304L/ER316L奥氏体不锈钢焊接板的点蚀行为

采用三氯化铁浸泡试验和电化学试验研究了核电站乏燃料池覆面用304L/ER316L/304L奥氏体不锈钢焊接板在3.5%(质量分数)NaCl溶液(溶液1),含2700mg/L B3+的纯硼酸溶液(溶液2)和含2700mg/L B3++200mg/L Cl-的混合溶液(溶液3)中的点蚀行为,同时研究了温度和氯离子对其点蚀行为的影响。结果表明:在三种溶液环境中,焊接板不同区域的耐点蚀性能由强到弱依次为焊缝区>母材区>热影响区。焊缝金属耐点蚀性能最优的主要原因是Ni、Mo含量较高,而热影响区的最差是由于显微组织不良。在30,40,60℃溶液2中,即使在高电位下也未观测到焊接板发生明显点蚀,而掺杂200mg/L Cl-后,焊接板的点蚀倾向显著增加,点蚀敏感性随温度升高而升高。符合设计参数的纯硼酸溶液是很好的服役环境,但当其中加入Cl-后,焊接板的耐点蚀性能会大幅降低,故乏燃料池在服役期间,应严格控制水温变化并监控水质,避免温度长时间过高及侵蚀性Cl-含量超标。

Pitting Behavior of 304L/ER316L Austenitic Stainless Steel Welded Plate

Pitting behavior of the 304 L/ER316 L/304 Laustenitic stainless steel welded plate for the spent fuel pool cover of nuclear power plant was studied in the solution containing 3.5%(mass fraction)NaCl(No.1 solution),containing 2 700 mg/L B3+(No.2 solution)and containing 2 700 mg/L B3++ 200 mg/L Cl-(No.3 solution)by ferric chloride immersion test and electrochemical test.The results show that in the three solution environments,the pitting resistance of different areas of the welded plate was weld metal> base metal> heat affected zone.The main reason for the best pitting resistance of weld metal was that the Ni and Mo content were high,and the poor pitting resistance of the heat affected zone was caused by poor microstructure.In No.2 solution at 30,40,60 ℃,no obvious pitting of the welded plate was observed even at high potential.After doping 200 mg/L Cl-in solution No.2,the pitting tendency of the welded plate increased remarkably,and the pitting sensitivity increased with the increase of temperature.A pure boric acid solution meeting the design parameters was a good service environment,but when Cl-was added,the pitting resistance of the welded plate was greatly reduced.Therefore,during the service period of the spent fuel pool,the water temperature change should be strictly controlled and the water quality should be monitored to avoid excessive temperature and excessive erosive Cl-content.