核电厂锡黄铜冷却盘管泄漏原因分析及改进措施

Tin brass cooling plate tube leakage in a nuclear power plant:reason analysis and countermeasures

针对某核电厂核岛应急通风系统的锡黄铜冷却盘管发生的泄漏事故,对泄漏管样进行了宏观检查、材质、腐蚀产物、电化学、裂纹宏微观和断口SEM形貌等分析。结果表明,冷却介质中亚硝酸盐环境下锡黄铜发生的应力腐蚀开裂(SCC)是导致其冷却盘管泄漏的主要原因。一方面是因为亚硝酸盐生成的NH4+使锡黄铜管对SCC特别敏感,另一方面锡黄铜管内的残余应力加剧了管的应力腐蚀倾向。对此,提出了将破损冷却盘管更换为紫铜管,并将缓蚀剂中TTA的含量由1.0mg/kg提高到10～20mg/kg等改进措施。

Leakage occurred on tin brass cooling plate tubes of emergency ventilation system in a nuclear power plant.Thus,several investigations were carried out,such as the macroscopic examination,broken tube material analysis,corrosion product analysis,electrochemical analysis,macro and micro analysis of crack and fracture,and the fracture SEM analysis.The results showed that,stress corrosion cracking(SCC) occurred on the tin brass in nitrite environment in the cooling medium was considered as the major reason.One of the reason is the NH4+ formed by nitrite made the tin brass tube particularly sensitive to the SCC.On the other hand,residual stress on the tin brass tube exacerbated the stress corrosion tendency.Several measurements were put forward,like replacing the broken cooling plate tubes for red copper tubes,increasing the TTA content in corrosion inhibitor from 1.0 mg/kg to 10-20 mg/kg,and so on.