堆芯熔融事故下反应堆压力容器超高温蠕变损伤机理和失效评价研究

The In-Vessel Retention (IVR) is one of the most important methods for preventing the leakage of radioactive materials when the pressure water reactor core in a nuclear plant begins to melt in extreme accidents. For achieving the effect of IVR, it is a prerequisite to keep the structure integrity of reactor pressure vessel (RPV) in the situation. The creep deformation, damage of RPV material and the structure integrity of RPV became complicated and no concrete solving plans was put forward until now since the RPV structure underwent the effect of ultra-high temperature, high temperature gradient and high stress gradient under IVR condition. In this research, the multi-axial creep experiments of the RPV material will be carried out under ultra-high temperature, effect of microscopic heterogeneity of the RPV material on transient creep behaviors is explored, and the multi-scale nonlinear creep damage mechanism of the material under super-high temperature is studied. The relationship between the microstructure evolution and creep characteristics will be unveiled based on the micromechanics theory and the creep damage constitutive equation of the RPV material under ultra-high temperature will also be established. In addition, the creep damage behavior of the RPV will be studied and assessment method of creep failure of the RPV structure will be proposed consequently. The research is significant for grasping and obtaining the breakthroughs in advanced nuclear power safety technology, as well as the structure integrity of a large pressure water reactor.

在极端条件下核电厂压水堆发生堆芯熔融事故时，压力容器内堆芯熔融物滞留（IVR）是防止放射性物质泄漏的重要策略之一，实现IVR的前提是保持反应堆压力容器（RPV）的结构完整性。IVR条件下RPV结构承受超高温、高温度梯度和高应力梯度作用，其材料蠕变变形、损伤和RPV结构完整性问题十分复杂，至今尚未解决。本研究拟开展超高温下RPV材料多轴蠕变试验研究；探索由相变作用引起的材料内部微观非连续性对瞬态蠕变变形行为的影响，揭示多尺度超高温非线性蠕变损伤机理；基于细观力学理论及微观组织分析方法探索微观组织演变与蠕变特征曲线之间内在联系，建立RPV材料超高温多轴蠕变损伤本构方程；探索RPV筒体结构蠕变损伤行为，提出RPV结构蠕变失效的评价方法。该研究对掌握和突破世界先进核电安全技术，保障大型压水堆结构完整性等具有重要意义。

在极端条件下，核反应堆可能发生堆芯熔融事故，导致放射性物质泄漏。堆芯熔融物堆内滞留（IVR）作为防止放射性物质泄漏和缓解堆芯熔融严重事故的重要策略之一，实现IVR的前提是保持反应堆压力容器（RPV）的结构完整性。IVR条件下，RPV结构承受高温、高温度梯度和高应力梯度的联合作用，导致其材料蠕变变形、损伤和RPV结构完整性问题十分复杂，亟需进一步的深入研究。本项目针对堆芯熔融事故下RPV超高温蠕变损伤机理和失效评价展开研究，研究内容和取得的主要成果包括：通过高温单轴和多轴蠕变试验，获得了国产RPV材料A508-Ⅲ钢蠕变性能；分析了RPV材料相变引起的组织演化及其对蠕变性能的影响机制，揭示了RPV材料超高温蠕变损伤机理；基于蠕变变形机制的真应力模型和三相复合体K-R多轴蠕变损伤修正模型建立了RPV材料的蠕变本构模型；分析事故条件下RPV结构不同时刻的极限承载能力，形成了IVR下RPV结构完整性评估方法。本项目的成果将为促进大型核电装备国产化和提高核电本质安全水平提供重要的科学支持。