Chapter 12 Nuclear Energy

3-Person Teams (without moving unnecessarily) Outline your group opinions on a whiteboard and be prepared to present you’re opinions to the class (and comment on other teams opinions) Did the US make the best decision to develop nuclear power? Explain. How would the US be different if we hadn’t chosen to develop nuclear power? WWII, Potential Cheap Power, Profit, Avoid being bullied by nuclear countries.

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

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

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 What else changes in order to release this energy? Mass is lost, it is converted to energy.

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 What particles or rays can be released? What are they? Alpha (Helium nucleus- 2P, 2N), Beta (electron from nucleus-Neutron changes to Proton), gamma rays (high frequency non-visible light)

Radioactive Isotope Half-lives What is a half-life? The time for ½ the radioactive substance to change into a different material.

Nuclear Fission Nuclear Fuel Cycle Power Process Waste Process Nuclear Fission Nuclear Fuel Cycle processes involved in producing the fuel used in nuclear reactors and in disposing of radioactive (nuclear) wastes The left column is the nuclear power process flow chart. The right column is the waste generation flow chart. Can you think of environmental impacts that might come from the right column? Dashed arrows in flow chart have not been happening; how do you feel about that?

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

How Electricity is Produced Reactor vessel is the orange structure, it is designed for containment. Primary circuit is orange (pressurized water to prevent steam), Secondary circuit is blue converts to steam and back (power production), the tertiary circuit removes heat from the second circuit. Reactor vessel is the orange structure, it is designed for containment. Primary circuit is orange (pressurized water to prevent steam), Secondary circuit is blue converts to steam and back (power production), the tertiary circuit removes heat from the second circuit.

Breeder Nuclear Fission A type of nuclear fission in which non-fissionable U-238 is converted into fissionable Pu-239 What is the percentage of Uranium that is 238? What is the percentage that is U235? >99%, <1%

Compare the relative benefits of Conventional and Breeder Reactors. Discuss and answer Compare the relative benefits of Conventional and Breeder Reactors. See next slide

Mr. H’s Thoughts Conventional: Uses only 0.7% of the Uranium orelots of hazardous waste. Breeders: Uses >99% of the Uranium ore Reactors are potentially highly explosive. Produce lots more weapons grade Plutonium. Produce more energy than conventional. Allow recycling of waste from conventional reactors.

Whiteboard Question How can Mixed Oxide Fuel (MOX) reactors play an important role in nuclear energy?

Mr. H’s Thoughts Book discussion of MOX is sketchy, but MOX apparently: doesn’t make weapons grade Plutonium. can use weapons grade Plutonium and U235 to produce electric (and reduce radioactive waste and eliminate stockpiles of weapons grade Plutonium).

Whiteboard Question In the Breeder Reaction, does U238 + 1 neutron = Pu239? Explain Now refer to Appendix 1, does your answer change? Click to next slide

Breeder Nuclear Fission A type of nuclear fission in which non-fissionable U-238 is converted into fissionable Pu-239 Where did the Proton come from to change Uranium into Plutonium? Where did the Proton come from to change Uranium into Plutonium?

Pros and Cons of Nuclear Energy vs Coal Pros: Less of an immediate environmental impact compared to fossil fuels, but nuclear has higher potential risks. 5 vs 5 overall

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 Disaster potential

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 Shut down costs can be substantial.

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) Japan

Three-Mile Island 1979- most serious reactor accident in US 50% meltdown of reactor core (close call) 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 at the time 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 Firefighters gave lives.

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 Several hundred metric tons of weapons grade plutonium worldwide, but just several kilogram would make a bomb.

Radioactive Waste Low-level radioactive waste (low radioactivity)- Radioactive solids, liquids, or gasses that give off small amounts of ionizing radiation High-level radioactive waste (high radioactivity)- 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 Not intended for permanent storage. Need approved permanent options soon. Short half-life fission material tricks body into believing they are nutrients. They bioaccumulate.

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

Case-In-Point Yucca Mountain 40,000+ tons of high-level radioactive waste already exist. Before long we will have more stored in temporary locations than the “permanent site could hold”. Transportation safety concerns. 2 dozen other countries store deep underground. Concern about rising water table. After an earthquake in 1992, the water table rose only 1 meter (not considered serious by experts). Obama killed the project early in first term.

Whiteboard Question Should we use Yucca Mountain for long-term storage of high-level nuclear waste? If not, then what should be done? Mr. H thinks we should finish and use Yucca Mountain, then investigate another site for the future. Doing nothing is the worst possible decision.

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)

Is nuclear power used too much or not enough in the U.S.? Why? Whiteboard Question Is nuclear power used too much or not enough in the U.S.? Why? .

Catastrophic potential Waste is awful Renewable options available Mr. H’s Thoughts Overused Expensive Catastrophic potential Waste is awful Renewable options available Mr. H thinks we should finish and use Yucca Mountain, then investigate another site for the future. Doing nothing is the worst possible decision.

Fusion Fuel= isotopes of hydrogen

How do you slow or stop a fusion reaction once it starts? Whiteboard Question How do you slow or stop a fusion reaction once it starts? .Turn off the supply of Tritium (not found in atmosphere)

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