A Study On The Compounding Recipe Of Cleanser For Nuclear Power Plant Heat Transfer Systems

This study is based on the requirements of nuclear power plant heat exchange systems'decontamination and scale removal, three scale samples and 1Cr18Ni9Ti stainless steels are selected. We select and optimize the detergent formulation and process by using dissolving scale experiments, weight loss corrosion testing, metallographic testing, AFM testing, electrochemical methods, X-ray fluorescence spectroscopy and elemental analysis. And then the non-destructive cleaning formulation, the destructive cleaning formulation and the cleaning process conditions are obtained. Equivalent circuit model which 1Cr18Ni9Ti stainless steel in those systems is established .The corrosion behaviors and corrosion mechanism are studied thoroughly, and the wastewater treatment process is studied preliminarily. The main conclusions are the following:10%HNO3 is selected as the basis of detergent solution by dissolving scale experiments. The HEDP, a non-destructive cleaning auxiliary agent is then added to the 10% HNO3. Then we get the 10%HNO3+5%HEDP cleaning system (NAP) which is used for chemical cleaning of in-service facilities.The corrosion of 1Cr18Ni9Ti in the NAP is very small when the temperature is below 50℃. We can't find localized corrosion, such as, pitting and intergranular corrosion. by using optical microscopy and scanning probe microscope. The average corrosion rate in 12 hours is less than 5nm/h. But the temperature has a great effect on the corrosion rate. When the temperature is 80℃, the corrosion rate is more than 10nm/h. In addition, 1Cr18Ni9Ti in 10% HNO3,5%HEDP and NAP has a better passivation performance and corrosion resistance. 1Cr18Ni9Ti's secondary passivation phenomenon is observed apparently in the single HEDP system, and 1Cr18Ni9Ti's pitting corrosion resistance is obviously better than that of the single 10%HNO3 system. NAP cleaning agent not only retains the secondary passivation characteristics and pitting resistance of HEDP, but also exist a certain synergy with HNO3 .1Cr18Ni9Ti's point corrosion electric potential in the NAP slightly is higher than the single HEDP system. Spot eroding resistance is improved.After a screening process, KMnO4 is selected as the destructive cleaning auxiliary agent. 10%HNO3+KMnO4 Cleaning system (HK) is used for retirement facilities chemical cleaning.To realize the corrosion rate's controllable, KMnO4's concentration range from 0.02% to 0.5%. As KMnO4's concentration increases in HK, and the average corrosion rate in 12 hours rise from 30nm/h to 90nm/h. The 1Cr18Ni9Ti's corrosion is serious and intergranular corrosion occurs seriously. Corrosion rate decreases with time after the first rise, and its equivalent circuit can be simulated by R(QR)(LR). As KMnO4's concentration increases in HK, 1Cr18Ni9Ti's charge transfer resistance decreases and corrosion resistance decreases; intergranular resistance decreases, intergranular corrosion increases; interface capacitance increases, the homogeneity of metal surface topography decreases.To slow down the corrosion rate of 1Cr18Ni9Ti in HK, benzotriazole (C6H5N3) is selected as HK's inhibitor. Therefore, we get 10%HNO3+KMnO4+C6H5N3 cleaning system (HKC). Intergranular corrosion is not found in HKC by using optical microscope. C6H5N3 in HK is a cathodic type inhibitor, which can form a film on the surface of 1Cr18Ni9Ti layer. When the concentration of C6H5N3 reaches 0.2%, the average corrosion rate in 12 hours is above 10nm/h, and its equivalent circuit can be simulated by R(Q(R(CR))). As C6H5N3's concentration increases, 1Cr18Ni9Ti's charge transfer resistance increases, the surface transfer resistance increases, the interface capacitance decreases, adsorption resistance increases, the adsorption capacitance decreases. And the "degradation" phenomenon of impedance spectroscopy occurs. As the immersion time prolongs, surface transfer resistance increases, the interface capacitance decreases, while the adsorption resistance and adsorption capacitance change little.Circulation loop cleaning experiments are simulated in the laboratory. And we find that bi-directional cleaning is better than one-directional cleaning; cleaning effect of a low flow rate is better than that of a higher velocity.Ion-exchanging resin and adsorption of activated carbon are used to treatment NAP cleaning waste. The cleaning effect of ion-exchanging resin is better than that of adsorption of activated carbon in Mn, Ca and so on; while the cleaning effect of adsorption of activated carbon is better than that of ion-exchanging resin in K, Na. From the various elements of liquid in the comprehensive effect, the cleaning effect of adsorption of activated carbon is better than that of Ion-exchanging resin.Three steps, which are neutralization, evaporation and ion-exchanging resin, are used to deal with HK and HKC cleaning waste. Almost all kinds of metal elements are removed effectively. The removal rate of Mn, Si and other elements is up to 100%,and the removal rate of Fe, Ca elements differs according to removal systems.