Stability and Economics of the Advanced High-Temperature Reactor

The Advanced High-Temperature ReactorAME 577 PresentationChris GilmerSai Sandeep Kaku

1PremiseAdvanced High Temperature Reactor (AHTR) brings together various technologies such as nuclear fuels with coated particles; Brayton power cycles; liquid salt coolants; and passive safety systems. The system delivers high performance and operates in a window of economic sustainability.

The objective of our presentation is to understand the important aspects of these technologies, the advantages they offer compared to the conventional technologies and how can they be integrated into a nuclear power plant. Finally we throw some light on the challenges that we have get our heads around before we can enjoy the fruit. 2OutlineNeed for Nuclear PowerQuick Overview of Nuclear EnergyNuclear Power GenerationTechnologies of AHTRThermodynamicsEconomicsBenefits ChallengesConclusions3Need for Nuclear PowerGlobal Warming - The threat posed by growing greenhouse gases emissions

Population Growth - The increasing need for energy to support the Earth's growing population

Nuclear Reality - The need to include nuclear energy as a part of long term energy solution.

Source: OECD/IEA World Energy Outlook 2006Electricity Demand4Nuclear Energy BasicsAn atom - The smallest particle of matterNeutrally charged in natureThe mass of the atom is concentrated in the nucleusMass-Energy Equivalence E=mcNuclear energy is released by three exothermic processes namely radioactive decay, fusion and fission.Fission is the splitting of the a heavy nucleus an atom into lighter nuclei involving release of large amounts of energy

3.2 10-11 J or 7.7 10-12 cal5Nuclear Power GenerationA nuclear reactor produces and controls the release of energy from splitting the atomsThe energy released from continuous fission of the atoms as heat is used to make steam. The steam is used to drive the turbines which produce electricity

Several components of a reactor include : Fuel Moderator Control rods Coolant Steam Generator Contaminant structure6Scope for Nuclear PowerNuclear Power TodayNuclear SafetyWaste Contamination and StorageCompetitive Nuclear FutureSustainable Development

Susquehanna Steam Electric Station, Pennsylvania, USA7Nuclear Power TodayTwo thirds of world population lives in nuclear powered nationsHalf the world's people live in countries where new nuclear power reactors are in planning or under constructionThis shows that a rapid expansion of global nuclear power would require no fundamental change

Nuclear SafetyZero reportable safety-related 'events Nuclear power plants rank among the strongest structures ever built.Perfect safety record while transportation

8Waste Contamination and StorageSmall amounts of waste compared to large and unmanageable waste from fossil fuelsGeological repositors -ensure harmful radiation would not reach the surface Competitive Nuclear FutureNarrowing costs between nuclear power and that from fossil fuelsA price tag on harmful emissions would make nuclear power the cheapest option

Sustainable FutureVast amounts of fuelVirtually no pollution

9Nuclear Power Today

10Layout-AHTR

11AHTR TechnologiesCoated-particle nuclear fuel(TRISO)Brayton power cycle instead of the traditional Rankine steam turbine cycleLow-pressure liquid-salt coolantsPassive Safety Systems and plant designs from liquid-cooled fast reactors12Nuclear FuelDefinition: Any material that can be consumed to derive nuclear energy

The most common type being heavy fissile elements that can be made to undergo fission , namely plutonium -239 and uranium-235

For use as nuclear fuel, enriched uranium hexafluoride is converted into uranium dioxide powder that is then processed into pellet form

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Coated Particle Nuclear Fuel (TRISO)Tristructural-isotropic (TRISO) fuel is a type of micro fuel particleIt consists of a fuel kernel composed of UOX pebble in the centerThis is surrounded by layers of carbon and silicon carbideThese particles may be arranged: in blocks - hexagonal 'prisms' of graphite, or in billiard ball-sized pebbles of graphiteCoated Particle Fuel(TRISO)What is it? Tristructural-isotropic (TRISO) fuel is a type of micro fuel particle It consists f a fuel kernel composed of UOX pebble in the center Coated with four layers of three isotropic materials The four layers are a porous buffer layer made of carbon, followed by a dense inner layer of pyrolytic carbon (PyC), followed by a ceramic layer of SiCWhy is it important? Retain fission products at elevated temperatures Give the TRISO particle more structural integrity Designed not to crack due to the stresses from differential thermal expansion or fission gas pressure Contain the fuel in the worst of accident scenarios in a properly designed reactor Ensure good heat transfer from fuel thereby preventing hot spots in the coreHow does it integrate with the system? TRISO fuel particles are fabricated into compacts and placed in a graphite block matrix

14Nuclear Fuel Rod AssemblySalient AttributesRetain fission products at elevated temperatures Give the fuel particle more structural integrity.Designed not to crack due to the stresses from differential thermal expansion or fission gas pressure.Contain the fuel in the worst of accident scenarios.Ensure good heat transfer from fuel thereby preventing hot spots in the core.

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Turbine Power CycleRankine (steam) power cycleIt directly employs steam to drive the turbinesAssociated problems include lower operating temperatures (lower efficiency), turbine blade fouling, larger equipment and wet cooling

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Brayton Cycle - PowerWorks on the principle of isentropic compression and expansion mediated by isobaric heat addition and heat rejection

Operates at higher temperatures enabling higher efficiencies and reducing total heat rejection

No moisture separation and steam extraction involved

Less expensive than Rankine cycle setup per unit of electrical output

Facilitates the option of dry cooling in cooling towers thereby reducing water consumptionBrayton Power CycleA constant pressure cycle named after a Boston engineer, George Brayton.

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Brayton Cycle - IntegrationUses the heat from the molten salt to reheat the working fluid thereby raising its temperature to maximum level

Employs up to four stages of reheating and up to eight stages of inter-cooling

Gas expansion takes place in three turbines in series, with reheating between them

The working fluid is typically Nitrogen or Helium

Brayton Power CycleWhat is it? A gas turbine cycle named after a Boston engineer, Georg Brayton It is a constant pressure cycle with nitrogen or helium being the working fluid(AHTR) Works on the principle of isentropic compression and expansion mediated by isobaric heat addition and heat rejectionWhy is it important? It has higher efficiencies than Rankine Cycle Simpler than steam cycle as there is no moisture separation and steam extraction involved Less expensive than Rankine cycle setup Operates at high temperature thereby reducing total heat rejection Facilitates the option of dry cooling in cooling towers thereby reducing water consumptionHow does it integrate with the system Uses the heat from the molten salt to reheat the working fluid thereby raising its temperature to maximum level Employs up to four stages of reheating and up to eight stages of intercooling Gas expansion takes place in three turbines in series, with reheating between them

18Low-Pressure Liquid SaltBasis for Fast Reactor layoutGood Heat Transfer PropertiesLow-Pressure OperationTransparent (In-Service Inspection)Clean Salt and Solid Fuel (not Molten Salt Reactor with Fuel in Coolant)Small Heat Gradients (~50C, as opposed to ~1000C Gas Cooled Reactors)Low Corrosion Rates

Low-Pressure Liquid-Salt CoolantsWhat is it?Optically TransparentClean fluid, not a Molten Salt Reactor (MSR)Fluoride saltsFreezing points near 400CAtmospheric boiling point 1400CWhy is it important?Heat transfer to an intermediate heat-transfer loopSecond liquid-salt coolant transfers to Brayton systemBetter heat transfer than gas coolantWell defined physical propertiesLow neutron-absorption cross sectionHow does it integrate with the system?Cools reactor coreTransports heat between core and Brayton system19Limits to Liquid Salt SelectionCurrent Usage in IndustryCross SectionCorrosion rateMelting PointBoiling PointToxicityCost

What are the properties?Is it being used?

20Liquid Salt Selection

*MP Melting Point21Salt Specific R&D NeedsSalt propertiesSeveral salts being considered (LiF, NaF, KF, etc.)Properties only partly knownImpact of impuritiesSalt instrumentationRequirements for online reactor monitoringSalt qualificationSalt purificationInitial productionReactor online purification22Passive Safety Systems

Passive decay-heat-removal systemReduced need for water Reduce heat transfer from reactor to guard vesselLarger Reactors PossibleEasier to remove passive decay heat with salt coolantFewer cost-prohibitive active systemsPassive Safety Systems and Plant Designs from Liquid-Cooled Fast ReactorsWhat is it?Passive Reactor Vessel auxiliary cooling (RVAC) systemWhy is it important?Increased safetyFewer cost-prohibitive active systemsCost reductionLocation is not dependent on availability of waterIncreased reactor sizeHow does it integrate with the system?Keeps liquid-salt coolant above reactor so reactor cannot lose coolant even if primary vessel fails because core remains covered with saltPool Reactor Heat is Transferred from the reactor core to the reactor vessel graphite reflector by natural circulation of the liquid saltsConducted through the graphite reflector and reactor vessel wall23Decay Heat RemovalSalt freezing points between 350C and 500CSalt boiling points up to ~ 1400CFuel temperature rated to ~ 1600CAccidentExit Coolant at ~ 1,000CPeak Fuel ~ 1,160C at 30hPeak Vessel ~ 750C at 45hNatural circulation provides ~ 50C heat gradient

The combination of a high-temperature fuel and a high-temperaturelow-pressure coolant 1,400C becomes the enabling technologyfor the construction of large high-temperature reactors withpassive safety systems.

24ThermodynamicsIdeal Brayton cycle under the cold air-standard assumptions

Processes 1-2 and 3-4 are isentropicPressure P2 = P3 and P4 = P1

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ThermodynamicsSubstitution yields

Efficiency Depends upon Temperature (T2)LWR 33%AHTR-LT (705C) 48.0%AHTR-IT (800C) 51.5%AHTR-VT (1000C) 56.6%

26AHTR Parameters

27Price of Electricity

2002 MIT Nuclear Power Study28Construction Costs

Per Peterson (Berkeley): American Nuclear Society 2004 Winter Meeting29Reduced Plant Size

30Economic Sustainability

31DOE-NE (2010 Roadmap Study)

32Benefits of AHTRCoated Particle Fuels Enable increased structural integrityResistance to cracking due to thermal stressesThe Brayton-cycle power technology uses higher operating temperatures (700C 1000C)Higher efficiency Produces less thermal pollution Enables use of dry cooling, reducing water consumption.In a breeder reactor, new fuel is produced as a part of the on the going fission reaction which can later be processed for further use33Benefits of AHTRLow-Pressure Liquid SaltsGood heat transfer characteristicsReduced temperature gradientsTransparent for inspectionPassive Safety SystemsRadioactive decay heat removalHeat characteristics nominal for accidentsSustainabilityReduced need for waterSmaller physical plant sizeEconomically feasible34R&D ChallengesMaterials: Needs are goal dependentQualified materials to 750 CCandidate materials requiring more testing to 850 CMajor R&D required for 1000 CReactor core designSalt selection and processing (several options)NeutronicsRefueling temperatures 350 to 500 C (avoid salt freezing)Related Salt Uncertainties35ConclusionThe AHTR is a reactor concept that maximizes the utility of individual technologies by combining them to achieve higher process efficiencies, greater power output, and better safety. These technologies show the potential for an economically and environmentally sustainable plant design.36ReferencesForsberg, C.W., Peterson, P.F., and Zhao, H. (Dec. 2006). Sustainability and Economics of the Advanced High-Temperature Reactor. Journal of Energy Engineering, ASCE, 132:3 (2006): 109 - 115Forsberg, C.W., Peterson, P.F., and Williams, D.F. (2005). Liquid-salt-cooling for advanced high-temperature reactors. Proc., 2005 Int. Congress on Advances in Nuclear Power Plants (ICAPP 05), American Nuclear Society, La Grange Park, Ill.Wikipedia, Nuclear Fuel, 9/21/2007, http://en.wikipedia.org/wiki/Nuclear_fuelWikipedia, Nuclear Power, 11/09/2007, http://en.wikipedia.org/wiki/Nuclear_PowerWikipedia, Economics of New Nuclear Power Plants, 11/09/2007, http://en.wikipedia.org/wiki/Economics_of_new_nuclear_power_plantsWikipedia, Brayton Cycle, 11/09/2007, http://en.wikipedia.org/wiki/Brayton_CycleThe Future of Nuclear Power, Massachusetts Institute of Technology, 2003, ISBN 0-615-12420-8, . Retrieved on 2006-11-10Nuclear Energy- http://www-formal.stanford.edu/jmc/progress/nuclear-faq.htmlNuclear Science & Tech- http://www.aboutnuclear.org/view.cgi?fC=NST

37World Nuclear Organization, Need http://www.world-nuclear.org/why/why.htmlWorld Nuclear Organization, Power Reactors - http://www.worldnuclear.org/how/npreactors.htmlWorld Nuclear Organization, Fuel Cycles-http://www.world-nuclear.org/how/fuelcycle.htmlWorld Nuclear Organization, Glossary-http://www.world-nuclear.org/info/inf51.htmlNuclear Waste - http://library.thinkquest.org/17940/texts/nuclear_waste_future/nuclear_waste_future.htmlBrayton Cycle- Brayton Cycle: The Ideal Cycle for Gas-Turbine Engines in Relation to Power Plants by Denise LaneThermodynamics and Power Cycles, Thermal Engineering 2 RajputImagery- Brayton Cycle http://images.google.com/images?hl=en&q=brayton+cycle&gbv=2Imagery- Rankine Cycle http://images.google.com/images?q=rankine+cycle&revid=1648754521&sa=X&oi=revisions_inline&resnum=0&ct=broad-revision&cd=1

38Imagery Nuclear Power Plant-http://images.google.com/images?svnum=10&hl=en&q=nuclear+power+plantTemperature Helium Brayton Cycles- Thermal Hydraulics Group, Thermal Labs IFE Experiment page, PetersonNuclear Technology- http://www.nuc.berkeley.edu/research/index.htmImagery, Commercial Nuclear Power Plants- http://upload.wikimedia.org/wikipedia/commons/1/18/Nuclear_power_stations.png

39Backup Slides

40ThermodynamicsEnergy Equation

Heat Transfer

41Operating Costs

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