Numerical prediction of dryout in a 19 rod bundle under the effect of eccentricity and blockage

Abstract

An accurate estimation of dryout power and its location (zcr) is central to the safety of nuclear reactors. In the present study, a sub-channel analysis code is developed by extending the standard single phase DIANA algorithm to two phase flow conditions. The mass, momentum and energy conservation equations are solved, using a mixture model, which is validated against available experimental data. Numerical simulations are performed to determine the dryout location for a circular 19 rod bundle, in conjunction with a film thickness model. In critical sub-channels, a sudden jump in wall temperature was noticed at the dryout location. The effect of eccentricity(e) on the dryout location was investigated in the range of 0.0⩽e⩽0.7, under different operating conditions. It was observed that, eccentricity causes flow maldistribution in different sub-channels, and in turn affects the dryout location. For low inlet mass fluxes, sub-channels which never experienced dryout (for e=0.0) were found to experience dryout (for e>0.0) The effect of blockage (b) was also systematically studied for 0.0⩽b⩽0.3. In flow regimes with higher vapor quality, the blockage leads to a disturbance in the continuous liquid film, resulting in an early occurrence of dryout. Two types of axial power distribution (APD) viz uniform and sinusoidal heat flux imposition were numerically simulated. The latter was found to delay the occurrence of dryout, compared to the former.