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Conference Article: Material variability in elastic assessment

Riou, B.; Sperandio, M. (NOVATOME, FRAMATOME, Lyon (France)); Guinovart, J. (European Commission, Bruxelles (Belgium))

Abstract

The structures of Fast Reactors (FRs) are subjected to high temperatures and their design is checked mainly against elastic rules. The aim of this paper is to study the influence of uncertainties in material properties on creep-fatigue assessment according to the elastic route of the RCC-MR code, so as to evaluate the subsequent margins. This work has been conducted by FRAMATOME, in cooperation with GEC, NNC and SIEMENS, in the frame of the activities of the Working Group on Codes and standards of DG XI/C (Nuclear Safety of Installations). The material considered is the 316L(N) austenitic stainless steel (RCC-MR 1S type material). The work is divided into two phases: the first one consists of the identification of the scatterband of material properties used in the elastic creep-fatigue assessment route of the RCC-MR code and the second of the study of the influence of the scatter on the results of elastic calculations and creep-fatigue assessment, with the aim to evaluate the difference in lifetime as a function of the set of material properties used and the relative importance of each material property. The latter will be based on one example of application typical of FRs structure. The example chosen consists of a plate to shell junction subjected to a thermal transient. Calculations are carried out using design material properties, mean material properties and properties leading to minimum and maximum life duration. Results of creep-fatigue analyses with material properties leading to minimum life duration are shown to be similar to those with design material properties, giving results of the same order to magnitude. Results with mean material properties and properties leading to maximum life duration exhibit significant margins compared to design analyses. Sensitivity analyses carried out on the basis of the maximum and minimum material property values show that properties which are the most significant for creep-fatigue assessment are the Sr curves, the Ks factor, the creep law as well as the cyclic curves. The influence of the fatigue curves was not significant in the benchmark considered.

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key words: Fast Neutron Spectrum Systems, Nuclear Technology
Reference:
Creep-fatigue damage rules for advanced fast reactor design. Technical committee meeting, Manchester (United Kingdom). 11-13 Jun 1996
International Atomic Energy Agency, Vienna (Austria)
IAEA-TECDOC--933, pp:13-29