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核废料储罐深地质处置环境下的腐蚀行为研究
郑珉1,2
学位类型硕士
导师黄彦良
2016-05-10
学位授予单位中国科学院大学
学位授予地点北京
学位专业海洋腐蚀与防护
关键词核废料储罐 地下水 深地质处置环境 腐蚀
其他摘要       核能利用过程中所产生的大量核废料一直是核能安全利用过程中急需解决的关键问题,一方面需要找到安全有效的处置方式,另一方面又需要确保在其处置过程中不会发生泄漏等安全隐患。目前,国际上普遍接受且可行的处置方法是“深地质处置”,是一种由固化体、外包装材料和缓冲回填材料构成的人工屏障以及围岩构成的天然屏障共同组成的“多屏障系统”。在深地质处置的过程中,伴随着地下水的不断渗入与核废料衰变裂变过程中大量的热能释放,形成了易于腐蚀发生的外部环境。同时储库环境会因初始截留氧气的逐渐消耗而变为一个长期的还原环境,析氢反应占据优势,储罐材料很可能会因氢的吸收与渗透发生不可预见的氢脆现象。由于核废料储罐是保证内部核废料密封的首道安全屏障,对于预期的数十万年甚至数百万年的深地质处置而言,有必要对深地质处置环境下的储罐材料进行大时间尺度下的腐蚀安全评估。
       本文通过电化学研究方法研究了三种核废料储罐备选材料(Q235钢,TA2和TA8-1)在我国高放射性核废料深地质储库预选区地下水及模拟深地质环境下的腐蚀发展规律。结果表明,三种材料在地下水溶液中高温环境的腐蚀趋势要低于低温环境,其产物膜保护性也较强。深地质处置环境相比单纯的地下水溶液环境能够有效降低金属材料的腐蚀速率,尤其对于钛(TA2)及钛合金(TA8-1),两种材料在饱和高压实膨润土中的腐蚀趋势要显著低于其他含水率条件;但对于深地质处置高压实膨润土含水率较高的非饱和条件下,三种材料又会因为膨润土达到饱和与非饱和两种水分状况的交界,使其腐蚀速率普遍高于其他含水率条件。高压实膨润土含水率的降低导致盐类物质水化的数量较少,导电离子的数量也相应较少,膨润土电阻率增大,成为低含水率高压实膨润土环境下腐蚀速度的主要控制因素,三种材料的腐蚀趋势大致随含水率的降低而逐渐降低;而对于高含水率的高压实膨润土环境,阴极氧气的扩散是腐蚀的重要影响因素。
       在深地质处置的过程中腐蚀电流密度最大值预计出现在储罐表面升温且膨润土含水率急剧上升的阶段或在膨润土刚饱和后的年代,其后受到降温与还原环境的共同影响,腐蚀速率在随后长期的地质处置年代下基本保持在较低的水平。;          The huge amount of nuclear waste generated inevitably during the period of nuclear usage has been a tough problem which aroused great attention. Considering the threat from its leakage if unreasonable disposal method is adopted, the urgent affairs are disposal method assessment and safety evaluation after a comprehensive discussion. The most acceptable and welcomed method is “deep geological disposal” including an artificial barrier and natural barrier which constitute the “multi-barrier system”. The artificial barrier involves the solidified nuclear waste, compacter and buffer backfilled materials and the natural barrier generally is the local rock. When underground water permeates to the surface of nuclear waste container through the buffer backfilled materials and the heat releases from the nuclear disintegration in the disposal period, an aggressive corrosion-oriented environment is generated. In the meanwhile, the trapped oxygen in the disposal will be consumed gradually during the initial years and hydrogen evolution will become the dominate reaction afterwards, contributing to the possible hydrogen brittlement of the waste container because of the hydrogen desorption and permeation. As the first protective parclose to ensure well sealing of the waste, nuclear waste container needs to be studied on the corrosion behavior in the long term disposal period.
        This paper studied the corrosion behavior of Q235 steel, TA2 and TA8-1 which were preselected as the container materials in simulated deep geological disposal environment of Beishan area to be served as the preselected high-level nuclear waste disposal area in our country. Electrochemistry technology was adopted in both underground water and highly compated bentonite environments. The results show that higher temperatures facilitate the performance of corrosion products compared with lower temperatures. The corrosion rate in highly compacted bentonite environment proves to be smaller than that of underground water environment especially for titanium and titanium alloy which present a much smaller corrosion rate in saturated compacted bentonite than that of lower water contents. However, the corrosion rate shows an obvious increase when it comes to the higher water content apart from saturated condition compared with the other water contents due to the boundary generated from saturated and unsaturated compacted bentonite. The decrease of water content in compacted bentonite limits the hydration of ions and the number decrease of conductive ions leads to a higher bentonite resistance, becoming the limitation step of corrosion in low water content. The decline of corrosive potential for all three materials keeps coherence with the water content decrease in general. What’s more, oxygen diffusion becomes the main corrosion controlling step for high water content benonite.
        The maximum of corrosion rate is predicted to exist in the temperature rapid increase stage when the bentonite water content rises abruptly or just after the bentonite saturation stage. Because of the temperature declining and long term deoxidation disposal environment, the corrosion rate holds a low extent.
学科领域海洋科学
语种中文
文献类型学位论文
条目标识符http://ir.qdio.ac.cn/handle/337002/112498
专题海洋腐蚀与防护研究发展中心
作者单位1.中国科学院海洋研究所
2.中国科学院大学
推荐引用方式
GB/T 7714
郑珉. 核废料储罐深地质处置环境下的腐蚀行为研究[D]. 北京. 中国科学院大学,2016.
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