Three-dimensional methodology to predict reversed flow in primary side of U-tube steam generator

Abstract

Reversed flow in u-tube steam generator (SG) can result in the reduction of normal flow area and the increase of total pressure drop of SG primary side. The primary coolant flow rate will be lowered when reversed flow takes place, especially under the condition of natural circulation. In the past, the reversed flow phenomena have been observed, while most of the available publications were carried out based on one-dimensional system code or over-simplified single tube model, and very limited work has been done with 3D models. The overall 3D characteristics of flow distribution in the steam generator have not fully revealed. In this work, a fully 3D CFD model combining the porous media and open media were built to study the reversed flow in u-tube SG. The critical mass flow rate for reversed flow was obtained, so does the fraction and location of reversed flow with mass flow rate. The location of reversed flow shifts from short to long tubes at first and then shifts back to short tube with reducing the total mass flow rate.