Surface charging patterns of stainless alloys - Effect of ageing in conditions of primary cooling circuit of pressurized water reactors

The predominance of electrostatic interactions in the mechanism of particle deposition onto solid surfaces is well documented. Therefore, an electrostatic approach has been used to predict the behavior of activated corrosion products in the primary cooling circuit of a pressurized water reactor (PWR). Only few results have been published on the potential at the interface of metallic alloys and aqueous solutions, even at room temperature. In this study, we present results about the characterization of representative materials such as Inconel 690, stainless steel 304 and Zircaloy 4 at room temperature, for pristine polished samples as well as after an 80-day ageing step in physico-chemical conditions similar to those of a primary circuit (360 °C, boron 1 g L−1 (as H3BO3), lithium 2 mg L−1 (as LiOH), hydrogen 30 cm3 kg−1). The surface potentials of these alloys have been determined using a streaming current method for pH from 3 to 7. Isoelectric points between 4.1 and 4.6 have been found for all samples and there is no effect of the ageing step. These values have been confirmed by adhesion studies of grafted latex particles either positively charged (amidine surface groups) or negatively charged (carboxylate groups) at pH 3.3 and pH 5.5. The results show that particles deposition is favored only when they carry a charge opposite to the substrate surfaces.