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. 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 • Nuclear fusion • Joining of two lightweight atomic nuclei into a single, heavier nucleus, accompanied by the release of a large amount of energy

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

5. 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 • Usually an atom has an equal number of neutrons and protons • If the number of neutrons is greater than the number of protons = isotope

6. Radioactive Isotope • Unstable isotope • Radioactive Decay • Emission of energetic particles or rays from unstable atomic nuclei • Example • Uranium (U-235) decays over time to lead (Pb-207) • Each isotope decays based on its own half-life

7. Radioactive Isotope Half-lives

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

9. Nuclear Fission • U-235 is bombarded with neutrons • The nucleus absorbs neutrons • It becomes unstable and splits into 2 neutrons • 2-3 neutrons are emitted and bombard another U-235 atom • Chain reaction

10. How Electricity is Produced

11. Breeder Nuclear Fission • A type of nuclear fission in which non-fissionable U-238 is converted into fissionable Pu-239

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

13. 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

14. 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

15. Safety Issues in Nuclear Power Plants • Meltdown • At high temperatures the metal encasing the uranium fuel can melt, releasing radiation • Probability of meltdown or other accident is low • Public perception is that nuclear power is not safe • Sites of major accidents: • Three Mile Island • Chornobyl (Ukraine)

16. Three-Mile Island • 1979- most serious reactor accident in US • 50% meltdown of reactor core • Containment building kept radiation from escaping • No substantial environmental damage • No human casualties • Elevated public apprehension of nuclear energy • Led to cancellation of many new plants in US

17. Chornobyl • 1986- worst accident in history • 1 or 2 explosions destroyed the nuclear reactor • Large amounts of radiation escaped into atmosphere • Spread across large portions of Europe

18. Chornobyl • Radiation spread was unpredictable • Radiation fallout was dumped unevenly • Death toll is 10,000-100,000

19. Nuclear Energy and Nuclear Weapons • 31 countries use nuclear energy to create electricity • These countries have access to spent fuel needed to make nuclear weapons • Safe storage and handling of these weapons is a concern

20. 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

21. 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

22. 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.

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

24. Decommissioning Nuclear Power Plants • Licensed to operate for 40 years • Several have received 20-year extensions • Power plants cannot be abandoned when they are shut down • Three solutions • Storage • Entombment • Decommissioning (dismantling)

25. Fusion • Fuel= isotopes of hydrogen

26. Fusion • Way of the future?? • Produces no high-level waste • Fuel is hydrogen (plenty of it!) • Problems • It takes very high temperatures (millions of degrees) to make atoms fuse • Confining the plasma after it is formed • Scientists have yet to be able to create energy from fusion