Lecture 1

Lecture 1 Introduction: Importance of Thermal HydraulicsDifferent Reactor Types1Nuclear Reactor Thermal HydraulicsHeat transfer phenomena play a significant role in the following:DesignOperationSafety of nuclear reactorsAmount of power which can be extracted from the reactor core depends on the following:Heat removal rateMaterial limitationsFor a given reactor core, higher the heat extraction capability, lower will be the cost of power Hence, the importance of thermal hydraulics Strong inter-relationship between heat transfer and fluid flow phenomenaDifferent reactor designsDifferent thermal hydraulic phenomena encountered2Fission EnergyThis is released in various forms, but mainly as kinetic energy of the following:Fission fragmentsFission neutronsBeta particles, resulting from the decay of fission productsDistribution of energy deposition (approximate)90% in fuel element5% in moderator5% in structures (gamma heating)Of the total energy generated, approximately 90% to 95% is released to the coolant3Fission EnergyDepending on the coolant used and the operational stateOne or more of the following three modes of heat transfer may come into play:ConductionConvectionRadiation4Reactor Thermal Hydraulics Heat is generated in the fuel rods due to nuclear fission Heat is transported from the fuel by the circulating primary coolantThe mechanisms include:Forced convection Natural convection Heat is transferred from the primary coolant to the secondary coolant in the steam generator However, in boiling water reactors: High pressure steam is generated in the reactor itself Low pressure steam may be generated in a steam generator (dual cycle)Even after the reactor is shutdown, decay heat continues to be generated (at a reduced level) owing to the decay of fission products It is removed by the primary coolant system/shutdown cooling system 5Reactor Thermal HydraulicsThe interaction between (and also the effects of) a number of factors need to be taken into account while deciding the design limitsThese factors include the following:Neutronics Metallurgy Fuel rod characteristics Core geometry Water chemistry Instrumentation and control Power removal capability, operability, maintainability, reliability and safety are also important factors

6General Framework of Analysis Neutron kinetics Reactor power and heat generation Fuel conduction Radial, except for transients such as rewettingFuel and clad temperature Thermal hydraulicsConservation and constitutive equations; state equation/property tables Pressure, flow rate, void fraction, density and fluid temperature7Fig. 1.1: Nuclear Reactor: Sectional View

8Fig. 1.2: Pressurized Water Reactor (PWR): Schematic

9

Fig. 1.3: Pressurized Water Reactor: Pressure Vessel and Internals10Fig. 1.4: Boiling Water Reactor (BWR): Schematic

11

STEAM DRYER ASSEMBLYSTEAM SEPARATOR ASSEMBLYFEEDWATER INLETFEEDWATER SPARGERCORE SRAY LINETOP GUIDECORE SHROUDCONTROL BLADECORE PLATERECIRCULATIONWATER OUTLET

SHIELD WALLCONTROL ROD DRIVE HYDRAULIC LINESIN-CORE FLUX MONITORCONTROL ROD DRIVESVESSEL SUPPORT SKIRTCONTROL ROD GUIDE TUBEFUEL ASSEBLIESJET PUMP/RECIRCULATION WATER INLETJET PUMP ASSEMBLYCORE SPRAY SPARGERLOW-PRESSURE COOLANT INJECTION INLETSTEAM DRYER LIFTING LUGVENT AND HEAD SPRAYSTEAM OUTLETCORE SPRAY INLETFig. 1.5: Boiling Water Reactor Details12Fig. 1.6: Simplified Schematic of a Fast Breeder Reactor

13

Fig. 1.7: Schematic of a PHWR (CANDU Reactor)LegendFuel bundle Calandria (reactor core) Adjuster rods Heavy water pressuriser Steam generator Light water pump Heavy water pump Fueling machines Heavy water moderator Pressure tube Steam going to steam turbine Cold water returning from turbine Containment building made of reinforced concrete 14Fig. 1.8: Primary Heat Transport System (PHTS) of a 220 MWe PHWR Storage TankSteam GeneratorPCP-1PCP-2PCP-3PCP-4North BankSouth BankReactor coreRIHRIHROHROHFeed ValveBleed ValveInstrumented Relief ValvesPrimary Pressurising PumpReflux Valve15Fig. 1.9: Simplified Schematic of Primary Coolant and Moderator Systems of PHWR

16Fig. 1.10: Primary Heat Transport System of a 500 MWe PHWR Storage TankPrimary Pressurising PumpReflux ValveSteam Bleed ValvesBleed Condenser Steam GeneratorFeed ValvePrimary Cir. PumpROHROHRIHRIH Pressuriser17

Fig. 1.11: Perspective View of Steam Generators and PHT System (One Bank)LegendCalandria End shield End fittings Feeders Reactor inlet header Reactor outlet header Primary heat transport pumpSteam generatorSteam outlet18Fig. 1.12: PHWR Calandria

19