Chapter 59
Future Code Needs for Very High Temperature Generation IV Reactors


Chapter 59, authored by William J. O'Donnell and Donald S. Griffin, describes the structural integrity issues in Section II, VIII, III, and Subsection NH (Class 1 Components in Elevated Temperature Service), and Code Cases that must be covered to support the licensing of High Temperature Generation IV Reactors. It also describes how the Code addresses these issues, and the need for additional criteria to cover unresolved structural issues for very high temperature reactors.

Since the 1980s, the ASME Code has made numerous improvements in elevated temperature structural integrity design criteria. These advances have been incorporated into Subsection NH of Section III of the Code. The current need for designs for very high temperature and for GEN IV systems requires the extension of operating temperature from about 1400°F (760°C) to about 1742°F (950°F) where creep effects limit structural integrity, safe allowable operating conditions, and design life.

Materials with more creep and corrosion resistance are needed for these higher operating temperatures. Material models are required for cyclic design analyses. Allowable strains, creep fatigue and creep rupture interaction evaluation methods are needed to provide assurance of structural integrity for very high temperature applications. These criteria intended to prevent through-wall cracking and leaking.

The detailed material properties needed for cyclic finite element creep design analyses are generally not provided in the Code. Chapter 59 describes the material models, design criteria and analysis methods which NRC has indicated are remaining needs in the ASME Code to cover Regulatory Issues for Very High Temperature Service:

1. Material cyclic creep behavior, creep-rupture, creep-fatigue interaction and environmental effects.

2. The structural integrity of welds.

3. The development of extended simplified analysis methods (to avoid dependence on “black box” finite element analyses (FEA) for cyclic creep).

4. Test verification of 1, 2 and 3.

  • Abstract
  • 59.1 Background
  • 59.2 Summary
  • 59.3 Structural Integrity Evaluation Approach
  • 59.4 Structural Integrity Evaluation Methods
  • 59.5 Regulatory Issues
  • 59.6 Current Regulatory Issues for Structural Design of VHTR and Gen IV Systems
  • 59.7 How Structural Integrity Issues are Addressed by Current ASME Code? Including Code Cases and Section IIII, Subsection NH, “Class 1 Components in Elevated Temperature Service”
  • 59.8 Material Models Design Criteria and Analysis Methods Needed in the ASME Code for Very High-Temperature Service
  • 59.9 Acknowledgement
  • 59.10 References

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