Development of Advanced Electrodes for Corrosion Monitoring in Nuclear Power Plants

摘要

Much of corrosion-related due to the piping material and coolant are generated for Nuclear Power Plants (NPPs) operation time. During normal-operation, operators manage main factors such as pH, ECP and impurities density by using optimized water-purity operation technique to maintain integrity of piping and structural materials. Various correlations related to the corrosion are developed between metal corrosion and ECP, pH and the effect on the piping and structural, which are the water chemistry factors. In this study, Ag/AgCl and Cu/Cu_2O(YSZ) pH-sensing electrode for measuring hydrochemistry factors such as ECP, pH operating in NPPs have been developed. The developed sensors are conducted performance tests to prove their validity under the NPPs conditions. In this study, the external Ag/AgCl electrode is developed to resolve the potential drift phenomenon, which is a general phenomenon of conventional Ag/AgCl electrodes, through using the ceramic tube as a potential sensing part and high temperature part, and a related equation is established to calculate the TLJP(Thermal Liquid Junction Potential). The Cu/Cu_2O electrode as a working electrode is developed using 8%-YSZ membrane. Its relational expression for converting the pH value is established with the Ag/AgCl reference electrode. The developed electrodes are tested to evaluate their response characteristics and stability in low/high temperature conditions. A titration test of the developed electrode is performed using 0.1m-NaCl and 0.01m-HCl solution under the test conditions of 300°C and 2700psi. The test results show that the response characteristics, stability and reproducibility of the manufactured electrodes. Base on the test results, the corrosion environment of carbon-steel (SA106Gr.C) is evaluated by using electrodes completed performance evaluation, and Fe-pourbaix-diagram is calculated for performance evaluation referred to EPRI report. The conditions of performance evaluation are 1000 ppm Boron and 2 ppm Lithium solution under the low/high temperature conditions.