Clean Air Act Amendments of 1990:Reading Highlights for the ER 200 Final ExamTable of ContentsDeutch and Lester, “Nuclear Power and Its Fuel Cycle” 1Farrell, et al, “Ethanol can contribute to energy and environmental goals” 4O’Rourke and Connolly, “Just oil? The distribution of environmental and social impacts of oil production and consumption” 5Collins, “The Physical Science Behind Climate Change” 7Kolbert, “The Climate of Man–I” 8Kolbert, “The Climate of Man–II” 10Kolbert, “The Climate of Man–III” 11Pacala and Socolow, “Stabilization wedges…” 13Masters, “Air Pollution” 13Jones, et al, “Driving Sustainable Consumption through Environmental Accounting of Retail Goods and Services” 15Asian Development Bank, “The Efficiency Power Plant: A Rapid, Low-Cost Path for Energy-Saving Investments in Shanghai” 16Deutch and Lester (2004) Worldwide, ~440 plants supplying 17 % of world’s electricity (highest dependence in France, Belgium, Japan, S. Korea) US, ``largest nuclear power program,’’ 104 plants supplying ~20 percent of nation’s electricity; but NOT being replaced so slated to DECLINE 7% by 2020 Nuclear Troubles Every country difficulty finding acceptable waste-disposal solution ``Impressive’’ safety record with ``dramatic exception’’ of Chernobyl in 1986 Risk of nuclear weapons or RDD proliferation to states or terrorists Biggest Obstacle: Too Expensive to Compete Present state of industry: Near ParalysisRadioactive Decay Introduces convention of listing the Z number, which is the atomic number or numberof protons, to the lower left of the elemental symbol, and the nuclear mass (M), or thetotal number of protons and neutrons, to the upper left, e.g.23592U23190Th+α This is Alpha Decay: An unstable, heavy nucleus decays by emitting a large, helium nucleus. Energy usually low enough that it cannot penetrate skin or paper but can do significant damage to soft internal tissue when ingested, inhaled. Beta Decay: In effect, neutron in nucleus becomes a proton and to conserve charge balance, the atom emits an electron. Mass of electron tiny but energy higher thanalpha decay; radiation travels farther and can cause skin burns; significant internal damage when ingested, inhaled. Gamma Decay: Nucleus drops to lower-energy state and emits a high-energy photon somewhat like X-rays but generally an order of magnitude more energetic. Gamma rays travel much farther than alpha or beta particles – about 100m before attenuated to half strength. Can penetrate concrete. Extreme hazard to humans. Decay Law: dN(t)/dt = -λN(t), where N is the number of nuclei of the isotope decaying over time t at rate lambda. The solution yields our exponential-growth equation: N(t) = N(0)e-λt  Half-life is: N(t1/2) = (N(0)/2 = N(O) exp(-λt1/2) Or more simply: t1/2 = (1/λ)ln2The Fission Process Fissionable fuel – usu. U-235 or Pu-239 – captures a neutron and the fuel nucleus splits into two smaller nuclei. Fission unleashes 200 MeV or 3.2 X 10-9J of energy and two or three neutrons that go on to split other nuclei. Neutron multiplication drives fission reactors, n. bombs, etc. The smaller nuclei or fission products can come in lots of combinations, more than 300. Adding up 200 MeV/fission for 1g U-235 = 1MWe-day = 2 million X energy in burning gram of coal = almost 14 bbl oil  Where does 200 MeV go? 165 MeV into kinetic energy of fission fragments and becomes thermal within a micron. Gamma rays and neutrons bouncing around add more. About 8 percent of fission energy (~15 MeV) released gradually through decay of fission products and heat. Fissile elements/material: Can be split by ``slow’’ or low-energy neutrons. Fissionableelements/material: Can be split by ``fast’’ or high-energy neutrons, i.e. those producedonce fission reactions get cranking. Criticality: A reactor is said to be critical when the rates of neutron creation and destruction are in balance. When there is net production of neutrons, a reactor is said to be supercritical. When there is net neutron destruction, a reactor is said to be subcritical. Reactor operators control this balance by adjusting control rods that absorb neutrons, e.g. boron. Other built-in safety factors: Some neutrons are delayed so overall production slow enough for human reaction time Neutron balance is temp sensitive so as core heats up, more neutrons get absorbed in non-fissile nucleiReactor Types Reactors divided by type of neutron: ``fast’’ or ``thermal’’ Most reactors today are thermal: low average energy neutrons, lots of collisions before absorption and reemission Fast reactors have higher average energy neutrons. Biggest advantage is as nuclear breeders, which may become important if U fuel runs thin. Thermal reactors use moderators, some lighter or low-Z material like water, heavy water and graphite to slow down the neutrons. Most reactors today are light-water reactors; most of these are Pressurized Water Reactors, which pipe water through the hot reactor core (300 C) under sufficient pressure to prevent boiling. This coolant passes thru a steam generator,where it interacts with low-pressure water in a secondary loop and causes it to boil into steam to drive a turbine. Other main type of light-water reactor is a boiling-water reactor or BWR, where the water coolant is partially converted to steam in the core. The steam is separated and sent to drive the turbine.Safety Issues Immediately after shutdown by full insertion of control rods in a 1000MW reactor, radioactive decay in core still is producing 200MW of heat that can melt cladding on fuel and cause ``energetic release of radionuclides;’’ steam explosions, etc. Worst case: Molten fuel melts thru containment vessel, into environment.  Must design reactor to remove this heat fast. Choice of Active Cooling (pumps & humans) or Passive Cooling (No pumps or humans required) leads in theory toward passive systems. But reactor economics drive toward compact cores (high power density or output for volume) and high power density suggests that purely passive systems may be insufficient to remove heat. Result: LWRs with heavily engineered active cooling systems and lots of redundancy in pumps, computers, fuses, etc. plus containment structure. Besides some near misses, only major safety problem with LWRs is at Three Mile