EXPERIMENTAL RESEARCH AND MATHEMATICAL MODELLING OF THE IMPURITIES CONCENTRATION PROCESSES INTO CANDU STEAM GENERATOR CREVICES

摘要

Crevice corrosion involves a number of simultaneous and interacting operations, including mass transfer processes, production of metal ions within the crevice and hydrolysis reactions, resulting in a very aggressive solution from the point of view of corrosion. These intermediary corrosion processes are in a complex interdependence and they imply a number of important parameters, including both the crevice gap and depth. The major goal of this paper was development of a mathematical model for the calculation of the impurities concentrations (Na~+, Cl~-, Fe~(2+)) into crevices and experimental research related to this process. They was identified the important experimental parameters that require further experimental research. This model considers all the processes that interfere in the impurities concentration mechanism achieved into the crevice but it also makes some assumptions for the easy solving of mathematical equations. Because into the steam generator the measurement of the impurities concentration and/or deposition in the crevices solutions is not achievable, one cannot estimate the corrosion intensity inside these spaces. The mathematical model presented in this paper may predict the impurities concentration in the crevices. Based on the results obtained in this study of corrosion, the scientist may appreciate the corrosion intensity of the crevices materials or may draw up an experimental program, which could lead at immediate results. The predictive quality of the model may contribute to the choice of new design solutions, development new alloys and of material selection criteria.