Nuclear EnergyNuclear Energy

Overview of Chapter 12Overview of Chapter 12

o Introduction to Nuclear PowerIntroduction to Nuclear Power• Atoms and radioactivityAtoms and radioactivity

o Nuclear FissionNuclear Fissiono Pros and Cons of Nuclear EnergyPros and Cons of Nuclear Energy

• Cost of Nuclear PowerCost of Nuclear Power

o Safety Issues at Power PlantsSafety Issues at Power Plants• Three Mile Island & ChornobylThree Mile Island & Chornobyl• Nuclear WeaponsNuclear Weapons

o Radioactive WasteRadioactive Wasteo Future of Nuclear PowerFuture of Nuclear Power

Introduction to Nuclear EnergyIntroduction to Nuclear Energy

o Nuclear energyNuclear energy• Energy released by nuclear fission or fusionEnergy released by nuclear fission or fusion

o Nuclear fissionNuclear fission• Splitting of an atomic nucleus into two Splitting of an atomic nucleus into two

smaller fragments, accompanied by the smaller fragments, accompanied by the release of a large amount of energyrelease of a large amount of energy

o Nuclear fusionNuclear fusion• Joining of two lightweight atomic nuclei into Joining of two lightweight atomic nuclei into

a single, heavier nucleus, accompanied by a single, heavier nucleus, accompanied by the release of a large amount of energy the release of a large amount of energy

Atoms and RadioactivityAtoms and Radioactivity

o Nucleus Nucleus • Comprised of protons Comprised of protons

(+) and neutrons (+) and neutrons (neutral)(neutral)

o Electrons (-) orbit Electrons (-) orbit around nucleusaround nucleus

o Neutral atomsNeutral atoms• Same # of protons Same # of protons

and electronsand electrons

Atoms and RadioactivityAtoms and Radioactivity

o Atomic massAtomic mass• Sum of the protons and neutrons in an atomSum of the protons and neutrons in an atom

o Atomic numberAtomic number• Number of protons per atomNumber of protons per atom• Each element has its own atomic numberEach element has its own atomic number

o IsotopeIsotope• Usually an atom has an equal number of Usually an atom has an equal number of

neutrons and protonsneutrons and protons• If the number of neutrons is greater than If the number of neutrons is greater than

the number of protons = isotopethe number of protons = isotope

Radioactive IsotopeRadioactive Isotope

o Unstable isotopeUnstable isotopeo Radioactive DecayRadioactive Decay

• Emission of energetic particles or rays from Emission of energetic particles or rays from unstable atomic nucleiunstable atomic nuclei

o ExampleExample• Uranium (U-235) decays over time to lead Uranium (U-235) decays over time to lead

(Pb-207)(Pb-207)

o Each isotope decays based on its own Each isotope decays based on its own half-lifehalf-life

Radioactive Isotope Half-livesRadioactive Isotope Half-lives

Nuclear FissionNuclear Fission

o Nuclear Fuel Nuclear Fuel CycleCycle• processes processes

involved in involved in producing the producing the fuel used in fuel used in nuclear reactors nuclear reactors and in disposing and in disposing of radioactive of radioactive (nuclear) wastes (nuclear) wastes

Nuclear FissionNuclear Fissiono U-235 is U-235 is

bombarded with bombarded with neutronsneutrons

o The nucleus The nucleus absorbs neutronsabsorbs neutrons

o It becomes It becomes unstable and unstable and splits into 2 splits into 2 neutronsneutrons

o 2-3 neutrons are 2-3 neutrons are emitted and emitted and bombard bombard another U-235 another U-235 atomatom

o Chain reactionChain reaction

How Electricity is ProducedHow Electricity is Produced

Breeder Nuclear FissionBreeder Nuclear Fissiono A type of nuclear fission in which non-A type of nuclear fission in which non-

fissionable U-238 is converted into fissionable U-238 is converted into fissionable Pu-239 fissionable Pu-239

Pros and Cons of Nuclear EnergyPros and Cons of Nuclear Energy

o ProsPros• Less of an immediate environmental Less of an immediate environmental

impact compared to fossil fuelsimpact compared to fossil fuels

Pros and Cons of Nuclear EnergyPros and Cons of Nuclear Energy

o Pros (continued)Pros (continued)• Carbon-free source of electricity- no Carbon-free source of electricity- no

greenhouse gases emittedgreenhouse gases emitted• May be able to generate H-fuelMay be able to generate H-fuel

o ConsCons• Generates radioactive wasteGenerates radioactive waste• Many steps require fossil fuels (mining and Many steps require fossil fuels (mining and

disposal)disposal)• ExpensiveExpensive

Cost of Electricity from Nuclear Cost of Electricity from Nuclear EnergyEnergy

o Cost is very highCost is very higho 20% of US electricity is from Nuclear 20% of US electricity is from Nuclear

EnergyEnergy• Affordable due to government subsidiesAffordable due to government subsidies

o Expensive to build nuclear power plantsExpensive to build nuclear power plants• Long cost-recovery timeLong cost-recovery time

o Fixing technical and safety issues in Fixing technical and safety issues in existing plants is expensiveexisting plants is expensive

Safety Issues in Nuclear Power Safety Issues in Nuclear Power PlantsPlants

o MeltdownMeltdown• At high temperatures the metal encasing the At high temperatures the metal encasing the

uranium fuel can melt, releasing radiation uranium fuel can melt, releasing radiation

o Probability of meltdown or other Probability of meltdown or other accident is lowaccident is low

o Public perception is that nuclear power is Public perception is that nuclear power is not safenot safe

o Sites of major accidents:Sites of major accidents:• Three Mile IslandThree Mile Island• Chornobyl (Ukraine)Chornobyl (Ukraine)

Three-Mile IslandThree-Mile Island

o 1979- most serious reactor accident in US1979- most serious reactor accident in USo 50% meltdown of reactor core50% meltdown of reactor core

• Containment building kept radiation from Containment building kept radiation from escapingescaping

• No substantial environmental damageNo substantial environmental damage• No human casualtiesNo human casualties

o Elevated public apprehension of nuclear Elevated public apprehension of nuclear energyenergy• Led to cancellation of many new plants in USLed to cancellation of many new plants in US

ChornobylChornobyl

o 1986- worst 1986- worst accident in historyaccident in history

o 1 or 2 explosions 1 or 2 explosions destroyed the destroyed the nuclear reactornuclear reactor• Large amounts of Large amounts of

radiation escaped radiation escaped into atmosphereinto atmosphere

o Spread across large Spread across large portions of Europeportions of Europe

ChornobylChornobyl

o Radiation Radiation spread was spread was unpredictableunpredictable

o Radiation Radiation fallout was fallout was dumped dumped unevenlyunevenly

o Death toll is Death toll is 10,000-10,000-100,000100,000

Nuclear Energy and Nuclear Nuclear Energy and Nuclear WeaponsWeapons

o 31 countries use nuclear energy to 31 countries use nuclear energy to create electricitycreate electricity

o These countries have access to spent These countries have access to spent fuel needed to make nuclear weaponsfuel needed to make nuclear weapons

o Safe storage and handling of these Safe storage and handling of these weapons is a concernweapons is a concern

Radioactive WasteRadioactive Wasteo Low-level radioactive waste- Low-level radioactive waste-

• Radioactive solids, liquids, or gasses that give off Radioactive solids, liquids, or gasses that give off small amounts of ionizing radiation small amounts of ionizing radiation

o High-level radioactive waste- High-level radioactive waste- • Radioactive solids, liquids, or gasses that give off Radioactive solids, liquids, or gasses that give off

large amounts of ionizing radiation large amounts of ionizing radiation

Radioactive WastesRadioactive Wastes

o Long term solution to wasteLong term solution to waste• Deep geologic burial –Yucca MountainDeep geologic burial –Yucca Mountain• As of 2004, site must meet EPA million year As of 2004, site must meet EPA million year

standard (compared to previous 10,000 standard (compared to previous 10,000 year standard)year standard)

• Possibilities:Possibilities:• Above ground mausoleumsAbove ground mausoleums• Arctic ice sheetsArctic ice sheets• Beneath ocean floorBeneath ocean floor

Radioactive WasteRadioactive Wasteo Temporary storage solutionsTemporary storage solutions

• In nuclear plant facility (require high In nuclear plant facility (require high security)security)

• Under water storageUnder water storage• Above ground concrete and steel casksAbove ground concrete and steel casks

o Need approved permanent options Need approved permanent options soon.soon.

Case-In-Point Yucca Case-In-Point Yucca MountainMountain

o 70,000 tons of high-70,000 tons of high-level radioactive wastelevel radioactive waste

o Tectonic issues have Tectonic issues have been identifiedbeen identified

Decommissioning Nuclear Power Decommissioning Nuclear Power PlantsPlants

o Licensed to operate for 40 yearsLicensed to operate for 40 years• Several have received 20-year extensionsSeveral have received 20-year extensions

o Power plants cannot be abandoned Power plants cannot be abandoned when they are shut downwhen they are shut down

o Three solutionsThree solutions• StorageStorage• EntombmentEntombment• Decommissioning (dismantling)Decommissioning (dismantling)

FusionFusion

o Fuel= isotopes of hydrogenFuel= isotopes of hydrogen

FusionFusion

o Way of the future??Way of the future??• Produces no high-level wasteProduces no high-level waste• Fuel is hydrogen (plenty of it!)Fuel is hydrogen (plenty of it!)

o ProblemsProblems• It takes very high temperatures (millions of It takes very high temperatures (millions of

degrees) to make atoms fusedegrees) to make atoms fuse• Confining the plasma after it is formedConfining the plasma after it is formed

o Scientists have yet to be able to create Scientists have yet to be able to create energy from fusionenergy from fusion