1Fri, Apr. 14, 2006 Phy107 Lecture 331Exam 3: Wed. Apr. 19Covers Quantum Physics, Solids, Nuclear PhysicsFrom last time…• Fission of heavy elements produces energy• Only works with 235U, 239Pu• Fission initiated by neutron absorption.• Fission products are two lighter nuclei, plusindividual neutrons.• These neutrons cause other fission events:chain reactionToday: controlled fission and fusion reactionsFri, Apr. 14, 2006 Phy107 Lecture 332Oil 37.5%Gas 21.1%Coal 21.8%Nuclear 6.0%Hydro 6.6%Traditional 6.4%Geothermal 0.12%Wind 0.04%Biomass 0.4%Solar 0.009%New renewables 0.57%Global energy production 2000Fri, Apr. 14, 2006 Phy107 Lecture 333Unpressurized steam reactorFri, Apr. 14, 2006 Phy107 Lecture 334Controlled Fission Reactors• The reactor in a nuclear power plant does the same thingthat a boiler does in a fossil fuel plant – it produces heat.• Basic parts of a reactor:– Core (contains fissionable material)– Moderator (slows neutrons down to enhance capture)– Control rods (controllably absorb neutrons)– Coolant (carries heat away from core to produce power)– Shielding (shields environment from radiation)• 1,000 megawatt light-water reactor has a core with~ 75 tons of uranium ~ 200 fuel assemblies.Fri, Apr. 14, 2006 Phy107 Lecture 335The Moderator• Slow neutrons are more likely to cause fission events• Most neutrons released in the fission process have energiesof about 2 MeV– In order to sustain the chain reaction, the neutrons must beslowed down• A moderator surrounds the fuel– Collisions with the atoms of the moderator slow the neutronsdown as some kinetic energy is transferred– Most modern reactors use heavy water as the moderatorFri, Apr. 14, 2006 Phy107 Lecture 336• Control rodsabsorb neutrons,taking them out ofthe reaction.• Moderator presentto slow neutronsfor capture.2Fri, Apr. 14, 2006 Phy107 Lecture 337Nuclear Waste• What is all the fuss about nuclear waste?• The atoms formed when uranium atoms are split up are usually very radioactive. The"used" fuel rods from a reactor [discarded when about 25% of the uranium has undergonefission] are kept in a cooling pond for months for the more intensely radioactive atoms todecay and release most of their energy. Then they have to be processed to separate"unused" uranium atoms from the remaining fission products that have to be storedsafely in barrels, often in underground bunkers (see photo, right).• TransmutationFri, Apr. 14, 2006 Phy107 Lecture 338fuel:Temperature: 400 million Cheat losshydrogenNuclear FusionFri, Apr. 14, 2006 Phy107 Lecture 339fuel: hydrogenhydrogen+-deuterium+-tritium+-Fri, Apr. 14, 2006 Phy107 Lecture 3310Fri, Apr. 14, 2006 Phy107 Lecture 3311deuterium tritium helium neutron→+fuel: hydrogenFri, Apr. 14, 2006 Phy107 Lecture 3312deuterium tritium helium neutron→+...carrying an incredibleamount of energy!fuel: hydrogen3Fri, Apr. 14, 2006 Phy107 Lecture 3313D + T He + n + energyLi + n T + He + energyThe fusionreactionFri, Apr. 14, 2006 Phy107 Lecture 3314Tritium productionIn addition, the fusion neutrons react with Lithium producing Tritium.This is re-cycled to be used in the burning fusion plasma.Fri, Apr. 14, 2006 Phy107 Lecture 3315D + T He + n + energyLi + n T + He + energyThe fusionreactionFri, Apr. 14, 2006 Phy107 Lecture 3316Terrestrial fusion reactions• Deuterium = nucleus of (1 proton & 1 neutron)• Tritium = nucleus of (1 proton & 2 neutrons)• Two basic fusion reations:– deuterium + deuterium -> 3He + n– deuterium + tritium -> 4He + nEnergy is released as result of fusion:D + T -> 4He (3.5 MeV) + n (14.1 MeV)Energy determined bymass differenceFri, Apr. 14, 2006 Phy107 Lecture 3317Routes to fusionLaser beams compress and heat thetarget; after implosion, theexplosion carries the energytowards the wall• Magnetic confinement in atorus (in this case a tokamak).• The plasma is ring-shaped andis kept well away from thevessel wall.Fri, Apr. 14, 2006 Phy107 Lecture 3318Inertial Confinement:National Ignition FacilityLead/Gold cylinder, 6mmx10mmCylinder contains plastic fusioncapsule. Fusion capsule lined with alayer of solid deuterium-tritium (DT) fusion fuel keptnear absolute zero.Energy of intense laser beamsconverted to thermal x-rays.x-rays heat and cause implosion/fusion of target.4Fri, Apr. 14, 2006 Phy107 Lecture 3319NIF building at LivermoreFri, Apr. 14, 2006 Phy107 Lecture 3320Fusion ChamberFri, Apr. 14, 2006 Phy107 Lecture 3321• Final plan: fuse 1 pellet / second• Future problems: manufacturing/supplying onepellet /second.• Extracting energy from the system.Fri, Apr. 14, 2006 Phy107 Lecture 3322Magnetic Confinement• Sun confines hot plasma with gravitational forces• Inertial confinement implodes the material withhigh pressures to produce high temperatures for avery short time.• Third alternative uses magnetic fields to confinethe plasma.Fri, Apr. 14, 2006 Phy107 Lecture 3323Fri, Apr. 14, 2006 Phy107 Lecture 3324ovenheating hydrogen gas5Fri, Apr. 14, 2006 Phy107 Lecture 3325ovenhydrogen plasmaheating Fri, Apr. 14, 2006 Phy107 Lecture 3326hydrogen plasmaovenhotHIGH heating Fri, Apr. 14, 2006 Phy107 Lecture 3327 problem:wall contact! HIGH heating hydrogen plasmahotFri, Apr. 14, 2006 Phy107 Lecture 3328HIGH heating avoid wall contact with magnetic fieldhydrogen plasmahotFri, Apr. 14, 2006 Phy107 Lecture 3329HIGH heating avoid wall contact with magnetic fieldhydrogen plasmahotFri, Apr. 14, 2006 Phy107 Lecture 3330HIGH heating hydrogen plasmahot6Fri, Apr. 14, 2006 Phy107 Lecture 3331 problem:end losses HIGH heating hydrogen plasmahotFri, Apr. 14, 2006 Phy107 Lecture 3332end losses avoid : torus ! Fri, Apr. 14, 2006 Phy107 Lecture 3333JET• JET is a Tokamak with:– Torus radius 3.1m– Vacuum vessel 3.96m highx 2.4m wide– Plasma volume 80m3– Plasma current up to 5MA– Main confining field up to4 Tesla (recently upgradedfrom 3.4 Tesla)Fri, Apr. 14, 2006 Phy107 Lecture 3334JET tokamak test reactor• Vacuum insidetorus.• Plasma confinedfrom walls bymagnetic field.• Fusion inducedby providinginput power.Fri, Apr. 14, 2006 Phy107 Lecture 3335Plasma in the JET torusFri, Apr. 14, 2006 Phy107 Lecture 3336ITER test reactorProposed ITERfusion test reactorSuperconductingmagnetPlasma confinementtorus7Fri, Apr. 14, 2006 Phy107 Lecture 3337Site for ITER chosen• Cadarache, FranceFri, Apr. 14, 2006 Phy107 Lecture 3338Fri, Apr. 14,
View Full Document
Unlocking...