Non-Linear Impact Analysis for Reverse Flow in CAN DU Reactor Fuel Channels

Abstract

This paper presents the analytical approach, the basic assumptions and the analysis results of a hypothetical reverse flow impact for the CANDU 3 reactor system configuration. Comparisons of the analytical results with the available experimental impact test data are also made. In the past, simple drop tests simulating the reverse flow conditions caused by a hypothetical header or feeder break had been conducted to determine the effects of the subsequent impact on the fuel bundles. Now, a comprehensive and yet simple analytical approach using the finite element analysis method has been developed. The analysis examines the effects of impact along the entire load path, from the bundles through the fuel channel to the reactor. It takes into account elastic-plastic behaviour of the materials, the special design limits of major structural components and the dynamics of the channel, the reactor and the fuelling machine system as well. Damping, gas and Coulomb friction are also included. The analysis model is quite flexible in accommodating the variations between different design concepts and the impact velocity for different scenarios, i.e. normal or refuelling operation. In its simplest form, the model and the results can be analysed to identify the critical components in the load path and to study the effects on the other structures during an impact. The analysis can easily be repeated to provide details of the impact by refining the models of the particular components in question. Buckling failure and the post-buckling behaviour of the components can also be assessed with an expanded model. The analytical approach described in this paper is also applicable to other CANDU reactor system configurations as well.