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Conference Article: Structural integrity evaluation of a helically-coiled He/He intermediate heat exchanger

Okubo, M.; Hada, K.; Baba, O. (Japan Atomic Energy Research Inst., Naka, Ibaraki (Japan). HTTR Designing Lab.)

Abstract

This paper presents structural integrity evaluation results for the heat transfer tubes, central hot gas duct, and hot header of the intermediate heat exchanger (IHX) of the High-Temperature Engineering Test Reactor (HTTR) under design in JAERI. Thermal transients and boundary conditions for the evaluation were defined through plant dynamic analyses. On the basis of the evaluation results, requirements for a high-temperature metallic material for the HTTR are discussed. It is revealed in this paper that origins of the thermal stresses are different among the structures. As for the heat transfer tubes, the thermal expansion stress is dominant, and the thermal stress due to temperature gradient across the wall is not so high. Of the central hot gas duct, the reducer (tapered pipe) is the most critical part. The thermal binding stress due to temperature gradient along the reducer is dominant. In the hot header, the highest thermal stress occurs at the boundary area separating the manifold (perforated pipe) and the rim. For these high-temperature structures, elastically-calculated stresses and strains cannot satisfy the design limits because no relaxations of thermal stresses are assumed. Therefore, an inelastic (elastic+creep without plasticity)-calculation-based evaluation is required. This paper presents the inelastic-calculation-based evaluation results for the above-mentioned high-temperature structures. Finally, requirements for the heat-resistant alloy are discussed on the basis of the evaluation results. Since environmental effects on material properties become remarkable at high temperatures, such material properties data have been accumulated in test environments of both air and HTTR coolant-simulated helium gas, so-called JAERI-B He gas, by JAERI and other organizations.

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key words: Gas Cooled Reactor, Nuclear Technology
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:41-48