某核电站蒸汽发生器杂质隐藏返回研究

Investigation of Hideout Return of Steam Generator Impurities in a Nuclear Power Plant

压水堆核电站运行过程中,蒸汽发生器二次侧流动受限区域的表面污垢及缝隙中的有害杂质离子(如Cl-,SO42-,Ca2+,Mg2+,Al3+等)因水的蒸发会出现局部浓缩.通过监测机组停运期间的水化学可以推断机组正常运行期间蒸汽发生器二次侧的杂质浓缩情况.本文分析和评估了某核电站降功率、降温期间蒸汽发生器的3次杂质隐藏返回试验数据.结果表明,隐藏区内的Al3+浓度逐年增加;根据隐藏返回数据得到的高温pH值(pHT)在正常的耐腐蚀pH值范围内;建议机组降温的时间应该进一步延长,以便杂质离子尤其是阴离子完全返回进入大空间溶液并通过排污水系统排出.

During ordinary operation of a pressurized water reactor （PWR） of nuclear power plant （NPP）, some deleterious ionic impurities such as Cl-, SO42-, Ca2＋, Mg2＋, AP＋ etc. hidden in fouling and crevices for secondary side of steam generator （SG） would concentrate especially in flow-restricted regions. Concentrating situation of the deleterious impurities could be evaluated through secondary water chemistry measurement. In this paper, evaluation and analysis were made from three sets of practical hideout retum （HOR） testing data for a NPP. The results indicated that pHT in crevice was in ordinary range from viewpoint of corrosion resistance according to HOR data. However, the concentration ofAP3＋ increased year by year and the reasons need to be further investigated. It is suggested that the time of hideout return tests during steady state should be extended so that the impurities could be completely returned.