Numerical evaluation of sloshing effects in ELSY innovative nuclear reactor pressure vessels seismic response

Abstract

Paper presented at the 6th International Conference on Heat Transfer, Fluid Mechanics and Thermodynamics, South Africa, 30 June - 2 July, 2008.In Europe a great effort has been made in the Lead-Bismuth Eutectic (LBE) technology, for use in the sub-critical reactors, and its natural development is represented by the use of pure lead that is less corrosive, chemically inert and in the foreseen environment has good neutronic and thermal-hydraulic characteristics, therefore it appears to be a suitable coolant for a fast reactor. The main purpose of this study deals with the evaluation of the sloshing dynamic effects of lead coolant during a safety shut down earthquake applied to a conceptual Lead-cooled Fast Reactor (LFR) Generation IV (GEN IV) Nuclear Power Plant design, with reference to the ELSY project system configuration that is under development within the ongoing European 7FW ELSY Program. ELSY is an innovative small size pool-type reactor (600 MWe) cooled by pure lead, characterized by a compact and simple integrated primary circuit; by the way this configuration is favourable from the point of view of the reduction of the seismic loads and of the negative effect of the high lead density. Therefore, the fluid-structure interaction problems and the free oscillations of the heavy metal primary coolant attracted the attention because during a strong motion earthquake the lead surrounding the internals may be accelerated and the so-called hydrodynamic interaction, due to the coolant sloshing, may significantly influence the stress level in the reactor pressure vessel (RPV). To the purpose, the effect of the rigidity of adjacent internals walls and coupling between coolant and vessel are considered An adequate numerical modelling, by means a 3-D finite element model, was set up and used for the foreseen structures dynamic analysis, due to the inability of linear theory to describe accurately the wave’s motion accounting for the complex considered RPV geometrical aspect as well as the material nonlinearities. Numerical results are presented and discussed highlighting the importance of the fluid-structure interaction effects in terms of stress intensity as well as the capacity of internals and vessel walls to withstand wave’s impact and prevent instabilities.