Pierre Ruyer

Eulerian Simulation of Interacting PWR Sprays Including Droplet Collisions

Abstract A numerical simulation of the interaction between two real pressurized water reactor containment sprays is performed with a new model implemented into the Eulerian computational fluid dynamics (CFD) code NEPTUNE_CFD. The water droplet polydispersion in size has been treated with a sectional approach. The influence of collisions between droplets is taken into account with a statistical approach based on the various outcomes of binary collision. Experiments were performed in a new facility, and data obtained are compared with this two-fluid simulation. The results show good agreement.

Taking Accurate Account of Radiative Heat Transfer for the Simulation of Core Reflooding

Abstract The reflooding of the reactor core during a loss-of-coolant accident (LOCA) in a pressurized water reactor is a rather complex conjugate heat transfer situation. In the mist flow regime downward from the quench front, the rod wall can reach temperatures up to 1400 K, and radiative heat transfer can play a significant role. The present study concerns the accurate numerical computation of radiative heat transfer throughout a subchannel with LOCA representative flow conditions resolved at a computational fluid dynamics–scale spatial discretization thus allowing the large gradients of two-phase-flow properties to be determined. The accuracy of several methods to solve the radiative transfer equations has been compared both in canonical test cases and in low-pressure LOCA conditions. The role of radiative transfer is obvious in all variables including those related to the dynamics of the flow. Analysis of the gap between the present estimation and a standard correlation has been performed. It leads to the conclusion that radiative transfer can be taken into account accurately by correlation as soon as well-defined radiative properties are considered. The transfer is very sensitive to droplet size and concentration and can be as large as the convective heat transfer.

Experimental Investigations on Heat Transfer in Transient Boiling

During reactivity initiated accidents in a core of a nuclear reactor, a power excursion occurs on some fuel rods. The consequent rapid boiling is a matter of study for the nuclear power plants safety evaluation, because of the risk for rod-clad failure. In order to better understand the influence of power excursions and to characterise the phases of the rapid boiling phenomenon, an experimental set-up has been built at the Institut de Mecanique des Fluides de Toulouse (IMFT). The test section is a semi annulus. The inner half cylinder is made of a stainless steel foil, heated by Joule effect. Its temperature is measured by an infrared camera filming the backside of the foil, coupled with a high speed camera for the visualization of the phenomena. Measurements were made when a square current signal is applied to the foil. They showed the influence of the supplied power and of the wall temperature increase rate during boiling.Copyright