Small Scale Reactors

James AndersonJohn HansenJoshua PerezClay TaubSmall Modular ReactorsOverviewBackground and MotivationToshiba 4SNuScaleBabcock and Wilcox mPowerPebble Bed Modular Reactor (PBMR)Hyperion Power Module (HPM)Power Reactor Innovative Small Module (PRISM)ChallengesBackground and MotivationSmall scale nuclear reactors are classified by the IAEA as delivering less than 300 MWe.Demand for energy continues to increase while heavily centralized grids are strained to provide supply.Remote communities require either dedicated fossil fuel power supply or long power lines, both of which are expensive and inefficient.Modular designs must be versatile, expandable, and safe.Battery type designs must be proliferation-resistant, safe and simple to operate.Toshiba 4S10 MWe (30 MWt) or 50 MWe (135 MWt)Liquid Sodium CoolantPower control using on mobile reflectors, coolant temperature, and central absorber rodMetallic U-10Zr Fuel (19.9% Enrichment)Toshiba 4S Fuel CycleFuel can either be metallic Uranium or Uranium and Plutonium, both with10 wt% Zirconium, with fissile material enrichment at or below 19.9%Fuel is to be bred within the reactor (breeding ratio of 0.69), in order to increase longevity rather than for fuel production.Refueling does not occur. After 30 years, the entire reactor vessel is removed and replaced with a new one (nuclear battery).

Fuel PinsReflectorsGas CavitiesControl RodToshiba 4S Heat RemovalPrimary and secondary sodium coolant loops cool the core, with steam generation taking place with the second loop.Primary sodium does not leave the reactor vessel, is circulated by EM pump through core and into intermediate heat exchanger (IHX) above core.Secondary coolant flows through top of reactor vessel, out of the core into double wall steam generator.Steam passes through turbine in adjoining facility and is condensed.Electromagnetic pump eliminates mechanical component of cooling within reactor vessel.Double wall steam generator lessens chance of water-sodium leak and interaction.Toshiba 4S Reactor ControlReflectors are used to manage neutron population and thermal power output.Six silicon carbide (SiC) reflectors encircle the bottom of core and are slowly moved up the core by 1 mm/day to compensate for burn-up during the reactor lifetime.Core can be shut down by allowing the reflectorsto fall below the core.Raising reflectors above the rest inserts negative reactivity,with up to -400 being inserted when 3 reflectors areat the bottom of the core and three are above them.Gas-filled cavities positioned above the reflectorsprevent reflection by sodium coolant.

Toshiba 4S Reactor Control (Cont.)Additionally, core inlet temperature can be reduced by increasing water flow rate through steam generator.This allows for fine control within 10% of rated power.If this is not adequate, reflectors are used for further reactivity control.A boron carbide (B4C) control rod is located in thecenter of the core.For the 50 MWe configuration, this rod is withdrawn after startup and is only used for shutdown of the core.For the 10 MWe configuration, this rod remains in the core for 15 years while the reflectors are moved up the core, then removed and reflector position reset to the bottom of the core for the next 15 years.Toshiba 4S SafetyBelow 350C, the stainlesssteel lifting mechanism doesnot grip Cr-Mo absorbing rodguide, preventing the rodfrom being withdrawn.Core section of reactorvessel is underground.Negative temperature and void coefficients of reactivity maintained throughout life of core

Toshiba 4S - SafetyIn the event of a loss of decay heat removal capability, PRACS and RVACS are utilizedPrimary Reactor Auxiliary Cooling System (PRACS) sinks heat from secondary sodium loop into air cooler; is a partially active system.Reactor Vessel Auxiliary Cooling System (RVACS) drafts heat around structures surrounding reactor vessel; is completely passive.Tests show these systems can operate at below half capacity and still effectively cool core, even in situations such as an aircraft attack.

Toshiba 4S Regulatory Status and FutureThe 4S design is currently under pre-application review and Toshiba expects design approval by 2014.The town of Galena, Alaska, hoping to replace its costly diesel generators as the main source of power, approached Toshiba and the US DOE to consider installing a 10 MWe 4S reactor to provide power and stimulate the local economy.The matter is still unresolved, but pending NRC approval, there is hope that the reactor will be in place before 2020.NuScale DesignCreated by NuScale Power Inc., is a 45 MWe (160 MWt) PWR which resembles PWR designs currentlyin use, but at a smaller scale and operating at lower pressure and temperature.Reactor vessel houses the core, primary water loop, and steam generators.RV is surrounded by vacuum in containment vessel, which is submergedin pool of water.Fuel: Uranium Dioxide

Babcock and Wilcox mPower125 MWe modular plant to be constructed on existing B&W manufacturing infrastructure currently used for US Navy nuclear power equipment.Design is similar to in-use PWR plants, and B&W possesses wealth of experience building small reactors for the Navy.Design certification to be applied for in 2012, and construction expected to begin in 2020.

Pebble Bed Modular ReactorSouth African design based on German AVR test reactor, using TRISO fuel and helium primary coolant loop, with intended 165 MWe (400 MWt) power output.Lost all government funding in 2010 and its future is in questionChina is considering a similardesign, currently embodiedby the HTR-10, acting as a testbed for modular nuclearpower and clean hydrogengeneration.

Hyperion Power Module (HPM)25 MWe (70 MWt) transportable design, fueled by uranium nitride and cooled by a lead-bismuth eutectic primary coolant loop within the reactor vessel.Intended to function as a nuclear battery (similar to 4S), completely sealed and refueled by replacing entire reactor.

GE Power Reactor Innovative Small Module311 MWe (840 MWt) modular reactor intended to operate in conjunction with Advanced Recycling Center, where spent LWR fuel is converted into metallic fuel for use in the PRISM reactor.Sodium cooled, with reaction control and shutdown mechanisms similar to the HPM and containment cooling systems similar to the 4S.Intended to burn actinides and breed fuel for further recycling.

n_flux3 Reactor ConfigurationUses three regions to simulate the 4S reactor:The Core region is a finite cylinder that is 4 meters tall, and .8 meters in diameter.The Neutron Absorber region is a finite cylinder 4 meters tall, and .16 meters in diameter. It can be raised and lowered by adjusting parameters in the n_flux3 program.The Reflectors region is made up of the six reflectors which are 1.5 meters tall, have a .2 meter radius, and a length of p/3 radians. Each reflector position is determined in the n_flux3 function call.

Neutron AbsorberCoreReflectorsn_flux3 Reactor Configuration

n_flux3 uses cylindrical and Cartesian coordinate systems for calculations, with the origin for both at the bottom of the core.Equivalent Core Diameter.8 mActive Core Length4 mReflector Length1.5 mReflector Thickness.2 mAbsorber Radius.08 mAbsorber Height4 mqryx0p/34p/3p2p/35p/3n_flux3 Flux Recordingn_flux3 divides up the entire reactor into small volumes, which are treated like bins.Each time a neutron interaction occurs in a particular small volume, n_flux3 tallies that interaction in the corresponding bin.The number of neutron interactions in each bin is weighted by the size of that bins small volume.The location of each bin is represented as a point in the center of its small volume.

r2D and 3D representationof a small volume

n_flux3 Flux Recording

All Reflectors UpReflectors are all raised to 2.751 million neutrons tested (287 seconds to run)Shown: All bins at Z= 2.25, reflector and neutron absorber outlines3 Reflectors up, 3 Down3 reflectors raised to center, other 3 reflectors fully lowered.1 million neutrons tested.Shown: All bins at Z= 2.25, reflector and neutron absorber outlines.All Reflectors DownAll reflectors lowered to bottom of core1 million neutrons tested.Shown: All bins at Z= 2.25, reflector and neutron absorber outlines.Effect of Reflector Height

Reflectors at z=1.0 m, 5 million neutrons.Effect of Reflector Height

Reflectors at z=1.5 m, 5 million neutrons.Effect of Reflector Height

Reflectors at z=2.0 m, 5 million neutrons.Effect of Reflector Height

Reflectors at z=2.5 m, 5 million neutrons.Effect of Reflector Height

Reflectors at z=3.0 m, 5 million neutrons.Effect of Reflector Height

Reflectors at z=3.5 m, 5 million neutrons.Effect of Reflector Height

Reflectors at z=4.0 m, 5 million neutrons.Intended Effect of Reflector Height

Edge of the Core

CoreReflectors at 2.75 m, 5 million neutronsEdge of the Core

Core PerimeterReflectors at 2.75 m, 5 million neutronsFlux in Reflectors

Reflector PerimeterReflectors at 2.75 m, 5 million neutronsTabulated FluxesLocationFluxAll Reflectors Up3 Reflectors Up1 Reflector UpAll Reflectors DownNeutron Absorberz = 1.75 m4.36E+074.35E+074.41E+074.46E+07Inner Core, r = .12 mz = 1.75 m3.60E+073.52E+073.54E+073.51E+07Core Perimeter, r = .36 mz= 1.75 m2.35E+071.82E+071.80E+077.04E+06Reflectorz = 1.75 m3.85E+062.42E+062.34E+063.40E+04Inner Core, r = .12 mz = 1.25 m3.45E+073.44E+073.49E+073.42E+07Inner Core, r = .12 mz = .75 m3.30E+073.41E+073.43E+073.39E+07Conclusions n_flux3Fuel, neutron absorber, and reflectors clearly shape the flux in the core.Reflectors raise flux around the core perimeter.Only sections near the reflectors experience substantial changes in flux, allowing control of the reactor.Partial lowering of reflectors has noticeable effect on neutron flux.

ChallengesThe current regulatory environment heavily favors large power output light water reactor designs very similar to facilities currently in use.Non-proliferation measures and maintaining security become paramount when the intended market includes third-world countries, and significantly add to cost.Down market has dampened hopes for speedy construction and installation, and has claimed casualties (PBMR), but other designs are moving forward.ReferencesInnovative small and medium sized reactors: Design features, safety approaches and R&D trends. Vienna, 711 June 2004. International Atomic Energy Agency, Vienna, Austria."Facts about the NuScale system and technology." NuScale Power, 2008. Web. 20, Oct. 2010. Boyack, B., Hochreiter, L., Kazimi, M., Reyes, J., Smith, K. Wallis, G. NuScale Preliminary Loss-of-Coolant Accident (LOCA) Thermal-Hydraulic and Neutronics Phenomena Identification and Ranking Table (PIRT). NuScale Power, Inc. June 2010.Reyes, Jos N. Introduction to NuScale Design. U.S. Nuclear Regulatory Commission Pre-Application Meeting. Rockville, MD. 24 July 2008.Mowry, Christopher M. Written Testimony of Christofer M. Mowry, President, Babcock & Wilcox Nuclear Energy, Inc. Committee on Science and Technology, US House of Representatives. 29 May 2010.Ion, S., Nicholls, D., Matzie, R., Matzner, D. Pebble Bed Modular Reactor: The First Generation IV Reactor To Be Constructed. World Nuclear Association Annual Symposium. London. 3-5 September 2003.Sun, Y., Xu, J., Zhang, Z. "R&R effort on nuclear hydrogen production technology in China." International Journal of Nuclear Hydrogen Production and Applications. Volume 1, Issue 2 (2006).Hyperion Power Generation. Initial Launch Design for Hyperion Power Module announced today at Winter Conference of American Nuclear Society in Washington, D.C. and Londons Powering Toward 2020 Conference. OECD/NEA Nuclear Science Committee, Working Party on Scientific Issues of the Fuel Cycle, Working Group on Lead-bismuth Eutectic. Handbook on Lead-bismuth Eutectic Alloy and Lead Properties, Materials Compatibility, Thermal-hydraulics and Technologies. OECD Nuclear Energy Agency, 2007.Adee, Sally and Guizzo, Eric. Nuclear Reactor Renaissance. IEEE Spectrum. August 2010. Loewen, Eric P. Advanced Reactors: NUREG 1368 Applicability to Global Nuclear Energy Partnership. GE Nuclear Infrastructure. RIC 2007: Advanced Reactor Designs. 15 March 2007.Preapplication Safety Evaluation Report for the Power Reactor Innovative Small Module (PRISM) Liquid-Metal Reactor. Office of Nuclear Reactor Regulation, US Nuclear Regulatory Commission. Washington, DC, February 1994.Minato, A., Handa, N. Advanced 4S (Super Safe, Small and Simple) LMR. Toshiba Power Systems and Services Company. Yokohama, Japan, 1994.Tsuboi, Y., Arie, K., Grenci, T. Design Features, Economics and Licensing of the 4S Reactor. Toshiba Corporation. ANS Annual Meeting. 13-17 June 2010.Toshiro, S., Inatomi, T., Nakamura, H., Fukachimi, K., Suzuki, T., Hasegawa, K., Tsuboi, Y., Kuramochi, M. Fast Reactor Having Reactivity Control Reflector. Toshiba Corporation. 30 June 2009.Safety Features of the Containment of a 4S Reactor-Based Power Generation Facility, Prepared for the City of Galena, Alaska. Toshiba Corporation. 3 December 2007.