Development of choking models for computer thermohydraulic codes

The results of experimental investigation of choking in vertical tubes with diameter 20, 30, and 40 mm and 19-rod assembly with pressure 0.6–4.1 MPa in the absence of directed circulation of the coolant and with water level above the section under study are presented. Previously determined correlations for determining the counterflow of the phases during choking for a wide range of pressure and diameter of the sections are refined. The results of calculations, performed with the KORSAR and RELAP5/MOD3.2, of choking in experimental sections are presented. Comparative analysis has revealed discrepancies between the computations and the experimental data. It is concluded on the basis of the results obtained that the models of choking for the tested codes need additional work with a correction of relations for the flow rate of the phases. It is recommended that this be done using the correlations obtained in the course of the present experimental study.