Materials forVery-High-Temperature Reactor

Bill Corwin, DirectorBill Corwin, DirectorNational Gen IV Materials Technology ProgramNational Gen IV Materials Technology Program

Oak Ridge National LaboratoryOak Ridge National Laboratory

Presented atPresented atCEA, CEA, SaclaySaclay

SaclaySaclay, France, FranceMay 28, 2003May 28, 2003

Advanced Materials Development andQualification Essential for All Gen IV Reactors

• Process-Heat Use for Large-ScaleHydrogen Generation Will Also RequireMaterials Compatibility with Heat-Transfer Media and Reactants

• Research Will Build upon ExtensivePrevious Materials Development forOther Reactor Systems

• Materials Will Be Exposed to HighTemperatures, Neutron Exposures, andCorrosive Environments

• 60-Year Operating Lives for Gen IVReactors Will Require Very Long-TermMaterials Stability

Preliminary Survey of Materials Needsfor VHTR Demonstration Plant Performed

Assumed Characteristics•He coolant•1000°C outlettemperature

•600 Mth

•Prismatic graphite blockcore based

•SiC-coated TRISO fuel•Direct cycle electricalproduction

•Process heat forhydrogen generation

Similar survey plannedfor pebble bed version

•Boundary Conditions•Deploy VHTR in 2015 - 2018•Very quick survey schedulerequired expert opinion

•Materials for hydrogengeneration plant notincluded

PreliminaryMaterials Survey

Used GT-MHRas Baseline

Cutaway DrawingShowing ReactorVessel and Power

ConversionArrangement

Reactor Pressure Vessel System CanLikely Use Code-Approved Material

• 9Cr-1Mo steel most likely near-term candidate material

• Extensive industrial fabricationand high-temperature serviceexperience

• Requires additional very long-term creep and creep-rupturedata

• High-temperature designmethodology needs updatingfor nuclear service

PCV

Crossvessel

RPV

Very Large Vessel Sizes Will RequireScale-up of Fabrication Methods

PWR ABWR GT-MHRPCV & RPV

• Nuclear service will also require:– Irradiation effects testing

– Emissivity verification

– Very high-temperature

fatigue and crack-growth

testing in helium

• Forging and joining of very large rings

• Transportation

• On-site welding, PWHT, and NDE

Previous Nuclear-GradeGraphites Are Unavailable

• Extensive properties and modelsdeveloped for H-451 for FSV, butprecursors no longer exist

• Data needs to be updated formodern, available grades

• Molded and extruded fine-grained, isotropic graphitesavailable for core and supportapplications

– Used in Japanese HTTR,Chinese HTR-10, and SouthAfrican PBMR

– Samples currently beingirradiated could acceleratequalification

Graphite FuelElement Blocks

Irradiation Data Needed to Validateand Benchmark Existing Behavior

• Graphite data needs include:– Physical, mechanical, and oxidation properties– Variability within and among billets– 200°C higher temperatures

• Qualification will build upon very large bases of data andexperience

• Possible to incrementally adjust existing design models• Must complete and approve ASME Sec III, Div 2,

Subsection CE, Design Requirements for Core andSupport Structures, issued for comment in 1990

Internal Reactor Metallic Components Will Be Significantly Challenged in VHTRs• Alloy 800H sufficient for most

GT-MHR needs, highertemperatures for VHTR willrequire higher temp matls

– Advanced metallic alloys• Hastalloy X or Alloy 617

– Carbon-Carbon Composites

• High-temperature metallicshave extensive design databases but cannot handle off-normal conditions, up to1200°C

• C-C composites maturetechnology but needarchitectures tailored to eachcomponent

ReserveShutdown

System

Core Barrel

Lower Core Supports

Control Rod Drive Guides

Hot Duct

C-C Composites Needed for HigherTemperature Internals in VHTRS

• Control rods, upper corerestraints, interior insulationcovers and supports

• Radiation effects data anddesign models must bedeveloped for C-Ccomposites

– VHTR will need to extend to200°C higher than current data

C-C compositemicrostructure

Fiber bundles

Very High-Temperature InsulationWill Be Required for Pressure

Boundaries and Turbomachinary• Fibrous Mats Supported by

Cover Structures

• In contact with hottest gas inreactor system

• Kaowool with Alloy 800Hcontainers adequate for lowertemperature GCRs

• VHTRs will need new coverstructure materials andcharacterization of ceramicinsulation

– Physical, mechanical,corrosion, and irradiationproperties

ContainerCover

Joint

Ceramic FiberInsulation

InsulatedStructure

Gap

1000°C Input Temperatures in VHTRsWill Strongly Challenge IHX Materials

• Varied materials compatibilityneeds (e.g. He, N2, molten salt, etc.)

• Containment within pressurevessel may minimize stress levels

– Secondary gas circuit for PCU

– Molten salts for gas generationmay operate at much lowerpressure

• Very high-temperature alloysrequired

– Hastelloy X or Alloy 617– Mechanical and corrosion

properties needed– Fabrication and joining

technology critical

Pump

Blower

IHX

REACTOR

H2

GEN

or

PCU

Heatric® Microchannel Printed-Circuit-TypeTechnology One Possible Approach for IHX

• Very compact and efficientindustrial design with currentASME Section VIII approval

• Already demonstrated– to 900°C– large units– > 1000 psi

• Fabrication technology for veryhigh-temperature alloys must bedemonstrated

– Diffusion bonding

• Assurance of primary circuitintegrity requires validated NDE orpressure testing

Structure of“Printed Circuit”Heat ExchangerAlternate Designs

Must Be Evaluated

Materials for Power Conversion SystemsLess Challenged than Fossil Plants

• Inlet turbine shroud, turbine diskand blades, and recuperator mostcritical components

• Nickel-based alloys (617) orC-C composites can be used forinlet shroud

– Properties at 950-1000°C needed

• Existing turbine blade and diskmaterials may work for VHTR butwill require property verification orcoating development

• Stainless steels likely okay for VTHRrecuperator for but scale-up of thin-sheet fabrication technologyrequired

VHTR Materials Needs Addressed by BothCrosscutting and Reactor-Specific Gen IV Tasks

• Crosscutting Materials Tasks–Materials for radiation service–Materials for high-temperature service–Microstructural analysis and modeling–High-temperature design methodology

• Reactor-Specific Materials Tasks–Graphite–Materials compatibility

• Reactor coolants• Hydrogen production

Collaboration with RelatedDomestic and ForeignPrograms Is Essential

Gen IV Materials Needs Are CurrentlyBeing Evaluated and Plans Developed

• Initial Focus Will Be on Commercial or Near-Commercial Materials for VHTR Applications

• Longer Term Focus Will Be on MoreAdvanced Materials for Other Reactor Needs

• Initial Study of Materials Needs for PrismaticVHTR Completed

• Similar Studies for Pebble-Bed VHTR, GFR,SCWR, and LFR Beginning

• Results Will Form Basis for Detailed ProgramPlan to Be Completed by Late Summer ‘03

• Experimental Work to Begin This Year, Basedon Overall Program Priorities