Synthesis Of Polyacrylic Acid And Its Scale Inhibition Performance In The Simulated Secondary Loop Media Of Pressurized Water Reactors

Secondary loop water chemistry in pressurized water reactors（PWRs）is very important for their steam generators（SGs）,and the secondary loop water quality is related to the operation safety of the SGs during the life of nuclear power plants.In the secondary loop of PWR nuclear power plants,SG tubes are the most prone to corrosion and scaling,resulting in the shutdown of plants to inspect and clean or replace the SG heat transfer tubes.At present,domestic nuclear power plants have obtained the satisfied corrosion inhibition effect by adding ethanolamine（ETA）,morpholine and other corrosion inhibitors in the secondary loop feedwater,but do not pay much attention to the scale inhibition in the secondary loop.Adding appropriate scale inhibitors to prevent the deposition of corrosion products（main component is iron oxide）in the secondary loop of PWRs can not only reduce the blockage of SG heat transfer tubes,but also inhibit the under-deposit corrosion in the system.In this paper,polyacrylic acid（PAA）scale inhibitors with different molecular weight were prepared by changing reaction conditions.According to their inhibition performance for the iron oxide scale,the best PAA was selected and its optimum synthesis process was determined.The scale inhibition effect of the selected PAA was evaluated in the simulated PWR secondary loop media with high temperature（T）and high pressure（P）.Then,the selected PAA was mixed with different scale inhibitors to improve its scale inhibition effect.Finally,the corrosion behavior of the PAA and its scale inhibition mechanism were studied by using weight-loss tests,x-ray diffraction（XRD）and scanning electron microscopy（SEM）analysis.The results show that the iron oxide scale inhibition rate of the PAA with the molecular weight of 459 can reach 100%under low temperature（50℃）and atmospheric pressure,and can still reach 80%under high T and high P（283℃,6.7 MPa）.The optimum used concentrations under different conditions for PAA were obtained and their scale inhibition effects for CaCO₃ scale were evaluated too.The results indicate that PAA nearly has no inhibition performance for the CaCO₃ scale under high T and high P conditions.There is no synergistic effect between the PAA and other different high temperature scale inhibitors（mainly used in boiler of thermal power plant）under the same condition.In the simulated media in the SG tubes（283℃,6.7 MPa）,the PAA does not show corrosion inhibition effect,but also does not accelerate the corrosion of the SG tubes.Finally,it is found that the main inhibition mechanism of PAA for the iron oxide scale is a dispersion effect.