湿空气在全尺寸压水堆燃料组件中的自然循环特性试验及理论研究

Experimental and theoretical study on the natural circulation characteristics of humid air in the fuel assembly of a full-scale pressurized water reactor

为开发一种不依赖于计算流体力学(Computational Fluid Dynamics,CFD)结果的燃料组件自然循环特性分析模型,以研究乏燃料水池在发生冷却剂丧失事故后的自然循环特性,本研究基于全尺寸压水堆燃料组件压降实验结果对Darcy-Forchheimer模型进行了修正,以预测湿空气流过燃料组件的压降,然后建立了燃料组件自然循环流量和峰值包壳温度的分析预测模型,并考虑了空气的相对湿度对模型计算结果的影响。结果表明:该模型可较为准确地预测不同加热功率下燃料组件的自然循环流量和峰值包壳温度,与实验测量值相比误差分别在25%和20%以内。并利用该模型研究了总加热功率、环境温度和相对湿度对燃料组件自然循环流量和峰值包壳温度的影响。因此,本研究所开发的模型可用于压水堆全尺寸燃料组件的自然循环特性研究。

[Background]Natural circulation systems are widely used in the nuclear industry for decay heat removal,post-accident containment cooling,and the cooling of radioactive waste storage facilities.Because a large number of spent fuel assemblies are densely arranged in the spent fuel pool,the spent fuel assemblies in the central area of the spent fuel pool can be approximated as having adiabatic boundary conditions.In the event of a coolant loss accident,the heat generated by the spent fuel assemblies can be exported only by the natural circulation of air.[Purpose]This study aims to develop analytical models for fuel assembly natural circulation characteristics independent of the results of computational fluid dynamics(CFD)to investigate the natural circulation characteristics of spent fuel pools following a coolant loss accident.[Methods]Based on the experimental results of a fuel assembly pressure drop of a full-scale pressurized water reactor(PWR),the Darcy–Forchheimer model was firstly revised to predict the pressure drop of humid air flowing through the fuel assembly.Models for the fuel assembly natural circulation flow rate and peak cladding temperature were then established,and the effects of the relative humidity of air on the models were considered.Finally,these models were applied to investigating effects of total heating power,ambient temperature,and relative humidity on the natural circulation flow rate and peak cladding temperature of the fuel assembly.[Results]The results show that the models accurately predict the natural circulation flow rate and peak cladding temperature of the fuel assembly under different heating powers,and the errors are less than 25%and 20%,respectively,as compared with the experimental measurement values.[Conclusions]The developed models in this study can be used to study the natural circulation characteristics of full-scale PWR fuel assemblies.