous cells in targeted organs

internal or external radiation source,

usually Cobalt-60Radiation treatment using

-rays from cobalt-60.


G. High level nuclear waste is produced from spent nuclear fuel and wastes from producing nuclear weapons.

H. High-level waste has high levels of radioactivity, is hard to store, and has very long half-lives (thousands to millions of years).


I. High-level nuclear waste often stays on-site until it can be shipped to a permanent repository (if one is available). Storage must be stable for thousands of years, and waste must be stored in specially shielded containers (casks) or in water pools.

III. Half-lifeIII. Half-lifeIII. Half-lifeIII. Half-life

A. Knowing how to calculate half-life is very important in determining how long things will stay radioactive, and how long materials need to be safely stored.

B. Half-life means the amount of time it takes half of the original material to decay to a stable, non-radioactive form.

C. Half-Life EquationsC. Half-Life EquationsC. Half-Life EquationsC. Half-Life Equations

Fraction remaining = 1/2n

n= number of half-lives elapsed

Amount remaining (g) =

Original amount x 1/2n

Nt = No x (1/2)n

IV. Storing Nuclear WasteIV. Storing Nuclear WasteIV. Storing Nuclear WasteIV. Storing Nuclear Waste

A. Containment – on-site storage and off-site disposal (Remember that every radioactive substance has a half-life, some only a few months, others hundreds of thousands of years.)

1) On-Site Storage – most common nuclear waste is spent fuel rods from nuclear power plants

-water pools-dry casks (concrete or steel)

2) Off-Site Disposal – disposal of nuclear waste is done with the intention of never retrieving the materials.

-77 disposal sites around the United States-new site near Las Vegas, Nevada Yucca Mountain

IV. Storing Nuclear IV. Storing Nuclear WasteWaste


C. Any long term storage site needs to be very geologically stable, and sites are evaluated for the following:

Volcanic activity Earthquake activity Characterization of groundwater flow Estimation of changes in storage environment over

long periods of time Depth of at least 2,000 ft underground Away from major cities/population centers



D. All High-level nuclear waste must be stored for a minimum of 10,000 years, and up to 240,000 years before it decays to stable radioactive levels.

E. Most scientists and engineers agree that deep burial is the safest and cheapest way to store high-level nuclear waste.



F. Yucca Mountain – 160 miles northwest of Las Vegas. Process to evaluate and open a long-term storage facility began in 1985, may start accepting waste by 2017. Controversial due to concerns about flooding and moving waste to be stored there.

G. WIPP – near Carlsbad, NM. Storage facility in salt band 2,150 feet underground. Opened in 1999 for long-term storage of nuclear weapons waste.



H. Some other suggestions for long term nuclear storage include paying to ship to other countries, permanently entombing old reactors in layers of steel and concrete, storing under the deep ocean, storing under large ice sheets (Antarctic, Greenland), shipping off on a rocket to space, or storing on the moon. As of yet, none of these have been deemed acceptable in terms of risk and ethics.

V. Effects of RadiationV. Effects of RadiationV. Effects of RadiationV. Effects of Radiation

A. Radiation is so harmful for living tissue because it can cause DNA damage and mutation, cell/tissue damage, and cell death.

B. Radiation at high enough doses is lethal, and at low doses can cause any of the following problems:

V. Effects of RadiationV. Effects of RadiationV. Effects of RadiationV. Effects of Radiation

- Cancer/tumorsBrain damageEye damage or cataractsGI damage from nausea and vomitingDamage and birth defects to fetusesBurnsDamage to bone marrow Impairment of the immune system

VI. Nuclear DisastersVI. Nuclear DisastersVI. Nuclear DisastersVI. Nuclear Disasters

A. The worst nuclear accident in U.S. history took place at Three Mile Island nuclear power plant in 1979. A valve malfunctioned and human errors led to a partial core meltdown. High levels of radiation were released into a containment structure, but only a small amount of radiation was released into the environment.


B. Although radiation release was small, the state of Pennsylvania was unprepared to deal with a nuclear problem, and the evacuation and aftermath was poorly organized and led to a huge public mistrust in nuclear power in the U.S.


C. Chernobyl, in 1986, was the world’s worst nuclear disaster. An explosion blew the top off a containment building, a reactor melted down, and a fire burned for 10 days, releasing more than 100 times the radiation released by the atomic bombs dropped by the U.S. in WWII.

D. A poor reactor design, combined with human error, caused the explosion.


E. In 2008, after 22 years, areas of the Ukraine and Europe are still dangerously contaminated with radioactive materials as a result of Chernobyl.

F. Eventual death estimates range from 9,000 to 212,000 from the accident, and in contaminated areas rates of birth defects, thyroid cancer, leukemia, and immune system abnormalities are very common.


G. Japan has come close to having a Chernobyl-type disaster. It is an earthquake-prone country that gets 39% of its power from nuclear reactors. In 2007 a huge earthquake caused severe damage to the world’s largest nuclear reactor.

Nuclear PoweR “The discovery of nuclear reactions need not bring about the destruction of mankind...

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