1. NUCLEAR POWER
APES
2009
CHAPTER 21

2. ISOTOPES
Isotopes- some atoms of the same element have different numbers of neutrons creating different mass numbers.
EX: Uranium has 92 protons, & most uranium atoms contain 146 neutrons & have a mass number of 238…
= 238
How many neutrons does U-235 have?

3. RADIOACTIVITY
Some isotopes are unstable and decay slowly, emitting particles & energy.
These are called radioactive atoms
Radioactive atoms eventually become stable and stop decaying.

4. Radiation can come from
Alpha particles
Beta particles
Gamma rays- used in radiation therapy for cancer patients.
When alpha or beta particles are given off, the mass # & atomic # change creating a different element.

5. Natural Radiation? Natural sources of radiation… Soil & rocks Water
Air
Cosmic rays

6. 2 radioactive isotopes of uranium are U-238 and
U-235 (know calculation!)
Both decay into stable form of lead.
The amount of time it takes for half of the atoms in a sample of a radioactive element to decay is called the isotope’s half-life.
Half-lives can be a few seconds or billions of years.
U-238 has half-life of 4.5 billion years.
U-235 has half-life of 700 million years.

7. REACTIONS & REACTORS
Nuclear Fission- releasing energy by splitting the nucleus of an atom apart.
This energy can be used to create electricity.

8. STEPS OF NUCLEAR FISSION
Neutron is fired into nucleus of U-235 atom.
Nucleus splits, forming two daughter nuclei
This reaction releases energy & several more neutrons.
This continuous action of neutrons splitting atomic nuclei is called a chain reaction.

9. NUCLEAR REACTORS Nuclear fuel is usually 97% U-238 and 3% U-235.
U-238 is not fissionable so it is not part of the nuclear reaction (but can be used in plutonium reactors)

10. NUCLEAR REACTORS
In the U.S., nuclear fission happens inside a nuclear reaction vessel
20 m tall with walls that are cm thick.
Large shield surrounds the vessel to contain any stray radioactive particles
The reactor is housed inside a concrete containment building.

11. NUCLEAR REACTORS
Fuel rods are filled with pellets that contain the U Positioned vertically in reactor so water can circulate betwn them.

12. NUCLEAR REACTORS Water is important because:
It absorbs heat & keeps core from melting.
It slows the movement of neutrons released during the chain reaction.

13. NUCLEAR REACTORS
Speed of chain reactions is controlled by control rods made of cadmium, boron, etc. that absorb neutrons.
Raise control rods out of reactor= absorb fewer neutrons, speed up reaction, hotter water.
Lower control rods into reactor= absorb more neutrons, slow reaction, cool water

14. NUCLEAR REACTORS
Hot water is passed to pipes where steam is created that turns turbines, creating electricity.
Water cooling system & control rods regulate heat. If they fail, it would cause a “nuclear meltdown” at the core.

16. BREEDER REACTORS U-238 is most plentiful, but non-fissionable.
Turn U-238 into plutonium-239 which is fissionable.
It creates more fuel than you start with.
Plutonium can be used to make atomic bombs as well as energy.
Breeder reactors not used in U.S. because of potential threat of nuclear terrorism.

17. RADIATION & HEALTH Radiation is unhealthy
Fast dividing skin cells & blood cells are particularly vulnerable
Large doses cause skin burns, anemia, death, miscarriage
Changes DNA leading to cancer & genetic mutations.
Can be passed on to offspring

18. www.geology.fau.edu/course_info/fall02/ EVR3019/Nuclear_Waste.ppt

19. RADIOACTIVE WASTE HIGH LEVEL Emit large amounts of radiation
Very dangerous & poisonous
Stored onsight in large containment vessels stored in water
Come from
Used uranium fuel rods
Control rods
Water used to cool & control chain reactions

20. RADIOACTIVE WASTE MEDIUM & LOW LEVEL Not as radioactive
A lot more are produced vs. high level
Pose a greater risk because they are more prevalent & not as obvious
Clothing of nuclear power plant workers
Tailings from uranium mines
Hospital & laboratory waste

21. WASTE DISPOSAL
Must be
stored in container that will last tens of thousands of years.
Stored in geologically stable area. No earthquakes!
Stored deep underground

22. PROBLEMS WITH WASTE DISPOSAL
Most high level wastes sit in storage tanks outside nuclear power & weapons plants. Some have begun to leak contaminating groundwater.
Between 1940 & 1970, most medium & low level wastes were sealed in concrete & dropped into the ocean, exposing that environment to potential leaks. Now, it is put into landfills

23. PROBLEMS WITH WASTE DISPOSAL
Send to Yucca Mountain in Nevada desert
160 miles from Las Vegas
Underground storage chamber
Cost $50 billion
All high level waste would have to be containerized, and transported by train or truck to site across country
Many people oppose because they do not want radioactive waste transported thru their cities.

24. Pros & Cons of Yucca Mountain
Desert- very little rain, reduce chance of corrosion
Secluded
Solid bedrock underneath- reduces chance of aquifer contamination
Has been geologically active- earthquakes
Cracks from slight earthquakes could allow water into tunnels, not to mention endanger the integrity of the storage casks
There is an aquifer underneath used for drinking & irrigating by desert population

25. Yucca Mountain
EVR3019/Nuclear_Waste.ppt

26. NUCLEAR MELTDOWN
Process by which nuclear chain reaction goes out of control & melts reactor core
Releases huge amounts of radiation into environment.

27. Three Mile Island
March 29, 1979, a reactor near Harrisburg, PA lost coolant water because of mechanical and human errors and suffered a partial meltdown
50,000 people evacuated & another 50,000 fled area
Unknown amounts of radioactive materials released
Partial cleanup & damages cost $1.2 billion
Released radiation increased cancer rates.

29. CHERNOBYL Located in Ukraine
1986 explosion killed 30 people immediately
116,000 had to leave homes permanently
May cause 15,000 cases of cancer.
62,000 sq mi contaminated
Cost $358 billion
Chernobyl was old & lacked safety equipment
Caused by human error

31. CONS OF NUCLEAR POWER PROS OF NUCLEAR POWER
Potential accidents
Radioactive waste disposal expensive & difficult
Safety equipment expensive
High cost of building new plants
Uranium is nonrenewable
Use very little material to get a lot of energy.
Does not produce much air pollution

32. Use of Nuclear Energy U.S. phasing out
Some countries (France, Japan) investing increasingly
France 78% energy nuclear
U.S. currently ~7% of energy nuclear
No new U.S. power plants ordered since 1978
North Korea is getting new plants from the US