2 Physical Aspects of Core Layout .............................. 23
2.1Overview on Physical Aspects of Core Layout and Design ofModularHTRPlants....................................... 23
2.2SomeAspectsofCriticality................................. 27
2.3In.uence of Re.ectors ....................................... 31
2.4Coef.cientsofReactivity .................................. 33
2.4.1 PrincipleConsideration ............................... 33
2.4.2 Temperature Coef.cients.............................. 34
2.5Demand of Reactivity Compensation and Worth of Control Systems .... 38
2.6Fast Neutron Doses on Re.ectors ............................. 43
2.7In.uenceofFlowofBalls,ActionontheBurnupofFuel ............ 46
2.8Distributions of Fuel, Neutron Flux, and Power Density intheReactorCore .......................................... 52
2.9PrinciplesofKineticsofNuclearReactors .................... 54
2.9.1 OverviewonSomeGeneralAspects ..................... 54
2.9.2 KineticEquations.................................... 58
2.9.3 Simple Solutions of the Kinetic Equations.... .... ..... .... 60
2.10 ProgramSystemsforPhysicalLayoutoftheCore .................. 61
2.10.1GeneralRemarks .................................... 61
2.11 AspectsofCoreLayoutandDesign ............................. 67
2.11.1General Overview and Aspects of Core and Fuel Element Design............................................ 67
2.11.2Discussions on Different Core Parameter . .... .... ..... 69
2.12Physical Aspect of the First Loading and Running in Period ofaPebbleCore ............................................ 74
2.13 DischargingofPebble-BedCores ............................... 80
References ....................................................... 80
3 Thermo-Hydraulic Aspects of Core Layout ......................... 83
3.1 HeatProductionInsidetheCore ................................ 83
3.2 ThermalPoweroftheCore.................................... 87
3.3 DataoftheCoolantGasHelium .......................... 88
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LL Contents
3.4 Basic Equations of the Thermo-Hydraulics of the Core . .... ..... .... 90
3.5 HeatingupofHeliumCoolantintheCore ........................ 94
3.6Temperature Pro.lesinFuelElements ........................... 98
3.7HeatTransferinthePebble-BedCore............................ 102
3.8Pressure Drops in the Core and Re.ectorStructures ................. 104
3.9Special Aspects of Thermo-Hydraulic Layout of the Core of Modular HTR..................................................... 107
3.9.1 MixingofHotGasBehindtheCore ..................... 107
3.9.2 In.uenceofBypassesontheCoreCooling ................ 110
3.9.3 Uncertainties of Calculation of Power Density and Other Thermo-HydraulicParameters .......................... 111
3.9.4 MeasurementofFuelTemperature....................... 112
3.9.5 c HeatingofCoreInternalsandCooling .................. 113
3.10 PrincipleofCoreLayout...................................... 114
3.11 Comparison of Data of Core Cooling in Some HTR Concepts ..... .... 117
3.12Comparison of Thermo-Hydraulic Aspects of Different ReactorTypes .............................................. 118 References ....................................................... 119
4 Fuel Elements.................................................... 121
4.1 DescriptionoftheComponent ................................. 121
4.2 AspectsofLayoutandDesignofHTRFuelElements ............... 123
4.3 Temperature Distributions in HTR Fuel Elements.. .... .... ..... .... 128
4.4 IrradiationBehaviorofFuelElements............................ 130
4.5 StressesinFuelElements ..................................... 134
4.6 CorrosionofFuelElements.................................... 138
4.7 Fission Product Release from Fuel Elements in Normal Operation .. .... 141
4.8DifferentTypesofSphericalFuelElements ....................... 150
4.9Some Further Experiences with HTR Fuel Elements.... .... ..... .... 151
4.10 ComparisonofLWRandHTRFuelElements ..................... 157
References ....................................................... 161
5 Reactor Components .............................................. 163
5.1 OverviewontheComponents .................................. 164
5.2 InternalReactorStructures .................................... 165
5.2.1 OverviewontheComponents .......................... 165
5.2.2 TechnicalAspectsofCoreInternals...................... 165
5.2.3 LoadsonCoreInternals............................... 175
5.2.4 GraphiteandItsIrradiationBehavior ..................... 178
5.2.5 Results of Analysis of Re.ector Structures During Operation .......................................... 183
5.3 PrimaryEnclosure ........................................... 186
5.3.1 Overview .......................................... 186
5.3.2 Aspects of Dimensioning and Materials for Pressure VesselsofPrimaryCircuit ............................. 189
5.3.3 Neutron Irradiation of Reactor Pressure Vessel andDesignAspects .................................. 197
5.3.4 ActivationoftheReactorPressureVessel ................. 201
5.4 Comparison of Different Reactor Pressure Vessles . .... .... ..... .... 203
5.5 ShutdownandControlSystems................................. 203
5.5.1 OverviewonReactivityAspects ........................ 203
5.5.2 WorthesofShutdownSystemsinHTR ................... 206
5.5.3 Technical Concepts of Control and Shutdown Systems ... .... 208
5.6 FuelHandlingSystem ........................................ 217
ContentsLLL
5.6.1 Overview .......................................... 217
5.6.2 Technical Aspects of the Fuel Handling System ... ..... .... 220
5.6.3 AlternativesfortheFuelHanding ....................... 226
5.6.4 SomeSpecialAspectsofFuelHandling .................. 231
5.7 Measurement Installations for Core Parameters .... .... .... ..... .... 233
5.7.1 MeasurementofNeutronFlux .......................... 233
5.7.2 Measurements of the Thermo-Hydraulic Parameters oftheCore......................................... 236 References ....................................................... 238
6.3 SteamGenerator ............................................ 257
6.3.1 GeneralDescriptionoftheComponent ................... 257
6.3.2 Thermo-HydraulicAspects............................. 267
6.3.3 PressureDrops ...................................... 273
6.3.4 FlowStabilityoftheSteamGenerator .................... 276
6.3.5 Aspects of Mechanical Design of Steam Generator Tubes . .... 278
6.3.6 Experiences with Steam Generators of Gas-Cooled Reactors........................................... 283
6.4 HeliumCirculator ........................................... 290
6.4.1 Overview Some Thermosdynamic Aspects ... .... ..... .... 290
6.4.2 Aspects of Technology of Helium Circulators . .... ..... .... 296
6.4.3 ConceptsofHeliumCirculators ......................... 298
6.5 Gas Puri.cationPlant ........................................ 306
6.5.1 Overview .......................................... 306
6.5.2 Concept of the Gas Puri.cation......................... 311
6.5.3 Experiences with Gas Puri.cationPlants .................. 314
6.6 HeliumCircuitsforDecayHeatRemoval ......................... 316
6.7 HeliumAuxiliarySystems .................................... 320
6.7.1 Overview .......................................... 320
6.7.2 AuxiliaryHeliumCircuits ............................. 320
6.7.3 MeasurementsinHeliumCircuits ....................... 322
6.8 ReactorProtectionSystem .................................... 326
References ....................................................... 327
7 Reactor Containment Building ...................................... 331
7.1GeneralRemarksandRequirements ............................. 331
7.2Aspects of LWR and HTR Containments or Containment Buildings .... 334
7.3Several Overview on Concepts of Reactor Containment Buildings forHTR .................................................. 336
7.4Overview on HTR Containments and Buildings Applied Until Now .... 337
7.5 PlanningWorkfortheContainmentsinthePast.................... 339
References ....................................................... 345
9 Operational Aspects............................................... 381
9.1 Overview on Requirements and Conditions of Plant Operation..... .... 381
9.2 BurnupofFuelandProductionofHigherIsotopes.................. 384
9.2.1 BurnupofFuel ..................................... 384
9.2.2 ProductionofHigherIsotopes .......................... 387
9.3 FissionProductInventory ..................................... 388
9.4 DynamicalEquationsfortheTotalPlant.......................... 395
9.4.1 PrincipleOverview .................................. 395
9.4.2 SystemoftheDynamicalEquations...................... 395
9.4.3 Program Systems for Evaluation of Dynamical Questions . .... 400
9.5 ApplicationsoftheDynamicalEquations ......................... 402
9.6 ConceptofControlandOperationofaModularHTR ............... 405
9.6.1 ConceptofControl .................................. 405
9.6.2 OperationofHTR ................................... 407
9.7 Xenon Dynamics and In.uenceofSamariumonReactivity ........... 411
9.8 DecayHeatRemovalDuringNormalOperation .................... 418
9.8.1 DecayHeatProduction ............................... 418
9.8.2 PrinciplesofDecayHeatRemoval ...................... 419
9.8.3 Decay Heat Removal in a Modular HTR During Normal Operation .......................................... 421
9.9 Release of Radioactive Substances During Normal Operation. ..... .... 423
9.10 AspectsofWasteManagementinModularHTR ................... 426
References ....................................................... 433
10 Safety Aspects and Analysis of Accidents ............................. 435
10.1 GeneralRemarks............................................ 436
10.2 OverviewonRelevantAccidents ............................... 444
10.3 LossofCoolantAccidents .................................... 449
10.4 TotalFailureoftheActiveDecayHeatRemoval ................... 450
10.4.1Decay Heat Production and Active Decay Heat Removal . .... 450
10.4.2Overview Over Different Cases of Loss of Active Decay HeatRemoval ...................................... 453
10.4.3Self-acting Decay Heat Removal Under Full Helium Pressure ........................................... 454
10.4.4The Concept of Self-acting Decay Heat Removal from the Depressurized Reactor Outer Surface Cooler Is Working .... 456
10.4.5Discussion of Parameters Relevant for the Concept ofSelf-actingDecayHeatRemoval ...................... 460
10.4.6Self-acting Decay Heat Removal from the Reactor, Total Loss of Active Cooling of the Core, and Failure of the Surface Cooler............................................ 464
10.4.7Change of Core Temperature in Accidents and Change ofStateofReactivity ................................. 466
10.4.8Self-acting Decay Heat Removal in Extreme Accidents ReactorCoveredbyRubble........................... 468
10.5 ReactivityAccidents ......................................... 470
10.5.1Overview .......................................... 470
10.5.2Extreme Reactivity Accidents in Modular HTR .... ..... .... 470
10.5.3Water Ingress into the Core, Change of the Moderation Ratio ............................................. 474
10.5.4General Considerations on Reactivity Accidents ... ..... .... 475
ContentsY
10.6 WaterIngressintothePrimarySystem ........................... 477
10.6.1Overview on General Aspects and Consequences oftheAccident ..................................... 477
10.6.2Estimation of Water Ingressing into the Primary Circuit .. .... 478
10.6.3Thermodynamic Equilibria for the SteamGraphite Reactions .......................................... 479
10.6.4Reaction Speed of Graphite Corrosion by Steam ... ..... .... 481
10.6.5Some Technical Aspects of Water Ingress into a Hot PebbleBed......................................... 484
10.6.6RiseinPressureinPrimaryCircuit ...................... 487
10.6.7Gas Formation During Water Ingress into the Reactor.... .... 489
10.6.8Reactivity Effects caused by Water Ingress ... .... ..... .... 493
10.6.9ValuationofWaterIngressAccidents .................... 494
10.7 IngressofAirintothePrimaryCircuit ........................... 497
10.7.1Overview on Aspects of Air Ingress Accidents .... ..... .... 497
10.7.2Thermodynamic Equilibria of Reactions . .... .... ..... .... 498
10.7.3Reaction Velocities of Air with Graphite . .... .... ..... .... 499
10.7.4ConsequencesofAirIngressAccidents ................... 501
10.7.5Principle Considerations on the Mass Flow of Air IngressingintothePrimarySystemofHTR ............... 501
10.7.6Conclusions on Results of Analysis of Air Ingress Accidents .......................................... 506
10.7.7Further Options to Reduce the Consequences of Air Ingress ............................................ 506
10.8 Accidents on the Secondary Side of the Steam Cycle ... .... ..... .... 507
10.8.1Overview .......................................... 507
10.8.2RuptureoftheMainSteamPipe ........................ 508
10.8.3Failure of the Turbine-Generator System; Load Rejection ofTurbine ......................................... 509
10.9 ImpactsfromtheOutsideontheReactorPlant ..................... 512
10.9.1OverviewonImpacts ................................. 512
10.9.2AirplaneCrash ...................................... 514
10.9.3Earthquakes ........................................ 519
10.10 ReleaseofFissionProductsDuringAccidents ..................... 521
10.10.1Overview on Source Terms of Radioactivity .. .... ..... .... 521
10.10.2Fission Product Release During Operation of the Plant Over the Entitle Lifetime First Source Term . .... ..... .... 525
10.10.3Fission Product Release During Core Heatup Accidents SecondSourceTerm ................................ 531
10.10.4Transport of the Released Radioactivity from the Core totheEnvironment .................................. 532
10.10.5Radioactive Source TermsConclusions .................. 535
10.11 Radiological Consequences of Accidents and Risk . .... .... ..... .... 536
10.11.1OverviewonConceptsofRisks......................... 536
10.11.2ImportanceofLandContaminations ..................... 540
10.11.3Dose Rates Caused by Accidents of Modular HTR . ..... .... 542
10.11.4General Remark on Risks Caused by Nuclear Technologies ....................................... 546 References ....................................................... 549