SOME ASPECTS REGARDING THE DEPOSITS REMOVAL FROM THE CANDU STEAM-GENERATOR, BY CHEMICAL METHOD

The removal of corrosion products opens the possibility to eliminate c auses of defects on heat transfer tubes by removing the corrosion prod ucts and trapped impurities. The purpose of this paper is to establish the corrosion behaviour of the Iy-800 (material of the tube) and SA 5 08 c1.2 (material of the tubesheet) after the chemical cleaning of the steam generator (SG) on the secondary circuit specific components. On the surface of these materials there are initial depositions consisti ng of oxides and corrosion products. The chemical cleaning was made at temperatures between 90-95 degrees C. The substances included in the chemical cleaning solution are: citric acid, Na(2)EDTA, HEDTA, ammoniu m citrate, hydrazine hydrate and thiourea. After the chemical cleaning the samples were passivated and corrosion-tested at the typical param eters of the SG secondary circuit (demineralized water pH=9.5 - AVT - at a temperature of 265 degrees C and a pressure of 5.1 MPa). The pape r presents the results of metallographic and X-ray diffraction examina tions as well as the reasons for selecting the best solution for the c hemical cleaning.