燃料污垢对典型事故工况的影响研究

Study of the Effect of Fuel Crud on Typical Accident Conditions

新版HAD 102/07—2020核动力厂反应堆堆芯设计中明确要求:设计分析应考虑反应堆冷却剂系统正常运行产生的腐蚀产物在包壳表面的沉积导致的燃料棒传热恶化。因此,有必要分析燃料污垢对事故工况下燃料棒传热性能的影响,特别是以燃料芯块温度和包壳温度为验收准则的典型事故工况。本文开发污垢计算模型,采用等效热导率关系式计算含污垢和氧化层的包壳热导率,即认为污垢、氧化层均匀分散在包壳层中,使得包壳热导率变化,该等效包壳层所引起的温度梯度与实际情况相同。随后,基于对“华龙一号”核动力厂事故分析结果,选取了典型非LOCA事故(弹棒事故、功率运行下单个控制棒失控抽出事故)和LOCA事故进行污垢影响研究。结果表明,考虑污垢后,事故过程中的燃料芯块中心峰值温度和包壳峰值温度均有显著上升,但依然满足事故验收准则要求。

In the new edition of HAD 102/07—2020 Nuclear Power Plant Reactor Core Design,it is clearly required that the design analysis should consider the deterioration of fuel rod heat transfer on the cladding surface caused by the deposition of corrosion products generated during normal operation of the reactor coolant system.Therefore,it is necessary to analyze the influence of fuel crud on the heat transfer performance of fuel rods under accident conditions,especially the typical accident conditions with fuel pellet center temperature and cladding temperature as acceptance criteria.In this analysis,the fuel crud calculation model is developed,and the equivalent thermal conductivity relationship is used to calculate the thermal conductivity of the cladding containing the crud and oxide layer,that is,it is considered that the fuel crud and oxide layer are evenly dispersed in the cladding,which changes the thermal conductivity of the cladding,but the temperature gradient caused by the equivalent cladding is the same as the actual situation.Then,based on the accident analysis results of HPR1000,typical non-LOCA accidents(RCCA ejection accident and the uncontrolled single control rod withdrawal at power)and LOCA accident are selected to study the impact of the fuel crud.The results show that the maximum fuel pellet temperature and the maximum cladding temperature for the hot-spot both increase significantly after considering the fuel crud,but it still meets the requirements of accident acceptance criteria.