Chemical cleaning of PWR steam generators with a low temperature process

Corrosion products generated in the steam, feedwater and condensate systems of a PWR will be transferred by the feedwater into the secondary side of the steam generators (SG). Up to several hundred kilograms of deposits may collect on the surfaces of the SG. These deposits not only reduce the efficiency of the SG by deterioration of the heat transfer, but also cause an acceleration of the corrosion of the SG tubes and blockage of support plate passages. The chemical removal of the corrosion products opens the possibility to eliminate causes of defects on heat transfer tubes by removing the corrosion products and trapped impurities. A low temperature cleaning process, based on the EPRI developed SGOG iron and copper solvents, was applied in November 1990 to remove the hard deposits from the tube sheets of a two-loop plant. The sludge containing over 60% copper was removed with the application of one iron removal step and several copper removal steps. Over 95% of the available sludge was removed. The corrosion of the unalloyed and low alloy materials was extremely low. The Incoloy 600 tubes showed no corrosion. In addition aspects of crevice cleaning at elevated temperatures are mentioned. (orig.)