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Chapter 16 – Nuclear Energy Pages 250 – 263 Mrs. Paul Environmental Science Parts of an Atom • 3 parts: – 1. Protons: positively charged particles in nucleus. – 2. Neutrons: particles in nucleus with no charge. – 3. Electrons: negatively charged particles that orbit the nucleus. • Nucleus: cluster of protons and neutrons in the center of the atom. • Atoms usually have the same number of electrons and protons = no charge. Atoms and Isotopes • Properties of atom determined by number of protons. • Atomic number: number of protons. – Ex: oxygen = 8; uranium = 92 • Atomic mass: protons + neutrons – Ex: oxygen = 16 (8 protons; 8 neutrons) • Isotopes: atoms of the same element that have different atomic masses (due to different numbers of protons). Radioactivity • Some isotopes are unstable. • Unstable atoms may change number of protons or neutrons in nucleus to become stable. • Radioactive atoms: Atoms that decay and emit particles and energy from their nuclei. • Radiation: alpha particles, beta particles and gamma rays given off in the decaying of unstable nuclei. • Radioactive particles: – 1. alpha particles: large particles made of 2 protons and 2 neutrons. – 2. beta particles: high speed electrons • Losing alpha particles changes an atoms atomic mass, causing it to become a different element (radioactive decay). • Half-life: amount of time in which half the atoms in a sample of a radioactive element decay. Fission: Splitting Atoms • Only about 17 % of the world’s electricity comes from nuclear power. • Nuclear power plants are powered by nuclear energy: energy inside the nucleus of an atom. An Atom!! • Forces holding the nucleus together are STRONG! • Atoms of uranium (an element) are used as fuel in nuclear power plants. • Nuclear Fission: splitting of an atom’s nucleus. – Nucleus is hit with neutrons (neutral atomic particles). – This causes neutrons and energy to be released from uranium’s nucleus as it splits. – Causes a chain reaction making other atoms undergo fission. Nuclear Fission • Example: atomic bomb is uncontrolled fission reaction. How Nuclear Energy Works • Nuclear reactor surrounded by thick pressure vessel filled with cooling fluid. – Pressure vessel will contain fission products in event of accident. – Thick concrete walls also surround reactor. • Inside reactor: – Metal fuel rods containing uranium pellets hit repeatedly with neutrons. – Chain reaction releases energy and more neutrons. – Reactor core contains control rods: control how quickly fission happens by absorbing neutrons which prevents them from causing fission reactions with uranium fuel. • Released heat used to generate electricity (heat steam in power plants, etc). • Breeder reactor: a reactor that generates fuel as it works. – Plutonium used as fuel in breeder reactor. – Produces heat energy too. Nuclear Power Plant • Example: Diablo Canyon nuclear power plant. – Generates enough energy for 2 million Californian households. – Equivalent to burning 20 million barrels of oil Advantages of Nuclear Energy • Nuclear fuel = concentrated energy source. • Power plants do not produce greenhouse gases = no global warming. • Release less radioactivity than coal-fired power plants. • France generates ¾ of its electricity from nuclear power and produces less than 1/5 the amount of pollution per person than the U.S. • Uranium occurs naturally in rock and soil. • As it decays it gives off radon: radioactive gas that is odorless and colorless. – Can seep into buildings from the surrounding rock and soil. – Dangerous levels can build up without proper ventilation. – Estimated that 5,000 to 20,000 people die each year from cancer caused by exposure to radon. Why Aren’t We Using More Nuclear Energy? • Building and maintaining a safe reactor is very expensive • Storing Waste – Fission products are dangerously radioactive for years. – The used fuel, liquids and equipment from the reactor core are hazardous wastes. – Storage sites must be in an area that will remain geologically stable for a long time. • Ex: Plutonium-239 waste will be dangerous for 192,000 years. • Safety Concerns – Potential for fission process to get out of control. – Ex: 1986- Chernobyl • Engineers turn off safety devices to run unauthorized test. • Test causes explosions that destroy reactor and release radioactive materials into the air. • Areas of Northern Europe and Ukraine are still contaminated. • Nuclear reactor had no containment building and safety guidelines were violated. • 50 people killed immediately; 116,000 leave their homes; approx 15,000 got cancer eventually. • Meltdown: process by which a nuclear chain reaction goes out of control and melts the reactor core. Release huge amounts of radiation into the environment. • Exposure to radiation can cause: nausea, vomiting, headache, loss of some white blood cells, cancer. • 25 rems = detectable changes in blood. • 100 rems = no immediate harmful effects. • >100 rems = start to show above symptoms. • 300 rems = hairloss, damage to nerve cells and cells that line the digestive tract, difficulty clotting, loss of white blood cells. • 50% of people exposed to 450 rems die. • 800 or more rems always fatal (no effective treatment). • In time, survivors can develop cancer. • Ex: X-ray = 0.1 to 1 rem Radioactive Waste • Waste is radioactive. – Approx. 1.4 tons of waste produced in one year from one fission plant. • Types of waste: – High-level wastes: radioactive wastes that emit large amounts of radiation. • Uranium fuel rods, control rods, water used to cool and control chain reactions, vessel that surrounds the fuel rods. – Medium-level and low-level wastes: not as radioactive, although a much larger volume of these are generated. • Mine wastes scattered around uranium mine, contaminated protective clothing from workers, also produced by hospitals and laboraties. The Future of Nuclear Power • Nuclear Fusion: lightweight atomic nuclei combine to form a heavier nucleus and release a LOT of energy. – This is the process that powers all the stars, including our sun. – Safer than fission because it creates less dangerous radioactive biproducts. • Difficult to achieve. – Nuclei must be heated to high temperatures. • 180,000,000 ⁰F – Nuclei must be maintained at high concentrations and properly confined.