Session: 07-07: Experiments and Analyses - VI

Paper Number: 135743

135743 - Experimental Study on the Operational Stability of Passive Residual Heat Removal System 

Abstract: 

       Passive safety systems are now widely used in advanced Generation III nuclear power plants (NPPs) due to its characteristic that they do not rely on external power sources, which allows the system to simplify. Consequently, passive safety systems have become a key technical indicator of third-generation nuclear power technology. The passive residual heat removal system is a crucial component of the passive safety system. It can remove heat from the reactor core under accident conditions, playing a vital role in ensuring the safe operation of NPPs. This paper presents an experimental study on the passive residual heat removal system, investigating the flow regime of natural circulation within the system and the heat transfer characteristics in the residual heat exchanger.

      The experimental system was designed based on the scaling analysis on the passive heat removal system of a certain ocean nuclear power plant. The experimental setup primarily comprises a heat exchanger, a visualized horizontal residual heat removal pipe, an electric oil heater, a return water pipeline, a cooling water tank, a data acquisition system, thermocouples, and associated components. In the prototype, residual heat from the coolant in the reactor is naturally expelled into the ocean through the circulation of seawater. In the experimental arrangement, the ocean is represented by a water tank, while seawater, coolant, and the reactor core are simulated by water, heat-conducting oil, and an electric oil heater, respectively.

      The study initially focused on the visual study of flow patterns in the heat exchanger and the horizontal visualized pipe. Three flow patterns were identified in the residual heat exchanger: single-phase flow, subcooled boiling, and saturated boiling. Within the passive residual heat removal pipe, single-phase flow, bubbly flow, slug flow, and condensation-induced water hammer were observed. Based on the results, a flow regime map under different operating conditions was constructed.

       Additionally, experiments were conducted to study the heat transfer characteristics in the residual heat exchanger. It was observed that due to subcooling water reflux and phase change, the obtained water-side heat absorption power was slightly lower than the heat transfer power of the residual heat, while the difference falls within a reasonable range. Analysis of the theoretical and actual overall heat transfer coefficients revealed that subcooling water temperature and the resistance coefficient in the return pipe had a minor impact on the overall heat transfer coefficient. The overall heat transfer coefficient increased with an increase in the residual heat inlet temperature and heat power. These findings provide valuable insights for optimizing nuclear power plant performance and enhancing our understanding of passive safety systems.

KEYWORDS: Passive residual heat removal system; Equal-height-difference natural circulation system; Flow regime transition; Heat transfer characteristics; Visualization experiment.

Presenting Author: Quanbin Zhao Xi'an Jiaotong University

Presenting Author Biography: Ph.D., Assistant Researcher, Department of Thermal Power and Control Engineering in Xi'an Jiaotong University

Authors:

Quanbin Zhao Xi'an Jiaotong University
Huchen Han Xi'an Jiaotong University