核废料储罐深地质处置条件下长期氢吸收和氢脆行为研究

The objective of this research is to solve the problems concerning the fundamental theory of long time scale hydrogen embrittlement risk assessment for carbon steel and titanium alloy nuclear waste containers under deep geological disposal conditions. Less research work was conducted concerning the corrosion of nuclear waste containers by mainland Chinese scholars. But many of them expressed the deep concern about nuclear waste, any negligence during the disposal of which may cast a terrible shadow to human life and survival. At present, deep geological disposal is the most realistic nuclear waste disposal method. It is necessary to improve the safety and reliability as far as possible. Neglecting the research on any of the possible problems is an act of committing crime to future generations. The international community take the research on the corrosion of nuclear waste containers seriously. The research on the corrosion of nuclear waste containers had already been initiated in 80's of last century in overseas countries. The International Workshop on Long Term Prediction of Corrosion Damage in Nuclear Waste System was first organized in 2001, and then held every three years. It attracted the participation of corrosion science researchers from key nuclear energy utilization countries. The nuclear energy utilization developed rapidly in China. China's nuclear waste disposal will also adopt the deep geological disposal. China's research on corrosion of nuclear waste containers has been lagged behind by developed countries. From the point of view for long-term development, it is necessary for China to carry out the basic research on the corrosion of nuclear waste containers. All types of corrosion failure are likely to pose a threat to long-term safe storage for nuclear waste. Hydrogen embrittlement is one kind of failure that is closely related with corrosion and the corrosion of metal nuclear waste container is controlled by the environment that it's surface contacts with. Research showed that hydrogen ion reduction would occur under aerobic corrosion conditions, and the hydrogen enters. Moreover,the circular tensile stress exists under nuclear decay thermal-mechanical coupling conditions.Therefore, it is necessary to study the hydrogen embrittlement due to the long-term entry of hydrogen into material. The hydrogen uptake and distribution will be studied in low oxygen formation water,bentonite and concrete pore solution of buffer layer, the mechanical properties and brittlement behavior under various hydrogen concentration and distribution characteristics evaluated, then the possibility of large time scale hydrogen embrittlement under deep geological disposal conditions predicted. This project will enable the establishment of long time scale hydrogen embrittlement prediction theory, promoting the waste container corrosion research, which has an important significance to safeguard the healthy development of the national nuclear industry.

本项目拟解决核废料储罐深地质处置条件下大时间尺度氢脆危险性评估的基础理论问题。核能利用上的任何疏忽都可能造成惨重的后果,给人类的生活乃至生存投下可怕的阴影，因此很多国人对核废料的处置表示担忧。深地质处置是核废料处置最现实的方法，应尽可能提高深埋处理的安全可靠性。国际上对核废料储罐腐蚀的研究很重视，上世纪80年代既已开展核废料储罐腐蚀研究，而我国相关研究较少，与国外相比差距较大，迫切需要开展该领域的研究工作。从可持续发展的观点来看，开展核废料储罐腐蚀与长期预测的基础研究对于我国核废料的安全处置是十分必要的。各种形式的腐蚀破坏都可能对核废料储罐的安全构成威胁。由于腐蚀过程中产生的氢长期向核废料储罐材料内部渗透及储罐在衰变热-力耦合作用下环向拉应力的存在，因此有必要研究氢脆问题。本项目将能建立大时间尺度氢脆危险性预测理论、促进核废料储罐腐蚀研究工作的开展，对于保障国家核工业的健康发展有重要意义。

核能利用过程中所产生的大量核废料是安全利用核能急需解决的关键问题。核废料储罐是保证内部核废料密封的首道安全屏障。由于地下水的浸透和氧的消耗，腐蚀的阴极过程会逐渐演变为以氢离子的还原为主，对于预期的数十万年甚至数百万年的深地质处置而言，有必要研究储罐材料大时间尺度下的氢脆危险性。本项目研究了Q235钢、TA2和TA8-1三种核废料储罐备选材料在我国高放射性核废料深地质储库预选区模拟深地质环境下的腐蚀发展规律。结果表明，三种材料在高温地下水溶液环境中的腐蚀趋势要低于低温环境,膨润土作为缓冲回填材料有效降低了金属材料的腐蚀速率。从腐蚀速率角度考虑钛及其合金要比碳钢更适宜作为大时间尺度存放的储罐材料。鉴于高放核废料的辐射性，还研究了三种金属材料在大剂量γ射线辐照后在饱和高压实膨润土中的腐蚀行为。结果表明，辐照对储罐金属材料的腐蚀速率有一定加速作用，高温环境影响较大，低温环境影响较小。由于整个处置阶段高温环境时段非常短，且实验所用辐照剂量远远大于实际剂量而加速腐蚀的作用有限，因此可认为辐照在整个深地质处置过程中影响不大。在储罐腐蚀速率随地质处置时间变化模型基础上，建立了渗氢效率随地质年代变化模型。Q235钢渗氢效率随着地质年代呈现增加趋势，但由于氢脆敏感性低，氢脆不是主要失效控制因素。因为钛氢化物的生成阻碍了氢的扩散，钛及其合金的渗氢效率则随着地质年代增加而降低。钛及其合金的氢脆敏感性与氢化物的分布有关，仅表层存在氢化物比氢化物均匀分布时的氢脆敏感性低。钛氢化物仅存在于储罐表面，1万年后仅几十微米。因此，钛及其合金从腐蚀速率和氢脆敏感性方面来说可以用于制作储罐材料。本项目深入研究了核废料储罐发生腐蚀以及氢脆的机理，分析了核废料储罐大时间尺度服役的安全性，为未来储罐的科学选材奠定了理论基础，对储罐的优化设计有重要指导作用，对于安全处置核废料保障国家核工业的健康发展有重要意义。