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원민구,정시화,허남수,김우곤,이형연 한국원자력학회 2024 Nuclear Engineering and Technology Vol.56 No.1
In this study, the influence of thermal aging on structural integrity is investigated for Gr. 91 steel. A commercial grade Gr. 91 steel is used for the virgin material, and service-exposed Gr. 91 steel is sampled from a steam pipe of a super critical plant. Time versus creep strain curves are obtained through creep tests with various stress levels at 600 C for the virgin and service-exposed Gr. 91 steels, respectively. Based on the creep test results, the improved Omega model is characterized for describing the total creep strain curve for both Gr. 91 steels. The proposed parameters for creep deformation model are used for predicting the steady-state creep strain rate, creep rupture curve, and stress relaxation. Creep-fatigue damage is evaluated for the intermediate heat exchanger (IHX) in a large-scale sodium test facility of STELLA-2 by using creep deformation model with proposed creep parameters and creep rupture curve for both Gr. 91 steels. Based on the comparison results of creep fatigue damage for the virgin and serviceexposed Gr. 91 steels, the thermal aging effect has been shown to be significant.
Non-linear modeling of stress relaxation curves for Grade 91 steel
김우곤,박재영,원민구,이형연,허남수 대한기계학회 2018 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.32 No.3
We focused on the modeling of the high-temperature Stress relaxation (SR) curves for Gr. 91 steel using two nonlinear models of a spring-dashpot and Peleg model to get a better fit to experimental relaxation data. A series of SR tests were performed under a constant strain of 0.6 % at 500, 550, 600 and 650 °C. The SR behavior of Gr. 91 steel was clarified based on the experimental data. In the modeling of the SR curves, each parameter value for the two models was optimized to give the best fit to the experiment SR data. The springdashpot model did not match the experimental data at 500 and 550 °C, although the model showed good agreement with the experimental data at 600 and 650 °C. However, the Peleg model was superior to the spring-dashpot model for all temperature conditions, and its parameter values followed temperature dependence well. Using the Peleg model, the SR curves for Gr. 91 steel could be suitably modeled at different temperature ranges. The confidence of the Peleg model was validated from elastic-creep finite element analysis. It is suggested that the Peleg model can be a useful tool to characterize the relaxation behavior of Gr. 91 steel.
크리프 영역 고온 압력기기 및 배관의 설계평가 프로그램, HITEP_RCC-MRx의 개발
이형연(Hyeong-Yeon Lee),원민구(Min-Gu Won),정시화(Si-Hwa Jeong),허남수(Nam-Su Huh) 대한기계학회 2019 대한기계학회 춘추학술대회 Vol.2019 No.11
A web-based high-temperature design evaluation program for a pressure boundary component and piping system subjected to high-temperature operation in creep regime has been developed. The program, called “HITEP_RCCMRx,” is based on French nuclear grade high-temperature design code of RCC-MRx and enables a designer to conduct high-temperature design evaluations for a pressure boundary component and piping system according to RCC-MRx. HITEP_RCC-MRx consists of two modules: “HITEP_RCC-DBA,” which is programmed for the design-by-analysis (DBA) evaluation for class 1 pressure boundary components such as the pressure vessel and heat exchangers according to the RB-3200 procedures and “HITEP_RCC-PIPE,” which is programmed for the design-by-rule (DBR) evaluation according to the RB-3600 procedures. The program has been verified with a number of relevant example problems on modules of DBA and Pipe. It was shown from the verification procedure that HITEP_RCC-MRx is capable of conducting elevated temperature design evaluations in an efficient and reliable way.
초임계압 화력 과열기 구조의 고신뢰도 건전성 평가 방법
이형연,주용선,최현선,원민구,허남수 한국압력기기공학회 2020 한국압력기기공학회 논문집 Vol.16 No.1
Integrity evaluations on a platen superheater were conducted as per ASME Section VIII Division 2(hereafter ‘ASME VIII(2)’) which was originally used for design with implicit consideration of creep effects. A platen superheater subjected to severe loading conditions of high pressure and high temperature at creep regime in a supercritical thermal plant in Korea was chosen for present study. Additional evaluations were conducted as per nuclear-grade high-temperature design rule of RCC-MRx that takes creep effects into account explicitly. Comparisons of the two results from ASME VIII(2) and RCC-MRx were conducted to quantify the conservatism of ASME VIII(2). From present analyses, it was shown that the design evaluation results exceeded allowable limits of RCC-MRx for the plant design conditions although limits of ASME VIII(2) were satisfied regardless of operation time, which means that design as per ASME VIII(2) might be potentially non-conservative in case of operation in creep range. A high-temperature design evaluation program as per RCC-MRx, called ‘HITEP_RCC-MRx’ has been used and it was shown that pressure boundary components can be designed reliably with the program especially for the loading conditions of long-term creep conditions.
오승혁,류태영,박승현,원민구,강석준,이경수,이성호,김문기,최재붕 대한기계학회 2015 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.29 No.3
Over the last decade, primary water stress corrosion cracking (PWSCC) has been frequently found in pressurized water reactor (PWR)applications. Especially, PWSCC has occurred in long-term operated PWRs. As this phenomenon leads to serious accidents, we must bebeforehand with the anticipated problems. A typical PWR consists of J-groove welded components such as reactor pressure vessel closurehead and nozzles. Reactor pressure vessel closure head is made of SA508 and it is covered by cladding. Alloy 600 is used for nozzles. And J-groove weld is conducted with alloy 82/182. Different material properties of these metals lead to residual stress and PWSCCconsequentially. In this study, J-groove weld residual stress was investigated by a three-dimensional finite element analysis with an actualasymmetric J-groove weld model and process of construction. Also crack growth rate of PWSCC was evaluated from cracks applied onthe penetration nozzles. Based on these two values, one cannot only improve the structural integrity of PWR, but also explain PWSCCbehavior such that high residual stress at the J-groove weld area causes crack initiation and propagation through the surface of nozzles. Inaddition, crack behavior was predicted at the various points around the nozzle.
이진행,조영갑,이효광,박창규,오종명,유연식,원민구,허형 한국원자력학회 2023 Nuclear Engineering and Technology Vol.55 No.12
Fuel locking mechanisms (FLMs) are essential in upward-flow research reactors to prevent accidental fuel separation from the core during reactor operation. This study presents a novel design concept for a remotely controlled plate-type nuclear fuel locking mechanism. By employing electromagnetic field analysis, we optimized the design of the electromagnet for fuel unlocking, allowing the FLM to adapt to various research reactor core designs, minimizing installation space, and reducing maintenance efforts. Computational flow analysis quantified the drag acting on the fuel assembly caused by coolant upflow. Subsequently, we performed finite element analysis and evaluated the structural integrity of the FLM based on the ASME boiler and pressure vessel (B&PV) code, considering design loads such as dead weight and flow drag. Our findings confirm that the new FLM design provides sufficient margins to withstand the specified loads. We fabricated a prototype comprising the driving part, a simplified moving part, and a dummy fuel assembly. Through basic operational tests on the assembled components, we verified that the manufactured products meet the performance requirements. This remote-controlled micro locking mechanism holds promise in enhancing the safety and efficiency of plate-type nuclear fuel operation in upflow research reactors.
[세션초청논문] 크리프 영역 고온 압력기기의 고신뢰도 건전성 평가를 위한 HITEP 플랫폼의 개발
이형연(Hyeong-Yeon Lee),이제환(Jewhan Lee),정시화(Si-Hwa Jeong),원민구(Min-Gu Won),허남수(Nam-Su Huh) 대한기계학회 2020 대한기계학회 춘추학술대회 Vol.2020 No.12
A high-reliability integrity evaluation platform of ‘HITEP’ has been developed with web-based language for a pressure boundary component and piping system subjected to high-temperature operation in creep regime. The platform program, called “HITEP” means ‘HIgh Temperature integrity Evaluation Program” which is for design evaluation of high-temperature pressure boundary components and piping as per the two major design codes of ASME Section III Division 5 Subsection HB (‘ASME-HB’) and RCC-MRx. The HITEP platform enables a user to provide information of current status and the optimal maintenance time based on the integrity evaluations. The design evaluation modules of the HITEP platform have been verified with a number of relevant example problems for RCC-MRx and ASME-HB. Because current high-temperature design codes of ASME BPVC Section VIII and ASME B31.1 being used for high temperature pressure vessel and piping were shown to be potentially non-conservative for long-term creep conditions in previous studies, the HITEP platform might be contributing to enhancing reliability of a high temperature pressure boundary components in thermal power plant and refinery plants as well operating at high temperature in creep range.