1. 15-5 What Are the Advantages and Disadvantages of Nuclear Energy?
Concept Nuclear power has a low environmental impact and a very low accident risk, but high costs, a low net energy yield, long-lived radioactive wastes, vulnerability to sabotage, and the potential for spreading nuclear weapons technology have limited its use.

2. How Does a Nuclear Fission Reactor Work? (1)
Controlled nuclear fission reaction in a reactor
Light-water reactors
Fueled by uranium ore and packed as pellets in fuel rods and fuel assemblies
Control rods absorb neutrons

3. How Does a Nuclear Fission Reactor Work? (2)
Water is the usual coolant
Containment shell around the core for protection
Water-filled pools or dry casks for storage of radioactive spent fuel rod assemblies 3

4. Light water reactors
85% of world’s nuclear generated electricity (100% in US)
High inefficient in terms of energy conversion (up to 83% lost as waste heat)

5. Nuclear fuel Made from uranium ore
Enriched to 3% of radioactive isotope U-235
Made into pellets, size of pencil, energy equivalent to 1 ton of coal
Pellets are packed into large pipes-fuel rods
Rods are grouped together into fuel assemblies, these assemblies are placed into reactor core

6. Controlling the reaction
Control rods placed between rods
Control rods moved in and out of the assemblies, absorbing neutrons which trigger the chain reaction
Water circulates through the assemblies, removing the heat, keeping the rods from melting

7. What happens if there is no water?

8. How nuclear reactors generate electricity
Superheated water turns into steam
Steam passed through turbine
Physical motion of the turbine is converted into electrical energy

9. Steam from Nuclear power plants
Superheated water after used in the turbines goes into a condenser
Condenser requires cold water source which is why most plants are located next to water
Pipes with the hot water are circulated through a container filled with cold water , heat is exchanged
Hot water is either discharged into river, ocean… or vented into the atmosphere as steam

11. Light-Water-Moderated and -Cooled Nuclear Power Plant with Water Reactor

12. Small amounts of radioactive gases Control rods Containment shell
Heat exchanger
Waste heat
Turbine
Generator
Steam
Uranium
fuel input
(reactor core)
Hot coolant
Useful electrical energy
25%–30%
Hot water output
Pump
Pump
Figure 15.17
Science: light-water–moderated and –cooled nuclear power plant with a pressurized water reactor. Some nuclear plants withdraw water for cooling from a nearby source of water and return the heated water to such a source, as shown here. Other nuclear plants that do not have access to a source of cooling water transfer the waste heat to the atmosphere by using one or more gigantic cooling towers, as shown in the insert photo of the Three Mile Island nuclear power plant near Harrisburg, Pennsylvania (USA). Question: How does this plant differ from the coal-burning plant in Figure 15-12?
Shielding
Coolant
Pump
Pump
Waste heat
Cool water input
Pressure vessel
Moderator
Coolant passage
Water
Condenser
Water source (river, lake, ocean)
Periodic removal and storage of radioactive wastes and spent fuel assemblies
Periodic removal and storage of radioactive liquid wastes
Fig , p. 387

13. Reactor in Japan

15. After 3 or 4 Years in a Reactor, Spent Fuel Rods Are Removed and Stored in Water

16. Spent Fuel rods
After about 3-4 years of use, the Fuel rods become spent-level of fission drops beneath a certain level
Rods are taken out of reactor stored nearby in water filled pools or dry casks
Stored until they cool down enough to be shipped for permanent storage or to be recycled
These storage facilities are next to the reactor plants, vulnerable to terrorist attack or accidents

17. Spent fuel reprocessing
The spent fuel rods are sent to a facility which separates plutonium from spent fuel for further use as a new generation of fuel or as material used to make atomic weapons.
First the fuel is chopped up, by remote control, behind heavy lead shielding.
These chopped-up pieces are then dissolved in boiling nitric acid, releasing radioactive gases in the process.
The plutonium is separated from the acid solution by chemical means, leaving large quantities of high-level radioactive liquid waste and sludge behind.
After it has cooled down for several years, this liquid waste will have to be solidified for ultimate disposal, while the separated plutonium is fabricated into nuclear fuel or nuclear weapons.

18. Japan and the Soviet Nuclear program connection
As a result of a successful program between the Soviet Union and USA, many nuclear weapons have been destroyed.
The fuel from a number of Soviet weapons was sold to Japan to be used for fuel in their reactors
So plutonium is used in at least one of the damaged reactors in Japan

19. What Is the Nuclear Fuel Cycle?
Mine the uranium
Process the uranium to make the fuel
Use it in the reactor
Safely store the radioactive waste
Decommission the reactor

20. Uranium-235 as UF6 Plutonium-239 as PuO2
Decommissioning of reactor
Fuel assemblies
Enrichment of UF6
Reactor
Fuel fabrication
(conversion of enriched UF6 to UO to UO2 and fabrication of fuel assemblies)
Temporary storage of spent fuel assemblies underwater or in dry casks
Conversion of U3O8
to UF6
Uranium-235 as UF6 Plutonium-239 as PuO2
Spent fuel reprocessing
Low-level radiation with long half-life
Figure 15.19
Science: the nuclear fuel cycle (Concept 15-5). As long as a plant is operating safely, this fuel cycle has a fairly low environmental impact and a very low risk of an accident. But costs are high, radioactive wastes must be stored safely for thousands of years, and facilities are vulnerable to terrorist attack. Also, the technology can be used to produce material for use in nuclear weapons, and an amount equal to about 92% of the energy content of the nuclear fuel is wasted in producing nuclear power. Questions: Do you think the market price of nuclear-generated electricity should include all the costs of the fuel cycle? Explain. If so, how would this affect the use of nuclear power to produce electricity?
Geologic disposal of moderate- and high-level radioactive wastes
Open fuel cycle today
Recycling of nuclear fuel
Fig , p. 389

21. What Happened to Nuclear Power?
Slowest-growing energy source and expected to decline more
Why?
Economics
Poor management
Low net yield of energy of the nuclear fuel cycle
Safety concerns
Need for greater government subsidies
Concerns of transporting uranium

22. Case Study: Worst Commercial Nuclear Power Plant Accident in the U.S.
Three Mile Island
March 29, 1979
Near Harrisburg, PA, U.S.
Nuclear reactor lost its coolant
Led to a partial uncovering and melting of the radioactive core
Unknown amounts of radioactivity escaped
People fled the area
Increased public concerns for safety
Led to improved safety regulations in the U.S.

23. Case Study: Worst Nuclear Power Plant Accident in the World
Chernobyl
April 26, 1986
In Chernobyl, Ukraine
Series of explosions caused the roof of a reactor building to blow off
Partial meltdown and fire for 10 days
Huge radioactive cloud spread over many countries and eventually the world
350,000 people left their homes
Effects on human health, water supply, and agriculture

24. Oak Ridge Reactor

25. Remains of a Nuclear Reactor at the Chernobyl Nuclear Power Plant

26. Level of contamination

27. Human casualties of Chernobyl
56 people lost their lives as a direct result of radiation poisoning or fire
Thyroid cancer
From drinking
Milk killed
10-12 thousand

28. Nuclear Power Has Advantages and Disadvantages

29. TRADE-OFFS Conventional Nuclear Fuel Cycle Advantages Disadvantages
Large fuel supply
Cannot compete economically without huge government subsidies
Low environmental impact (without accidents)
Low net energy yield
High environmental impact (with major accidents)
Emits 1/6 as much CO2 as coal
Moderate land disruption and water pollution (without accidents)
Environmental costs not included in market price
Risk of catastrophic accidents
Figure 15.21
Advantages and disadvantages of using the nuclear power fuel cycle (Figure 15-19) to produce electricity (Concept 15-5). Question: Which single advantage and which single disadvantage do you think are the most important? Why?
Moderate land use
No widely acceptable solution for long-term storage of radioactive wastes
Low risk of accidents because of multiple safety systems (except for Chernobyl-type reactors)
Subject to terrorist attacks
Spreads knowledge and technology for building nuclear weapons
Fig , p. 391

30. TRADE-OFFS Coal vs. Nuclear Coal Nuclear Ample supply
Ample supply of uranium
High net energy yield
Low net energy yield
Very high air pollution
Low air pollution
High CO2 emissions
Low CO2 emissions
Much lower land disruption from surface mining
Figure 15.22
Comparison of the risks of using the nuclear power fuel cycle and coal-burning plants to produce electricity. A 1,000-megawatt nuclear plant is refueled once a year, whereas a coal plant of the same size requires 80 rail cars of coal a day. Question: If you had to choose, would you rather live next door to a coal-fired power plant or a nuclear power plant? Explain.
High land disruption from surface mining
Moderate land use
High land use
Low cost (with huge subsidies)
High cost (even with huge subsidies)
Fig , p. 392

31. Nuclear Power Plants Are Vulnerable to Terrorists Acts
Explosions or meltdowns possible at the power plants
Storage pools and casks are more vulnerable to attack
60 countries have or have the ability to build nuclear weapons

32. Dealing with Radioactive Wastes Produced by Nuclear Power Is a Difficult Problem
High-level radioactive wastes
Must be stored safely for 10,000–240,000 years
Where to store it
Deep burial: safest and cheapest option
Transportation concerns
Would any method of burial last long enough?
There is still no facility: NIMBY scenario
Can the harmful isotopes be changed into harmless isotopes? (working on it, $$$)

33. Case Study: Experts Disagree about What to Do with Radioactive Wastes in the U.S.
1985: plans in the U.S. to build a repository for high-level radioactive wastes in the Yucca Mountain desert region (Nevada)
Problems
Cost: $58–100 billion
Large number of shipments to the site: protection from attack?
Rock fractures
Earthquake zone
Decrease national security

34. What Do We Do with Worn-Out Nuclear Power Plants?
Decommission or retire the power plant
At least ½ of US plants are scheduled to close by next year
Some options
Dismantle the plant and safely store the radioactive materials
Enclose the plant behind a physical barrier with full-time security until a storage facility has been built
Enclose the plant in a tomb
Monitor this for thousands of years

35. Nuclear power plants: no CO2 emission
Can Nuclear Power Lessen Dependence on Imported Oil, Reduce Global Warming?
Nuclear power plants: no CO2 emission
Complete Nuclear fuel cycle: emits CO2 (not like Fossil fuels)
Opposing views on nuclear power and global warming
Nuclear power advocates
2003 study by MIT researchers: low grade ore
2007: Oxford Research Group: reactor a week for 70 years still only produce 20%

36. Will Nuclear Fusion Save Us?
“Nuclear fusion is the power of the future and always will be”
Still in the laboratory phase after 50 years of research and $34 billion dollars: energy
2006: U.S., China, Russia, Japan, South Korea, and European Union
Will build a large-scale experimental nuclear fusion reactor by 2040

37. Experts Disagree about the Future of Nuclear Power
Proponents of nuclear power
Fund more research and development
Pilot-plant testing of potentially cheaper and safer reactors
Test breeder fission and nuclear fusion
Opponents of nuclear power
Fund rapid development of energy efficient and renewable energy resources

38. Science Focus: Are New and Safer Nuclear Reactors the Answer? (1)
Advanced light-water reactors (ALWR)
Built-in passive safety features
High-temperature-gas-cooled reactors (HTGC)
Avoids problems with present water based systems, but still not 100% reliable

39. Alternatives Pebble bed modular reactor (PBMR)
Pros: no need to shut down for refueling
Cons: graphite protective coatings, vulnerable
China, South Africa
Breeder nuclear fission reactors
Creates plutonium from uranium
France built one then shut it down 2 years later

40. Pebble Bed Reactors

41. Breeder reactors

42. Science Focus: Are New and Safer Nuclear Reactors the Answer? (2)
New Generation nuclear reactors must satisfy these five criteria
Safe-runaway chain reaction is impossible
Fuel can not be used for nuclear weapons
Easily disposed of fuel
Nuclear fuel cycle must generate a higher net energy yield than other alternative fuels, without huge government subsidies
Emit fewer greenhouse gases than other fuels

43. Exit questions for 15.5 Describe the nuclear fuel cycle
How do we deal with the highly reactive radioactive wastes produced by nuclear power plants? How should we?
What is the difference between nuclear fusion and fission? What is fusion’s potential as a energy source
Summarize arguments for and against nuclear power