What if we spend all our petroleum and natural gas

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Unformatted text preview: l 1 013 kg of CO2 produced – atmosphere is about 5.3 1018 kg – each year, contribute 2 ppm by mass, 1.3 ppm by volume – graph shows current rate of 1.5 ppm by volume Winter 2007 3 • CO2 was steady at about 280 ppm until the industrial was revolution (data is from ice core samples) • Now at 370 ppm: 32% increase over natural level ppm: 33 Winter 2007 UCSD: Physics 121; 2007 What’s ahead? What’ 34 UCSD: Physics 121; 2007 Nuclear: the finite uranium resource • Uranium cost is about $23/kg • If we spend all our petroleum and natural gas, plus similar contribution from coal, we’ll add another 250 ppm for a total of we’ 620 ppm – about 1% of cost of nuclear power • As we go for more, it’s more expensive to get it’ – 2.2 times pre-industrial level – more if we keep using coal after the others are gone – IPCC guesses 500–1000 ppm by the year 2100 if no global environmental policies are enacted – depleted the easy spots • 3 million tons available at cost < $230/kg • Need 200 tons per GW-yr • Now have 100 GW of nuclear power generation • IPCC is Intergovernmental Panel on Climate Change • WMO (World Meteorological Org.) is also relevant – in about 100 plants; 1 GW each • CO2 hangs around a good long while, so even if we stopped hangs producing it today we’d still be in trouble today we’ • 3 million tons will last 150 years at present rate – only 30 years if nuclear replaced all electricity prod. – 4,000 years if breeders are used, but this has problems in proliferation of plutonium • Nuclear waste issues have not yet been solved Winter 2007 Lecture 16 35 Winter 2007 36 9 Energy, Sustainability 03/15/2007 UCSD: Physics 121; 2007 UCSD: Physics 121; 2007 Artificial fusion Deuterium everywhere • 16 million degrees in sun’s center is just enough to keep the sun’ just enough process going • Natural hydrogen is 0.0115% deuterium – Lots of hydrogen in sea water (H 2O) – but sun is h uge, so it seems prodigious • Total U.S. energy budget (100 QBtu = 1020 J per per year) covered by sea water contained in cubic volume 170 meters on a side • In laboratory, need higher temperatures still to get worthwhile rate of fusion events – like 100 million degrees • Bottleneck in process is the reaction: 1H + 1H 2H + e+ + ( or proton-proton – – – – deuteron) • Better off starting with deuterium plus tritium – 2H and 3 H, sometimes called 2D and 3 T • Then: corresponds to 0.15 cubic meters per second about 1,000 showers at two gallons per minute each about one-millionth of rainfall amount on U.S. 4 gallons per person per year!!! 2H + 3H 4He + n + 17.6 MeV (leads to 81 MCal/g) compare to 16 MCal/g for uranium fission, 10 Cal/g gasoline Winter 2007 37 Winter 2007 38 UCSD: Physics 121; 2007 UCSD: Physics 121; 2007 Tritium nowhere Nasty by-products? • Tritium is unstable, with half-life of 12.32 years • Practically none: not like radioactive fission products • Building stable nuclei (like 4He) – thus none naturally available • Can make it by bombarding 6Li with neutrons – maybe our voices would be higher… – extra n in D-T reaction can be used for this, if reaction core is surrounded by “lithium blanket” • Tritium is only radioactive substance – energy is low, half-life short: not much worry here • Lithium on land in U.S. would limit D-T to a hundred years or so • Extra neutrons can tag onto local metal nuclei (in surrounding structure) and become radioactive – maybe a few thousand if we get lithium from ocean – but...
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