Evaluating corrosion resulting from repeated chemical cleaning

Abstract

The coolant systems of pressurised, water‐cooled, nuclear reactors become radioactively contaminated. Since reactors, like other process equipment, require personnel for operation and maintenance, this coolant system contamination and associated radiation may pose difficult operating problems. Inefficiencies in personnel utilisation result as the radiation levels increase. Generally the radiation levels tend to increase with time. Decontamination is then required to lower radiation levels and to improve personnel utilisation. During a reactor's lifetime, the coolant systems may be decontaminated a number of times to keep radiation levels within acceptable limits. Since this decontamination operation involves chemical cleaning of the reactors' coolant system it has a certain corrosive effect upon the components of the system. To determine these corrosive characteristics, a procedure simulating the cyclic filming and defilming in the pressurised water system is employed in the USA. Special equipment is needed to simulate reactor conditions and to allow evaluation of decontamination methods. Although this article is focused on nuclear reactor systems, the technique of cyclic filming and defilming could be used readily to determine long‐term corrosion effects in other industrial systems where chemical cleaning is frequently employed, such as in boilers, heat exchangers, evaporators, reactors, condensers, and process vessels. Equipment designs and operating procedures would be formulated so as to simulate process and chemical cleaning conditions for the particular system of interest.