Chapter 16

1. Chapter 16 Nuclear Energy

2. Review • What are atoms? • What are the 3 particles of an atom? • What are the parts of an atom? • What is an atomic number? • What is a mass number? • What are isotopes?

3. Review: Atoms • All matter made up of atoms • 3 particles- protons, neutrons, electrons • Nucleus- protons & neutrons • Atomic number= number of protons • Proton number determines basic properties of atom • Mass number= # of protons & neutrons • Isotopes- atoms of same element with same # of protons, but different number of neutrons • Individual atoms of element can have different mass #

4. Radioactivity • Radioactive atoms- some isotopes are unstable and decay- emitting particles and energy • Marie Curie- coined term radioactive • After series of decay radioactive element become stable & stop decaying

5. Radiation’s effects • Alpha, beta particles and gamma rays given off by decaying unstable nuclei • Decay from Alpha particles(losing 2 neutrons & 2 protons) • Changes can alter atomic number and mass number of atoms • Decay changes 1 element into another element • Decay of Radon to Polonium

6. Half Life • Amount of time it takes for half of the atoms in a sample of radioactive element to decay • Example: • Uranium-238 (U-238) and Uranium-235 (U-235) eventually decay to lead • U-238= 99% of all uranium found in the world • Half life= 4.5 billion years • U-235 half life= 700 million years

7. Nuclear fission- reaction in which nucleus of a large atom is split into smaller nuclei Emits large amounts of energy which can be used to generate electricity Fissionable atom- nucleus easily splits when it is struck by a neutron 16-2 Reactions and Reactors

8. Nuclear Reactors • Produce electricity by generating heat through nuclear fission to boil water and power turbines • Similar to electricity created from burning fossil fuels • Nuclear fuel= 97% U-238 and 3% U-235 • Components: • Nuclear Reactor Vessel- site of fission • Heat exchanger- site of electricity generator • Cooling tower

9. Nuclear Reactor Vessel • Where fission takes place • Walls surrounded by a shield that prevents neutrons & other radiation from escaping • Housed inside thick, concrete containment building

10. Fuel Rods & Water • Fuel Rods containing pellets of fissionable U-235 • Kept vertically in water to allow it to circulate around it • Water • Coolant- absorbs heat & keeps core from melting • Slows movement of neutrons released during chain reaction • Slower neutrons able to split U-235

11. Control Rods • Regulate speed of reaction by absorbing neutrons • Lowering into reactor absorbs neutrons and slows down reaction rate • Raising control rods- fewer neutrons absorbed reaction rate is increased • Usually- cadmium or boron

12. Power from Steam • Coolant water temperature usually 275° C • Moves into pipes to heat exchanger where it heats water for steam • Steam turns turbines in electric generator • Hot water is than sent to cooling towers to cool off

13. 16-3 Radioactive Waste • 32 metric tons of nuclear waste is produced each year by 1 1000 Mega Watt nuclear reactor • Radiation is unhealthy- dividing cells are especially sensitive • Skin & bone marrow • Amount of exposure determines extent of damage • Immediate damage from large dose- skin burns, anemia, death • Change in DNA – cancer & genetic mutations

14. Types of Waste • High Level Waste- radioactive wastes that omit large amounts of radiation • Used fuel rods, control rods, coolant water • Dangerous to handle & may be poisonous • Med-to Low Level Waste- not as radioactive as High Level, but produced in larger amounts • waste is more common it poses a greater risk for human health • Med- uranium mine waste & contaminated work clothes • Low- hospital and lab wastes

15. Waste Disposal • Very difficult because of long half life of contaminants • Low level- could be dangerous for 300 yrs • High level- thousands of years • P-239 half life= 24,000 yrs--- dangerous for 192,000 yrs • Cost of disposal is very high • Storage issues for High Level Waste • Containers must not corrode for thousands of years • U.S.A uses glass • Storage site must be geologically stable • No earthquakes or volcanoes near site • Must be stored deep under ground

16. Disposal Methods • Low Level- often buried or were enclosed in concrete and disposed of at sea • Medium Level- most not disposed of permanently, same issues as High Level Waste Disposal • Safety issue with transport of radioactive waste- • Current issue with states not wanting waste to be transported across them on its way to disposal site

17. Safety & Cost of Nuclear Energy • Safety very important because of danger of contamination • Cooling and control systems of reactor failing could result in core failure- uncontrolled reaction • Temps rise, causing core, reactor vessel, & fuel rods to melt • Meltdown- process by which nuclear chain reaction goes out of control and melts the reactor core • Huge amounts of radiation can be released into environment • Chernobyl & Three Mile Island

18. Safety & Cost: Chernobyl • Nuclear reactors are built to prevent and contain a meltdown • 1986- Chernobyl, Ukraine reactor melted down • Worst nuclear accident in history • Level 7 • Fuel rods were graphite and caught on fire • Released radioactivity across a large area • 30 people died instantly, 336,000 displaced from their homes • Approximately 15,000 cancer cases projected • Plant was old and lacked newer safety features- 1977 • Accident was result of human error • Reactor exploded- resulting in fires