Comparative analysis of RBMK core channel void fraction determined by RELAP5, KOBRA, and a new drift flux correlation

Simpler algebraic void fraction functions are derived from complicated thermohydraulics codes, such as RELAP5/MOD3, RELAP5/MOD2, and KOBRA. This is a void fraction equation as a function of pressure, vapour volumetric flux, and liquid volumetric flux. It provides a common basis for fruitful comparative analysis of void fraction between complicated code calculations. The comparative analysis also includes the void fraction calculated by a newly developed drift flux correlation and several sets of experimental data. In this paper, good agreement and large deviation are clearly observed for a wide range of thermohydraulic conditions. It is also concluded that simpler drift flux model gives void fraction with accuracy similar to complicated RELAP5/MOD3 code without outstanding numerical problem. A numerical oscillatory problem is encountered in RELAP5/MOD3 calculations. Further investigation is needed to understand the causes of large deviation and numerical oscillation. (orig.)