The Broyden method applied for the analysis of two-phase flow in a BWR fuel bundle based on the drift-flux model

Abstract

Boiling flows in a BWR rod bundle is studied using the Drift Flux Model solved by the Broyden method. Four constitutive equations in the drift flux model plus auxiliary lateral momentum equations are discretized via the mesh staggered finite volume method. Then, the Broyden method is invoked for solving the resulted nonlinear system of equations. Accurate forms and fast techniques are employed for the solution of equations, especially for vapor generation, drift velocity, exchanges mass, energy and momentum among sub-channels. It was found that the Broyden method used in this study can be much faster in comparison with the Newton method solved through either the inverse Jacobian matrix or the LU factorization of Jacobian matrix. As a major objective, the change in the outlet void fraction is investigated as a function of inlet mass flux, inlet subcooling, and wall heat flux. Important changes e.g. outlet mass flux vs. inlet mass flux and void fraction are analyzed in different sub-channel positions. In comparison, the approach adopted in this article shows better compatibility with the experimental data than other similar works. Results are in generally good agreement with the outcome of F-COBRA-TF code, too, with partial superiority in a number of sub-channels. Also, it is shown that the accurate solution of constitutive equations especially for void drift and turbulent mixing terms that transfers mass, energy and momentum between sub-channels are major contributors to the aforementioned superiority.