2014 Volume 28 Issue 1 Pages 55-61
After termination of natural circulation during hypothetical accidents in light water reactors, vapor generated by decay heat forms two-phase flow in stagnant coolant liquid and rises in a reactor core. In these conditions, void fractions in the reactor core affect the two-phase mixture level and cooling of fuel rods. In this study, numerical simulations were carried out for a 4×4 rod bundle which was a mock-up of the PWR core by using the computational fluid dynamics (CFD) software, FLUENT 6.3.26. Simulated void fractions showed a similar trend to air-water data but were about 0.10 higher than measured void fractions at large air volumetric fluxes. Over-prediction of void fractions might be due to severe flooding at the upper end of the bundle.
