Lecture 1 : CANDU Reactor Design

MAAE 4903 AReactor Thermal Hydraulic FundamentalsLecture 1 : CANDU Reactor DesignExtracts from : “The Essential CANDU, A Textbook on the CANDU Nuclear PowerPlant Technology”, Editor-in-Chief Wm. J. Garland, Chapters 6 & 7, UniversityNetwork of Excellence in Nuclear Engineering (UNENE), ISBN 0-9730040.Textbook retrieved from: www.nuceng.ca/canduvinh.tang@carleton.caOffice: ME2186Vinh Q. Tang, Ph.D., P.EngAdjunct Recearch ProfessorCarleton UniversityDepartment of Mechanical and Aerospace EngineeringWinter 20181

Course Contents Part 1: Thermal Hydraulic Design (Chapter 6 oftextbook) Part 2: Thermal Hydraulic Analysis Part 3: Safety RegulationsWinter 20182

Part 1: Thermal Hydraulic Design(Chapter 6 of textbook)Contents CANDU Reactor Design (Lecture 1)Thermal Hydraulic Design RequirementsThermal Hydraulic Design Limits and MarginsThermal Hydraulic Design FundamentalsHeat Transfer and Fluid Flow DesignWinter 20183

CANDU Reactor Design (Lecture 1)Contents(Section numbers are kept as in the textbook)Chapter 62. Reactor Types2.1 CANDU reactor design (Lecture 1)2.1.1 Reactor core and calandria vessel2.1.2 Primary heat transport system design2.1.3 Steam generators2.1.4 Pressurizer. (next slide)Winter 20184

2.1.5 Primary pumps2.1.6 Primary heat transport piping2.1.7 Secondary heat transport system design2.1.8 Turbine2.1.9 Condenser2.1.10 Heat exchangers and pumps2.2 ProblemsWinter 20185

Introduction In this section some generic background willbe presented (that do not follow thematerial in the referenced textbook) After the introduction we will follow thesections in Chapter 6 more closely.Winter 20186

Figure 1 Heat engine conceptsWinter 20187

The heat source in a reactor is the energygenerated from the fission process taken placewithin the uranium fuel The energy deposited in the fuel is transferredto the reactor coolant by conduction,convection and radiationWinter 20188

Stored energy in the coolant is then usedto produce steam to drive the turbine(. for the purpose of generatingelectricity, for example)Winter 20189

PWR Video from YoutubeImage from CNSC websiteHeat Source(see next slide)Heat SinkWinter 201810

Heat SourceFigure obtained from CNSC websiteWinter 201811

56From CNSC websiteWinter 201812

2. Reactor Types(Section numbers are kept as in the textbook) Pressurized Water Reactors Boiling Water Reactors Gas-cooled Reactors– Magnox Reactors– Advanced Gas-cooled Reactor (AGR)– High Temperature Gas Cooled Reactor (HTGCR) Channel-type Reactors– Steam Generating Heavy Water Reactor (SGHWR)– CANDU Reactor– RBMK reactor (the acronym is for High Power Channel TypeReactor in Russian) Fast Breeder ReactorsWinter 201813

Pressurized water reactors (1)Winter 201814

Pressurized water reactors (2)PWR primary coolant loop cross sectionWinter 201815

Pressurized water reactors (3)(typical data)ReactorFuelThermal output: 3800 MWthFuel pellet material :UO2Electrical output: 1300 MWePellet outer diameter:8.19 mmThermal efficiency:Rod outer diameter:9.5 mm34 %Specific power: 33 kW/kg(U)Power density :102 kW/LAve. linear heat flux: 17.5 kW/mZircaloy cladding thickness: 0.57 mmRods per bundle (17 x 17): 264Bundles in core:Winter 201819316

Pressurized water reactors (4)(typical data)VesselOuter diameter: 4.4 mHeight:13.6 mWall thickness:0.22 mCoreLength:4.17 mOuter diameter:3.37 mPressure:15.5 MPaInlet temperature: 292 COutlet temperature : 329 CMass flow rate:531 kg/sWinter 201817

Pressurized water reactors (5)(typical data)Steam GeneratorNo.Outlet pressure:Outlet temperature:Mass flow rate:46.9 MPa284 ⁰C528 kg/sWinter 201818

Boiling water reactors (1)Winter 201819

Boiling water reactors (2)Typical BWR reactorcoolant circulationWintervessel201820

2.1 CANDU Reactors Design Nuclear Power Demonstration (NPD) CANDU designDouglas PointPickering A and BBruce A and BCANDU 6DarlingtonAnd others:––––Advanced CANDU designsCANDU 3, CANDU 9, and ACR-700ACR-1000Enhanced CANDU 6Winter 201821

Figure 2 : Typical CANDU plantWinter 201822

Figure 3 CANDU 6 reactor cooling loopsWinter 201823

2.1.1 Reactor core and calandria vesselFigure 4a) : Typical CANDU reactor andWinter 2018heat transport system24

Fuel bundle,See next slideFigure 4b) : Typical CANDU fuel channelWinter 201825

Figure 4c) : Typical CANDU fuel bundleWinter 201826

Winter 201827

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2.1.2 Primary heat transport system designRecall that the CANDU heat transport systemconsists of1. Primary loop2. Secondary loop, and3. Tertiary loop(Recall Figure 2)Winter 201829

a) Primary Loopb) Secondary Loopc) Tertiary LoopFigure 56: Reactor cooling systemsWinter 201830

REACTORa) Primary Loop FlowWinter 201831

b) Secondary Loop FlowWinter 201832

c) Tertiary Loop FlowWinter 201833

This section addresses the Primary loop or Primary heat transport system There are several variations of the CANDUheat transport system design. The CANDU 6 heat transport system design isdescribed in the following sections.Winter 201834

The primary heat transport system (PHTS)circulates pressurized D2O coolant throughthe fuel channels to remove the heatproduced by fission in the nuclear fuel. The coolant transports the heat to steamgenerators, where heat energy is transferredto light water to produce steam to drive theturbine.Winter 201835

WinterShutdown2018CANDU 6 Primary andCooling Loops36

PressurizerSGROHPumpRIHSGROHPumpReactor CoreCalandria(Moderator)Fuel channels:- Calandria tubes- Pressure tubes- Fuel bundlesSimple Sketch of Primary Cooling Loop(referred to as Figure-of-Eight)RIH

Major components in PHTSExamples Steam generatorsPressurizerPrimary PumpsPrimary heat transport pipingWinter 201838

Figure 6 : CANDU primary heat transport systemWinter 201839

2.1.3 Steam generators The steam generator has a very important rolein energy transport from the reactor core tothe turbine because it connects the primaryand secondary loops. The CANDU steam generators consist of aninverted U-tube bundle within a cylindricalshell. Heavy water coolant passes through the Utubes.Winter 201840

Figure 7 : Typical steam generator designWinter 201841

The primary coolantmoves through the Utubes from right toleft in the diagram,starting as saturatedwith a certainpercentage of qualityand becoming subcooled as it transfersthe heat to thesecondary side.Winter 201842

The secondary coolant(feedwater) enters subcooled and, as itreceives heat from theprimary side, heats upto saturation.Thereafter, thesecondary coolant boilsoff as it receives moreheat through thesteam generator.Winter 201843

2.1.4 Pressurizer The pressure in the reactor primary coolantsystem is maintained at a controlled level by apressurizer. The pressurizer contains steam in the uppersection of its cylinder and water in the lowersection.(See figure)Winter 201844

Figure 8 : Typical pressurizer designWinter 201845

The pressurizer is connected to theprimary loop through a surge nozzle at thebottom. Heaters are provided at the bottom of thepressurizer internals, and a spray nozzle, relief nozzle, and safetynozzle are installed at the top of thepressurizer head.Winter 201846

A “positive surge” of water from the primaryloop due to increasing loop pressure iscompensated for by injecting cold water fromthe top of the pressurizer to condense steamWinter 201847

A “negative surge” of water empties thepressurizer, reducing steam pressure atthe top of the pressurizer and thus looppressure.In this situation, the electrical heaters atthe bottom of the pressurizer areautomatically activated, converting aportion of the water into steam, resultingin a loop pressure increaseWinter 201848

2.1.5 Primary pumps The primary pumps used in the CANDU heattransport system are vertical, centrifugalmotor-driven pumps with a single suction anda double discharge.Winter 201849

Figure 9 : Typicalprimary pumpdesignWinter 201850

As shown in Figure 9, the pumpimpeller is at the bottom of the pump, and the pump shaft extends upwardto the pump motor, passing through anumber of pump seals and holding thepump flywheel.Winter 201851

In the event of electrical power supplyinterruption, cooling of the reactor fuel ismaintained by– the rotational momentum of the heat transportpumps during reactor power rundown and– by natural convection flow after the pumps havestopped.Winter 201852

2.1.6 Primary heat transport piping The CANDU reactor contains a relatively largenumber of pipes, called feeders, and manifolds, called headers, in the primary heattransport system, which are used to distribute coolant to thefuel channels in the core.Winter 201853

Figure 3a : CANDU 6 reactor cooling loops(HTS & shutdownWintercoolingloops)201854

PrimaryheattransportsystemModeratorcircuitWinter 201855

2.1.7 Secondary heat transportsystem design The nuclear power plant’s (NPP’s) secondaryheat transport system transfers the generatedenergy from the primary closed circuit to thesecondary,– where the heat energy is transformed intomechanical energy of rotation in the turbine andthen into electrical energy by the electricgenerator.Winter 201856

The main components of the secondary heattransport system are–the steam turbine,–condenser,–heat exchangers,–feedwater pumps,–valves and piping;Winter 201857

Secondary heat transport systemWinter 201858

2.1.8 Turbine The CANDU steam turbine is typically atandem compound unit, directly coupled to anelectrical generator by a single shaft. It consists of one double-flow high-pressurecylinder followed by external moistureseparators, five steam reheaters, and threedouble-flow low-pressure cylinders. The turbine is designed to operate withsaturated inlet steamWinter 201859

2.1.9 Condenser The turbine condenser consists of threeseparate shells. Each shell is connected to oneof the three low-pressure turbine exhausts. Steam from the turbine flows into the shell,where it is condensed by flowing over a tubebundle assembly through which cooling wateris pumped.Winter 201860

The condenser cooling water typically consistsof a once-through circuit that uses water froman ocean, lake, or river or is connected tocooling towers. The condensed steam collects in a tank at thebottom of the condenser called the “hotwell”. A vacuum system is provided to remove airand other non-condensable gases from thecondenser shellWinter 201861

2.1.10 Heat exchangers and pumps The condensate from the condenser ispumped through the feedwater heatingsystem before returning to the steamgenerators Typically, it first passes through three lowpressure feedwater heater units.Winter 201862

Next, the feedwater enters a deaerator,where dissolved oxygen is removed. From the deaerator, the feedwater ispumped to the steam generators throughtwo high-pressure feedwater heatersWinter 201863

Problems (Lecture 1)1.1 Name and describe the function of the main componentsof the CANDU primary heat transport system.1.2 Describe the main components of the pressurizer in aCANDU reactor, with a detailed explanation of the methodit uses to control the primary heat transport systempressure.1.3 Provide a description of the steam generator function,with specific reference to its role in the relationshipbetween the primary and secondary heat transportsystems. Discuss the relationship of these systems with theoverall size of a steam generator.Winter 201864

2.1.8 Turbine The CANDU steam turbine is typically a tandem compound unit, directly coupled to an electrical generator by a single shaft. It consists of one double-flow high-pressure cylinder followed by external moisture separators, five steam reheaters, and three double-flow low-pressure cylinders.