A two-phase pressure drop calculation code based on a new method with a correction factor obtained from an assessment of existing correlations

Although the average exit enthalpy of a current generation PWR core under normal operation does not exceed the saturation value, bulk boiling can occur in a hot channel. Moreover, in the event of a reactor transients, such as a small or a large break LOCA, bulk boiling can occur throughout the core. For both steady and transient conditions it is necessary to predict the pressure loss as accurately as possible for a two-phase mixture since pressure drop not only influences flow distribution and pumping power requirements but also the hot channel is limiting from DNB considerations. Various approaches for two-phase flow pressure drop predictions have been proposed during the past two decades. Idsinger et al. compared a large number of existing correlations against data for conditions representing transient as well as steady-state BWR operation, and showed that the correlations which had the least RMS error overall for the normal BWR operation conditions is the Armand-Treschev Correlation. Also, they reported that the correlations which have shown the best overall performance were, homogeneous theory, the Thorn correlation, and the Baroczy correlation. The purpose of this paper is first, to present the results of an assessment of existing correlations for their applicability to PWR conditions; and secondly, to present the outlines of a computer code entitled K-TWOPD for two-phase pressure drop calculation