Study theoretically on two-phase circulation flow characteristics under ERVC condition in advanced PWR

• The cubic equation based on one-dimensional homogeneous flow model was constructed and solved.
• Differentiation method was utilized to calculate the void fraction along the heating portion of ERVC system.
• The three empirical formulae were used respectively to calculate the velocity of circulation flow rate.
• The solutions are close to the experimental and simulation data respectively.
• Effects of configuration and thermal-hydraulic parameters were investigated.

For the problem of two-phase natural circulation flow in gap clearance between reactor vessel lower head and insulator in the condition of severe accident, one-dimensional steady-state natural flow analysis code was written by utilizing FORTRAN. Based on the code, the effects of different correlations for friction coefficient and the number of nodes of heating section on mass flow rate of two-phase natural circulation flow were studied. And the results are compared with that of Chinese REPEC experiment and simulation using RELAP5 program so as to verify the rationality and correctness of the code. Based on the experiment data, simulation results and the model, friction coefficient and the void fraction condition under ERVC correlation are obtained by fitting. The results calculated by the model using fitting friction coefficient correlation agree well with ULPU V test data. Furthermore, the effect of power, pressure, inlet area, gap diameter, flooding level and inlet water subcooling on mass flow rate and void fraction of two-phase natural circulation were studied utilizing this code.