核电站服役的高温高压水回路中闭塞区的流动不充分, 可能产生异常水化学条件而导致材料服役性能弱化. 本文利用国产核级304不锈钢制备了一种简单的模拟闭塞区样品, 放入含有Ni2+的高温含氧水中浸泡并对生成的氧化膜进行表征. 结果表明: 闭塞区从外到内氧化膜外层中的尖晶石结构相的比例逐渐减小, 而赤铁矿结构相的比例逐渐增大, 膜表层的Ni含量逐渐降低. 分析表明, Ni2+浓度会显著影响核级不锈钢的氧化行为, 闭塞结构会在一定程度上阻碍本体溶液中的Ni2+向闭塞区内扩散, 使Ni$^{2+}$沿闭塞区深度方向形成浓度梯度, 导致氧化膜的生长特征沿梯度方向发生明显变化.
In the occluded volume of high temperature pressurized water loop in nuclear power plants, poor-controlled water chemistry due to sluggish flowage could induce accelerated degradation of structural materials. In this paper, an occluded volume shaped nuclear-grade 304 stainless steel sample was immersed in oxygenated high temperature water containing a certain concentration of Ni2+. It was found that from the outer to the inner side of the sample, the proportion of spinel in the oxide film decreased while that of hematite increased and Ni content in the outer oxide film decreased. It was thought that the concentration of Ni2+ could influence the oxidation behavior of material significantly. The occluded volume could impede the inward diffusion of Ni2+, causing a concentration gradient of Ni2+ along depth of the volume and gradual change of oxide film characteristic.
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