EDF feedback on recent EPRI SGOG SG chemical cleanings applications for TSP blockage reduction and heat transfer recover

Between 2007 and 2008, six Steam Generators Chemical Cleanings (SGCC) with the inhibitor free high temperature process were applied on EDF PWR units. The main goal was to reduce the excessive Tube Support Plate blockages observed on several units of the EDF fleet and the consequences on wide range levels and the risk of tube cracks. The heat transfer recovery was the second objective. Despite the correct results obtained, the corrosion impact of the high temperature process on internal metallic surfaces, higher than expected, and the environmental issues led EDF to move to a new cleaning process. The low temperature process developed by EPRI SGOG and applied for many years was selected for the same purpose. Some qualification laboratory tests were performed by Dominion Engineering Inc (DEI) to demonstrate the innocuousness an the efficiency of the process to achieve these goals. The EPRI SGOG process was then applied seven times by Westinghouse on the EDF units Cruas 3, Cruas 2, Belleville 1, Cattenom 1, Cattenom 3, Chinon B3 and Cattenom 4 between 2008 and 2010. All these units operate from the initial start at low AVT pH 25^oC (9,2) in the secondary circuit. Due to copper presence in the deposits to remove, the cleaning sequence 'Copper - Iron - Copper steps' was performed each time. After a short description of the process, including the specific adaptation in France, lessons learned are reported in this paper in the following areas: process monitoring, corrosion, efficiency, liquid and gaseous wastes, chemical pollution during start-up. Based on the 3 first applications in 2008, some modifications of the process were implemented, particularly for the copper step. For the units cleaned, 1100 to 4500 kg of deposits per SG have been removed, including TS sludge lancing. The reduction of TSP blockages was satisfying. The effect on steam pressure improvement and the wide range level is then discussed. The paper concludes on EDF perspectives for soft cleanings applications, for which some qualifications have been performed on several processes (ASCA/DMT), to prevent problems linked to high deposit loading (excessive TSP blockage, loss of heat transfer). (author)