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Conference Article: Mechanical design of the hot steam headers of the THTR-300 steam generators

Blumer, U. (Sulzer Brothers Ltd., Winterthur (Switzerland)); Stumpf, M. (EVT Stuttgart, Stuttgart (Germany))

Abstract

The high pressure steam headers of the THTR steam generators have been subject to special attention during the design phase due to the following reasons: these components are the pressure retaining parts with the heaviest wall thickness in the region of the steam generators. They therefore are sensitive to thermal transient conditions. They are operated in the elevated temperature regime, where creep effects cannot be neglected. There is almost no service experience from fossil steam generators with this type of material (Alloy 800). Safety consideration therefore have been rather extensive and have focussed on two main areas which will be treated in this paper: 1. Analytical investigations on the cyclic material behaviour under all specified operating conditions, taking into account the non-elastic response of the material. 2. Limitation of the consequences of a header rupture by installation of heavy whip restraints. Elastic-plastic-creep analyses: The analyses were performed in different stages and are explained in the corresponding order: Evaluation of the critical location on the header and establishment of a simplified model of a nozzle region for further analysis. Preliminary thermal analyses of all specified transient conditions on simplified procedures, in order to establish a severity ranking of the conditions. Establishment of representative loading blocks. Evaluation of the material properties for thermal and structural, especially non-elastic behaviour. Detailed thermal analyses. Detailed structural analyses of the non-elastic cyclic response. Extrapolation for all cycles and assessment of the results by design codes. Discussion of the results. Header whip restraint design: In addition to the above analysis efforts, heavy whip restraints were provided to assure limitation of the effects of a header failure. This pager shows the measures that were taken to restrain the movement in case of longitudinal and transverse breaks: The anti-whip designs are presented as well as the analyses that were performed to show their structural adequacy.

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key words: Gas Cooled Reactor, Nuclear Technology
Reference:
Specialists' meeting on technology of steam generators for gas-cooled reactors Winterthur (Switzerland) 9-12 Mar 1987
International Atomic Energy Agency, International Working Group on Gas-Cooled Reactors, Vienna (Austria)
IWGGCR--15, pp:97-106