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#4 Structural Materials Performance and Mechanical Integrity under the Effects of Radiation and Thermo-mechanical Loadings in Blankets and PFCs 1 S. Sharafat.

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Presentation on theme: "#4 Structural Materials Performance and Mechanical Integrity under the Effects of Radiation and Thermo-mechanical Loadings in Blankets and PFCs 1 S. Sharafat."— Presentation transcript:

1 #4 Structural Materials Performance and Mechanical Integrity under the Effects of Radiation and Thermo-mechanical Loadings in Blankets and PFCs 1 S. Sharafat – FNST Aug 2009 - UCLA

2 The Grand Thermo-mechanical Challenges In Developing Fusion Test Reactor Structures  The mechanical loads in combination with high temperatures and intense neutron and particle radiation fields and chemically reactive environments could lead to severe degradation of performance sustaining properties, internal damage, macroscopic cracking, corrosion-erosion and inherent dimensional instabilities due to irradiation creep and possibly swelling of Fusion Structural Materials.  The unprecedented demands on fusion structures derive from severe time varying thermal-mechanical loading of complex, large scale and highly interconnected heat transfer-energy conversion structures.  Non-irradiation environments typically require 10–20 years for development of incrementally improved structural materials.  Neither the materials, nor the requisite computational tools, nor the underlying knowledge base is currently sufficient for reliable integrity and lifetime assessments of fusion reactor structures. 2 S. Sharafat – FNST Aug 2009 - UCLA

3 Radiation Damage Based Challenges In Developing Fusion Test Reactor Structures  Radiation tolerant structures including the synergistic effects of radiation damage and nuclear transmutants are required: 3 Workshop on Science Applications of a Triple Beam Capability for Advanced Nuclear Energy Materials, Cochairs Michael and Wayne E. King (LLNL), April 2009 Major Radiation Damage Phenomena Synergistic Effect Example S. Sharafat – FNST Aug 2009 - UCLA

4 Thermal-mechanical Challenges for Fusion Test Reactor Structures 4  Accumulation of radiation damage due to atomic damage is minimal at high temperatures, with the exception of irradiation creep.  Stress driven  Stress driven growth and coalescence of cavities due to formation of helium bubbles at grain boundaries at high temperature can severely degrade creep rupture properties (impact of field gradients).  Even without radiation damage the challenges of developing a FW structure are unprecedented, particularly because of interaction of various synergistically interacting phenomena:  High-cycle fatigue and fracture growth due to flow induced vibrations  Low-cycle thermal mechanical fatigue resulting in cyclic softening  Irradiation creep and possible radiation damage induced dimensional strains and stress redistribution  Thermal creep, creep rupture, creep-fatigue interactions and crack growth  Microstructural instabilities and softening due to thermal aging S. Sharafat – FNST Aug 2009 - UCLA

5 Objectives and Required R&D 5  OBJECTIVES: (1) Establish the feasibility of designing, constructing and operating a fusion energy system with materials and components that can survive the fusion environment and meet safety, environment and performance criteria. (2) Meet the enormous challenge of developing material systems and multifunctional structures for predictably operating reliable, safe, and long-lived first wall, blanket and divertor structures.  REQUIRED R&D: Develop underlying knowledge base and computational tools for reliable integrity and lifetime assessments of fusion reactor structures, which include: o Revolutionary experimental methods to understand the interplay between high performance demands and eroding in-service property limits o Synergistic effects of radiation damage, transmutation products, and thermo- mechanical loading in structures (including associated gradients) o Establish Essential Databases: Properties for Engineering Design Materials Production, Component Fabrication, and Joining Reactor Assembly and Integration Technology S. Sharafat – FNST Aug 2009 - UCLA

6 6 MATERIALS SCIENCE AND ENGINEERING CONCEPT DEVELOPMENT CONCEPT DEVELOPMENT DESIGN OF SUBSYSTEMS & INTEGRATION INTO POWER PLANT COMPONENT & SUBSYSTEM MANUFACTURE TEST REACTOR CONSTRUCTION OPERATION Material Properties & Fundamental Interactions Performance Goals/Requirements Properties for Engineering Design Materials Production, Fabrication& Joining Assembly & Integration Technology Specifications of Operating Conditions/Limits (e.g. corrosion) (after D.T. Hoelzer) Radiation Resistant Materials Material Systems and Multifunctional Structures Radiation Resistant Materials alone can no longer address the larger challenge of Material Systems and Multifunctional Structures Material Technology or Component Technolgy S. Sharafat – FNST Aug 2009 - UCLA

7 #6 Fabrication and Joining of Structural and Functional Materials 7 S. Sharafat – FNST Aug 2009 - UCLA

8 Fabrication and Joining Issues 8  Multifunctional fusion structures are very complex and involve the use of many different materials, including structural alloys, ceramics and composites, breeding and neutron multiplying media, coolants, and thermal-electrical insulators, which need to be fabricated and assembled or joined into components, such as divertors or blankets.  Fabrication of complex fusion reactor structures and components is an enormous challenge in that performance and reliability criteria of fusion components are unprecedented. Divertor vertical target qualification prototype (EU). Holtkamp,2009 EU Helium Cooled Pebble Bed (HCPB) TBM Concept  There are 2 primary weld/joint concerns: 1.Structural integrity (will the weld withstand thermo-mechanical and chemical loads) 2.Leakage of coolant (probability of leakage is ~10 times higher than weld failure) (1) Weld Integrity: Welds, joints, or coated materials need to withstand the hostile fusion environment (temperatures, radiation fluxes, transmutation products, field gradients, etc.) as well as, if not better than the base structural materials: If the weld or joint fails it does not matter how well the base materials perform. (2) Leakage: Even if the weld holds thermo-mechanically, if it leaks as little as a pin hole, the entire TBM module might have to be removed and/or even replaced S. Sharafat – FNST Aug 2009 - UCLA

9 Major Joining Challenges  WELDS AND JOINTS: The microstructure at/or near welds, bond joints, and coatings almost always differs from base material (  different properties).  Invariably fabrication and joining alters the microstructure of the nearby host material, which is subject to the same harsh fusion environment as the base material  BOND COATS: –Low-Z (Be) or high-Z (W) armor on FW/Divertor require joining/coating of multilayered components. –Beryllium is chemically active and forms stable, strong and brittle intermetallic compounds, which reduce the mechanical performance (ductility and toughness):  relatively low bonding strength.  Preventing de-bonding of similar and dissimilar metal joints made of different materials such as Ferritic Steel and W or Be may be difficult due to large coefficient of thermal expansion mismatches and the formation of brittle interlayer phases; also a challenge: Austenitic/Ferritic steel pipe weld.  ADDITIONAL FUSION ENVIRONMENT CHALLENGE: Accumulation of He/H in bonded joint interfaces, along with significant time-dependent stresses, inelastic strains and displacements, spatially dependent thermal expansions, thermal and irradiation creep, and potential swelling (Be) are but a few of the scientific and technical challenges that must be overcome for reliable functioning of multilayered and simply bonded fusion components (& coolant chemistry: corrosion subcritical cracking). 9 Eurofer Weld Microstructure SEM image and EDX line profiles at a X-sectional surface of Be and FMS bond. Lee, FED2009 S. Sharafat – FNST Aug 2009 - UCLA

10 Objectives and R&D 10  OBJECTIVES: The First Wall (FW) of the US DCLL TBM (2009) alone has tens of meters of Diffusion Bond. In addition internal rib structures, top and bottom caps, manifolds, and back plates have to be joined using a variety of welding techniques, such as EB and LW. A FW Beryllium coating would add a total bond coat area of over 0.8 m 2. The structural integrity as well as the leak-tightness of the welds and bonds plays a very significant role in the reliability of fusion components. Lack of any knowledge of the synergistic effects of irradiation damage, He and H accumulation, and coolant chemistry (He and PbLi) on welds, joints, and bond coats requires a significant uptick in scientific and technical efforts to develop fully functioning joining techniques.  Required Key Bonding R&D: 1.Assessment of PWHT* on HAZ* of TIG* for Eurofer97 and/or F82H; 2.Creep performance of HAZ before and after PWHT; 3.Effect of irradiation on PWHT of weld materials (HAZ, TIG, or EB welds); 4.Impact of pulsed operation resulting in high temperature irradiation followed by relatively long periods of cold non-neutron environments; 5.Potential radiation induced segregation and/of phase instabilities in HIP joints, 6.Knowledgebase of multi-layered (Be-steel, W-FMS) bonding strengths. 7.Impact of synergistic effects of irradiation damage, He/H production, and coolants. 8.Detailed characterization of joint properties has not been done systematically but will be necessary for code qualification and licensing. *PWHT: Post Weld Heat Treatment; HAZ: Heat Affected Zone; TIG: Tungsten Inert Gas S. Sharafat – FNST Aug 2009 - UCLA


12 Radiation Damage Challenges In Developing Fusion Power Reactor Structures  Radiation induced microstructural evolutions, which are controlled by the combination of many variables and synergistic interactions between displacement-induced defects and transmutation products (He & H), are a major source of property degradation, internal damage, and failure. Five major radiation damage phenomena: 12 1. Radiation hardening & embrittlement: 0.1 dpa 2. Phase instabilities from radiation-induced precipitation: 10 dpa 3. Irradiation creep: 10 dpa 4. Volumetric swelling from void formation: 10 dpa 5. High temperature Helium-embrittlement: >0.5 T M ; > 10 dpa after S. Zinkle (2005) S. Sharafat – FNST Aug 2009 - UCLA

13 13 Radiation Damage Challenges In Developing Fusion Test Reactor Structures S. Sharafat – FNST Aug 2009 - UCLA

14 Challenges for Development of Fusion Test Reactor Structures 14  A 500 – 700 m 2 First Wall (FW) removes about 10% of fusion power experiencing high thermal loading from a combination of charged particle and radiation fluxes at ~ 0.5 to 1 MW/m 2 PLUS volumetric heating.  FW is a few mm thick  Reliability of very large, thermally loaded, pressurized (~8 MPa He) thin wall structures, erosion due to sputtering and an ability to survive disruption induced large and rapid thermal and structural load transients are the major mechanical challenges.  Temperature window for TMS is primarily dictated by embrittlement and loss of ductility below 350 o C and thermal creep strength above ~500 o C, however effects of high He & H levels may shrink TMS temperature window in both high and low temperature regimes (due to degradation of fracture toughness).  Heat flux of the FW comparable to fast reactor fuel cladding, but geometry is much more complex, plus pressurized coolants (8 MPa He) result in combination of thermal and primary stresses.  Stresses also arise from thermal expansions and gradients that occur over large distances of meters in 3-D (several cm displacement in an unconstrained FW).  Stresses in FW are time dependent due to irradiation and thermal creep during quasi steady state operation. Stresses and dimensional instabilities may also arise from density decreases due to helium bubble and void swelling, or slight density increases due to precipitation.  Neutron flux varies spatially  corresponding irradiation creep strain and stress relaxation also varies with position in the fusion structures. S. Sharafat – FNST Aug 2009 - UCLA


16 Fabrication and Joining R&D 16  Bonding and welding has been identified as a key fabrication and assembly issue for TBM.  Joining R&D falls into two categories (1) manufacturing of structures (FW), and (2) welding/bonding to form component (TBM). Japan and the EU are developing both, structure fabrication techniques, based on HIPing and Diffusion Welding, and various welding techniques, including TIG*, EB (Electron Beam), and LW (Laser Welding).  Eurofer97 bonds have been irradiated up to 2.5 dpa @ 300°C in Sodium, and F82H bonds up to 2.5 & 10 dpa @ 275°C in He. Below 300 o C all welds experience shift in DBTT saturating around 2 dpa. Post Weld Heat Treatment (PWHT) can lower DBTT shift of welds. Mutliple PWHT of Eurofer97 TIG weld produced the best DBTT results  HIPed Bonds: The shift in DBTT of HIPed Eurofer97 is similar to that of Eurofer97 base material (base material  DBTT ~100 o C at 2.5 dpa; ~150 C at 8 dpa irradiated at 300 o C).  EB Welds: Eurofer97 EB welds show shifts in DBTT of about 70 o C – 120 o C for PWHT welds (2.6 dpa at 300 o C). F82H EB welds exposed to 2.2 dpa at 275 o C (no PHWT) show a shift in DBTT of ~250 o C. F82H EB weld results are inconclusive (no PHWT) and can not be compared with the Eurofer97 EB welds.  TIG Welds: Eurofer97 TIG shows a shift in DBTT from about -25 oC to about +100 o C (2.6 dpa at 300 o C). TIG welded F82H show an increase DBTT from about -75 o C to about +50 o C (2.28 dpa and 8.94 dpa irradiated at 300 o C). *TIG: Tungsten Inert Gas welding is an arc welding process S. Sharafat – FNST Aug 2009 - UCLA

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