Dynamic inelastic structural response associated with large sodium-water reactions in LMFBR heat transport systems

Models are developed for the dynamic plastic response of the shell structures within the heat transfert system and also the dynamic plastic response of the relief system rupture discs. These two problems require completely different mathematical formulations for efficient solution. A comparison between the two methods is included as well as their relationship to the comprehensive analysis system being developed for treating the entire sodium/water reaction event. For the shell problems, the method chosen is based on endochronic theory of viscoplasticity. The formulation treats essentially arbitrary material property descriptions, includes strainrate dependence, but not requires the definition of a yield surface. A method-of-characteristics solution of the governing equations was used. Determination of the dynamic response of rupture discs differs in that it is essentially a small strain, large displacement phenomena. This has been modeled through the use of a convected coordinate finite element method. Results obtained illustrate dynamic plastic wave propagation in a steam generator shell and final deformations resulting from typical pressure pulses generated by large sodium/water reactions. For similar pressure loadings, the early dynamic behavior of typical secondary system rupture discs is illustrated in a series of parametric studies. Since both methods are capable of treating certain special problems not involving large displacements, a sample problem of this type is included. The relationship of these predictions of structure response to the on-going development of the comprehensive sodium/water reaction code SWAAM-I are discussed