Simulation of flow redistribution in 7 × 7 ballooned fuel bundle experiments using DRACCAR code

Abstract

IRSN has developed DRACCAR code in order to model loss of coolant accidents (LOCA) in a light water nuclear reactor. The physics during a hypothetical loss of coolant accident involves several phenomena such as heat and mass transfers, fluid dynamics, mechanics, and chemistry. Even if a simulation requires modeling these conjugated processes, it is important to validate them separately first—for example, fluid dynamics calculations of the flow redistribution after the clad ballooning that can occur during a LOCA. In this paper, we present DRACCAR simulations of the fluid dynamics in two 7 × 7 ballooned bundles with different blockage, two ballooned lengths and with two different flow rates, one laminar and the other turbulent. DRACCAR results for the axial velocities are compared to experimental data obtained by MRI techniques on the MASCARA facility. The present results show that, in most of the sub-channels studied, DRACCAR is capable of predicting correctly the velocity profiles for both bundles and flow rates. In general, DRACCAR provided fairly accurate estimates of the axial velocity, especially for the intact and less-blocked sub-channels. For the most blocked subchannel, DRACCAR is able to estimate the majority of the axial velocity in a margin of ±15% with respect to the MASCARA values, except for the most blocked bundle at laminar flow where only 20% of the calculated velocities were found within this margin.