고온 고압 환경 부식생성물에 의한 금속 표면 침착(fouling) 저감 연구

다국어 초록 (Multilingual Abstract)

Fouling can be generally defined as a state of deposited material layers in the water contained of various kinds of foreign substances for the heat exchanger surface or structural shapes over a long period of time depending on the chemically, biologically or physically accumulated, and could degrade the capabilities of own original capabilities. In this study, an experiment for the deposition of corrosion products as fouling in nuclear fuel cladding was simulated. Dispersion and corrosion tests were performed using dispersants in order to reduce the fouling due to corrosion products.
A test loop was designed to simulate the attachment of crud on the nuclear fuel cladding. The formation of deposits was measured in the boiling region and the non-boiling region. The amounts of formed deposit were very low in the non-boiling condition, while those of formed deposit were increased in the region in which the boiling occurred. Deposit was analyzed using EDS, and B was detected by SIMS analysis. The deposited amounts were found to be reduced by increasing the pH with adjusting the concentration of lithium and boron. For the power plant which experienced AOA, the plant was advised to use 3.5 ppm Li at the beginning of a cycle and to operate at pH 7.1 according to the recent EPRI guidelines. However, the recent experimental data from the test loop in this study showed that the amounts of formed deposit on fuel cladding surface were reduced with 5.0 ppm Li at the beginning of a cycle and operating at pH 7.4, hence AOA is considered to be decreased. The deposit of Ni and Fe was tended to increase in the test of the initial operation conditions rather than the test after the middle of operation conditions. Thus, the initial operation conditions may be more likely to influence on the AOA of nuclear power plants.
SNB phenomenon of the fluid passing through the surface of heated rods was evaluated for the thermal-hydraulic behavior of simulated test loop. In this experiment, the phase transfers were increased with higher heat flux, which was supplied to the wall of the heated rods, and the vapor volume fraction increased.
The characteristics of crud specimen attached to the real fuel cladding was analyzed. The crud was mainly found in the upper part of the fuel cladding wall and the thickness of the crud was thin in the lower part of the fuel cladding wall. The curd deposited in the fuel cladding from Plant B suffered from AOA was thicker than that of Plant A.
Sedimentation experiment was performed using dispersants of lower concentrations. Higher concentrations of PAA improved the dispersal capability from the sedimentation tests depending on various concentrations of PAA. The dispersal capability tests were carried out for type and concentration ratio (Fe: candidate dispersant) of candidate dispersants with high concentrations of dispersants. Fe-dispersant concentration ratio has a significant effect on the dispersion stability. The tendency of aggregation was found in PAA and PMAA with Fe-dispersant concentration ratio of 1, but PAA and PMAA with Fe-dispersant concentration ratio of 0.01, performance of dispersal capability was improved until 14 days. Dispersant, PAA-co-MA had an adverse effect on dispersion stability due to remarkable cohesion from the beginning in the case of high Fe concentration (Fe 10,000 ppm). Therefore, appropriate Fe-dispersant concentration ratio is recommended to add as a dispersant because Fe-dispersant concentration ratio and Fe concentration has significant impact on the stability of dispersion. Finally, improvements for dispersion stability were evaluated using dispersant infection for long periods (14 days).
Dispersal capability through transmittance measurements was performed to evaluate quantitatively the performance improvement by injecting dispersants. Dispersant injection showed improved dispersal capability when compared to the condition with no dispersants. Dispersal capability has not seemed to have proportional to the concentrations of dispersants. The dispersion efficiency was improved when the Fe-dispersant ratio was from 0.1 to 0.01. The Fe-dispersant ratio of 0.1 showed the highest dispersal capability.
Corrosion test was performed to determine the corrosion effects under the corrosive environments, low dispersant concentration (0~100 ppb PAA) and temperature (300℃) on carbon steel specimen. Protective oxidative layer was formed on all of the carbon steel specimen over time, and corrosion rate was decreased. All specimens were considered to form a protective oxide layer regardless of whether dispersant injection, and had corrosion rate of about 0.2 mpy (mils per year) after 180 days. PAA concentration of 1 ppm was estimated to have no effect on the behavior of oxide layer formation according to corrosion test in this study.
Assessment results of corrosion test on carbon steel (SA 106) specimen with corrosive environments, high concentration of dispersant concentration (PAA, 0~100 ppm) and temperature (40℃, 65℃, 93℃) are as follows. Corrosion rate was increased with higher temperature and amounts of dispersant infection. Injection under 30 ppm did not increase the corrosion rate largely, but 60 ppm of PAA sharply increased the corrosion rate. At the highest concentration, 100 ppm, corrosion rate had about 4 mpy, and this is considered that the corrosion rate was significantly increased about 10 times compared to no PAA injected condition.
Assessment of resuspension behavior of iron oxide deposited in the fluid flowing environment by resuspension experiment is as follows. Total amounts of Fe (total Fe ion concentration) suspended in water for 24 hours were found to increase with the amount of dispersant increased. Total Fe ion concentration when the PAA is 1 ppm increased about 2.5 times than PAA 100 ppm. The floating effect of dispersant was the greatest when the dispersant concentration was 100 ppm.

목차 (Table of Contents)

• Ⅰ. 서론 1
• Ⅱ. 이론적 배경 6
• 2-1. 표면 침착(Fouling) 6
• 2-1-1. 표면 침착의 종류 6
• 2-1-2. 표면 침착 기구 10
• 2-1-3. 표면 침착 모델 15
• 2-2. 고분자 분산제를 통한 표면침착억제 21
• 2-2-1. PAA 화학특성 21
• 2-2-2. PAA 열분해특성 25
• Ⅲ. 고온 고압환경 금속 표면 침착(fouling)모사 37
• 3-1. 저온 침착 모사시험 37
• 3-1-1. 저온 침착 모사시험장치 및 실험방법 37
• 3-1-2. wire heating 침착기초시험 40
• 3-2. 고온 고압환경 금속표면침착 실증시험장치 열수력해석 43
• 3-2-1. 금속표면침착 실증시험장치 열원부 모델링 43
• 3-3. 고온 고압환경 금속표면침착 모사 46
• 3-3-1. 고온 고압환경 금속표면침착 실증시험장치 46
• 3-3-2. 고온 고압환경 금속표면침착 모사 시험방법 52
• 3-4. 원전 피복관 크러드 분석 56
• 3-4-1. 원전 크러드 시편분석 56
• Ⅳ. 고분자 분산제를 통한 표면 침착 억제 시험 58
• 4-1. 고분자 분산제 분산성능시험 58
• 4-1-1. 침강시험 58
• 4-1-2. 투과율 측정 61
• 4-2. 일반부식시험 65
• 4-2-1. 분산제 부식시험(고온) 65
• 4-2-2. 분산제 부식시험(저온) 66
• 4-3. 재분산도 시험 68
• 4-3-1. 실험방법 68
• Ⅴ. 실험결과 및 고찰 71
• 5-1. 침착 모사 예비시험결과 71
• 5-1-1. 저온 침착시험 실험결과 71
• 5-1-2. Wire heating 침착기초실험결과 79
• 5-2. 고온 고압환경 금속표면침착 실증시험장치 열수력해석 결과 92
• 5-2-1. 금속표면침착 실증시험장치 열수력해석결과 92
• 5-2-2. 가동원전 원전연료 열수력 거동 평가분석결과 96
• 5-3. 고온 고압환경 금속표면침착 모사시험 98
• 5-3-1. 고온 고압환경 금속표면침착 실증장치 시험결과 98
• 가. 농도, 유지시간 영향 98
• 나. pH 영향 108
• 다. 수소농도영향 123
• 5-4. 원전 피복관 크러드 분석 133
• 5-5. 고분자분산제 분산성능 시험 결과 141
• 5-5-1. 침강시험 141
• 5-5-2. 투과율측정 151
• 5-6. 일반부식시험 162
• 5-6-1. 분산제 부식시험(고온)결과 163
• 5-6-2. 분산제 부식시험(저온)결과 168
• 5-7. 재분산도 시험 191
• Ⅵ. 결론 197
• 참고문헌 202
• 요약 213