板状燃料元件流道堵塞事故预防与探测技术研究

Research on prevention and detection technology of flow channel blockage accident of plate-type fuel elements

板状燃料元件用于研究堆中表现出良好的辐照性能。通过对国内外一些使用板状燃料元件研究堆堵流事故实例的调研,发现板状燃料元件板间的栅距通常很小,堆芯冷却剂流道狭窄,堵流事故的发生大都由异物进入流道或燃料肿胀引起。选取中国先进研究堆(China Advanced Research Reactor,CARR)作为特征研究对象,采用RELAP5/MOD3.2热工计算程序,对CARR堆芯、堆本体、单盒组件、堆外冷却回路等进行了热工水力模拟计算,结果表明:当反应堆功率提升时,堵塞的流道内燃料组件温度上升,冷却剂开始发生沸腾,功率会发生明显波动。通过中子注量率与功率的监控以及燃料温度的分析,有助于及早探知和预防堵流事故的进一步发展扩大。

[Background]Plate-type fuel element exhibits excellent irradiation properties in research reactor while the grid spacing between the fuel element plates is usually very small.Most of the blockage accidents are caused by foreign matters entering the flow channel or fuel swelling due to the narrow coolant flow channel in the core.[Purpose]This study aims to analyze the process of blockage accidents,and put forward effective preventive measurements and detection methods.[Methods]Based on the investigation of some typical accidents abroad,China advanced research reactor(CARR)was taken as a feature research object,and the thermal hydraulic simulation calculation of CARR core,reactor body,single fuel assembly and cooling circuit outside the reactor was carried out by using the RELAP5/MOD3.2 thermal calculation program.Modeling and analysis of the specific flow channel blockage accident process on CARR was finished.[Results]Simulation results show that the temperature of the fuel assembly in the blocked flow passage will increase when the reactor power is raising,then the coolant will begin to boil,and the power will fluctuate significantly.[Conclusions]It is necessary to strictly control the quality of core operation.The monitoring of neutron flux rate and reactor power,and analyzing fuel temperature are helpful to detect and prevent the further development of the blockage accident.