CFD analysis of effects of cross flow on water injection of DVI+

Recently constructed and proposed nuclear power plants have increasingly adopted the direct vessel injection (DVI) type emergency core cooling system (ECCS) instead of the conventional cold leg injection (CLI) type one. For such a design, concern has been raised that the ECC water injected through the DVI nozzle is more easily bypassed out to the broken cold leg by a cross flow of high-speed steam in the downcomer than that of CLI during the reflood phase in the event of a large break loss-of-coolant accident (LBLOCA). Thus, an emergency core barrel duct (ECBD) has been introduced to reduce the ECC bypass in an advanced DVI (DVI+) system for the new APR+ design. The present study numerically investigated the effects of the cross flow on the DVI+ water injection by computational fluid dynamics (CFD) analysis of a simple air-water system with the ECBD. The performance of ECBD, i.e., bypass fraction of the injected water due to the cross flow with variation of Reynolds number of the cross flow was calculated. It was found that the inflow rate into the ECBD is strongly dependent on the cross flow. To consider the effect of the ECBD in a system thermal-hydraulic code calculation, the loss coefficient at the junction of the ECBD inlet was determined as a function of Reynolds number of the cross flow using the CFD results.