Presentation on theme: "Material Selection For Long Term Application used in Heat Exchangers in High Temperature Reactors Catherine Bartholomae MANE6980 - Engineering Project."— Presentation transcript:
Material Selection For Long Term Application used in Heat Exchangers in High Temperature Reactors Catherine Bartholomae MANE Engineering Project Advisor: Sudhangshu Bose 9/30/10
Abstract Very High-Temperature Reactors (VHTR) are being designed to provide new energy options for the future. The heat exchanger sees temperatures around 1000 o C. Material selection is one of the main challenges in the new concept because of : Creep Behavior Fatigue Properties Environmental Resistance Important factors besides just material properties: It is also important to consider fabricability and component behavior: Workability Weldability Non-destructive Testing And more..
Introduction This project will focus on the heat exchanger of the VHTR and materials being researched for its high temperature application as well as other requirements such as being environmentally resistant to the highly corrosive coolant that passes through it. Helium serves as a primary coolant and can contain traces of reactive impurities such as hydrogen, methane, carbon monoxide and water vapor.
Problem Description and Expected Outcomes To perform a critical review of literature regarding materials expected to be used in the VHTR heat exchanger. The expected outcome for the project is to gather a detailed analysis of materials found and compile them into one technical paper including recommendations for use in industry.
Current Design Currently in use are Generation II and Generation III Reactors. Generation III reactors are upgrades or improvements to Generation II designs that have evolved over time. In this figure: 1. Charge Tubes 2. Control Rods 3. Graphite Moderator 4. Fuel Assemblies 5. Concrete pressure vessel and radiation shielding 6. Gas circulator 7. Water 8. Water Circulator 9. Heat Exchanger 10. Steam Advanced Gas-Cooled Reactor
Current Design Continued The AGR, which uses graphite as a neutron moderator and carbon dioxide as its coolant, was developed from the Magnox Reactor mainly comprised of Magnesium. Outlet temperature was designed at 648 o C. Figure shows differences in temperatures.
Proposed Design The concept for the VHTR is a graphite- moderated core with a once through uranium fuel cycle. It is expected to have outlet temperatures of ~1000 o C.
Proposed Design Continued This is one of 6 proposed designs for the Generation IV reactors and is unique because of its capability for hydrogen production as well as energy. High outlet temperature and helium coolant change material requirements from current design.
Requirements for Proposed System Melting Point -Material must withstand high temperatures; at least greater than 1000 o C outlet temperature. Creep Resistance -High creep strength is required in this environment. Material properties become weak in the high temperature and failure becomes more likely. Environmental Resistance- Impurities in the helium can cause high levels of corrosion. Any cracking or pitting resulting from fatigue will only increase oxidation or carburization.
Materials Investigated Materials that have been researched for Generation IV reactors include: Nickel Based Alloys Specifically Inconel 617,Hastelloy X, and Incoloy 800H Ceramic Materials Specifically Silicon Carbide/Silicon Nitride Ceramics
Suggested Material Inconel 617 It is widely read that Alloy 617 exhibits high levels of creep strength at high temperatures It has already been approved for applications with temperatures up to 982 o C by ASME VIII- Div.1 Annealing becomes in issue if system is started up or shut down. Inconel 617 shows a good combination of thermal conductivity and thermal expansion at 1000 o C.
Suggested Material Continued… As expected maximum allowable stresses decrease with temperature which is expected of a materials mechanical properties.
Suggested Material Continued… Inconel Corrosion Resistance: As discussed corrosion is mainly caused by impurities in the coolant, helium. It has been tested at 950oC, Inconel 617 forms an Al 2 O 3 layer which prevents carburization and internal oxidation.
Suggested Material Continued… Hastelloy X: Similar to Inconel 617 this alloy exhibits high creep strength, exceptional strength, and oxidation resistance. Typical applications now are in jet engine tailpipes or other aircraft components. It has been proven to maintain it’s properties well for elongated periods of time at high temperatures.
Suggested Material Continued… Creep curves in helium environment show similar and lower strain rates to that of Inconel 617 and at much smaller time intervals.
Suggested Material Continued… Corrosion Resistance: Research states that corrosion also affects the ductility and creep rupture life of the material. Surface Corrosion on all 3 alloys after 500 hrs.
Suggested Material Continued… Incoloy 800H High creep strength as well however not as susceptible to the high temperatures Inconel 617 can sustain. Incoloy Well characterized and readily available and also in consideration for other proposed reactor designs at lower design temperatures. Similar to other alloys including Hastelloy X, Incoloy 800 was altered to Incoloy 800H to provide higher creep strength
Suggested Material Continued… Compared to other alloys it has the lowest rupture strength.
Suggested Material Continued… Environmental Resistance: At 850oC this alloy form carbides and oxides due to reaction with the coolant. Internal oxidation of Al 2 O 3 is formed about 40 m below the surface.
Suggested Material Continued… Ceramic Matrix Composites (CMC) These composites have been evaluated for use in high temperature applications due to their strength, resistance to high temperatures, and light weight. Most common for high temperature use would be Silicon Carbide (SiC) or Silicon Nitride (SiN) Creep Rates: In composites creep occurs by deformation of the grains themselves.
Suggested Material Continued… Here we see tensile creep behavior of 3 SiC composites and one SiN composite. Hexaloy (SiC) has highes creep resistance and can be used in materials up to 1500 o C. SiN Material has second highest creep resistance and can be used in materials up to 1390 o C.
Suggested Material Continued… CMC-When exposed to oxidizing gasses will corrode as shown. CMC Coatings are being researched and have been successful.
Recommendations These materials are currently being studied for use in high temperature nuclear application. Through research I have seen that once a researcher recognizes a component of a material that may cause increase creep rupture strength or higher corrosion resistance they are then able to alter the alloy’s composition to increase or decrease a specific element. It is my recommendation that this continue to occur and that these elements become stronger and even surpass the requirements for the harsh environment of a VHTR. Incoloy 800-Incolloy 800H Hastelloy X- Hastelloy XR- Hastelloy XR2
Recommendations Similar to the coatings that were produced for CMC materials I recommend further research into possible coatings for nickel-based allows that will increase corrosion resistance.
Summary Nickel-Based Alloys are the most researched material for this application so far. Based on the knowledge from the research done I’d recommend Inconel 617 as a material to be used in these high temperature nuclear reactors however further research should be done to enhance the alloy to make it stronger.
Milestones Submit Draft Proposal 9/23/10 Submit Proposal and Brief Presentation 9/30/10 Begin research and obtain 12 technical papers 9/30/10 Attend The Cole Library in Hartford 10/7/10 Based on prior research continue research of papers found in Hartford 10/14/10 Submit 1st Progress Report 10/21/10 Compile all pros and cons thus far for each technical paper 10/28/10 Begin writing final report and continue research 11/4/10 Submit 2nd Progress Report and Presentation 11/24/10 Continue writing report between 11/24/10 and 12/2/10 Submit Final Draft 12/2/10 Finalize paper between 12/2/10 and 12/16/10 Submit Final Report and Presentation 12/16/10
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