核级乙烯基电缆聚合物材料辐照老化剂量率效应研究

To ensure the reliability under normal service conditions and the safety under accidental conditions for the nuclear cables of nuclear power plants, it is necessary to carry out accelerated irradiation ageing testing and service life prediction upon the most-used base material for their insulation and sheath, i.e. the vinyl-based polymers. Indeed, relevant researches have been conducted abroad, however the majority of them only focused on the effects of absorbed doses without systematic consideration of the dose rate effects, and the specimens were also the commercial products with patented formulations. That is to say, these results seem not theoretically and practically applicable to China. In order to meet the requirements of the Chinese national major engineering programs and to make sense of the scientific difficulties in understanding the dose rate effects, this project is proposed to quantitatively study the dose rate effects by means of the specific irradiation ageing testing from four dimensions upon the domestically manufactured vinyl-based polymers used for nuclear cables in the self-reliance advanced pressurized water reactors in China. In detail, it will encompass the zero-dimensional study on determination of the critical dose rate between the homogeneous oxidation and the heterogeneous oxidation; the one-dimensional study on determination of the dose rate ranges for the thermal dominated region, the irradiation dominated region, and the heterogeneous oxidation region, respectively; the two-dimensional study on determination of the boundary conditions of the life prediction models for the synergistic effects from both thermal and irradiation; and the three-dimensional study on the ageing mechanisms across the whole cross sections of the specimens with the help of infrared microscope and Raman microscope. If approved, the achievement of this project would deepen the understanding of the theories and the models of irradiation ageing upon polymers, and would also facilitate the improvement of the equipment qualification standards and programs for nuclear cables, which has both the scientific significance in theories and the practical values in engineering.

为确保核电站中核级电缆在服役工况下的可靠性及在事故工况下的安全性，需对其用量最大的乙烯基聚合物基材开展辐照老化加速试验并预测使用寿命。尽管国外开展过相关研究，但大多只关注累积剂量影响，未对剂量率效应进行系统研究；且对象是其具有特定配方的成熟产品，缺乏对我国相关产品的理论与实践支撑。为适应国家重大工程需求并解决以上科学难点，项目拟对自主化先进压水堆核电站实际使用的国产核级乙烯基电缆聚合物材料实施辐照老化试验，从四个维度开展剂量率效应的定量研究，包括：确定均相氧化与非均相氧化临界剂量率的零维；界定热主导、辐照主导、非均相氧化等区域具体剂量率范围的一维；建立热与辐照协同老化寿命预测模型边界条件的二维；及运用显微红外与显微拉曼技术揭示老化机理在材料剖面分布规律的三维。若得以开展，既能深入理解聚合物材料辐照老化的理论与模型，又能帮助改进核级电缆合格鉴定试验标准，具有重要的科学理论意义和工程应用价值。

为确保核电站中核级电缆在服役工况的可靠性及在事故工况的安全性，需对其绝缘和护套用聚合物材料开展辐照老化加速试验以预测使用寿命。尽管国内外开展过相关研究，但大多只关注累积剂量的影响，未对剂量率效应进行系统研究；且研究对象是具有特定配方的成熟产品，缺乏对我国相关产品的理论与实践支撑。为服务我国大型先进压水堆核电站国家科技重大专项及相关工程建设，本项目以工程实际使用的国产核级乙烯基电缆聚合物材料为研究对象，对其辐照老化的剂量率效应进行研究，取得以下主要成果：1）建立了核级电缆聚合物材料的性能与辐照剂量间相互关系的数学模型，即材料的断裂伸长率与辐照累积剂量间呈一阶指数衰减规律。并且考虑到工程上的适用性和便利性，在此基础上又提出简化的指数模型。通过将实验数据和文献数据代入模型，发现与预测值之间的误差最大不超过10%，证明模型具有良好的工程应用价值。2）建立了γ与β两种射线对核级电缆聚合物材料等效损伤剂量的转换方法。在一阶指数衰减模型的基础上，对γ与β两种射线对材料不同的损伤影响进行比较研究，建立了一种能将两种射线辐照损伤剂量等效转换的标准方法，有助于解答国际上一直悬而未决的两种射线的辐照损伤到底孰强孰弱的问题。3）提出了核级电缆聚合物材料热老化表观活化能的快速试验方法。通过大量试验，比较研究了若干种常用的热老化表观活化能的测试方法，在此基础上提出了一种兼具准确性、便利性、分析速度的快速试验方法，所得结果与文献和其它试验得到的结果接近，在核电工程中具有良好的应用前景。4）开发了核级电缆聚合物材料辐照氧化扩散规律的原位微区分析法。创新地利用显微红外和显微拉曼等表征手段，开发了原位微区分析法，能对核级电缆聚合物材料老化前后的特征官能团、主链结构等微观成分和结构进行原位定量表征，获得材料的氧化程度、速度、深度在材料整个剖面的分布规律，从而对后续开展扩散控制辐照氧化动力学的科学问题研究打下基础。