• Nuclear Engineering and Technology
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• v.25 no.4
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• pp.515-528
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• 1993

In a Passive PWR, the successful actuation of Automatic Depressurization System (ADS) is essentially required so that no core damage is occurred following small LOCA. But it has been shown in the previous studies that Core Damage Frequency (CDF) from small LOCA is significantly caused by unavailability of ADS. In this study, the design vulnerabilities impacting the ADS unavailability have been identified and the design improvement items have been proposed through the system reliability assessment using the fault tree methodology The impacts on CDF according to the change of system unavailability have also been analyzed. In addition, small LOCA simulation using RELAP5/MOD3 code has been performed to show the thermal-hydraulic feasibility of the suggested design enhancements.

• Proceedings of the Korean Nuclear Society Conference
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• 1996.05b
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• pp.713-718
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• 1996

Risk Monster는 한국원자력연구소에서 개발한 risk monitor로서 발전운영시 및 정비계획시 원전의 기기 운영 상태 (=Configuration)의 실제 변경이나 계획시 이에 따른 원전의 안전성 (또는 Risk)를 평가 및 감시하는 시스템이다. 안전성은 노심손상 빈도를 가지고 평가하며 이 Risk Monster의 국내 원전에의 활용, 특히 on-line maintenance시의 활용을 모색하였다. 외국에서처럼 국내 원전에서도 risk monitor를 이용한 on-line maintenance를 실시 하여 원전의 경제성 및 안전성을 향상 시켜야 한다.

• Journal of the Earthquake Engineering Society of Korea
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• v.11 no.3 s.55
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• pp.33-42
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• 2007

In this study, for research on an improvement of the seismic safety of an EDG system, a small scale EDG system was manufactured. For the isolation system, the Coil Spring-Viscous Damper systems were selected. For the shaking table test, 3 kinds of seismic motions were selected which had different frequency contents. In this study, the isolation effects were different and they depended on the input seismic motion. In the case of an NRC earthquake which had low fiequency contents, the isolation effects of the horizontal direction were 20%. But for the seismic motions which had high fiequency contents, the isolation effects were $50{\sim}70%$. In the case of the vertical direction, poor isolation effects were observed. It was because the design properties and the real properties of the isolation system were a little different.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.36 no.1
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• pp.97-102
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• 2012

Alternate alternating current (AAC) is used in nuclear power plants (NPPs) in order to cope with station black outs (SBOs). AAC has been provided using diesel engine drive types in Korea's NPPs. The structure of gas turbine generators (GTGs) is simpler than that of diesel generators (DGs), and GTGs have the advantage of longer maintenance intervals. However, GTG-AAC was not used in NPPs in Korea because of the lack of operation/maintenance experience. The purpose of this paper is to analyze the safety of APR+ considering a diversity of AAC types. This paper analyzes reliability data, mechanical specifications of DGs and GTGs, and the sensitivity of core damage frequency to the ACC type.

• Nuclear Engineering and Technology
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• v.21 no.1
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• pp.1-11
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• 1989

Numerous losses of decay heat removal capability have occurred at U during stutodwn while its significance to safety is needless to say. A study is carried out as an attempt to assess what could be done to lower the frequency of these events and to mitigate their consequences in the unlikely event that one occurs. The shutdown risk model is developed and analyzed using Event/Fault Tree for the typical pressurized water reactor. The human cognitive reliability (HCR) model, two-stage bayesian approach and staircase function model are used to estimate human reliability, initiating event frequency and offsite power non-recovery probability given loss of offsite power, respectively. The results of this study indicate that the risk of a Pm at shutdown is not much lower than the risk when the plant is operating. By examining the dominant accident sequences obtained, several design deficiencies are identified and it is found that some proposed changes lead to significant reduction in core damage frequency due to loss of cooling events.

• Proceedings of the Korea Institute of Fire Science and Engineering Conference
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• 2011.11a
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• pp.231-234
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• 2011

기존 국내원전의 화재 PSA는 기존 EPRI가 개발한 방법론을 이용하여 화재 PSA를 수행하여 오고 있다. 미국 NRC는 EPRI와의 공동연구를 통하여 새로운 PSA 방법론(NUREG/CR-6850)을 개발하였고, NFPA-805 코드를 적용하는 미국 원자력발전소들에 대해서 이 방법론을 적용한 PSA를 수행하는 것을 권고하고 있다. 본 논문에서는 국내 원전의 참조 주제어실을 대상으로 신규 방법론을 적용하여 노심손상빈도 영향을 평가하였고, 국내원전에 신규 방법론 적용시 논의되어야 할 사항들을 포함하였다.

• Proceedings of the Korean Society of Disaster Information Conference
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• 2022.10a
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• pp.87-88
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• 2022

"국민안심" 구현을 위한 가동원전의 안전성 확보에 대하여 예측, 예방, 대응 분야에서 연구를 진행하고 있으며,노심손상빈도(CDF)를 1/2수준으로 저감하기 위한 가동원전 심층방어 강화 기술에 대한 연구를 진행하고 있다. 가동원전의 화재 방호 설비를 강화하고자 디지털 트윈 기반의 플랫폼을 구축하여 화재 감지 시스템과 화재 진압 설비에 대한 개발을 진행하고 있다. 원전 자체 소방대가 화재현장을 원활하게 진입할 수 있게 가능하며 더 나아가 CDF를 저감하기 위해 화재 진압실패확률(Non-Suppression Probability)을 낮추고자 하였다. 본 연구를 통해 기존대비 효과적인 화재 방호 설비 기술이 개발될 것으로 보이며 이와 더불어 비즈니스 모델을 구축하여 신사업을 도모할 수 있을 것으로 기대된다.

• Proceedings of the KSME Conference
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• 2007.05b
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• pp.3464-3466
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• 2007

Power uprate is the process of increasing the maximum power level at which a commercial nuclear power plant may operate. Power uprate applications(113 units) for NPPs(Nuclear Power Plants) were recently approved in the United States. Utilities have been using power uprates since the 1970s as a way of increasing the power output of their nuclear plants. To increase the power output of a reactor, typically more highly enriched uranium fuel and/or more fresh fuel is used. This enables the reactor to produce more thermal energy and therefore more steam, driving a turbine generator to produce electricity. In this paper, the propriety of power uprate is explained through the review on the power uprate method and the changes of the physical parameters due to power uprate. The analysis results showed that the CDF(Core Damage Frequency) and LERF(Large Early Release Frequency) are affected in the current probabilistic safety assessment (PSA) model.

• Journal of the Korean Society for Nondestructive Testing
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• v.34 no.4
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• pp.311-317
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• 2014

The Pressurized water reactor owners group (PWROG) developed and applied a risk-informed in-service inspection (RI-ISI) program, as an alternative to the existing ASME Section XI' sampling inspection method. The RI-ISI programs enhance overall safety by focusing inspections of piping at high safety significance (HSS) locations where failure mechanisms are likely to be present. Additionally, the RI-ISI program can reduce nondestructive evaluation (NDE) exams, man-rem exposure for inspectors, and inspection time, among other benefits. The RI-ISI method of in-service piping inspection was applied to 3 units (KSNPs: Korea standard nuclear power plants) and is being deployed to the other units. In this paper, the results of RI-ISI for a Framatome type (France CPI) nuclear power plant are presented. It was concluded that application of RI-ISI to the plant could enhance and maintain plant safety, as well as provide the benefits of greater reliability.

• Journal of the Korean Society of Safety
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• v.28 no.3
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• pp.123-128
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• 2013

The Advanced Power Reactor Plus(APR+), which is a GEN III+ reactor based on the APR1400, is being developed in Korea. In order to enhance the safety of the APR+, a passive auxiliary feedwater system(PAFS) has been adopted in the APR+. The PAFS replaces the conventional active auxiliary feedwater system(AFWS) by introducing a natural driving force mechanism while maintaining the system function of cooling the primary side and removing the decay heat. As the PAFS completely replaces the conventional AFWS, it is required to verify the cooling capacity of PAFS for the core damage frequency(CDF) evaluation. For this reason, this paper discusses the cooling performance of the PAFS during transient accidents. The test case and scenarios were picked from the result of the sensitivity analysis in APR+ Probabilistic Safety Assessment(PSA). The analysis was performed by the best estimate thermal-hydraulic code, RELAP5/.MOD3.3. This study shows that the plant maintains the stable state without the core damages under the given test scenarios. The results of PSA considering this analysis' results shows that the CDF values are decreased. The analysis results can be used for more realistic and accurate performance of a PSA.