Assessment of Post-CHF Heat Transfer Models for the SPACE Code

The SPACE (Safety and Performance Analysis Code) which is based on a multi-dimensional two-fluid, three-field model is under development for a licensing purpose of pressurized water reactors in Korea. A total of 12 wall-to-fluid heat transfer modes were defined and a heat transfer mode selection logic was developed according to the noncondensable gas quality, the void fraction, the degree of subcooling and the wall temperature. Among the constitutive equations of the SPACE code, post-CHF heat transfer models are considered to have the most significant uncertainties because their physical phenomena are not fully understood yet. Though a variety of models and correlations for the post-CHF heat transfer are available, there is no reliable model to reproduce the heat transfer rate as realistically as possible. Several post-CHF heat transfer models are implemented into the SPACE code; critical heat, transition and film boiling models. The present paper describes the model assessment progress which was done for the transition and film boiling models of the SPACE code. A heat flux partition into the continuous liquid, entrained droplet and vapor fields should be taken into account in order to be in line with physical phenomena as the SPACE code has three-field equations in its hydraulic solver. Existing energy partitioning methods were peer-reviewed in order to determine the best model which can be applicable to the SPACE code. The present work will help to consolidate the developed wall-to-fluid heat transfer package of the SPACE code.