• 산업경영시스템학회지
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• 제41권3호
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• pp.186-193
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• 2018

Modern manufacturing industries is to produce both precise and robust mechanical parts without failure while they are in service. In order to prevent a part failure for its lifetime, a mechanical design for a part should be examined on a basis of mechanical simulation. A nozzle plate, being a key part in steam engines, changes flow directions of steam in a turbine used in power plant. This paper is to the design and test for part safety and durability. Currently, nozzle plates are fabricated by welding nozzles to their plates. Welding causes some defects on the used materials while they are being manufactured. Another major defect is un-even pitches between welded nozzles. Welding causes phase changes because of high melting temperature of metal. This leads to decay on the welding spots, which weakens their structural strength and then, may lead to early damages on mechanical structures. This research proposes assembly-typed nozzle plate without welding. From the beginning, nozzle and plate are designed for insertion-typed assembly. Nozzle head and foot are designed in accordance with the grooves on outer ring and inner ring of a plate to make mating surfaces. Then the nozzle plate should be proved for structural and fatigue safety before they are put in manufacturing. This research adopts commercial softwares for modeling and mechanical simulation. The test result shows that the design with smaller mating area and deeper insertion produces higher safety in terms of structure and durability. From the conclusion, this paper proposes the assembly-typed nozzle plate to replace the welding typed.

• Nuclear Engineering and Technology
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• 제55권6호
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• pp.1974-1987
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• 2023

The load-following operation of small modular reactors (SMRs) requires accurate prediction of transient behaviors that can occur in the balance of plants (BOP) and the nuclear steam supply system (NSSS). However, 1-D thermal-hydraulics analysis codes developed for safety and performance analysis have conventionally excluded the BOP from the simulation by assuming ideal boundary conditions for the main steam and feed water (MS/FW) systems, i.e., an open loop. In this study, we introduced a lumped model of BOP fluid system and coupled it with NSSS without any ideal boundary conditions, i.e., in a closed loop. Various methods for coupling boundary conditions at MS/FW were tested to validate their combination in terms of minimizing numerical instability, which mainly arises from the coupled boundaries. The method exhibiting the best performance was selected and applied to a transient simulation of an integrated NSSS and BOP system of a SMART. For a transient event with core power change of 100-20-100%, the simulation exhibited numerical stability throughout the system without any significant perturbation of thermal-hydraulic parameters. Thus, the introduced boundary-condition coupling method and BOP fluid system model can expectedly be employed for the transient simulation and performance analysis of SMRs requiring daily load-following operations.

• 전력전자학회:학술대회논문집
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• 전력전자학회 2001년도 Proceedings ICPE 01 2001 International Conference on Power Electronics
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• pp.56-59
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• 2001

An effective method of detecting inter-turn short circuits on round rotor windings is described. Shorted-turns can have significant effects on a generator and its performance. A method of detecting inter-turn short circuits on rotor windings is described. The approach used is to measure the rate of change of the air-gap flux density wave when the rotor is at operating speed and excitation is applied to the field winding. The inter-turn short circuits sensor for synchronous generator's field winding has been developed. The sensor, installed in the generator air-gap, senses the slot leakage flux of field winding and produces a voltage waveform proportional to the rate of change of the flux. For identification of reliability for sensor, a inter-turn short circuits test was performed at the West-Inchon combined cycle power plant on gas turbine generator and steam turbine generator. This sensor will be used as a detecting of shorted-turn for field winding of synchronous generator. The purpose of this paper is to describe the design and operation of a sensitive inter-turn short circuits detector. In this paper, development of inter-turn short circuits sensor for field winding of synchronous generator and application in a field.

• 동력기계공학회지
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• 제13권5호
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• pp.95-102
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• 2009

A steam generator (boiler) in thermal power plants, consisting of more than 30,000 parts and components, can lead to the plant shutdown with damage to even the small part of the components; esp., like weld failures on boiler tubes. Consequently it is greatly demanded to improve the quality of the weld on the boiler tube for the stable operation of the power plants. Because of the feature of the welding, which is done past by melting the work pieces and adding a filler material that cools to become a strong coalescence, there is a great possibility that weld failures take place. As a result, it is regulated to make a non-destructive testing, like radiography test, to detect defects and flaws in the weld. The current film radiography test provides a lower image quality exceeding 2.0% of a basic quality level for a penetrameter, it is very likely to fail to detect micro defect. As a result, the prevention for the boiler tube failure has not been made effectively. In this study, computed radiography technology has been applied as a digital radiography test to the boiler tube weld, and Se-75 radiation source was used to improve the image quality, instead of Ir-192 source. As a result of this study, it is proven to save the time and cost for test and to enhance the quality level of penetrameter penetrating image, which enables to upgrade the quality of radiography test to the boiler tube weld.

• 한국압력기기공학회 논문집
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• 제6권2호
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• pp.20-27
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• 2010

In order to prevent the corrosion of component contacted primary water designed alloy 600 material in the nuclear power plant. But the primary water stress corrosion cracking(PWSCC) of alloy 600 and weld area occurs continuously due to the residual stress. The leakage accident resulted from PWSCC in the drain nozzle of the steam generator of domestic power plants. Heater sleeves of the pressurizer are welded with alloy 600 weld material and therefore exposed to the primary water environment. PWSCC occurred in heater sleeve material and weld area of many foreign power plants. The current issue of domestic nuclear power plants are consequently concentrated to PWSCC of similar material. In order to improve the detection and the sizing of the PWSCC in the welding sleeve of the pressurizer, the automatic UT system and multi-directions probe sets have been developed. The experimental studies have been performed using the mock-up block containing artificial reflectors(ID connected EDM notch) and semi-artificial cracks made from thermal fatigue. The automatic UT System is applied in the detection and the length sizing of the ID/OD on the tube and the J-groove weld area of the artificial reflectors and results of the detection and the sizing are compared respectively. Also, the developed automatic UT system is successfully accomplished to inspect the heater sleeve and the J-groove weld area on the pressurizer for the detection of PWSCC.

• 한국유체기계학회 논문집
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• 제16권4호
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• pp.35-43
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• 2013

Most of the nuclear power plants(NPPs) adopts pressure difference type flow meters such as venturi and orifice meters for the measurement of feedwater flow rates to calculate reactor thermal power. However, corrosion products in the feedwater deposits on the flow meter by fouling as operating time goes. These effects lead to severe errors in the flow indication and then determination of reactor thermal power. The averaging BDFT, which has developed by Yun et al., has a potentiality to minimize this problem thanks to its inherent measurement principle. Therefore, it is expected that the averaging BDFT can replace the venturi meter for the feedwater pipe of steam generator of NPPs. The present work compares the amplification factor, K, based on CFD calculation against the K obtained from experiments in order to confirm whether a commercial CFD code can be applicable to the evaluation of characteristic for the averaging BDFT. In addition to this, the simulations to take into account of fouling effect are also carried out by rough wall option. The results show that the averaging BDFT is a promising flow meter for the accurate measurement of flow rates in the fouling condition of the NPPs.

• 열처리공학회지
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• 제35권3호
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• pp.121-129
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• 2022

Recently the growth of the renewable energy production has caused the flexible operation in LNG combined cycle power plant. Due to the rapid start and stop operations, large CrMoV castings used for turbine casings and valve bodies could be distorted and lead to replacement or welding repair. This study was performed to find out the characteristics of the repair welding for a damaged CrMoV casting steel. A typical field repair method (arc & TIG welding) was applied to making specimens. The degraded N2 packing head sample from the steam turbine was used. The evaluations of weldments were carried out in terms of microstructural characterization, microhardness measurements, tensile, creep-rupture and fatigue tests. Color etching was also applied for better understanding of welding microstructures. As the boundary between HAZ and base material was deteriorated by welding, it caused microstructural changes formed during PWHT and the shortening of the remaining residual life. By comparing the properties according to repair welding method, it was possible to derive what important welding factors were. As a result, arc welding method is more suitable for repair welding on CrMoV castings.

• Nuclear Engineering and Technology
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• 제25권2호
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• pp.276-284
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• 1993

ABB-CE사의 System-80 설계 특성 중 원자로 출력 급감발 제어계통(RPCS : Reactor Power Cutback System)은 2개의 주급수 펌프 중 1대가 정지하거나 전출력 부하 상실사고인 경우에도 원자로 정지없이 운전하게 함으로써 원전의 경제성 향상에 도움을 주고 있다. 이러한 RPCS의 적용 범위를 확대하여 단일제어봉 낙하를 포함한 제어봉 인입편차(inward deviation)가 발생하는 경우에도 RPCS를 작동시키면 원자로를 정지시키지 않고 운전을 계속할 수 있는지를 분석하였다. 즉 제어봉 인입편차가 발생시 제어봉을 순간적으로 낙하시켜 1차계통의 출력을 낮추면서 원자로를 정지시키지 않고도 과도현상을 수습할 수 있는지 분석하였다. 이렇게 확대된 RPCS는 미국 EPRI의 개량형 경수로 요건사항을 만족하는 것이며 제어봉 인입편차의 과도상태를 수용할 수 있도록 하는 ABB-CE사의 System-80+ 설계 항목에도 포함되어 있다. 본 연구에서는 System-8O+에 대하여 RPCS의 작동에 의한 제어봉의 삽입과 그에 따른 핵증기 공급계통의 변화를 모사할 수 있는 노심해석 모델을 개발하였다. 연구 결과 단일 제어봉 낙하를 포함한 제어봉 인입편차가 발생되어도 원자로 출력 급감발 제어를 확대 적용하는 경우 원자로 정지를 방지할 수 있게 되어 원전의 이용율을 향상시킬 수 있을 것으로 검토되었다.

• Nuclear Engineering and Technology
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• 제18권1호
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• pp.9-16
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• 1986

1984년 11월 14일 원자력 1호기에서 발생된 주급수 상실사고에 대한 계통의 열수력학적인 거동을 모의·해석하고, 발전소 실측자료와의 비교를 통하여 사용된 전산코드의 신뢰도를 평가하였다. 모의된 열수력학적 변수들은 발전소 실측자료와 비교적 잘 일치하였으나 원자로 트립시에 증기발생기 증기유량과 주 냉각재 계통 평균온도에 있어서 약간의 차이를 보였다. 이는 원자로 트립시 깎은 시간에 급격한 노심 출력의 감소로 인하여 열·수력학적 변수들에 큰 변화를 야기하여 발전소 실측자료가 과도상태에서의 불학실성을 내포하기 때문으로 예측되었다. 해석에 사용된 전산코드는 RELAP5/MOD1/CY018로부터 불합리한 oscillation을 일으키는 interphase drag 및 wall heat transfer model의 수정을 통하여 개발된 RELAP5/MOD1/NSC이다.

• 대한토목학회논문집
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• 제32권2A호
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• pp.123-130
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• 2012

증기를 발생시켜 터빈(turbine)을 회전시키는 화력 및 원자력 발전 계통에서 냉각시설은 필수적인 구조물이며, 냉각수 순환 계통은 일반적으로 해수를 취수하여 발전소 내의 복수기까지 유입시켜 증기와 열 교환 후 다시 외해로 배출시키는 형태를 취하고 있다. 최근 냉각수 취 배수 방식을 표층 취 배수 방식이 아닌 심층 취 배수 방식으로 변경하고 있는데, 기존 원전의 재순환 온도에 대한 영향을 최소화 하고, 온배수 방류시 밀도차로 인한 부력으로 온배수 혼합효과를 높여 온배수에 의한 환경피해 범위를 최소화하기 위해서이다. 특히, 하절기에 저층의 저온 냉각수를 취수할 수 있다는 이점 때문에 향후 계획되는 발전소들도 심층 취 배수 방식을 도입할 것으로 예상된다. 본 연구에서는 원자력 발전소의 냉각시설 중 심층 취 배수 구조물의 입구 주변을 3차원 전산유체역학 코드인 $FLOW-3D^{(R)}$로 모사하여 그 흐름특성을 분석하였다. 취수구(intake)의 경우 연직취수 조건에서 유속 덮개(Velocity cap), 배수구(diffuser)의 경우 방류수의 분사방향에 변화를 주어 모의하였으며, 그 결과 취수구의 경우 유속덮개에 의한 연직 유속성분의 현저한 감소로 인한 어류 유입영향을 최소화할 수 있을 것으로 판단되며, 배수구 희석효과는 Jirka 및 Harleman이 제시한 2차원 온배수 프룸(frume)과 잘 일치 하는 것으로 나타났다.