Analysis of Post-Accident Debris Transport Performance in In-Containment Refueling Water Storage Tank in Nuclear Power Plants

Abstract

To avoid the blockage of strainer in the in-containment refueling water storage tank (IRWST) and guarantee the safe operation of the pump downstream the IRWST after accident occurrence, the debris transport performance in the IRWST must be evaluated carefully. For the double-loop pool-type IRWST of a nuclear power plant (NPP), the Computational Fluid Dynamics (CFD) method is adopted to simulate the flow field of this IRWST, and the volume ratio of the high velocity region and high turbulent kinetic region is used to quantitatively evaluate the debris transport performance of the IRWST. The results indicate that the debris transport ratio of IRWST does not exceed the design value of the strainer under various post-accident conditions, which ensure the safety of the strainer and its connected systems after accident occurrence; the strainer load reaches the maximum value when only the strainer A in the inner loop is put into operation; and the post-accident debris transport performance is mainly affected by the high velocity region in the flow field. As a result, this paper proposes the optimization scheme, namely, increasing the diameter of the mixing pipeline in the outer loop, for the existing IRWST layout. This scheme can reduce greatly the debris transport ratio in the IRWST after accident occurrence and thus improve the post-accident safety of the NPP.