Spectrophotometric on-line monitoring of traceable corrosion products under primary reactor water conditions

Abstract

Corrosion products in the primary reactor coolant negatively affect the performance and integrity of nuclear power plants through axial offset anomaly (AOA) and reduction of heat transfer efficiency. In addition, corrosion products become radioactive by capturing neutrons, which may be the primary source of radiation exposure to workers during overhaul and refueling. Despite harmful consequences, the concentration of corrosion products has not yet been analyzed during the operation. Therefore, the development of a sensitive analytical method is necessary to monitor and measure corrosion products within primary reactor coolant. In this study, an on-line monitoring system was developed based on UV-Vis absorption spectrophotometry coupled with liquid waveguide capillary cell (LWCC). 2-(5-bromo-2-pyridylazo)-5-(N-propyl-N-3-sulfopropylamino) phenol (Br-PAPS) was used for sensitive absorption photometric measurements. In addition, non-ionic surfactant Triton X-100 was applied to increase the solubility and stability of metal Br-PAPS chelates within the capillary cell. In order for solving severely overlapping absorption spectra of metal chelates, a partial least squares (PLS) regression approach was adopted. Under optimized analytical conditions, detection limits for iron, cobalt, nickel, copper and zinc were found to be less than 0.03 ppb. For most cases, the proposed method provides relative analytical errors less than 5% at sub-ppb concentrations. For deeper understanding of the chelation, the structure of the chelate and its formation mechanism was investigated by use of density functional theory (DFT) and time-dependent DFT (TDDFT). The DFT calculation indicates that the internal rotation occurs in order to form the most stable N,N,O tridentate. The TDDFT calculation with LC-PBE0 functional provides results in a good agreement with the experimental data. In this dissertation, a successful on-line monitoring system for primary reactor coolants was developed to allow more accurate analysis of corrosion products being omnipresent in nuclear power plants.