The flow and heat transfer in the rod bundle channel in the natural circulation system for heaving and rolling conditions

Abstract

Floating nuclear power plants are continually exposed to sea waves, which leads to rolling and heaving movement of the fuel assembly in the nuclear reactor. The majority of heat transfer experiments were carried out at low pressure, which is far from the operating pressure of nuclear power plants. Moreover, the effects of heaving on thermal hydraulics characteristics were barely experimentally investigated. The impact of heaving and rolling on the mass flux, flow resistance, rod wall temperatures and heat transfer coefficients (HTCs) of single-phase flow in a 3 × 3 rod bundle in a natural circulation loop are acquired experimentally in this research. The experimental findings suggest that the mass flux variation plot is very close to a sinusoidal curve pattern during heaving process. Rolling amplitude has a large effect on the average mass flux and fluctuation amplitudes of mass flux. In the cases where the rolling amplitude reaches a rather large angle, the average mass flux throughout rolling operation descends. The transient wall temperatures and HTCs did not change much during the heaving process, while the fluctuations of HTCs and rod wall temperatures are more drastic in rolling process. As the rolling amplitude reaches 30°, it can be clearly observed that the average HTC throughout the entire rolling operation exceeds the steady state HTC before rolling. The fluctuation of Re in the heaving process is not the main factor of the HTC fluctuation. Instead, the key factor contributing to the HTC fluctuation is the crossflow within the sub-channels.