Chapter 12 Nuclear Energy

Overview of Chapter 12 Introduction to Nuclear Power Nuclear Fission 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

Introduction to 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

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

Radioactive Isotope Unstable isotope Radioactive Decay Example 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

Radioactive Isotope Half-lives

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

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

How Electricity is Produced

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

Pros and Cons of Nuclear Energy 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 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

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)

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

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

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

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

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

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.

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

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)

Fusion Fuel= isotopes of hydrogen

Fusion Way of the future?? Problems 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