IMPROVEMENT OF RELAP5 MODELS FOR CONDENSATION OF STEAM AND STEAM-GAS MIXTURE IN HORIZONTAL AND INCLINED TUBES

摘要

The presented work is focused on condensation of steam and steam-gas mixture in horizontal and sloped tubes. Presence of noncondensable gas (NCG) in coolant system of pressurized water reactor (PWR and VVER) has number of potential effects on thermal hydraulics (TH) of the system. One of the major effects is deterioration of heat transfer at steam generator, mainly in the condensation regime. After deep analysis of condensation models in RELAP5 computer code, a set of improvements is proposed. Major modifications are usage of Jaster-Kosky correlation for horizontal condensation and extension of application of horizontal condensation to wider range of tube slopes. Both the original and modified versions of code are assessed against data from separate and integral test facilities. Results show improved capability to predict condensation heat transfer and removal of some unphysical behavior in condensation in volumes with small non-zero slope.