Nuclear power is one of the most feared and misunderstood energy sources available, and its unique advantages - extraordinary power production with no emissions - weigh against its disadvantages - possibility of meltdowns, difficulty of waste disposal, and potential weaponization. This session will explore some of the basics of nuclear power through a variety of interactive activities for students and give an overview of the economics and risks associated with nuclear power. It will also discuss potential future technologies, including fusion, and how they would change worldwide energy production

Dong, Peter

Hawker, Eric

Martinez, Elizabeth

English

Illinois Mathematics and Science Academy: DigitalCommons@IMSA

Dr. Peter DongDr. Eric HawkerProfessional Development DayMarch 2, 2018Nuclear Energy: Then, Now, and the Future➢ Why nuclear power?➢ Basic nuclear physics➢ Nuclear power: Pros and Cons○ Energy Yield○ Emissions○ Radiation○ Waste○ Proliferation○ Future technologiesOutlineWhy Nuclear Power?The use of fossil fuels to produce energy is the leading cause of global climate changeIPCC AR5BerkeleyEarth.orgIPCC AR5RPC stands for Representative Concentration Pathway. These are different scenarios for future greenhouse gas emissions by humanity. Intergovernmental Panel on Climate ChangeNuclear Physics➢ Most people are afraid of the images and concepts brought to mind by the words nuclear or radiation or radioactive.➢ How dangerous are these things? ➢ Should you be scared or worried?  ➢What should you know about nuclear physics in this day and age of nuclear power and nuclear weapons?The Atom➢ This is the picture of an atom that most students first learn about. It is made of○ Electrons (-)○ Protons (+)○ Neutrons (0)○ With the electrons orbiting the nucleus.➢ This is a much more realistic picture of an atom, with a “cloud” of electrons taking up 99.9% of the space in the atom, and a tiny nucleus with 99.9% of the mass of the atom.Energy and Nuclear Physics➢ Most of the sources of energy we use in our lives comes from chemical interactions that involve the electrons in atoms.➢ Nuclear reactions involve only the nuclei of atoms.➢ Where does this energy come from in these reactions?  Mass!!E = mc2➢ Since there is thousands of times more mass in the nucleus, nuclear reactions can involve thousands of times more energy! Nuclear Radiation➢ An element is defined by how many protons are in the nucleus.➢ While an isotope is defined by how many neutrons. 816O, 819O➢ Not all isotopes of an element have stable nuclei, these unstable nuclei will decay at some time. ➢ When a nucleus decays, it emits energy in the form of particles. There are many different types of nuclear decay, and different particles can be emitted.... alpha particles, beta particles, gamma rays, and etc.➢ We call these particles ionizing radiation. They can penetrate your body and deposit their energy, damaging your cells.➢How Radioactive is it?○ https://youtu.be/XTIvoTiTTSU if you don’t have the equipmentRadioactivity activitiesNuclear Radiation➢ You cannot see, feel, hear, smell, or taste these particles, which is probably why people are so afraid of radioactivity and “radiation”.➢ Your body can repair the damage done by ionizing radiation, and does so on a daily basis, since you are constantly exposed to a very low natural dose of ionizing radiation.➢ Every once in a while, when some DNA in a cell is damaged, errors occur in the repairs, and you get cancer. But considering how much natural ionizing radiation you are exposed to in your life, this is veryrare! Nuclear Safety➢ It is actually difficult for most ionizing radiation to make another nucleus unstable. This means just being exposed to ionizing radiation usually does not make something radioactive.➢ How can be safe from radioactivity? There are two basic ways.○ Shielding... put lots of stuff between you and something radioactive, the ionizing radiation will interact in the stuff, and not in you.○ Distance.... the farther away you are, the less likely the ionizing radiation will hit you in the first place.➢ The most dangerous place for something radioactive to be is in you!Nuclear SafetyUsually radioactive contamination means dust, water, or air that is radioactive. These workers wear suits not to protect themselves from direct radiation, but to prevent them from breathing or picking up radioactive dust.➢Half Life Lab○ https://youtu.be/214cwT4v3D8 to be able to collect data without buying the equipmentRadioactivity activitiesNuclear Fission➢ There are two basic nuclear reactions used to create energy from mass. ○ Fusion - what occurs in the Sun○ Fission - used in nuclear power plants.➢ Some very large nuclei can decay by the process of fission - they split almost in half. U235 →  Sr97 + Cs136 + 2n➢ When this happens the mass of the “daughters” is less than the mass of the original nucleus, and the missing mass is released as energy!Nuclear FissionFission process occur very rarely - it would take several billion years to release most of the energy in a 50 kg (110 lb) lump of uranium.This would not be good for a reactor! What we need is for one uranium fission to cause  two or more other fissions to occur. This would create a chain reaction - an exponential growth in the number of decays - lots of energy very quickly!Chain ReactionAnswer: Neutrons!If you hit an uranium nucleus with a neutron it can cause it to fission.If you use the right isotope of uranium (U235) you also get 2 new neutrons from each fission!If these new neutrons also cause fission to occur you get a chain reaction!Critical Mass➢ If the neutrons leave the uranium the chain reaction stops. ➢ So you need enough uranium - a critical mass -around the initial fission for the neutrons to hit more uranium nuclei.➢ Unfortunately, other uranium atoms (U238) absorb neutrons, stopping the process.➢ Bad news - U238 is 99% of all naturally occurring uranium!➢Critical Mass Simulation○ http://blog.nuclearsecrecy.com/2015/04/10/critical-mass/○ http://blog.nuclearsecrecy.com/misc/criticality/Critical mass activityRefinement◻ Uranium has to be enriched to have enough U235 to sustain a chain reaction.◻ Use giant centrifuges to separate⬜ Reactor-grade (enriched) uranium is from 3-19% U235⬜ Weapons-grade (highly enriched) uranium is about 90-95% U235◻ Note that weapons-grade uranium can be made from reactor-gradeModerators◻ U238 does not absorb slow neutrons, only fast ones◻ A moderator (water, graphite) slows down neutrons so they are only absorbed by U235, not U238Nuclear power plants◻ Generate a sustained, controlled fission reaction◻ Use heat to boil water◻ Use steam to turn turbine to run generator◻ Radiation does not escape the enclosure!➢Radiation and Shielding Project○ Handouts○ https://www.spenvis.oma.be/intro.phpRadiation shielding activityNuclear power: a comparisonA comparison: Energy yieldFuel Energy per pound (MJ)Coal 16Natural gas 20Gasoline 22Crude oil 24Natural uranium 72,000Uranium-235 37,000,000Source: https://www.ocean.washington.edu/courses/envir215/energynumbers.pdfwww.ct.gov/deep/lib/deep/energy/energyprice/energy_conversion_factors.pdfA comparison: CostMethod Cost per kilowatt hourCoal 9.5¢Natural gas 6.6¢Solar 21.1¢Wind 9.7¢Hydro 0.9¢Nuclear 11.4¢Source: U.S. Energy Information Administration, Annual Energy Outlook 2011IPCC AR5A comparison: PowerMethod Amount needed for 1 GW (about 300,000 homes)Coal 800 pounds (a 1.5-foot sphere) per hourNatural gas 3.5 million cubic feet per hourSolar 18 million PV cells - about 12 square milesWind 500 turbines - about 75 square milesHydro ½ of Hoover DamNuclear 75 pounds uranium (a 3-inch sphere) per hourSource: https://www.energy.gov/eere/articles/how-much-power-1-gigawattRichard Muller, Energy for Future Pesidents➢Nuclear Power Plant Simulation○ http://www.nuclearpowersimulator.com➢Simpler introduction○ https://phet.colorado.edu/en/simulation/nuclear-fissionNuclear power plant activityThe problem of renewables➢ Solar: Only works during sunny days - storage currently impractical➢ Wind: Only works in windy areas and windy days -transfering power inefficient and expensive➢ Hydroelectric: Only works in large rivers - with environmental impactsWhat’s the catch?➢ Danger of meltdown or radiation leakage➢ Waste➢ Nuclear Weapon ProliferationNuclear accidents➢ Some perspective on past nuclear accidents:○ The Chernobyl accident killed about 30 people directly, perhaps 4000 total due to cancer deaths○ The much smaller Fukushima accident killed none from direct radiation and may cause 300 cancer deaths eventually○ The Three Mile Island accident caused no harm except for increased stressSource: http://www.who.int/mediacentre/news/releases/2005/pr38/en/Compared to other sourcesSource: Lancet 2007; 370: 979–90Nuclear waste◻ Nuclear waste is extremely dangerous⬜ Residual radioactivity⬜ Temperature⬜ Use in “dirty bombs”◻ The best solution: store it in Yucca Mountain⬜ This is a political problem, not an engineering problem◻ Nuclear waste is the only industrial waste with a disposal plan⬜ Coal and natural gas expel their waste into the atmosphere and waterProliferation➢ Nuclear reactors are closely related to nuclear weapons.➢ If you can refine fuel for a reactor, you can refine fuel for a bomb.➢ Uranium bombs are unfortunately easy to build.➢ Breakout - the conversion of a civilian program to a military one - is a real problemProliferation - plutonium➢ Plutonium is a more fissile material than uranium.➢ Plutonium is naturally produced in nuclear reactors from U238.➢ Fortunately, plutonium bombs are much harder to build.Proliferation - solutions◻ Heavy-water reactors work on unrefined uranium, due to the highly effective moderator◻ Some proposed small modular reactors can be buried underground, preventing unauthorized access◻ Hope may lie in future technologies◻ Thorium reactors use a neutron source to turn thorium into uranium, which then fissions.◻ Thorium is more abundant and easier to mine than uranium.◻ Because the uranium is produced and used on the spot, proliferation is much more difficult.◻ Much less waste (as much as 1000 times less) is produced.Future technologies - ThoriumFuture technologies - Fusion◻ The same process that powers stars and hydrogen bombs.◻ Requires extremely high temperature to fuse light particles into heavier ones, releasing energy.◻ Releases ten times the energy, per pound, as fission.◻ Ideally, uses hydrogen (water) as its fuel, and helium as its waste◻ The perfect energy source!Future technologies - Fusion◻ We have worked on fusion for a long time.◻ Still a long way away.◻ The ITER experiment should produce sustained fusion some time in the 2030s.◻ Commercial fusion will be a while after that.Conclusion◻ Nuclear power sounds scary, but is much less dangerous than fossil fuel alternatives.◻ Nuclear power can provide a large amount of energy, especially useful in countries with few fossil fuel resources.◻ As with all power sources, it has advantages and disadvantages.◻ There is always a shortage of nuclear engineers - in terms of job security, this is a good field!Thank you!➢ https://www.youtube.com/watch?v=ciStnd9Y2ak➢ https://www.youtube.com/watch?v=ZwY2E0hjGuU➢ https://www.youtube.com/watch?v=uU3kLBo_ruo➢ “Energy For Future Presidents the science behind the headlines” by Richard A MullerUseful referencesBackup slidesFission process occur very rarely - it would take several billion years to release most of the energy in a 50 kg (110 lb) lump of uranium.This would not be good for a bomb or a reactor! What we need is for one uranium fission to cause  two or more other fissions to occur. This would create a chain reaction - an exponential growth in the number of decays - lots of energy very quickly!Nuclear FissionBoom!!!Answer: Neutrons!If you hit an uranium nucleus with a neutron it can cause it to fission.If you use the right isotope of uranium (U235) you also get 2 new neutrons from each fission!If these new neutrons also cause fission to occur you get a chain reaction!Critical Mass - the big IFIf the neutrons leave the uranium the chain reaction stops. So you need enough uranium - a critical mass -around the initial fission for the neutrons to hit more uranium nuclei.If you have a sub-critical mass, there are two ways to make it go critical.1) just add more mass (easy to do, but slow)2) squeeze it to get a higher density (hard to do, but fast)Critical MassOne key achievement of the Manhattan project was to develop the formulas needed to calculate what the critical mass is for uranium.Nowadays these formulas and solutions can be found on the web, and be used by anyone.For a bomb you need to make a greater than critical mass of uranium, and make sure it stays critical until most of the uranium has fissioned. This has to be done fast..... or it will fizzle.UraniumOver 99% of the uranium found in ores is U238 and only 0.7% is U235. To be useful it needs to be “enriched”. This is a long and difficult process using centrifuges, gas diffusion, or other methods. To be used in power plants uranium needs to be enriched so that it is 3 - 5% U235.To be used in a bomb uranium needs to be highly enriched so that it is about 90% U235.UraniumOnce you know the critical mass and have that much highly enriched uranium, it is straight forward to make a nuclear bomb.Use high explosives to ram two pieces of sub-critical U235together to make a super-critical mass.PlutoniumThe other material that can be used for a bomb is plutonium (Pu239).Pu239 is readily made in nuclear reactors, and is much easier to purify than U235.When Pu239 fissions it releases 3 new neutrons instead of 2 like U235. There are two important consequences of this.1) the chain reaction proceeds much faster2) the critical mass is much less (11 kg vs 56 kg)PlutoniumBecause the chain reaction proceeds faster in Pu239 you need to have a different bomb design.Plutonium weapons need to reach critical mass by compression -squeezing the plutonium to higher density.This is technically very challenging, and these bombs are much more complex than uranium weapons.Plutonium          vs           UraniumPu239 is relatively easy to produce in nuclear reactorsSmaller critical massMore difficult to make a weaponUranium is difficult to enrich to bomb purityLarger critical massRelatively simple to make a weapon

Session 1e: Nuclear Energy: Then, Now and the Future

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Session 1e: Nuclear Energy: Then, Now and the Future

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