Nuclear Powe R The discovery of nuclear reactions

Nuclear Powe. R “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 Generate Power ª 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.

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

I. Using Nuclear Reactions to Generate Power ª C. A radioisotope is a radioactive isotope (remember different number of neutrons). Uranium-235 is the radioisotope used in nuclear reactors to produce energy. ª 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 16 tons of coal.

I. Using Nuclear Reactions to Generate Power ª E. A nuclear reactor is just a complex device used to boil water, generate steam, and use that steam to turn a turbine. ª F. Four critical components to any nuclear reactor are shielding, fuel, control rods, and coolant.

I. Using Nuclear Reactions to Generate Power ª 1) shielding – radiation absorbing material that is used to decrease exposure to radiation.

I. Using Nuclear Reactions to Generate Power ª 2) fuel – uranium is most often used

I. Using Nuclear Reactions to Generate Power ª 3) control rods – neutron absorbing rods that help control the reaction by limiting the number of free neutrons

I. Using Nuclear Reactions to Generate Power 4) coolant – water acts as a coolant and transports heat between the reaction and the steam turbines to produce electric current Steam

ª G. A light water reactor is the type of reactor used most in the world (85% worldwide, 100% in the U. S. ). ª 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 Nuclear Ample Supply Ample supply of uranium High net energy yield Low net energy yield Very high air pollution Low air pollution High carbon dioxide emissions Low 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 Waste ª A. Radioactive waste is the huge longterm problem with nuclear reactors. ª B. There are two types of radioactive wastes, low-level and high-level wastes. ª 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).

II. Radioactive Waste ª D. Low level wastes includes most medical and university research. ª 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 Produce Low. Level Waste 1) Carbon-14 dating – Used to determine the age of historical artifacts 2) Radioactive Tracers ª In medicine: w absorbed by specific organs and used to diagnose disease (Iodine-131)

3. Nuclear Medicine ª Radiation Treatment w larger doses are used to kill cancerous cells in targeted organs w internal or external radiation source, usually Cobalt-60 Radiation treatment using -rays from cobalt-60.

II. Radioactive Waste 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).

II. Radioactive Waste ª I. High-level nuclear waste often stays onsite 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-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 Equations Fraction remaining = 1/2 n n= number of half-lives elapsed Amount remaining (g) = Original amount x 1/2 n Nt = No x (1/2)n

IV. Storing Nuclear Waste A. Containment – on-site storage and off-site disposal (Remember that every radioactive substance has a halflife, 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 Waste ª C. Any long term storage site needs to be very geologically stable, and sites are evaluated for the following: ª ª Volcanic activity Earthquake activity Characterization of groundwater flow Estimation of changes in storage environment over long periods of time ª Depth of at least 2, 000 ft underground ª Away from major cities/population centers

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

IV. Storing Nuclear Waste ª 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. ª 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.

IV. Storing Nuclear Waste ª 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 Radiation ª A. Radiation is so harmful for living tissue because it can cause DNA damage and mutation, cell/tissue damage, and cell death. ª B. Radiation at high enough doses is lethal, and at low doses can cause any of the following problems:

V. Effects of Radiation ª - Cancer/tumors ª Brain damage ª Eye damage or cataracts ª GI damage from nausea and vomiting ª Damage and birth defects to fetuses ª Burns ª Damage to bone marrow ª Impairment of the immune system

VI. Nuclear Disasters ª 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.

VI. Nuclear Disasters ª 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.

VI. Nuclear Disasters ª 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. ª D. A poor reactor design, combined with human error, caused the explosion.

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

VI. Nuclear Disasters ª 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.