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Conference Article: A proposal to develop a high temperature structural design guideline for HTGR components

Abstract

This paper presents some proposals for developing a high-temperature structural design guideline for HTGR structural components. It is appropriate that a basis for developing high-temperature structural design rules is rested on well-established elevated-temperature design guidelines, if the same failure modes are expected for high-temperature components as considered in such design guidelines. As for the applicability of ASME B and PV Code Case N-47 to structural design rules for high-temperature components (service temperatures >= 900 deg. C), the following critical issues on material properties and service life evaluation rules have been pointed out. (i) no work-hardening of stress-strain curves at high temperatures due to dynamic recrystallization. (Ii) issues relating to very significant creep. (Iii) ductility loss after long-term ageing at high temperatures. (Iv) validity of life-fraction rule (Robinson-Taira rule) as creep-fatigue damage evaluation rule. Furthermore, the validity of design margins of elevated-temperature structural design guidelines to high-temperature design rules should be clarified. Solutions and proposals to these issues are presented in this paper. Concerning no work-hardening due to dynamic recrystallization, it is shown that viscous effects cannot be neglected even at high extension rate for tensile tests, and that changes in viscous deformation rates by dynamic recrystallization should be taken into account. The extension rate for tensile tests is proposed to change at high temperatures. The solutions and proposals to the above-mentioned issues lead to the conclusion that the design methodologies of N-47 are basically applicable to the high-temperature structural design guideline for HTGR structural components in service at about 900 deg. C.

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Reference:

High temperature metallic materials for gas-cooled reactors. Proceedings of a specialists meeting held in Cracow, 20-23 June 1988

International Atomic Energy Agency, Vienna (Austria). International Working Group on Gas-Cooled Reactors

IWGGCR--18, pp:27-33