摇摆条件下棒束通道自然循环核热耦合特性实验研究

Experimental study on natural circulation neutronic-thermo-hydraulic coupling characteristics of rod bundle channel under rolling motion condition

为研究海洋条件下核热耦合对棒束通道自然循环热工参数波动特性的影响,在机械摇摆台上设计并搭建了5×5棒束通道自然循环实验回路。基于单群点堆中子动力学模型,通过实时采集热工参数并计算实时核功率,实现了运动-热工-物理的耦合。对棒束通道单相自然循环核热耦合的瞬态特性进行了实验研究,研究结果显示:在静态工况下,核热耦合使得系统功率发生小幅度波动,当温度反馈系数低于-5×10^(-4)℃^(-1)时,燃料温度反馈对功率的影响比冷却剂温度反馈更大。核热耦合对热工系统的时均参数无显著影响,增大燃料温度反馈系数会降低系统的稳定性。在摇摆运动工况下,摇摆幅度越小或摇摆周期越短,核热耦合引入的功率波动幅度就越小。此外,在摇摆运动启动的瞬态过程中,核热耦合使得系统重新建立稳定自然循环的时间大幅延长。

[Background]The floating nuclear power plant(FNPP)is a vital energy supply method for future ocean exploitation and island construction.The typical fuel type of FNPP is similar to the onshore nuclear power plant,i.e.,the rod bundle fuel assembly.Due to the effect of ocean waves and wind,the FNNP would be in continuous motion.Rolling is one of the most common types of motion.It can induce the periodical change of the inertial force field of the coolant and the change of flow and heat transfer characteristics of the rod bundle channel.Coupling with neutronic and thermohydraulic,as a result,the operation characteristics,safety,and economics of the FNPP can be affected.[Purpose]This study aims to investigate the impact of neutronic-thermo-hydraulic coupling on natural circulation characteristics with the rod bundle channel under rolling motion condition.[Methods]A natural circulation system with a 5×5 square array basic rod bundles channel was taken as research object,and it was designed and built on a mechanical rolling platform.Then,based on the point reactor kinetic model,the coupling of neutronic-thermohydraulic-motion was achieved by real-time data acquisition of thermal parameters and calculation of real-time nuclear power,and the effects of fuel temperature feedback and coolant temperature feedback on single-phase natural circulation were considered.Finally,an experimental study on the low-pressure single-phase natural circulation under rolling motion condition was carried out.[Results]Under static conditions,neutronic-thermo-hydraulic coupling makes the power fluctuate slightly,reactivity and power fluctuation amplitude increase with the increase of temperature feedback coefficient.When the feedback coefficient is lower than-5×10^(-4)℃^(-1),fuel temperature feedback has a greater impact on power than coolant temperature feedback.Increasing the fuel temperature feedback coefficient reduces system stability.Under rolling motion conditions,the smaller the rolling amplitude or the shorter the rolling period,the smaller the amplitude of the introduced power fluctuations.During the initiation of the rolling motion,neutronic-thermo-hydraulic coupling significantly increases 50%of the time for the system to establish a new stable circulation.[Conclusions]These results provide a valuable application for further investigations of the FNNP's design and validation.