1. Chapter 12 Nuclear Energy

2. 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

3. 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: (happens in stars)
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. Atoms and Radioactivity
8 P
8 N
Oxygen
6 P
6 N
Carbon
Differing # proton = different atom

7. Radioactive Isotope Results in an isotope
Carbon
If actual atomic mass > normal atomic mass  typically caused by greater number of neutrons
Results in an isotope
Chemical behavior identical to normal atom.
Many are radioactive

8. 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

9. Radioactive Isotope Half-lives

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

11. 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

12. How Electricity is Produced

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

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

15. 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

16. 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

17. 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)
Fukushima, Japan (still assessing)

18. 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

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

20. Chornobyl Radiation spread was unpredictable
Radiation fallout was dumped unevenly
Death toll is 10, ,000

21. Fukushima
2011- Due to damage of cooling system from a level ‘9’ earthquake, then a Tsunami, complete meltdown/through of reactor occurred. Due to the exposure of core and fuel rods, radiation was released.

22. Fukushima

23. 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

24. 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
Lastly, Decommisioning the Nuclear Power Plants is costly and difficult due to ….

25. Radioactive Wastes Long term solution to waste
Deep geologic burial –Yucca Mountain
As of 2011, site must meet EPA million year standard (compared to previous 10,000 year standard)
Possibilities:
Above ground mausoleums
Arctic ice sheets
Beneath ocean floor
SPACE?

26. 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.

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

28. 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)

29. Fusion
Fuel= isotopes of hydrogen

30. 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

31. The Future of Nuclear Energy?
In the 1950’s and 60’s work was done to find other ways to produce energy.
Produces nearly no waste, can actually dispose of other nuclear waste products (plutonium) in the process.
A summary of how this technology works:
1) You start with a fluoride salt. In this reactor it will be heated so much that it melts.
2) You dissolve thorium fluoride in the liquid salt.
3) Thorium-232 absorbs neutrons and turns into Uranium-233.
4) The Uranium-233 fissions and produces heat plus more neutrons.

32. Liquid Fluoride Thorium Reactors
Advantages include: 1) There is no pressure – unlike traditional nuclear reactors which contain high pressure steam. So the reactor cannot explode. 2) The fuel does not need to be shaped into pellets 3) The reactor can add fuel and remove waste at any time 4) There are no weapon-grade materials involved 5) Thorium is abundant and most of it is used up in the reaction