PWR Description - MIT OpenCourseWare

1 PWR DescriptionJacopo BuongiornoAssociate Professor of nuclear Science and : Engineering of nuclear SystemsPressurized Water Reactor (PWR) Pressurized Water Reactor (PWR) Public domain image from PLANTSCHEMATIC OF A PWRSCHEMATIC OF A PWR Major PWR vendors include Westinghouse, Areva and Mitsubishi source unknown. All rights reserved. This content is excluded from our Creative Commons license. For more information, see Coolant Circuits PWR Coolant Circuits INDIRECT CYCLE: Primary and Secondary Coolant Loops Singgle Phase ((Liqquid)) Reactor Coolant [Tin= C, Tout=324 C, P= MPa, Tsat= C] Two-Phase (Steam-Water) Power Conversion Cycle Loop [TSG,in=227 C, TSG,out=285 C, P= MPa, Tsat=285 C] [][TCondenser= C, P= kPa] Condenser [MPa]Phase Diagram of WaterPhase Diagram of Water Pressure 69 Vapor Vapor 38 100 227 285 343 Temperature 288 324 Saturation line i PWR secondary system PWR primary system Liquid Condenser [ C] PWR Vessel, Core and Primary SSystem ARRANGEMENT OF THE PRIMARY SYSTEM FOR A WESTINGHOUSE 4-LOOP PWR Nero, Jr.

2 , A Guidebook to nuclear Reactors, 1979 University of CA press. All rights reserved. This content is excluded from our Creative Commons license. For more information, see PATH WITHIN REACTOR VESSEL CR gui de t u be s Barrel flange Up pe r s upp or t plate Hot nozzle Water in at Wa te r ou t a t 324 C To p of active fu el Cold nozzle 288 C 324 C Core Lo wer co re p lat e Bottom of active fuel REACTOR VESSEL AND INTERNALS source unknown. All rights reserved. This content is excluded from our Creative Commons license. For more information, see domain image from from: M. Kanda, Improvement in US-APWR design from lessons learned in Japanese May 2007 (top), and EPR brochure available at (bottom two) TYPICAL 4-LOOP REACTOR VESSEL PARAMETERS Overall length of assembled vessel, closure head, and nozzles mInside diameter of shell439mInside diameter of mRadius from center of vessel to nozzle face Inlet m 312 Outlet mNominal cladding thickness mm Minimum cladding thickness mm Coolant volume with core and internals in place m3 Operating pressure MPa Design pressure17 24 MPaDesign pressure MPaDesign temperature C Vessel material Carbon steel l ddii lillCladding material Stainless steelNumber of vessel material surveillance capsules, total 8 TYPICAL 4-LOOP CORE TYPICAL 4 LOOP CORE Masche, G.

3 , Systems Summary: W PWR NPP, 1971 Image by MIT of the fuel Geometry of the fuel Cross Section of a Representative Fuel Pin (not drawn to scale) mm (in.) BWR PWR 2ro ( ) ( ) 2rco ( ) ( ) t ( ) ( ) Image by MIT by MIT OpenCourseWare . source unknown. All rights reserved. This content is excluded from our CreativeCommons license. For more information, see the fuel/clad gap?Why the fuel/clad gap? Provides clearance forProvides clearance for fuel pellet insertion during fabrication Accommodates fuel swelling without breaking the clad Filled with helium ggas Example of a Cracked Fuel Cross Section Source: Todreas & Kazimi, Vol. I, p. 333 14 Taylor & Francis. All rights reserved. This content is excluded from our Creative Commons liceFor more information, see TYPICAL FUEL ROD PARAMETERS TYPICAL FUEL ROD PARAMETERS Outside diameter mm Cladding thickness mm Diametral gap Diametral gap 0166 mm mm Pellet diameter mm Pitch cm Rods arrayy in assemblyy 17x17 Fuel rods per assembly 264 Total number of fuel rods in core 50,952 CUTAWAY OF TYPICAL ROD CLUSTER CONTROL ASSEMBLY (RCCA) ASSEMBLY (RCCA) From: EPR brochure.

4 Available at Masche, G., Systems Summary: W PWR NPP, 1971 source unknown. All rights reserved. This content is excluded from our Creative Commons license. For more information, see Control Rod ((gWestinghouse RCCA))Made of Ag-In-Cd ( black rods for scram) or Inconel ( gray rods for fine tuning)Control rod guide tube (24)Instrument thimblePublic domain image from wikipedia. source unknown. All rights reserved. This content is excluded from our Creative Commons license. For more information, see means to control reactivity in PWRs Boron (boric acid, H3BO3) dissolved in coolant. Compensates for loss of reactivity due to fuel burnup. High concentration at BOC (beginning of cycle), progressively decreased to zero at EOC (end(beginning of cycle), progressively decreased to zero at EOC (end of cycle) Pros: uniform absorption throughout core, concentration is easily controlled Cons: makes coolant sliggyhtly acidic ((reqquires addition of other chemicals to re-equilibrate pH), can deposit (come out of solution) as crud on fuel rods, can make moderator reactivity feedback positive at high concentration 8000700060005000400030002000100000510152 0253035404550 Core critical boron concentration (ppm)Exposure (GWD/MTU)Enrichment = 5W/0 U235 Enrichment = 6W/0 U235 Enrichment = 7W/0 U235 Image by MIT means to control reactivity in PWRs (2) Burnable absorbers ( poisons ) loaded in fuel.))

5 Gd (Gd2O3)has higher a than 235U, thus it burns faster than fuel, which tends to increase k over time increasekeff overtime. Pros: no impact on coolant corrosion or moderator reactivity feedback Cons: lowers melting point and thermal conductivity of UO2, cannot burn out completely by EOCcompletelybyEOC No Poison24 BA Pins32 BA Pins36 BA Pins40 BA Pins44 BA exposure (GWD/MTU)0102030405060kImage by MIT OpenCourseWare . source unknown. All rights reserved. This content is excluded from our Creative Commons license. For more information, see GRID SPACERS From: Mitsubishi US-APWR Fuel and core desiggn. DOE Technical session UAP-HF-07063. June 29, 2007. Masche, G., Systems Summary: W PWR NPP, 1971 Hold fuel rods in place prevent excessive vibrations Have mixing vanes enhance coolant mixing and heat transfer Connection of PWR Core Desiggn to Neutronics Why is Zr used as structural material in fuel assemblies?

6 What functions does water perform? What functions does water perform? What determines the fuel rod spacing? Why are the fuel rods so small? Why are the control rods arranged in clusters? Why is boron dissolved in the coolant? What is Gd used for? Why is boron dissolved in the coolant? What is Gd used for? source unknown. All rights reserved. This content is excluded from our CreativeCommons license. For more information, see Bundle Design Advances PWR Bundle Design Advances Extended burnup features (OAdvanced cladding (ZIRLO , M5)) Annular blankets Larger gas plena Improved mechanical performance Improved debris filters Low growth, wear-resistant materials Improved economic and operational performance Natural uranium blankets Flow mixing grids to enhance margin to DNB Reduced O&M costs Low cobalt steel alloys to reduce exposure Reduced inspection requirements REPRESENTATIVE CHARACTERISTICS OF PWRs Nero, Jr.

7 , A Guidebook to nuclear Reactors, 1979. Parameter4-loop ,7291. PlantNumber of primary loopsReactor thermal power (MWth)Total plant thermal efficiency (%)Plant electrical outputPower generated directly in coolant (%)Power generated in the fuel (%)2. CoreCore barrel inside diameter/outside diameter (m)Rated power density (kW/L)Core volume (m3)Effective core flow area (m2)Active heat transfer surface area (m2)Average heat flux (kW/m2)Design axial enthalpy rise peaking factor (FDh)Allowable core total peaking factor (FQ)3. Primary CoolantSystem pressure (MPa)Core inlet temperature (oC)Average temperature rise in reactor (oC)Total core flow rate (Mg/s)Effective core flow rate for heat removal (Mg/s)Average core inlet mass flux (kg/m2-s)Parameter4-loop * Fuel AssembilesNumber of assembliesNumber of heated rods per assemblyFuel rod pitch (mm)Fuel assembly pitch (mm)Number of grids per assemblyFuel assembly effective flow area (m2)Location of first spacer grid above beginningof heated length (m)Grid spacing (m)Grid typeNumber of control rod thimbles per assemblyNumber of instrument tubesGuide tube outer diameter (mm)6.

8 Rod Cluster Control AssembliesNeutron absorbing materialType 304 SSCladding thickness (mm)53/8 Number of clusters Full/Part length24 Number of absorber rods per cluster*Employs mixing vanes50, Fuel RodsTotal numberFuel density (% of theoretical)Fuel pellet diameter (mm)Fuel rod diameter (mm)Cladding thickness (mm)Cladding materialActive fuel height (m)Image by MIT PRESSURIZER Pressurizer (Saturated Liquid-Steam System: P= MPa, T= C) Controls pressure in the primary system 2 m Hot leg From cold leg LiquidSpray Steam - Pressure can be raised by heating water (electrically) Liquid - Pressure can be lowered by Electric heaters condensing steam (on sprayed droplets)droplets) Surge Line Masche, G., Systems Summary: W PWR NPP, 1971 PRESSURIZER TYPICAL DESIGN DATAN umber and typeOverall heightOverall diameterWater volumeSteam volumeDesign pressureDesign temperatureType of heatersNumber of heatersInstalled heater powerNumber of relief valvesNumber of safety valvesSpray ratePressure transientContinuous Shell materialDry weightNormal operating weightFlooded weight ( )

9 1 Two-phase water and steam cu cu MPa360oCElectric immersion781800 kW2 Power-operated3 Self-actuating3028 L/mMn-Mo steel, clad internally with stainless steel106,594 kg125, 191 kg157,542 kgImage by MIT Coolant Pumps Reactor Coolant Pumps - Large centrifugal pumps - Utilize controlled leakage shaft seal - Have large flywheel to ensure slow coast-down upon loss of electric powerupon loss of electric powerto the motor PWR Secondary System PWR STEAM GENERATORS Primaryy side,, Hot ((Tin = 324 C,, Tout = 288 C)): Higgh Pressure Liqquidin out Secondary side, Cold (Tsat = 285 C): Lower Pressure Steam and Liquid Water Boils on Shell Side of Heat E changer -Water Boils on Shell Side of Heat Exchanger - Steam Passes through Liquid Separators, Steam Dryers -Liqquid Water Naturallyy Recirculates via Downcomer - Level Controlled via Steam and Feedwater Flowrates U-TUBE U TUBE STEAM GOGENERATOR chure.

10 Available at source unknown. All rights reserved. This content is excluded from our Creative Commons license. For more information, see : EPR broONCE-THROUGH nuclear STEAM GENERATOR Used only in old B&W plants B&W, Steam, Its Generation & Use, 1972. source unknown. All rights reserved. This content is excluded from our Creative Commons license. For more information, see Babcock & Wilcox. All rights reserved. This content is excluded from our Creative Commons license. For more information, see , G., Systems Summary: W PWR NPP, 1971 TYPICAL DESIGN DATA FOR STEAM GENERATORSN umber and typeHeight overallUpper shell ODLower shell ODOperating pressure, tube sideDesign pressure, tube sideDesign temperature, tube sideFull load pressure, shell sideMaximum moisture at outlet (full load)Design pressure, shell sideReactor coolant flow rateReactor coolant inlet temperatureReactor coolant outlet temperatureShell materialChannel head materialTube sheet materialTube materialTube ODAverage tube wall thicknessSteam generator weightsDry weight, in placeNormal operating weight, in placeFlooded weight (cold)