Mathieu Guingo

Dispersed Two-Phase Flow Modelling for Nuclear Safety in the NEPTUNE_CFD Code

The objective of this paper is to give an overview of the capabilities of Eulerian bifluid approach to meet the needs of studies for nuclear safety regarding hydrogen risk, boiling crisis, and pipes and valves maintenance. The Eulerian bifluid approach has been implemented in a CFD code named NEPTUNE_CFD. NEPTUNE_CFD is a three-dimensional multifluid code developed especially for nuclear reactor applications by EDF, CEA, AREVA, and IRSN. The first set of models is dedicated to wall vapor condensation and spray modelling. Moreover, boiling crisis remains a major limiting phenomenon for the analysis of operation and safety of both nuclear reactors and conventional thermal power systems. The paper aims at presenting the generalization of the previous DNB model and its validation against 1500 validation cases. The modelling and the numerical simulation of cavitation phenomena are of relevant interest in many industrial applications, especially regarding pipes and valves maintenance where cavitating flows are responsible for harmful acoustics effects. In the last section, models are validated against experimental data of pressure profiles and void fraction visualisations obtained downstream of an orifice with the EPOCA facility (EDF R&D). Finally, a multifield approach is presented as an efficient tool to run all models together.

Presentation of the Multi-Phase CFD Solver NEPTUNE_CFD

The NEPTUNE project constitutes the thermal-hydraulic part of the long-term EDF-CEA-AREVA-IRSN joint research and development program for the next generation of nuclear reactor simulation tools. The project aims at developing high modeling capabilities for advanced two-phase flow thermal-hydraulics covering the whole range of modeling scales. The CFD scale for flow description is covered with NEPTUNE_CFD code. The multiphase approach, developed in the NEPTUNE_CFD code for nuclear engineering, is based on separate Eulerian transport equations for mass, momentum, energy, and turbulent quantities of the different fluids, which are coupled through inter-phase transfer terms. This model is primarily dedicated to the simulation of multiphase flows containing one continuous fluid always present, which carries dispersed fluids present in the form of bubbles, droplets, particles, whose dimensions are much smaller than the spatial resolution length of the model. The simulation of all range of multiphase flow situation, such as dispersed and liquid/gas stratified (separated) flows, which can be encountered in nuclear PWR circuits and pipes under nominal or incidental conditions, remain challenging cases for multiphase volume averaged flow models. The paper deals with a short presentation of NEPTUNE_CFD model, dedicated to incompressible, weakly compressible, unsteady, and turbulent 3D two-phase flow computations. Some modeling strategies will be detailed through the examples of two validations of semi-integral cases.