Chemical Effects on PWR Sump Strainer Blockage after a Loss-of-Coolant Accident: Review on U.S. Research Efforts

반치범 한국원자력학회 2013 Nuclear Engineering and Technology Vol.45 No.3

Industry- or regulatory-sponsored research activities on the resolution of Generic Safety Issue (GSI)-191 were reviewed,especially on the chemical effects. Potential chemical effects on the head loss across the debris-loaded sump strainer under a post-accident condition were experimentally evidenced by small-scale bench tests, integrated chemical effects test (ICET), and vertical loop head loss tests. Three main chemical precipitates were identified by WCAP-16530-NP: calcium phosphate,aluminum oxyhydroxide, and sodium aluminum silicate. The former two precipitates were also identified as major chemical precipitates by the ICETs. The assumption that all released calcium would form precipitates is reasonable. CalSil insulation needs to be minimized especially in a plant using trisodium phosphate buffer. The assumption that all released aluminum would form precipitates appears highly conservative because ICETs and other studies suggest substantial solubility of aluminum at high temperature and inhibition of aluminum corrosion by silicate or phosphate. The industry-proposed chemical surrogates are quite effective in increasing the head loss across the debris-loaded bed and more effective than the prototypical aluminum hydroxide precipitates generated by in-situ aluminum corrosion. There appears to be some unresolved potential issues related to GSI-191 chemical effects as identified in NUREG/CR-6988. The United States Nuclear Regulatory Commission, however,concluded that the implications of these issues are either not generically significant or are appropriately addressed, although several issues associated with downstream in-vessel effects remain.

원자력발전소 비안전등급 배관의 내진해석 방법론 연구

서건창,반치범 한국압력기기공학회 2022 한국압력기기공학회 논문집 Vol.18 No.1

Currently, there is no technical standard and regulation for seismic analysis of non-nuclear safety piping. Accordingly, ASME Sec.III ND, a standards applied to safety class 3 piping, is applied. However, the technical standard applied for other than seismic analysis is ASME B31, which leads to controversy. In this study, the feasibility of applying ASME B31E was confirmed by reviewing rulescomparing technical standards, and evaluating piping allowable stress margins. The evaluation revealed that applying ASME B31.1 as a technical standard is too conservative compared to ASME Sec.III ND. On the other hand, ASME B31E (issued at the request of the industry) clearly presents the technical standards for seismic analysis of ASME B31 piping, and shows a similar level of conservatism compared to ASME Sec.III ND. It is expected to reduce the controversy over technical standards for seismic analysis of non-nuclear safety piping by applying ASME B31E.

고전압차단기 유압식 조작기 Pilot Valve 유밀부 누설 원인 분석 및 예비변형에 따른 내부 누유방지 방안 연구

안형환,반치범 대한기계학회 2023 大韓機械學會論文集A Vol.47 No.3

While the high voltage circuit breaker hydraulic actuator valves open and close for a very short period of time (~ms), the pilot valve sealing failure which open close at first, and the behavior of the oil-sealing according to repeated loads wer analyzed. As a very high impact load is applied when opening and closing the oil-sealing part, cracks in the oil-sealing part or uneven deformation between the parts forming the oil-sealing part may occur, and unnecessary maintenance costs may occur due to the failure of the oil-sealing part. To prevent this, the convergence value of the oil-sealing deformation according to the repeated impact load of the oil-sealing portion was checked, and a method was developed and demonstrated to prevent internal leakage by applying a preload to the oil-sealing portion. 매우 짧은 시간(~ms) 동안 개폐되는 고전압차단기 유압식 조작기 valve 중 가장 먼저 개폐되는 pilot valve 유밀부의 유밀 실패사례를 분석하고 반복하중에 따른 유밀부의 거동을 분석하였다. 유밀부 개폐 시 매우 높은 충격하중이 가해짐에 따라 유밀부의 깨짐 혹은 유밀부를 형성하는 부품 간의 불균일한 변형이 발생할 수 있으며 이로 인한 유밀 실패로 불필요한 유지보수 비용이 발생할 수 있다. 이를 방지하기 위해 유밀부의 반복 충격하중에 따른 유밀부 변형의 수렴 값을 확인하고, 이를 이용하여 유밀부에 예비하중을 가하여 내부 누유를 방지할 수 있는 방법을 개발 및 입증하였다.

증기발생기 전열관 충격 미끄럼 마모 모델 개발

권대엽,반치범,신희재,오영진 한국압력기기공학회 2023 한국압력기기공학회 논문집 Vol.19 No.2

The phenomenon of fretting wear due to the flow-induced vibration in steam generator (SG) tube is a significant degradation mechanism in nuclear power plants. Fretting wear in SG tube is primarily attributed to the friction and impact forces between the SG tube and the tube support structures, experienced during nuclear power plants operation. While the Archard model has generally been used for the prediction of fretting wear in SG tube, it is limited by its linear nature. In this study, we introduced an "Impact Shear Work-rate" (ISW) model, which takes into account the combined effects of impact and sliding. The ISW model was evaluated using existing experimental data on fretting wear in SG tube and was compared against the Archard model. The prediction results using the ISW model were more accurate than those using the Archard model, particularly for impact forces.

원전 이용률의 의의 및 증진방안 고찰

이돈국,반치범 한국압력기기공학회 2022 한국압력기기공학회 논문집 Vol.18 No.2

Unit capacity factor (utilization rate) of nuclear power plants (NPPs) is an important performance indicator. Since the first commercial operation of Kori Unit 1 began in April 1978, the utilization rate of domestic NPPs has gradually increased, reaching 90% from the end of the 1990s. However, due to various issues such as the Fukushima accident in 2011, corrosion of the CLP, the utilization rate dropped to 65∼80%. In the early 1980s, the utilization rate of the U.S. NPPs was around 60%. However, since 2004, it has been consistently maintained above 90%. Therefore, in this study, we first examined the causes of declining the utilization rate in domestic NPPs. Next, the significances of the utilization rates are reviewed in five aspects: investment capability, electricity rate, safety and export, etc., with discussion on the current status of the utilization rates in the U.S. Based on this, three key factors are derived as the reasons of the increasing: equipment reliability program, on-line maintenance and the pursuit of institutional rationality. And finally, by synthesizing above results, the measures for increasing the utilization rate of domestic NPPs are proposed in terms of equipment management, institutional improvements, and personnel resources.

대기 노출된 Al6061 알루미늄 합금 산화막에 대한 미세조직 분석

조준영,권대엽,최원준,반치범 한국표면공학회 2022 한국표면공학회지 Vol.55 No.5

Al6061 aluminum alloy specimens were exposed to atmospheric conditions for maximum 24 months. 24-month exposure specimen showed some more frequent and larger size of corrosion products and pitting on the surface compared with the 12-month exposure specimens. The XRD examination revealed the dominant surface oxide phases of Al2O3 and Al(OH)3. The oxide thickness at uniform oxidation (or non-pitting) region was not much changed over exposure time. The 1.2 μm deep oxygen penetration area was found in the 12-months exposed specimen near the thin uniform aluminum oxide film. The line-EDS was conducted through the penetration regions and non-penetrated grain boundary. There were signs of O and Si concentration through the penetration region, whereas non-penetration region showed no concentration of O or Si. It was confirmed that pitting is a more severe degradation mode in Al6061 (max. >4 μm deep) compared with the uniform oxidation (max. ~200 nm deep) up to 24-months exposure.

시계열 피로 데이터를 이용한 MCMC 기반 확률론적 피로수명 예측

박재필(Jae Phil Park),반치범(Chi Bum Bahn),Subhashish Mohanty 대한기계학회 2018 대한기계학회 춘추학술대회 Vol.2018 No.12

원전 격납건물 라이너플레이트 소재인 탄소강의 환경영향인자에 따른 부식 거동 연구

최원준(Won Jun Choi),반치범(Chi Bum Bahn) 대한기계학회 2019 대한기계학회 춘추학술대회 Vol.2019 No.4

Bayesian approach for prediction of primary water stress corrosion cracking in Alloy 690 steam generator tubing

팔라크 다위 파이지로르,반치범 한국원자력학회 2022 Nuclear Engineering and Technology Vol.54 No.9

Alloy 690 tubing has been shown to be highly resistant to primary water stress corrosion cracking (PWSCC). Nevertheless, predicting the failure by PWSCC in Alloy 690 SG tubes is indispensable. In this work, a Bayesian-based statistical approach is proposed to predict the occurrence of failure by PWSCC in Alloy 690 SG tubing. The prior distributions of the model parameters are developed based on the prior knowledge or information regarding the parameters. Since Alloy 690 is a replacement for Alloy 600, the parameter distributions of Alloy 600 tubing are used to gain prior information about the parameters of Alloy 690 tubing. In addition to estimating the model parameters, analysis of tubing reliability is also performed. Since no PWSCC has been observed in Alloy 690 tubing, only right-censored free-failure life of the tubing are available. Apparently the inference is sensitive to the choice of prior distribution when only right-censored data exist. Thus, one must be careful in choosing the prior distributions for the model parameters. It is found that the use of non-informative prior distribution yields unsatisfactory results, and strongly informative prior distribution will greatly influence the inference, especially when it is considerably optimistic relative to the observed data.

Statistical analysis of parameter estimation of a probabilistic crack initiation model for alloy 182 weld considering right-censored data and the covariate effect

박재필,박찬석,오영진,김지현,반치범 한국원자력학회 2018 Nuclear Engineering and Technology Vol.50 No.1

To ensure the structural integrity of nuclear power plants, it is essential to predict the lifetime of Alloy182 weld, which is used for welding in nuclear reactors. The lifetime of Alloy 182 weld is directly relatedto the crack initiation time. Owing to the large time scatter in most crack initiation tests, a probabilisticmodel, such as the Weibull distribution, has mainly been adopted for prediction. However, since statisticallymore advanced methods than current typical methods may be applied, we suggest a statisticalprocedure for parameter estimation of the crack initiation time of Alloy 182 weld, considering rightcensoreddata and the covariate effect. Furthermore, we suggest a procedure for uncertainty evaluationof the estimators based on the bootstrap method. The suggested statistical procedure can be appliednot only to Alloy 182 weld but also to any material degradation data set including right-censored datawith covariate effect.