基于COMSOL的核电站安全壳钢衬里外侧腐蚀研究

Research on Corrosion Mechanism of Steel Liner of Nuclear Containment Vessel Based on COMSOL Model

基于COMSOL建立了钢衬里外侧腐蚀细观模型,在总结多国核电站钢衬里外侧腐蚀案例基础上,从异物、离子侵蚀两个方面对钢衬里外侧腐蚀成因及腐蚀机理展开计算分析。结果表明:混凝土浇筑前钢衬里在海洋环境中的长期暴露可引起侵蚀离子的表面不均匀积累,引发钢衬里发生以微电池为主的腐蚀,腐蚀速率随留存最大Cl^(-)浓度的增大而增快;混凝土浇筑过程中遗留的异物(以木块为主)导致的钢衬里腐蚀以宏电池腐蚀为主,随着接触面处异物尺寸的减小,阴阳极面积比增大,腐蚀速率加快;同时,提高混凝土电阻率可有效降低钢衬里腐蚀速率。研究成果将为核电站安全壳的老化机理和防治措施提供技术参考。

Nuclear containment vessel is the third barrier to avoid the nuclear leakage.It is noted that severe outer corrosion of steel liners happened in several containment vessels around the world,which greatly threatened the integrity and tightness of liners of containment vessel.The outer corrosion is a great safety risk because it is perceptually invisible and hard to be maintenance.To the authors'knowledge,researches related to the ratter of outer corrosion are scare.No authoritative corrosion mechanism has been proposed.Based on the operating reports of several nuclear power plants and a mesoscopic corrosion models established by COMSOL,the corrosion mechanisms of the outer corrosion of steel liners were analyzed in the views of effects of corrosive ions and foreign materials.Results revealed that a long-time exposure of steel liners in the marine environment will generate the non-uniform accumulation of corrosive ions on the outer surface of liners,which is the reason for the microcell corrosion of outer corrosion of steel liners.Corrosion rate in this condition is decided by the maximum content of the non-uniformly distributed chloride.Besides,foreign materials(mainly wood blocks)unintended left behind during pouring concrete will also lead to electro-chemical corrosion,in which macrocell corrosion plays an important role.The corrosion rate was accelerated along with the decrease of the touching surface size between foreign materials and steel liners and with the increase of area ratio of cathode and anode.Meanwhile,the corrosion rate can be effectively mitigated by enhancing the concrete resistivity.The achievements in this paper can provide technical reference for the aging mechanisms and aging prevention measures of nuclear containment.