Space and temporal evolution of density wave oscillations in multi-phase flow channels of boiling water reactors

Abstract

In this paper, a time dependent model for studying BWR in phase instabilities in the nonlinear regime is developed. This model is based on solving the mass energy and momentum conservation equations, for the single phase region and for both phases in the sub-cooled boiling and the bulk boiling regions. The model has been implemented in a code that also integrates: the recirculation loop dynamics equation; the heat transfer dynamic equations between the fuel and the channel; and the neutron kinetics equations. Special attention has been given in this paper to the sub-cooled boiling region and to the consequences of the degree of sub-cooling on the bubble dynamics. Also the direct heating of the water channel by neutrons and gamma rays has been considered. The result is a code called DYNAMICS that is able to perform in the time domain quantitative analysis of all the processes that affect the reactor stability. Keywords: density wave oscillations, two phase flow channels, in phase oscillations in BWR, sub-cooled boiling.