Announcements. Projected Energy Consumption. Fossil fuel issues. By the end of class today

Transcription

1 Announcements Projected Energy Consumption Ecological Footprint assignment starts this afternoon to be completed by 10 AM Thursday Today: Alternatives to fossil fuels? Nuclear power Energy efficiency Thursday: Renewable energy Fossil fuel issues Inflexible end uses: Transportation = oil Electricity = coal + natural gas Industrial and residential = oil + natural gas Environmental issues Air pollution: sulfur dioxide, nitrogen dioxide, mercury, Green-house gas emissions & climate change Strip mining, fracking, oil spills By the end of class today Learn how a nuclear power plant works Consider the environmental and economic advantages and disadvantages of nuclear power Understand the causes and consequences of nuclear accidents Recognize that energy efficiency is a resource and is the key to reducing environmental effects of energy production and use (Joel Swisher, IES) 1

2 "The most important responsibility of this atomic energy agency would be to devise methods whereby this fissionable material would be allocated to serve the peaceful pursuits of mankind. Experts would be mobilized to apply atomic energy to the needs of agriculture, medicine and other peaceful activities. A special purpose would be to provide abundant electrical energy in the power-starved areas of the world" Dwight D. Eisenhower on the International Atomic Energy Agency (1953) U92Nuclear Power ATOMIC NUMBER: number of protons MASS NUMBER: number of protons + neutrons ATOMIC MASS: mass of atom in atomic units ISOTOPES: forms of an element with different mass numbers EXAMPLES: 238 U, 235 U, 236 U are isotopes of uranium RADIOACTIVITY: Spontaneous conversion of one element to another through the emission of radiation Types of radioactivity Alpha decay: Emission of an alpha particle (2 protons, 2 neutrons) from an atom s nucleus reduces p:n ratio Beta decay: Emission of a beta particle (an electron) from the atom s nucleus increases p:n ratio Gamma decay: Emission of gamma rays from an atom s nucleus following alpha or beta decay Spontaneous Fission Fissile isotopes: 235 U, 233 U, 239 Pu, 241 Pu 2

3 Nuclear Fission 1n U 140 Ba + 93 Kr + 3n (slow) (or 140 Cs + 93 Rb + 3n) Mass of 235 U + 1n > mass of 140 Ba + 93 Kr + 3 n Nuclear Power Step-by-step E = mc 2 Refine uranium from uranium-bearing rock Enrich the uranium in 235 U (~ 0.7% of total U) (4% 235 U), very difficult to separate 235 U from 238 U Methods: Diffusion of UF 6 through a membrane, centrifugation Create a fuel geometry that can be controlled Fuel rods: contains the uranium ore Moderator: slows neutrons Control rods: absorbs neutrons to stop the nuclear reaction Connect the nuclear vessel to a steam generator and turbine for producing electricity 3

4 Controlling the nuclear reaction Heat released generates steam, which turns a turbine, which turns a generator to make electricity Control rods absorb neutrons stopping reaction (cadmium) Moderator (H 2 O) slows neutrons to allow fission Nuclear disasters Loss of coolant Reactor cores and spent fuel rods remain hot for many years after fission stops Causes of coolant loss: human error, design flaws, natural disasters 3 Mile Island March 1979, Middletown PA Meltdown of reactor 2 due to loss of coolant water, ambiguous warning indicators, and inadequate operator training. Radiation leaked into atmosphere and into Susquehanna River Timing coincided with release of the movie The China Syndrome. Unit 2 permanently shut down. Unit 1 still producing electricity 4

5 Chernobyl: Чорнобильська катастрофа Chernobyl (1986) 1000s of miles of fallout Design flaws + human error -> coolant circulation failure Fuel melted creating heat, reactions inside the reactor produced hydrogen -> explosion Fallout was global Deaths (between 28 and 28,000?) Area the size of Florida is still contaminated Other reactors remained running until December 2000 Fukushima Daiichi nuclear disaster Controlling a nuclear power plant 9.0 magnitude earthquate caused shutdown of reactors 1-3 Tsunami flooded and destroyed generators that pumped coolant Units 1-3 experienced full meltdown An explosion in unit 4 occurred near spent fuel pool Hydrogen produced by heat and chemical reactions exploded, emitting radiation into atmosphere. Seawater was used to flood the reactors, sending radioactive waste into the ocean Two months later, tuna off California had measureable levels of radioactivity from the Fukushima plant 5

6 Nuclear Power around the world Nuclear power in the U.S Nuclear power plants in operation today Hanford, WA Belarus Armenia Iran Netherlands Slovenia Bulgaria Japan Mexico Romania South Africa Argentina Brazil Pakistan Hungary Finland Slovakia Switzerland Czech Republic Taiwan Belgium Spain Germany Sweden Ukraine United Kingdom China Canada India South Korea Russia France United States Data from the IAEA Number of nuclear power plants has not grown since mid-1980s Why not? Why no new nuclear power plants in US for > 25y? High up-front costs (~7 billion) Long construction times Difficult to finance Public concerns 6

7 Nuclear Power Hazards Uranium mining and purification is not clean (e.g., Hanford, WA) Spent fuel toxic for ten thousand to 1 million years 239 Pu made (24,000y half life) in nuclear plants from 238 U Storage sites: At nuclear power plants (most waste) Yucca mountain, Nevada (rejected by congress) Waste Isolation Pilot Plant, New Mexico Potential for accidents (e.g., Chernobyl, Fukushima) Potential for theft of fissionable material - during storage, transport Potential for nuclear weapons proliferation 239 Pu production for WWII Manhattan project 40 billion gallons of waste dumped into soil 177 huge underground tanks, ⅓ leaking in 2001 Contaminated groundwater moving toward Columbia R. 60 billion spent on cleanup so far, 200 billion more estimated World s largest cleanup site Hanford Site U.S. Options for Electricity Coal Nuclear 7