Verification of subcooled void fraction calculations for one-dimensional mechanistic models

Full text of publication follows: Modeling and calculation for two-phase subcooled boiling flows is important for the accurate prediction of void fraction distributions in the reactor's core, and it is necessary for carrying out of various analyses, first of all, for the lost of coolant accidents. The most advanced published models - mechanistic models for subcooled boiling - were developed and tested for normal regimes of power nuclear reactors, that is, at high pressures and moderate (several m/sec) coolant velocities. New projects of power nuclear installations (including those with natural circulation) and also problems in analysis of accidental situations, associated with coolant loss, demand a more strict and complete accounting for phases' heat and dynamic non-homogeneity influences. Therefore, remains actual their verification and comparison with the new models in vast region of regime conditions, including coolant's low pressures and velocities causing highest level of processes non-homogeneity. A considerable potential to accomplish physical- mathematical models of the considered processes has author's quasi-one-dimensional approach, which makes it possible by one-dimensional notions for two- dimensional non-homogeneous processes to parametrically allow for the effects of phases nonhomogeneous distributions. The present paper is dealing with a comparison and verification of the author's quasi-one-dimensional model for calculating thermal-hydraulic characteristics of subcooled boiling flow with the best known methods by Y.S. Molochnikov et al. and R.T. Lahey methods realized in a number of domestic and foreign codes. Models by Y.S. Molochnikov et al. and R.T. Lahey differ from the proposed by the author quasi-one-dimensional description in interpreting vapor generation and condensation as the two separate processes. That is why, calculated with them void fractions turn out to be more subject to the model assumptions and 'fitting' coefficients than in the case of quasi-one-dimensional method. Comparison of void fractions values calculated with the considered models showed that, with the accordance of the statistical evaluations, the proposed quasi-one- dimensional model proves to be more precise in case of low pressures and coolant's mass velocity. (author)