Examination of chemical and physical effects on sump screen clogging of containment materials used in Korean plants

In this study, we have investigated the chemical and physical effects on the mechanism of sump screen clogging of containment materials that are used in most Korean nuclear power plants, such as N-102, N-108 as coating materials, NUKON as insulating materials, and CLP and SSLP as pipe materials. The experimental conditions for dissolution were pH = 8.0 at 88 °C, and those for precipitation were pH = 8.5 at 60 °C. The concentration of both dissolved and precipitated species were evaluated by using an ICP-AES and a particle size analyzer, respectively. From the obtained dissolution/precipitation data, we derived a unique two-step mechanism for the sump screen clogging process. In the first step, the screen was sparsely covered with needle-shaped silicon fiber debris that formed from the insulating materials; in the second step, it was finally clogged with a few micrometer-sized metal hydroxide precipitate particles (predominantly calcium hydroxide) that were generated from the dissolved metal ions. Hence, it can be concluded that the silicon fibers deployed for the insulating materials should be replaced with alternative materials that generate no needle-shaped debris after breakage, and the gypsum component in the coating should be reduced as much as possible.