THE EFFECT OF RISER CONDENSATION ON THE TWO-PHASE FLOW STABILITY

摘要

A one-dimensional analytical model has been developed tornbe used for the frequency domain linear analysis of density-wavernoscillations in CAREM-25 nuclear reactor prototype.rnThe natural circulation loop is divided into a single-phasernand a two-phase region. The two-phase region is representedrnby the drift-flux model. The model accounts for aphasic sliprnand subcooled boiling. The exact equation for the total looprnpressure drop is perturbed around the steady state. Thernstability characteristics of the loop are investigated using thernroot finding method. The marginal stability boundary (MSB)rnis determined in the two-dimensional thermodynamicrnequilibrium space parameters, the subcooled boiling numberrnand the phase change number ,plane. The flow instabilityrnregions are appeared at low and high core power. In the lowrnheat flux range, the trends of the thermal equilibrium - equalrnvelocity (homogeneous) model and the thermal nonrnequilibrium - non equal velocity model are the same becausernthe steam quality is small. In the high heat flux range, (a)rnfrom high subcooled boiling number to reaching a criticalrnvalue, the steam quality calculation of the first model isrngreater and has the effect of stabilizing the system more thanrnthe second one, (b) from the critical value to low subcooledrnboiling number, the two-phase region length calculation ofrnthe first model is smaller and has the effect of stabilizing thernsystem less than the second one. As the inlet restriction andrnthe riser condensation are increased, the model predicts a more stable system, the stable region is broadened at allrnpower ranges. As the exit restriction is decreased and thernsystem pressure is increased, the model predicts a morernstable system, the stable region is shifted to the right.