Numerical simulation of inherent boric mixing phenomenon inside reactor annular down-comer

Abstract

The inherent boric mixing phenomenon inside the reactor down-comer was numerically investigated by this paper. The boric tracer distribution was compared with the experimental data, and the renormalization group model (RNG) was considered as the most suitable turbulence model. When the boric solution entered the down-comer through the inlet, it dispersed radially in the disk shape and spread along the annulus. As the injection arrived at the position of 120°, the transverse velocity decayed and the vertical velocity increased significantly. Subsequently, the injection tended to fall vertically into the lower space. Two flow stagnant zones were discovered, which were unfavorable for the homogeneous mixing. The down-comer was divided into the first mixture zone, the second mixture zone and the ambient water zone. The mass fraction of the first zone was homogeneously distributed, and the mass fraction gradient of the second zone was quite large. The injection accumulated in the upper space of the down-comer when the inlet Reynolds number was 2272. As the Reynolds number was increased to 13632, the injection entered the lower space by the disk-shaped scattering flow. The flow stagnant area was compressed when the thickness of the down-comer was reduced. According to the coefficient of variation analysis, increasing the inlet Reynolds number and decreasing the down-comer thickness were beneficial to the inherent boric mixing.