Thermal-hydraulic stability analysis of steam generators

An analytical model was formulated for the analysis of density-wave oscillations in a counter-flow once-through steam generator, which is currently of interest in LMFBR technology. A compugter code, STEAMFREQ-X, was developed for the calculations. This model provides a comprehensive description of the different phenomena that are important to steam generator stability analysis. The secondary loop is modeled by five regions--unheated single-phase region, heated single-phase region, two-phase region, superheat region and adiabatic two-phase or superheat region. Included in the model are separated flow (drift-flux model) in the two-phase region, variable steam properties (from steam table) in superheater, variable heat transfer coefficients and consideration of heat capacity of tube walls. The analysis uses linearized on-dimensional mass, momentum and energy equations for the water (secondary) channel, energy equation for the sodium (primary) channel and the Laplace transformed radial conduction equation for the tube wall. This system of coupled differential equations is solved analytically for the single-phase region and numerically for the two-phase and superheat region. Transfer functions for the pressure drop perturbations are calculated and stability of the system is assessed by using linear control theory. An important feature of this model is the rigorous description in modeling the flux-flow coupling between the primary and secondary sides