Recent Improvements of Physical Models in the CATHARE Code and Their Validation

CATHARE is a system code developed by CEA, EDF, FRAMATOME-ANP and IRSN for Pressurized Water Reactor (PWR) safety analysis. Two-phase Flows are described using a Two-Fluid Six-equation model (1 D module) and the presence of non-condensable gases can be taken into account by one to four additive transport equations. The code allows a three-dimensional modelling of the Pressure Vessel (3D module). Successive sets of closure laws are developed in an iterative methodology of improvement. The main recent developments are presented and discussed. Film condensation of steam in presence of nitrogen and helium in a tube has been investigated in the COTURNE experiment. The liquid film heat transfer coefficient is first investigated in pure saturated steam for the wavy laminar film regime. In presence of non-condensable gases, the mass diffusion of steam in the gas mixture is modelled using a Sherwood number and a heat and mass transfer analogy. The code shows good agreement with the COTURNE tests and with other experimental data of Siddique & al and Nagasaka & al. The CATHARE capability to well represent the entrainment of liquid from the upper plenum to the steam generator inlet chamber is validated using MHYRESA experimental data. A new stratified interfacial friction based on experimental data analysis leads to satisfactory CATHARE predictions compared to MHYRESA and UPTF-TRAM data. The CATHARE 3D module capability to well calculate the refilling phase of the lower plenum considering the multi-dimensional effects is validated using UPTF tests. Two types of tests are considered to separate mechanical and condensation effects. Considering a specific entrainment rate and condensation rate for such an annular downcomer, CATHARE predictions are in good agreement with the experimental results. The BETHSY test 9.1b (ISP27) consists of 2-inch cold leg break with an ultimate procedure actuated on a cladding temperature criterion. The comparison between the calculation and the experimental data shows a rather good agreement.