堆芯跌落事故下反应堆结构功能性评定

Evaluation of reactor structural function during core drop accident

堆芯跌落事故会造成堆芯吊篮及支承结构跌落并对压力容器内表面形成冲击,为保证反应堆功能完整性,采用Ludwik扩展来拟合材料应力–应变曲线,考虑堆芯自重、浮力、热膨胀等因素的影响,计算了材料在冷态和热态条件下的应变率,求得堆芯跌落引起的冲击载荷为8294482 N(冷态)和6064537 N(热态),小于压力容器可承受的许用冲击载荷。求得跌落高度为47.44 mm(冷态)和27.63 mm(热态),小于堆芯上板定位销与燃料组件有效配合长度。对受压组件进行了稳定性分析,均不发生屈曲现象。评定结果表明堆芯跌落事故不会影响堆芯功能性。

Background： A core drop accident causes the core barrel and supporting structure to drop and impact on the bottom of the reactor vessel. Purpose： To ensure the scram functionality is maintained. Methods： The stress-strain curves applicable to the material are approximated by Ludwik＇s expression. Considering the core deadweight, buoyancy force and heat expansion, material train ratios for both cold and hot conditions are calculated. Results： Vessel impact load （8294482N in cold condition ＆ 6064537N in hot condition） is determined, which remains within the vessel design specification limits. The calculated drop length （47.44 mm in cold condition ＆ 27.63 nun in hot condition） is less than the fuel pin full-diameter engagement length, so the fuel assembly top nozzle will remain engaged during a core drop. Finally the compressive assemblies are evaluated, which would not buckle due to the core drop accident loads. Conclusions： A core drop will not affect the scram function.