Modelling of a converging/diverging tube using CATHARE-3 two-phase flow system code for sodium cavitation studies

Abstract

For reactor design and safety purposes, the French Alternative Energies and Atomic Energy Commission (CEA) is currently working on Sodium Fast Reactor (SFR) thermal-hydraulics. A SFR is a system composed of three circuits (primary and secondary: liquid sodium and tertiary: nitrogen gas or water) and designed to both produce electricity and optimize nuclear fuel cycle. In such SFR systems, primary pumps are associated as a parallel circuit. Then, throughout primary pump seizure transients, cavitation may occur in non-affected pumps because of the induced hydraulic resistance drop. Studying sodium flow cavitation occurring in simple geometries such as a Venturi tube (converging/diverging tube) is the first step to better understand the phenomenon and its sensitivities. The long term aim is to validate the flashing model used for sodium applications in the CATHARE-3 code in order to be confident when simulating more complex geometries. In this article, a Venturi tube test section experimented in the CANADER facility at CEA Cadarache in the 1980s and its modelling are presented. Cavitation is obtained by flow rate variation at fixed tank pressure and circuit temperature conditions. Several computations are made in order to study the sensitivity of results to numerical and physical parameters. A set of parameters supposed to constitute the most representative case is defined and comparison of the predicted Thoma number against the experimental one is made. Detailed results of quantities of interest as profiles along the test section and evolutions during the transient are also presented.