Session: 08-03: Computational Fluid Dynamics (CFD) and Applications - III

Paper Number: 134856

134856 - Numerical Analysis of Flow Field and Phase Distribution Characteristics of Subcooled Boiling Flow in the Psbt 5×5 Fuel Bundle Channel 

Abstract: 

Rod-bundle coolant channel is the key component of the primary loop in pressurized water reactor. Its local thermal-hydraulic behavior is associated with safety and economics of nuclear power plants. Due to the complex subchannel geometry as well as the wide range of high temperature and pressure conditions in fuel assemblies, it was very difficult to obtain details of the three-dimensional flow filed and phase parameter distribution in the PWR coolant channels. Recently, with the development of computing power and two-phase flow model, Computational Fluid Dynamics has become one of the most feasible approaches to simulate the subcooled boiling flow phenomenon of the fuel assembly. In this paper, based on Euler-Euler two-fluid model method coupled with the wall heat flux partition model, the flow boiling performance in the PSBT 5×5 fuel bundle with three types of spacer grids was investigated numerically using Star-CCM+ code. The void fraction experiments for PSBT 5×5 full-scale rod bundle with uniformly heated condition have been adopted to validate this CFD model. Predictions of sub-channel averaged void fraction profiles were in a good agreement with the experimental data. Then, void fraction distribution near the fuel rod and transverse velocity field in PSBT 5×5 rod bundle channels were analyzed under three axial heat flux profiles. With the increase of the heating power, void fraction on all the fuel rods surface increase gradually. Especially, a large number of vapor bubbles were observed to occur near the cold rods located at the certain positions. Comparative analysis of the transverse velocity filed downstream from the last mixing vane spacer grid showed that the lateral flow downstream from the mixing vane spacer grid was the main factor that influences phase distribution in the fuel bundle channels. The Swirl flow occurred in central sub-channels promoted vapor bubbles in the vicinity of fuel rod to accumulate in center of sub-channels and induced the liquid to continuously wet the heated wall, which can enhance heat transfer behavior. However, due to the limitation of the flow shroud and the configuration of mixing vane, there was no swirl flow in the center of side and corner sub-channels of PSBT 5×5 rod bundle. Besides, the complex cross flow around fuel rods in the side or corner sub-channels may guide the liquid away from cod rod surfaces, causing a substantial increase of near-wall void fraction as the heating power increased and ultimately heat transfer deterioration. The research rules in this paper provide an excellent support for a deep understanding of the evolution of the phase distribution from the spacer grid in 5×5 rod bundle.

Presenting Author: Hengji Liao Harbin Engineering University

Presenting Author Biography: Mr. Hengji Liao is a Ph.D. candidate at Harbin Engineering University. He works on boiling two-phase flow in complex rod-bundle channels with the mixing spacer grid.

Authors:

Hengji Liao Harbin Engineering University
Xiao Yan Harbin Engineering University
Haifeng Gu Harbin Engineering University
Shengjie Qin Nuclear Power Institute of China