Development of countermeasure against scale deposition at steam generators of PWRs

Scale deposition has occurred at steam generators of several PWRs. The scale deposition may lead to reduction of flow rate of coolant, deterioration of heat exchanging efficiency and so on. These phenomena affect plant operation performance. Thus, elucidation of the mechanism of the scale deposition and some effective countermeasure are required. In CRIEPI (Central Research Institute of Electric Power Industry), the scale deposition is studied from two aspects: fluid dynamics and water chemistry. Concerning the water chemistry, we think that electro-kinetic behavior of scale, that is, metal oxides is of great importance. The final goal of the water chemical approach is to evaluate electro-kinetic potential (zeta potential) of metal oxides such as magnetite (Fe3O4) and hematite (Fe2O3), and to develop some countermeasure of the scale deposition based on the electro-kinetic data. As a first step, the zeta potential of 25 μm Fe3O4 particles was measured by the streaming potential method at room temperature, and effect of dispersant addition was studied. The dispersants examined were poly-acrylic acid (PAA, Mw ∝ 25,000) and polyvinylpyrrolidone (PVP, Mw ∝ 40,000). It has been found that the addition of PAA of more than 10 ppm lowers the zeta potentials by 5 - 15 mV in whole pH range, and that the addition of PVP of more than 10 ppm reduces absolute value of the zeta potentials. (authors)