Chapter 12 Nuclear Energy

Overview of Chapter 12* Introduction to Nuclear Power – Atoms and radioactivity Nuclear Fission Pros and Cons of Nuclear Energy – Cost of Nuclear Power Safety Issues at Power Plants – Three Mile Island & Chornobyl – Nuclear Weapons Radioactive Waste Future of Nuclear Power

How do we make Electricity? Need fuel source – – to boil water – to make steam – to turn a turbine – to convert mechanical energy into electrical energy Fuel sources = fossil fuels, nuclear Exceptions – solar – converts solar energy into electrical energy – wind – turns turbine itself

How Burning Coal Produces Electricity

How Nuclear Fission Produces Electricity

How much energy is produced? Nuclear power is an extremely rich energy source. One gram of Uranium-235 delivers as much energy as 3.5 metric tons of coal!!! One in every 5 houses in the U.S. is supplied with nuclear energy. – So what percentage of US electricity comes from nuclear?

Pollution: nuclear vs. coal Pollution TypeNuclear Power Plant Coal Fired Power Plant CO 2 SOx & NOx Mercury Particulates Thermal

Pollution: nuclear vs. coal Pollution TypeNuclear Power Plant Coal Fired Power Plant CO 2 No Yes SOx & NOxNo Yes MercuryNo Yes ParticulatesNo Yes Thermal Yes No

Where are Nuclear Power Plants located? Energy Information Administration

Where are Nuclear Power Plants located?

Introduction to Nuclear Energy Nuclear energy – Energy released by nuclear fission or fusion Nuclear fission – Splitting of an atomic nucleus into two smaller fragments, accompanied by the release of a large amount of energy – Process used by nuclear power plants Nuclear fusion – Joining of two lightweight atomic nuclei into a single, heavier nucleus, accompanied by the release of a large amount of energy – Process that powers the sun

Atoms and Radioactivity Nucleus – Comprised of protons (+) and neutrons (neutral) Electrons (-) orbit around nucleus Neutral atoms – Same # of protons and electrons

Atoms and Radioactivity Atomic mass – Sum of the protons and neutrons in an atom Atomic number – Number of protons per atom – Each element has its own atomic number Isotope (Greek for “at the same place”) – Different forms of the same element have same number of protons have different number of neutrons – Some isotopes are radioactive

Examples of Isotope Carbon – Carbon-12: 6 protons & 6 neutrons (stable) – Carbon-14: 6 protons & 8 neutrons (radioactive) Uranium – Uranium-235: 92 protons & 143 neutrons (radioactive) – Uranium-238: 92 protons & 146 neutrons (radioactive)

Elements which contain at least one stable isotope; Radioactive elements: the most stable isotope is very long-lived, with half-life of over four million years; Radioactive elements: the most stable isotope has half- life between 800 and 34,000 years; Radioactive elements: the most stable isotope has half-life between one day and 103 years; Highly radioactive elements: the most stable isotope has half-life between one minute and one day; Extremely radioactive elements: the most stable isotope has half-life less than a minute. Very little is known about these elements due to their extreme instability and radioactivity.

Radioactive Isotope Radioactive Decay – Emission of energetic particles or rays from unstable atomic nuclei Alpha Decay – Loss of 2 protons and 2 neutrons – Lose four mass units – Lose two atomic numbers – so move to the left 2 spaces on the periodic table Beta Decay – Loss of electron from a neutron – Gain one atomic number - so move right 1 space on the periodic table – Gain no mass units

Half-life TIME it takes for half of a radioactive element’s atoms to decay, or change, into a more stable element. range from a fraction of a second to billions of years – 4.5 billion for uranium 238. the longer the half-life, the less intense the radiation each isotope decays based on its own half-life example: Uranium (U-235) decays over time to Lead (Pb-207) Parent Material = original radioactive material Daughter Product = new, stable material

Radioactive Isotope Half-lives

Calculating Half Lives DRAW PICTURE FIRST Half-life l Starting Point ex: 200g of X 1 l 100g 2 l 50g 3 l 25g Half-life l Starting Point ex: what percent…? 1 l 50% 2 l 25% 3 l 12.5%

Half Life Calculations 1. How many half-lives will pass by the time a 100g sample of Au-198 to decay to 6.25g? 2. How many half-lives will pass by the time a 60g sample of Co-60 decays to 7.5g? 3. How many half-lives does it take a 180g sample of Au-198 to decay to 1/8 its original mass?

4. If a 700g sample of I-131 undergoes 4 half- lives, how much material remains? 5. What is the half-life of a radioisotope if 1/16 of it remains after 4 days? 6. If 5 half-lives pass, what percent remains of the original radioisotope?

7. What is the half-life of a radioactive isotope if a 500g sample decays to 62.5g in 24.3 hours? 8. How many years would it take for a 1g sample of Krypton-85 with a half-life of 10.4 years to decay to about 31.25mg?

Released Question from Exam Uranium-235 has a half-life of 710 million years. If it is determined that a certain amount of stored U-235 will be considered safe only when its radioactivity has dropped to 0.10 percent of the original level, approximately how much time must the U-235 be stored securely to be safe? A.7.1 x 10 6 years B.7.1 x 10 7 years C.7.1 x 10 8 years D.7.1 x 10 9 years E.7.1 x years

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Nuclear Fuel Cycle processes involved in: producing the fuel used in nuclear reactors and disposing of radioactive (nuclear) wastes

Pros and Cons of Nuclear Energy Pros – Less of an immediate environmental impact compared to fossil fuels

Pros and Cons of Nuclear Energy Pros (continued) – Carbon-free source of electricity- no greenhouse gases emitted – May be able to generate H-fuel Cons – Generates radioactive waste – Many steps require fossil fuels (mining and disposal) – Expensive

Cost of Electricity from Nuclear Energy Cost is very high Expensive to build nuclear power plants – Long cost-recovery time Fixing technical and safety issues in existing plants is expensive 20% of US electricity is from Nuclear Energy – Affordable due to government subsidies

Radioactive Waste Low-level radioactive waste- – Radioactive solids, liquids, or gasses that give off small amounts of ionizing radiation High-level radioactive waste- – Radioactive solids, liquids, or gasses that give off large amounts of ionizing radiation

Radioactive Wastes Long term solution to waste – Deep geologic burial –Yucca Mountain – As of 2004, site must meet EPA million year standard (compared to previous 10,000 year standard) – Possibilities: Above ground mausoleums Arctic ice sheets Beneath ocean floor