Chapter 12 Nuclear Energy

1. Chapter 12Nuclear Energy

2. 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

3. How do we make Electricity? • Need fuel source to …

4. 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

5. How Burning Coal Produces Electricity

6. How Nuclear Fission ProducesElectricity

7. 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

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

9. 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

10. 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)

11. 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.

12. 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

13. Half-life • TIMEit 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

14. Radioactive Isotope Half-lives

15. 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%

16. 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?

17. 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?

18. 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?

19. 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? • 7.1 x 106 years • 7.1 x 107 years • 7.1 x 108 years • 7.1 x 109 years • 7.1 x 1010 years

20. STOP HERE

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

22. Pros and Cons of Nuclear Energy • Pros • Less of an immediate environmental impact compared to fossil fuels

23. 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

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

25. 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

26. 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

27. Radioactive Waste • Temporary storage solutions • In nuclear plant facility (require high security) • Under water storage • Above ground concrete and steel casks • Need approved permanent options soon.

28. Case-In-Point Yucca Mountain 70,000 tons of high-level radioactive waste Tectonic issues have been identified

29. Types of Waste* • High-Level Waste • The most dangerous radioactive waste • Spent fuel comes from nuclear reactors (52,000 tons) • liquid and solid waste from plutonium production (91 million gallons). • About 70 percent of the available storage space is now filled with used fuel assemblies at Turkey Point.

30. Types of Waste* Transuranic Waste Includes clothing, tools, and other materials contaminated with plutonium, neptunium, and other synthetic elements heavier than uranium. (11.3 million cubic feet)

31. Types of Waste* Low and Mixed Low-Level Waste Includes radioactive and hazardous wastes from hospitals, research institutions, and decommissioned power plants (472 million cubic feet) Turkey Point produced annually on average about 2,500 cubic feet of low-level waste. This amount of waste could be contained within an area about the size of a 30'x30' room.

32. Types of Waste* • Uranium Mill Tailings • Residues left from the extraction of uranium ore (265 million tons).