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.
원전 1차 계통수 내 존재하는 부식생성물은 비정상 출력분포와 같은 문제들을 일으키며 원전의 건전성 및 효율에 부정적인 영향을 끼친다. 이들은 계통수 내 ppb 수준 농도로 매우 미량 존재하기 때문에 농도를 정확히 측정하는데 어려움이 있다. 본 논문에서는 액체 광도파 모세관 셀을 적용한 자외선-가시광선 흡수분광법을 이용한 분석방법을 개발하였다. 원전 1차 계통수 내 존재하는 다양한 중금속 이온들(철, 코발트, 니켈, 구리, 아연)을 검출하기 위해 Br-PAPS 시약을 이용하여 상기 중금속 이온들을 0.03 ppb 이하 농도에서 분석 가능함을 보였다. 흡수스펙트럼 겹침 문제를 해결하기 위해 부분최소제곱 회귀분석을 이용한 다중원소분석을 수행하였고 1.5 ppb 이하의 낮은 농도범위에서 상대오차 5% 이하로 정확히 정량분석 할 수 있음을 보였다. 추가적으로 밀도 범함수 이론을 통해 착물 구조 및 형성 메커니즘을 규명하였고 내부회전을 통해 가장 안정한 N,N,O 세자리 착물이 형성됨을 보였다. LC-PBE0 범함수를 통해 얻은 흡수스펙트럼은 실험결과와 정성적으로 유사하였다. 본 논문에서 개발한 분석법은 원전 1차 계통수 내 존재하는 부식생성물 온라인 감시도구로 활용될 것으로 기대된다.
