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Communication Dans Un Congrès Année : 2019

A mechanistic flashing model for critical flowrate prediction using CATHARE 3 system code

Résumé

The Code for Analysis of Thermalhydraulics during an Accident of Reactor and safety Evaluation (CATHARE) is designed to perform Pressurized Water Reactor (PWR) safety analysis. This system-scale code includes a one-dimension, two-phase, six-equation model (mass, momentum and energy balance for each phase) used to represent pipe geometries. During a Loss Of Coolant Accident (LOCA), it is essential to accurately estimate the critical mass flow at the break, requiring to model the flashing process. The current CATHARE model used to predict the vaporization rate in case of flashing is based on a semi-empirical correlation. The present study main goal is to test a mechanistic model developed by Berne. In this model, the bubbles grow first at constant number, until a critical breakup diameter is reached. This critical diameter is controlled by turbulence, assuming that breakup is due to turbulent eddies having the same size as bubbles. Then Berne characterizes the interfacial heat exchange with both a convective and a conductive mode. According to Berne, the liquid-to interface heat transfer seems to be mostly convective. The present study revisits this previous works by taking into account both the convective and conductive contribution of liquid to interface heat transfer, also by assessing the flashing correlation on a larger experimental data base, including nozzles such as Super Moby Dick and Bethsy. And, finally, by carrying out a sensitivity study on the most influent parameters of the Berne's model. As a conclusion of this study, the Berne convective models gives similar results for the critical mass flow in comparison with the current semi-empirical model. Moreover assumptions made to build the model are questionable at high void fraction. The sensitivity analysis showed the importance of the bubble diameter for the estimation of the critical mass flow. To go further, it may be interesting to have a better estimation of the interfacial area for improving the model. This could be done by comparing with other models of the literature, for both the initial bubble number density and the turbulent kinetic energy dissipation rate. Furthermore, a sensitivity study on the interfacial friction coefficient should be carried out for saturated inlet tests.

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Dates et versions

cea-04217103 , version 1 (25-09-2023)

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  • HAL Id : cea-04217103 , version 1

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Maxime Vernassiere, Philippe Fillion, Dominique Bestion. A mechanistic flashing model for critical flowrate prediction using CATHARE 3 system code. ICAPP 2019 - 2019 International Congress on Advances in Nuclear Power Plants, May 2019, Juan-les-pins, France. ⟨cea-04217103⟩
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