Presentation on theme: "1 The Promise and Problems of Nuclear Energy II Lecture #13 HNRS 228 Energy and the Environment."— Presentation transcript:
1 The Promise and Problems of Nuclear Energy II Lecture #13 HNRS 228 Energy and the Environment
2 Chapter 6 Summary Again History of Nuclear Energy Radioactivity Nuclear Reactors Boiling Water Reactor Fuel Cycle Uranium Resources Environmental and Safety Aspects of Nuclear Energy Chernobyl Disaster Nuclear Weapons Storage of High-Level Radioactive Waste Cost of Nuclear Power Nuclear Fusion as a Energy Source Controlled Thermonuclear Reactions A Fusion Reactor
3 Review of Fission 235 U will undergo spontaneous fission if a neutron happens by, resulting in: – two sizable nuclear fragments flying out – a few extra neutrons – gamma rays from excited states of daughter nuclei – energetic electrons from beta-decay of daughters The net result: lots of banging around – generates heat locally (kinetic energy of tiny particles) – for every gram of 235 U, get 65 billion Joules, or about 16 million Calories – compare to gasoline at roughly 10 Calories per gram a tank of gas could be replaced by a 1-mm pellet of 235 U!!
4 Enrichment Natural uranium is 99.27% 238 U, and only 0.72% 235 U – 238 U is not fissile, and absorbs wandering neutrons In order for nuclear reaction to self-sustain, must enrich fraction of 235 U to 3–5% – interestingly, it was so 3 billion years ago – now probability of wandering neutron hitting 235 U is sufficiently high to keep reaction crawling forward Enrichment is hard to do: a huge technical roadblock to nuclear ambitions
5 iClicker Question Which is closest to the half-life of a neutron? – A5 minutes – B10 minutes – C15 minutes – D20 minutes – E30 minutes
6 iClicker Question Which is closest to the half-life of a neutron? – A5 minutes – B10 minutes – C15 minutes – D20 minutes – E30 minutes
7 iClicker Question What is the force that keeps the nucleus together? – Aweak force – Bstrong force – Celectromagnetic force – Dgravitational force
8 iClicker Question What is the force that keeps the nucleus together? – Aweak force – Bstrong force – Celectromagnetic force – Dgravitational force
9 iClicker Question A neutron decays. It has no electric charge. If a proton (positively charged) is left behind, what other particle must come out if the net charge is conserved? – ANo other particles are needed. – BA negatively charged particle must emerge as well. – CA positively charged particle must emerge as well. – DAnother charge will come out, but it could be either positively charged or negatively charged. – ENeutrons cannot exist individually.
10 iClicker Question A neutron decays. It has no electric charge. If a proton (positively charged) is left behind, what other particle must come out if the net charge is conserved? – ANo other particles are needed. – BA negatively charged particle must emerge as well. – CA positively charged particle must emerge as well. – DAnother charge will come out, but it could be either positively charged or negatively charged. – ENeutrons cannot exist individually.
11 iClicker Question How many neutrons in U-235? – A141 – B142 – C143 – D144 – E145
12 iClicker Question How many neutrons in U-235? – A141 – B142 – C143 – D144 – E145
13 iClicker Question How many neutrons in Pu-239? – A141 – B142 – C143 – D144 – E145
14 iClicker Question How many neutrons in Pu-239? – A141 – B142 – C143 – D144 – E145
15 iClicker Question If a substance has a half-life of 30 years, how much will be left after 90 years? – Aone-half – Bone-third – Cone-fourth – Done-sixth – Eone-eighth
16 iClicker Question If a substance has a half-life of 30 years, how much will be left after 90 years? – Aone-half – Bone-third – Cone-fourth – Done-sixth – Eone-eighth
17 iClicker Question If one of the neutrons in carbon-14 (carbon has 6 protons) decays into a proton, what nucleus is left? – Acarbon-13, with 6 protons, 7 neutrons – Bcarbon-14, with 7 protons, 7 neutrons – Cboron-14, with 5 protons, 9 neutrons – Dnitrogen-14, with 7 protons, 7 neutrons – Enitrogen-15, with 7 protons, 8 neutrons
18 iClicker Question If one of the neutrons in carbon-14 (carbon has 6 protons) decays into a proton, what nucleus is left? – Acarbon-13, with 6 protons, 7 neutrons – Bcarbon-14, with 7 protons, 7 neutrons – Cboron-14, with 5 protons, 9 neutrons – Dnitrogen-14, with 7 protons, 7 neutrons – Enitrogen-15, with 7 protons, 8 neutrons
19 iClicker Question Basically, what is the nature of the alpha particle? – Aan electron – Ba proton – Ca helium nucleus – Da uranium nucleus – Ean iron nucleus
20 iClicker Question Basically, what is the nature of the alpha particle? – Aan electron – Ba proton – Ca helium nucleus – Da uranium nucleus – Ean iron nucleus
21 iClicker Question Basically, what is the nature of the beta particle? – Aan electron – Ba proton – Ca helium nucleus – Da uranium nucleus – Ean iron nucleus
22 iClicker Question Basically, what is the nature of the beta particle? – Aan electron – Ba proton – Ca helium nucleus – Da uranium nucleus – Ean iron nucleus
23 Brief History of Nuclear Power 1938– Scientists study Uranium nucleus 1941 – Manhattan Project begins 1942 – Controlled nuclear chain reaction 1945 – U.S. uses two atomic bombs on Japan 1949 – Soviets develop atomic bomb 1952 – U.S. tests hydrogen bomb 1955 – First U.S. nuclear submarine
24 “Atoms for Peace” Program to justify nuclear technology Proposals for power, canal-building, exports First commercial power plant, Illinois 1960
25 Emissions Free Nuclear energy annually prevents – 5.1 million tons of sulfur – 2.4 million tons of nitrogen oxide – 164 metric tons of carbon Nuclear often pitted against fossil fuels – Some coal contains radioactivity – Nuclear plants have released low-level radiation
26 Early knowledge of risks 1964 Atomic Energy Commission report on possible reactor accident – 45,000 dead – 100,000 injured – $17 billion in damages – Area the size of Pennsylvania contaminated
28 Nuclear power around the globe 17% of world’s electricity from nuclear power – U.S. about 20% (2nd largest source) 431 nuclear plants in 31 countries – 103 of them in the U.S. – Built none since 1970s – U.S. firms have exported nukes. – Push from Bush/Obama for new nukes.
29 Countries Generating Most Nuclear Power CountryTotal MW USA99,784 France58,493 Japan38,875 Germany22,657 Russia19,843 Canada15,755 Ukraine12,679 United Kingdom11,720 Sweden10,002 South Korea8,170
32 Nuclear Fuel Cycle Uranium mining and milling Conversion and enrichment Fuel rod fabrication POWER REACTOR Reprocessing, or Radioactive waste disposal – Low-level in commercial facilities – High level at plants or underground repository
33 iClicker Question About what percentage of U.S. electricity is derived from nuclear power? – A10 – B20 – C30 – D40 – E50
34 iClicker Question About what percentage of U.S. electricity is derived from nuclear power? – A10 – B20 – C30 – D40 – E50
35 iClicker Question Which of the following countries has the highest percentage of electricity generated by nuclear power? – AUnited States – BUnited Kingdom (Great Britain) – CJapan – DFrance – ERussia
36 iClicker Question Which of the following countries has the highest percentage of electricity generated by nuclear power? – AUnited States – BUnited Kingdom (Great Britain) – CJapan – DFrance – ERussia
38 Uranium tailings and radon gas Deaths of Navajo miners since 1950s
39 Radioactivity Basics Radioactivity – The spontaneous nuclear transformation of an unstable atom that often results in the release of radiation, also referred to as disintegration or decay. Units Curie (Ci) the activity in one standard gram of Radium = 3.7 x 10 10 disintegrations per second Becquerel (Bq) 1 disintegration per second – International Units (SI)
40 Radioactivity Basics Radiation – Energy in transit in the form of electromagnetic waves (gamma-γ or x-ray), or high speed particles ( alpha-α, beta-β, neutron-η, etc.) Ionizing Radiation – Radiation with sufficient energy to remove electrons during interaction with an atom, causing it to become charged or ionized. – Can be produced by radioactive decay or by accelerating charged particles across an electric potential.
41 Radioactivity Basics Roentgen R the unit of exposure to Ionizing Radiation. The amount of γ or x-ray radiation required to produce 1.0 electrostatic unit of charge in 1.0 cubic centimeter of dry air. Rad the unit of absorbed dose. Equal to 100 ergs per gram of any material from any radiation. SI unit = Gray 1 Gray = 100 rads REM the unit of absorbed dose equivalent. The energy absorbed by the body based on the damaging effect for the type of radiation. REM =Rad x Quality Factor SI unit = Sievert 1 Sv = 100 Rem
42 iClicker Question Which of the following describes the Roentgen? – A the unit of absorbed dose equivalent. – B the unit of absorbed dose. – C the unit of exposure to ionizing radiation – D all of the above – E none of the above
43 iClicker Question Which of the following describes the Roentgen? – A the unit of absorbed dose equivalent. – B the unit of absorbed dose. – C the unit of exposure to ionizing radiation – D all of the above – E none of the above
44 iClicker Question Which of the following describes the RAD? – A the unit of absorbed dose equivalent. – B the unit of absorbed dose. – C the unit of exposure to ionizing radiation – D all of the above – E none of the above
45 iClicker Question Which of the following describes the RAD? – A the unit of absorbed dose equivalent. – B the unit of absorbed dose. – C the unit of exposure to ionizing radiation – D all of the above – E none of the above
46 iClicker Question Which of the following describes the REM? – A the unit of absorbed dose equivalent. – B the unit of absorbed dose. – C the unit of exposure to ionizing radiation – D all of the above – E none of the above
47 iClicker Question Which of the following describes the REM? – A the unit of absorbed dose equivalent. – B the unit of absorbed dose. – C the unit of exposure to ionizing radiation – D all of the above – E none of the above
48 ALARA A philosophy, necessary to maintain personnel exposure or the release of radioactivity to the environment well below applicable limits by means of a good radiation protection plan, through education, administrative controls and safe lab practices. As Low As Reasonably Achievable
49 ALARA Principles Distance Inverse Square Law – radiation intensity is inversely proportional to the square of the distance from the source – Use remote handling tools, or work at arms length – Maximize distance from source of radiation
50 ALARA Principles Shielding Any material between a source of radiation and personnel will attenuate some of the energy, and reduce exposure Select proper shielding material for type of radiation, use less dense material for β’s, to minimize Bremsstrahlung (braking) radiation
51 Background Radiation Natural Sources (300 mREM): "Natural" background radiation consists of radiation from cosmic radiation, terrestrial radiation, internal radionuclides, and inhaled radon. Occupational Sources (0.9 mREM): According to NCRP Report No. 93, the average dose for workers that were actually exposed to radiation in 1980 was approximately 230 mREM. The Nuclear Fuel Cycle (0.05 mREM): Each step in the nuclear fuel cycle can produce radioactive effluents in the air or water. Consumer Products (5-13 mREM): The estimated annual dose from some commonly-used consumer products such as cigarettes (1.5 pack/day, 8,000 mREM) and smoke detectors (1 mREM) contribute to total annual dose. Miscellaneous Environmental Sources (0.6 mREM): A few environmental sources of background radiation are not included in the above categories. Medical Sources (53 mREM): The two contributors to the radiation dose from medical sources are diagnostic x-rays and nuclear medicine. Of the estimated 53 mREM dose received annually, approximately 39 mREM comes from diagnostic x-rays. Below are estimates of natural and man-made background radiation at sea level at middle latitudes. The total averages 400 – 500 mREM/yr
53 Maximum Permissible Dose Equivalents for Radiation Workers Avg dose/ week (rem) Max 13 week dose (rem) Max yearly dose (rem) Max lifetime dose a (rem) Radiation controlled areas: Whole body, gonads, blood- forming organs, and lens of eye 0.1355(N - 18) d Skin of whole body–1030– Hands and forearms, head neck, feet, and ankles –2575– Environs: Any part of body.01–0.5– Notes: Avg week dose is for design purposes only 1 REM assumed = 1 R Note a: N = age in years For minors, dose limits are 10% of adult limits and radiation work is not permitted Source: National Bureau of Standards Handbook 59 (1958) with addendums.
54 Occupational Exposure In terms of absolute energy content, 1 RAD is not a lot (i.e., ~ 0.01 joule absorbed/kg). The main risks associated exposure to analytical X-rays are –High Intensity Exposures: Skin burns and lesions and possible damage to eye tissue –Long-term chronic Exposures: Possible chromosomal damage and long term risk of skin cancer Goal of all Radiation Safety practice is ALARA – As Low as Reasonably Achievable
55 Long-term Effects of Radiation Exposure Long-term effects are usually related to increased risk of cancer, summarized in the table below: DiseaseAdditional Cases per 100,000 (with one-time 10 REM dose) * Adult leukemia95 Cancer of digestive system230 Cancer of respiratory system 170 * Source: Biological Effects of Ionizing Radiation V (BEIR V) Committee Radiation-induced life shortening (supported by animal experiments) suggests accelerated aging may result in the loss of a few days of life as a result of each REM of exposure Genetic Effects of radiation fall into two general categories –Effect on individuals: Can change DNA and create mutation but long term effects not well understood. Biological repair mechanisms may reduce importance. –Effect of offspring: Exposure to a fetus in utero can have profound effects on developing organs resulting in severe birth defects. For this reason pregnant women should avoid any non-background exposures
56 Bioeffects on Surface tissues Because of the low energy (~8 keV for Cu) of analytical x-rays, most energy will be absorbed by skin or other exposed tissue The threshold of skin damage is usually around 300 R resulting in reddening of the skin (erythema) Longer exposures can produce more intense erythema (i.e., “sunburn”) and temporary hair loss Eye tissue is particularly sensitive – if working where diffracted beams could be present, eye protection should be worn
57 Uranium Enrichment U-235 – Fissionable at 3% – Weapons grade at 90% U-238 – More stable Plutonium-239 – Created from U-238; highly radioactive
58 Radioactivity of Plutonium Life span at least – 240,000 years Compare to – Last Ice Age glaciation 10,000 years ago – Neanderthal Man died out 30,000 years ago
59 Largest industrial users of water, electricity – Paducah, KY, Oak Ridge, TN, Portsmouth, OH Cancers and leukemia among workers – Fires and mass exposure. – Karen Silkwood at Oklahoma fabrication plant. Risk of theft of bomb material. Risks of Enrichment and Fuel Fabrication
60 Nuclear Fission Reactors Nuclear fission is used simply as a heat source to run a heat engine By controlling the chain reaction, can maintain hot source for periods greater than a year Heat is used to boil water Steam turns a turbine, which turns a generator Efficiency limited by familiar Carnot efficiency: = (T h - T c )/T h (about 30–40%, typically)
62 The Core of the Reactor not shown are the control rods that absorb neutrons and thereby keep the process from running away
63 Fuel Packaging Want to be able to surround uranium with fluid to carry away heat – lots of surface area is good Also need to slow down neutrons – water is good for this So uranium is packaged in long rods, bundled into assemblies Rods contain uranium enriched to ~3% 235 U Need roughly 100 tons per year for a 1 GW plant Uranium stays in three years, 1/3 cycled yearly
64 Control Rod Action Basic Concept – need exactly one excess neutron per fission event to find another 235 U Inserting a neutron absorber into the core removes neutrons from the pool Pulling out rod makes more neutrons available Emergency procedure is to drop all control rods at once
65 California Nuclear Plant at San Onofre 10 miles south of San Clemente Easily visible from I-5 2 reactors brought online in 1983, 1984 – older decommissioned reactor retired in 1992 after 25 years of service 1.1 GW each PWR (Pressurized Water Reactor) type No cooling towers – the ocean is used
66 The relative cost of nuclear power safety regulations tend to drive cost
67 Sidebar Regarding Nuclear Bombs Since neutrons initiate fission, and each fission creates more neutrons, there is potential for a chain reaction Have to have enough fissile material around to intercept liberated neutrons Critical mass for 235 U is about 15 kg – for 239 Pu it’s about 5 kg – need highly enriched (about 90% 235 U for uranium bomb) Bomb is relatively simple – separate two sub-critical masses and just put them next to each other when you want them to explode! – difficulty is in enriching natural uranium to mostly 235 U
68 From: National Institutes of Health Sources of Radiation Exposure
69 Useful Radiation Effects I Nuclear Power Nuclear fission for electricity Thermoelectric for spacecraft Medical: Diagnostic scans, tracers Cancer radiation treatment Plutonium powered pacemaker Medical, dental sterilization
70 Useful Radiation Effects II Polymer cross-linking Shrink tubing (e.g., turkey wrapping) Ultra-strong materials (e.g., Kevlar) Tires (replaces vulcanization) Flooring Food irradiation Sterilization of meat De-infestation of grain and spices Increase shelf life (e.g., fruits, veggies)
72 Useful Radiation Effects III Sterilization of food for hospitals and space travel Radioactive dating Insect control Semiconductor doping Testing of space-hardened computer technology Environmental studies in air purity, global warming, ozone
73 The finite uranium resource Uranium cost is about $23/kg – about 1% of cost of nuclear power – more expensive to get as we deplete the easy spots Estimated 3 million tons available at cost less than $230/kg Need 200 tons per GW-yr Now have 100 GW of nuclear power generation – about 100 plants @ 1 GW each 3 million tons will last 150 years at present rate – only 30 years if nuclear replaced all electricity production
74 Breeder Reactors The finite resource problem goes away under a breeder reactor program Neutrons can attach to the non-fissile 238 U to become 239 U – beta-decays into 239 Np with half-life of 24 minutes – 239 Np beta-decays into 239 Pu with half-life of 2.4 days – now have another fission-able nuclide – about 1/3 of energy in normal reactors ends up coming from 239 Pu Reactors can be designed to “breed” 239 Pu in a better-than-break-even way
76 Breeders, continued Could use breeders to convert all available 238 U into 239 Pu – all the while getting electrical power out Now 30 year resource is 140 times as much (not restricted to 0.7% of natural uranium), or 4200 yr Technological hurdle: need liquid sodium or other molten metal to be the coolant – but four are running in the world Enough 239 Pu falling into the wrong hands spells: – BOOM!!
77 Reactor Risks Once a vigorous program in the U.S. – in France 80% of electricity is nuclear No new orders for reactors in U.S. since late 70’s – aftershock of Three-Mile Island Reactor failure modes: – criticality accident: runaway chain reaction meltdown – loss of cooling: not runaway, but overheats meltdown – steam or chemical explosions are not ruled out meltdown – N.B. reactors are incapable of nuclear explosion
78 Risk Assessment Extensive studies by agencies like the NRC 1975 report concluded that: – loss-of-cooling probability was 1/2000 per reactor year – significant release of radioactivity 1/1,000,000 per RY – chance of killing 100 people in an accident about the same as killing 100 people by a falling meteor 1990 NRC report accounts for external disasters (fire, earthquake, etc.) – large release probability 1/250,000 per RY – 109 reactors, each 30 year lifetime 1% chance
80 The Three-Mile Island Accident, 1979 The worst nuclear reactor accident in U.S. history Loss-of-cooling accident in six-month-old plant Combination of human and mechanical errors Severe damage to core – but containment vessel held No major release of radioactive material to environment Less than 1 mrem to nearby population – less than 100 mrem to on-site personnel – compare to 300 mrem yearly dose Instilled fear in American public, fueled by movies like The China Syndrome
82 Health around TMI In 1979, hundreds of people reported nausea, vomiting, hair loss, and skin rashes. Many pets were reported dead or showed signs of radiation Lung cancer, and leukemia rates increased 2 to 10 times in areas within 10 miles downwind Farmers received severe monetary losses due to deformities in livestock and crops after the disaster that are still occurring today.
83 Plants near TMI -lack of chlorophyll -deformed leaf patterns -thick, flat, hollow stems -missing reproductive parts -abnormally large TMI dandelion leaf at right
84 Animals Nearby TMI Many insects disappeared for years. – Bumble bees, carpenter bees, certain type caterpillars, or daddy-long-leg spiders – Pheasants and hop toads have disappeared.
85 The Chernobyl Disaster Disregard of safety standards plus unstable design led to disaster Chernobyl was a boiling-water, graphite-moderated design – unlike any in the USA – used for 239 Pu weapons production – frequent exchange of rods to harvest Pu meant lack of containment vessel like the ones in USA – positive-feedback effect It gets too hot, it runs hotter runaway possible – once runaway, control rods ineffective
86 Chernobyl, continued On April 25, 1986, operators decided to do an “experiment” as the reactor was powering down for routine maintenance – disabled emergency cooling system!!! – withdrew control rods completely!!! – powered off cooling pumps!!! – reactor went out of control, caused steam explosion that ripped open the reactor – many fires, exposed core, major radioactive release
87 Chernobyl after-effects Total of 100 million people exposed (135,000 lived within 30 km) to radioactivity much above natural levels Expect from 25,000 to 50,000 cancer deaths as a result – compared to 20 million total worldwide from other causes – 20,000,000 becomes 20,050,000 (hard to notice… – …unless you’re one of those 50,000 31 died from acute radiation exposure at site – 200 got acute radiation sickness
90 Radiation and Health Health effects as a result of radiation exposure: -increased likelihood of cancer -birth defects including long limbs, brain damage, conjoined stillborn twins -reduced immunity -genetic damage
91 “It Can’t Happen Here” Soviet reaction to Three-Mile Island, 1979 – Blamed on Capitalism and pressurized- water reactor design U.S. reaction to Chernobyl, 1986 – Blamed on Communism and graphite reactor design No technology 100% safe – Three-Mile Island bubble almost burst
92 iClicker Question Consider all of the people throughout history who have been exposed to man-made nuclear radiation, such as Hiroshima and Nagasaki, Chernobyl, Three Mile Island, nuclear bomb tests, accidental spills, etc. Which number most nearly approximates how many children conceived and born later to these people suffered genetic damage due to a parent’s exposure, excluding exposure during pregnancy? A.~ millions B.~ thousands C.~ hundreds D.~ zero
93 iClicker Question Consider all of the people throughout history who have been exposed to man-made nuclear radiation, such as Hiroshima and Nagasaki, Chernobyl, Three Mile Island, nuclear bomb tests, accidental spills, etc. Which number most nearly approximates how many children conceived and born later to these people suffered genetic damage due to a parent’s exposure, excluding exposure during pregnancy? A.~ millions B.~ thousands C.~ hundreds D.~ zero
94 Nuclear Proliferation The presence of nuclear reactors means there will be plutonium in the world – and enriched uranium If the world goes to large-scale nuclear power production (especially breeder programs), it will be easy to divert Pu into nefarious purposes But other techniques for enriching uranium may become easy/economical – and therefore the terrorist’s top choice Should the U.S. abandon nuclear energy for this reason? – perhaps a bigger concern is all the weapons-grade Pu already stockpiled in the U.S. and former U.S.S.R.
96 Nuclear Waste Each reactor has storage pool, meant as temporary holding place – originally thought to be 150 days – 40 years and counting Variety of radioactive products, with a wide range of half-lives – 1GW plant waste is 70 MCi after one year; 14 MCi after 10 years; 1.4 MCi after 100 years; 0.002 MCi after 100,000 years – 1 Ci (Curie) is 37 billion radioactive decays per second
97 Storage Solutions No failsafe storage solution yet developed EPA demands less than 1000 premature cancer deaths over 10,000 years!! – hard to design and account for all contingencies USA proposed site at Yucca Mountain, NV – Good and bad choice geologically: cracks and questionable stability
98 Burial Issues Radioactive emissions themselves are not radioactive – just light, electrons/positrons and helium nuclei – but they are ionizing: they rip apart atoms/molecules they encounter Absorb emissions in concrete/earth and no effect on biology – so burial is good solution Problem is the patience of time – half lives can be long – geography, water table changes – nature always outlasts human structures – imagine building something to last 10,000 years!!
102 Kyshtym waste disaster, 1957 – Explosion at Soviet weapons factory forces evacuation of over 10,000 people in Ural Mts. – Area size of Rhode Island still uninhabited; thousands of cancers reported Orphans
104 Risk of terrorism (new challenge to industry) 9/11 jet passed near Indian Point
105 iClicker Question Suppose that all of the electrical energy for the world for the next 500 years were obtained from nuclear reactors. Further suppose that all of the nuclear waste from these reactors were dissolved and spread uniformly throughout the oceans of the world. Which statement is true: A.The oceans would be a vast wasteland, unable to support life. B.Much death and damage to ocean life would be caused. C.Any effect would be so small that it would be virtually impossible to see.
106 iClicker Question Suppose that all of the electrical energy for the world for the next 500 years were obtained from nuclear reactors. Further suppose that all of the nuclear waste from these reactors were dissolved and spread uniformly throughout the oceans of the world. Which statement is true: A.The oceans would be a vast wasteland, unable to support life. B.Much death and damage to ocean life would be caused. C.Any effect would be so small that it would be virtually impossible to see.
107 Fusion: The big nuclear hope Rather than rip nuclei apart, how about putting them together? Iron is most tightly bound nucleus Can take loosely bound light nuclei and build them into more tightly bound nuclei, releasing energy Huge gain in energy going from protons ( 1 H) to helium ( 4 He). It’s how our sun gets its energy Much higher energy content than fission proton dueterium tritium alpha ( 4 He)
108 Thermonuclear Fusion in the Sun Sun is 16 million degrees Celsius in center Enough energy to ram protons together (despite mutual repulsion) and make deuterium, then helium Reaction per mole ~20 million times more energetic than chemical reactions, in general 4 protons: mass = 4.029 4 He nucleus: mass = 4.0015 neutrinos, photons (gamma rays)
109 E=mc 2 balance sheets Helium nucleus is lighter than the four protons! Mass difference is 4.029 – 4.0015 = 0.0276 a.m.u. – 0.7% of mass disappears, transforming to energy – 1 a.m.u. (atomic mass unit) is 1.6605 10 -27 kg – difference of 4.58 10 -29 kg – multiply by c 2 to get 4.12 10 -12 J – 1 mole (6.022 10 23 particles) of protons 2.5 10 12 J – typical chemical reactions are 100–200 kJ/mole – nuclear fusion is ~20 million times more potent stuff! – works out to 150 million Calories per gram compare to 16 million Cal/g uranium, 10 Cal/g gasoline
110 Artificial Fusion 15 million degrees in Sun’s center is just enough to keep the process going – but Sun is huge, so it seems prodigious In laboratory, need higher temperatures still to get worthwhile rate of fusion events – like 100 million degrees Bottleneck in process is the reaction: 1 H + 1 H 2 H + e + + (or proton-proton deuteron) Better to start with deuterium plus tritium – 2 H and 3 H, sometimes called 2 D and 3 T – but give up some energy: starting higher on binding energy graph Then: 2 H + 3 H 4 He + n + 17.6 MeV(leads to 81 MCal/g)
112 Deuterium everywhere Natural hydrogen is 0.0115% deuterium – Lots of hydrogen in sea water (H 2 O) Total U.S. energy budget (100 QBtu = 10 20 J per year) covered by sea water contained in cubic volume 170 meters on a side – corresponds to 0.15 cubic meters per second – about 1,000 showers at two gallons per minute – about one-millionth of rainfall amount on U.S. – ~4 gallons per person per year
113 Tritium Nowhere Tritium is unstable, with half-life of 12.32 years – thus none naturally available Can make it by bombarding 6 Li with neutrons – extra n in D-T reaction can be used for this, if reaction core is surrounded by “lithium blanket” Lithium on land in U.S. would limit D-T to a hundred years or so – maybe a few thousand if we get lithium from ocean D-D reaction requires higher temperature, but could be sustained for many millennia
114 By-products? Not like radioactive fission products Building stable nuclei (like 4 He) Tritium is only radioactive substance – energy is low, half-life short: not much worry here Extra neutrons can tag onto local metal nuclei (in surrounding structure) and become radioactive – but this is a small effect, especially compared to fission
115 Why don’t we embrace fusion? A huge technological challenge Always 20 years from fruition – must confine plasma at 50 million degrees 100 million degrees for D-D reaction – all the while providing fuel flow, heat extraction, tritium supply, etc. – hurdles in plasma dynamics: turbulence, etc. Still pursued, but with decreased enthusiasm, increased skepticism – but payoff is huge: clean, unlimited energy
116 Fusion Successes? Fusion has been accomplished in labs, in big plasma machines called Tokamaks – got ~6 MW out of Princeton Tokamak in 1993 – but put ~12 MW into it to sustain reaction Hydrogen bomb also employs fusion – fission bomb (e.g., 239 Pu) used to generate extreme temperatures and pressures necessary for fusion – LiD (lithium-deuteride) placed in bomb – fission neutrons convert lithium to tritium – tritium fuses with deuterium
117 Other Forms of Nuclear Power? Three main nuclear power reaction types – Radioactive Decay Atomic Batteries Passive beta decay collectors Radioisotope thermoelectric generators Passive application of Peltier and Seebeck effects – Nuclear Fusion Already discussed – Nuclear Fission Already discussed
118 Passive Radioactive Decay Radioisotope Thermoelectric Generator – Obtains power from passive radioactive decays – Utilized in satellites and space probes – Seebeck/Peltier effect Junction of two dissimilar metals at different temperatures create a current – Fuel Long half life, low shielding (beta decay) Plutonium 238 most common
119 Discovered by Thomas Johann Seebeck in 1821. He accidentally found that a voltage existed between two ends of a metal bar when a temperature gradient existed within the bar. The Peltier/Seebeck Effect By Jacob McKenzie, Ty Nowotny, Colin Neunuebel
120 The Seebeck Effect A temperature difference causes diffusion of electrons from the hot side to the cold side of a conductor. The motion of electrons creates an electrical current. The voltage is proportional to the temperature difference as governed by: V=α(T h -T c ) where α is the Seebeck coefficient of the couple
121 History of Peltier devices The Peltier effect is named after Jean Charles Peltier (1785-1845) who first observed it in 1834. The Peltier effect had no practical use for over 100 years until dissimilar metal devices were replaced with semiconductor Peltiers which could produce much larger thermal gradients. Peltier Cooler - produce a temperature gradient that is proportional to an applied current
122 Peltier Effect With Dissimilar Metals At the junction of two dissimilar metals the energy level of conducting electrons is forced to increase or decrease. A decrease in the energy level emits thermal energy, while an increase will absorb thermal energy from its surroundings. The temperature gradient for dissimilar metals is very small. The figure of merit is a measure of thermoelectric efficiency.
123 Sidebar: Semiconductor Peltier Bismuth-Telluride n and p blocks An electric current forces electrons in n type and holes in p type away from each other on the cold side and towards each other on the hot side. The holes and electrons pull thermal energy from where they are heading away from each other and deliver it to where they meet.
124 Sample Peltier Temperature Gradient Carnot Efficiency Nc @ 12v: =1-T c /T h =1-283.6/342.3 =17.1%
125 Applications Deep space probes Microprocessor cooling Laser diode temperature stabilization Temperature regulated flight suits Air conditioning in submarines Portable DC refrigerators Automotive seat cooling/heating Radioisotopic Thermoelectric Generator (RTG)
126 RTG Pros and Cons Pros Solid state (no moving parts) No maintenance Long service lifetime – Relatively constant power production – Solar Panels not needed Cons Good for low electrical power requirements Inefficient compared to phase change cooling – Decays over time – Requires shielding – Radioactive waste
128 Wikipedia Reports on Disaster at Fukushima “An earthquake categorized as 9.0 on the moment magnitude scale occurred on 11 March 2011, at 14:46 Japan Standard Time (JST) off the northeast coast of Japan. On that day, reactor units 1, 2, and 3 were operating, but units 4, 5, and 6 had already been shut down for periodic inspection. When the earthquake was detected, units 1, 2 and 3 underwent an automatic shutdown (called scram). “After the reactors shut down, electricity generation stopped. Normally the plant could use the external electrical supply to power cooling and control systems, but the earthquake had caused major damage to the power grid. Emergency diesel generators started correctly but stopped abruptly at 15:41, ending all AC power supply to the reactors. The plant was protected by a sea wall, but tsunami water which followed after the earthquake topped this sea wall, flooding the low lying generator building… “After the failure of the diesels, emergency power for control systems was supplied by batteries that would last about eight hours. Batteries from other nuclear plants were sent to the site and mobile generators arrived within 13 hours, but work to connect portable generating equipment to power water pumps was still continuing as of 15:04 on 12 March. Generators would normally be connected through switching equipment in a basement area of the buildings, but this basement area had been flooded by the tsunami.”