1 / 25

NEEP 541 Design of Irradiated Structures

NEEP 541 Design of Irradiated Structures. Fall 2002 Jake Blanchard. Outline. Design of Irradiated Structures ASME Boiler and Pressure Vessel Code Loads Limits Examples. ASME Boiler and Pressure Vessel Code. Designed to enhance safety of pressure vessels

ziv
Télécharger la présentation

NEEP 541 Design of Irradiated Structures

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. NEEP 541Design of Irradiated Structures Fall 2002 Jake Blanchard

  2. Outline • Design of Irradiated Structures • ASME Boiler and Pressure Vessel Code • Loads • Limits • Examples

  3. ASME Boiler and Pressure Vessel Code • Designed to enhance safety of pressure vessels • 1600 explosions of boilers from 1898 to 1903 (killing 1200 people) • Code was adopted in 1915 • It has been continuously revised and enhanced ever since • It does not cover corrosion, erosion, instabilities, etc.

  4. Organization of Code • Power Boilers • Material Specifications • General requirements (Nuclear Components) • Division 1 (Class 1, 2, 3 and Supports) • Division 2 (Concrete Reactor Vessels and Containments) • Heating boilers • Nondestructive examination • Care and Operation of Heating Boilers • Care of Power Boilers • Pressure Vessels • Welding and Brazing • Fiberglass-Reinforced Plastic Pressure Vessels • Inservice Inspection

  5. Component Classification • Purpose: recognizes different levels of importance in relation to safety • Owner is responsible for classification • 10-CFR-50 requires that components of reactor coolant pressure bounday be class 1 • Others defined with respect to consequences of failure

  6. Design Basis • Design conditions • Pressure, temperature, mechanical loads • Service limits • Level A: normal • Level B: highly probable, unplanned, component must withstand damage and continue to operate without service • Level C: low probability, unplanned, must be recoverable, but may require repair • Level D: component may suffer gross deformation

  7. Loading • Bulk heating: Level A • Coolant pressure: level A • Surface flux on cladding or first wall: level A • Seismic loads: level B or C • Transients: level B, C, or D

  8. Types of Stresses

  9. Definitions • Primary Stress=any stress developed by an imposed load which is necessary to satisfy equilibrium of external forces and moments • Not self-limiting • Examples include pressure and dead-weight

  10. Definitions • Secondary Stress=any stress developed by constraint of adjacent material or self-constraint • Self-Limiting • Examples include thermal stresses

  11. Definitions • Peak Stress=an increment of stress over and above the primary and secondary stresses, caused by discontinuities or local thermal stress • No gross deformation • Can be a concern with respect to cracking • Examples include stresses near discontinuities (holes, for instance)

  12. Definitions • Membrane Stress=any stress which is uniform over the thickness of a thin component • Bending Stress=any stress which varies linearly over the thickness of a thin component

  13. Allowable Stresses • The stress limits in the code are based on the yield, ultimate, and creep strengths, with appropriate safety factors • The fundamental limit is that the stress should be less than the minimum of Sm and St

  14. Definitions

  15. Design Stress varies with Service Level

  16. Design Stress varies with Service Level

  17. Why are Primary Stresses Worse? • Consider a perfectly plastic material • Compare failure due to both a constant force loading and a constant strain loading stress YS strain

  18. Comparison • For constant load, a force that causes a stress just beyond the yield stress will cause failure • For constant strain, a strain that causes a strain just beyond the yield strain will still be far from the failure strain • Pressure stresses are analogous to constant load, while thermal strains are analogous to constant strain

  19. Why is Bending More Forgiving in Terms of Allowable Stress? • Consider a beam with an applied moment y M M stress

  20. Bending (continued) • Peak stresses are at edge • When the beam begins to yield, only the edges will yield and the central portion of the beam will still be elastic (and able to support load) • Hence, a beam under pure bending can safely go further beyond the yield point that something experiencing a membrane load • This is only true for ductile materials!

  21. Biaxial Stresses • Everything discussed so far assumes that stresses are uniaxial • Stress is actually a tensor, so it has three normal components and three shear components

  22. Yield Theories • There are two theories for yielding under multiaxial stress states • Maximum Shear (Tresca): yielding occurs when the maximum shear stress reaches a critical value • The maximum shear can be found by taking the difference of the largest and smallest principle stresses (yielding when 1-3=YS)

  23. Yield Theories • Von Mises: yielding occurs when equivalent stress reaches the yield stress

  24. ASME Code Approach • The Code uses stress intensity • Stress intensity= 1-3 • All previous allowable stress limits are valid if stress is replaced by stress intensity

  25. Example

More Related