Renewable/Alternative Energy

1. Renewable/Alternative Energy • Alternative = not fossil fuels • Renewable energy sources effectively cannot be depleted through overuse. • However, they can be used to a theoretical maximum capacity. • Renewable sources of energy are renewed constantly, on a human timescale, from much larger external sources of energy (solar fusion, gravity, geologic radioactive decay, etc…) RenewableNot Renewable Solar Fossil Fuels Wind Nuclear Hydroelectric Geothermal (some) Biomass Wave, Tidal Geothermal (some)

2. Nuclear Energy • Not from solar radiation; comes from nuclear forces • Electrical energy from controlled nuclear reaction (fission) • Fusion is interesting, but not feasible yet • NON-RENEWABLE (must burn up U fuel) • U.S. history: • Developed in the 1960’s and 1970’s • 53 plants by 1975 with 170 plants planned; last order placed in 1978; currently (2008) 104 plants in U.S. • U.S. (2008): ~20% of electrical power • In other countries: • Most popular in France (77% of electricity) • Also popular in other European countries, Japan (31% of electricity) • Of growing interest in China & India (currently ~2-3% of electricity)

4. Worldwide Distribution of Nuclear Power Plants http://www.ehponline.org/members/2005/113-11/focus.html Argonne National Laboratory

7. Nuclear Energy • Fuel: Uranium-235 • Only naturally-occurring fissionable isotope (fission = heavy element spontaneously “splits” into two or more lighter daughter products) • Natural abundance is low (99.3% U-238, 0.7% U-235) • Plutonium-239 is also fissionable, but must be manufactured • Isotopes • Isotope number (e.g., 235, 238, 239) refers to number of protons and number of neutrons in the nucleus (mass number) • Chemical elements are defined by the number of protons in the nucleus (e.g. 92 for U) This is how we write U-235

8. Nuclear Energy: U-235 Fission • Extremely energetic reaction: yield from 1lb UO2 same as from ~50 tons of coal • Force reaction to occur by bombarding U-235 nucleus with a neutron • Splits U-235 into fission fragments, neutrons, lots of energy • Extra neutrons may create chain reaction • Critical Mass: amount of material required to start chain reaction, increases probability of fission from product neutrons hitting another U-235 to 100% (15kg for U-235, 4.4 kg for Pu-239, less if packed with “reflectors”) • Nuclear Weapon: critical mass assembled by conventional weapon trigger

10. Fission Nuclear Reactor • Controlled Chain Reaction: moderators (H2O, graphite) are used to absorb some emitted neutrons & prevent runaway chain reaction • FUEL RODS: contain pellets of U or UO2 • Requires 2-3% U-235 (much enriched compared to natural) • Separation is difficult, expensive (new techniques are cheaper --problem for nuclear proliferation) • CONTROL RODS: contain neutron absorber (Cd, B) • Lower between fuel rods to maintain chain reaction • Complete insertion typically halts reaction • Pulling rods out accelerates reaction • WATER BATH: surrounds fuel, control rods • Coolant • Slows neutrons to increase fission probability (moderator) • Used to convey heat to drive steam turbines (create electricity)

12. Nuclear vs. Coal (1000 MW plant) • Fuel • Coal: 2-3 million tons (strip mining, hazardous underground mining, acid mine drainage) • Nuclear: 30 tons enriched U (75000 tons of ore) • CO2 Emissions • Coal: >7 million tons • Nuclear: 0 • SO2 and other Emissions • Coal: >300,000 tons of SO2, particulates, other air pollutants (acid rain, low level air pollution) • Nuclear: 0

13. Nuclear vs. Coal (1000 MW plant) • Radioactivity • Coal: 100x more than nuclear (U, Th in coal) • Nuclear: very low levels of radioactive gases • Solid Waste • Coal: 600,000 tons of ash • Nuclear: 250 tons of highly radioactive waste • Accidents • Coal: possible fatalities to workers, destructive fires • Nuclear: minor radioactive gas release to catastrophic release of radioactivity is possible

14. Nuclear Power Hazards • REACTOR SAFETY • Typical nuclear reactor contains same amount of radioactivity as Hiroshima • Concern: if coolant is not in place, heat can cause meltdown, explosion, release of radioactive material (e.g. Chernobyl!) • WEAPONS PROLIFERATION • >93% U-235 needed for weapons, not easy to manufacture (separate) • Pu-239 is more problematic -- it is produced in conventional nuclear reactors and can be separated fairly easily • WASTE DISPOSAL • Accidents are rare, but dangerous radioactive waste is a routine byproduct • HLW (high level waste) is a serious threat -- must be contained for very long periods of time (thousands or tens of thousands of years)

17. Long-term Waste Disposal:Yucca Mountain • near Nevada Test Site (904 atomic bomb tests between 1945 and 1992) and Nevada Test and Training Range • Geology: arid (desert) – deep water table (~1000 ft); welded tuff (12 million yrs old), fractured • Standards: safe for 10,000 years; later changed to 1,000,000 years • Study of site begins in 1978; in 1984 selected as one of 10 possible sites for nuclear waste repository • Nuclear Waste Policy Act (1982, amended in 1987) designates it as sole national repository for high level nuclear waste

18. Long-term Waste Disposal:Yucca Mountain • Site approved by Congress & Bush administration in 2002 for long term nuclear waste storage • In 2007, plans announced to double size of repository at Yucca Mountain • Obama administration states site is no longer an option, eliminates all funding (2009) • Opposition mostly NIMBY, other concerns • Transportation of waste (>3000 shipments have been made thus far without incident) • Archaeological surveys suggest use by early hunter gatheres; some religious Native Americans view area as culturally significant

20. Long-term Waste Disposal:Yucca Mountain • What Now? • Stephen Chu (DOE) putting together blue ribbon panel • Reprocess, reuse spent fuel when possible • Place stuff that can’t be reprocessed into salt domes (no longer accessible, but geologically quite stable) • For now, 1987 Nuclear Waste Policy Act stands and Yucca remains the official national waste repository

21. Potential for Accidents:Chernobyl • April 26, 1986 • Chernobyl Nuclear Power Plant in Ukraine (Soviet Union) • Worst nuclear power plant in history; steam explosion and fire; meltdown of reactor core; massive release of radioactivity (20,000 roentgens/hr – lethal dose is 500 roentgens per 5 hrs) • Explosion/meltdown was due to unauthorized experiments with safety mechanisms disabled • 2005 Report World Health Organization & International Atomic Energy Agency attributes <50 direct depths & ~4000 additional cancer deaths to accident

22. Potential for Accidents:Chernobyl • 237 people had acute radiation sickness, 31 of these died within 3 months – many were firefighters; 135,000 people evacuated from area • All humans evacuated 24 yrs ago, but wildlife remains (an official wildlife sanctuary now!) • 17 mile exclusion zone, but some 10,000 people, mostly elderly (60-90) have returned, younger family members only permitted short visits • Radiation levels remain 10 to 100 times higher than normal background levels near Chernobyl • Reactor core now encased in concrete sarcophagus – supposed to be rebuilt in 2005, but delayed, now expected to be complete in 2012

23. CHERNOBYL SARCOPHAGUS

24. Chernobyl aerial view into the core, smoke from the graphite fire and core melt down. The photo was taken from a helicopter on May 3, 1986, of the destroyed Unit 4. The image was taken from the North of the subject. Wikipedia

25. Fusion Reactors? • Extremely energetic reaction – combine H into He (as in Sun or H bomb) • Requires very high temperatures (~3 million degrees Celcius) – high enough to vaporize all known materials • How to contain? • Tokamak design: use magnetic field to contain hot H • Laser fusion: use laser to heat a tiny pellet of H dropped into beam • Z machine: deliver short, powerful energy pulse through wires to create X-ray blast (not hot enough yet) • Future remains uncertain, but lots of $ being invested (e.g. $14 billion International Thermonuclear Experimental Reactor in France to test Tokamak design)