• 한국지진공학회:학술대회논문집
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• 한국지진공학회 2000년도 춘계 학술발표회 논문집 Proceedings of EESK Conference-Spring
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• pp.97-104
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• 2000

Evaluating a Review-Level Ground Motion is a key to efficiently perform Seismic Margin Assessment of nuclear power plants whose purpose is to determine a ground motion level for which a plant has high-confidence-of-a-low-probability of seismic-induced core damage and to identify any weaker-link components. In this study a method to obtain RLGMs is reviewed which is recommended by Electric Power Research Institute and implemented to be applied to Limerick site in eastern and central U. S as a case study. This method provides reasonable and site-specific RLGMs as minimum required plant HCLPF for SMA that meet a target mean seismic core-damage frequency based on seismic hazard results and generic values of uncertainty and randomness parameters of the core-damage fragility curves. In addition high-frequency RLGM is justifiably modified to reflect the increased seismic capacity of high-frequency components and spatial variation and incoherence of input ground motion on a basemat of large structures by establishing a method to obtain high0-frequency reduction factors according to EPRI guidelines.

• Nuclear Engineering and Technology
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• 제50권8호
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• pp.1217-1233
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• 2018

Following a surge of interest in multi-unit risk in the last few years, many recent studies have suggested methods for multi-unit probabilistic safety assessment (MUPSA) and addressed several related aspects. Most of the existing studies though focused on two-unit nuclear power plant (NPP) sites or used rather simplified probabilistic safety assessment (PSA) models to demonstrate the proposed approaches. When considering an NPP site with three or more units, some approaches are inapplicable or yield very conservative results. Since the number of such sites is increasing, there is a strong need to develop and validate practical approaches to the related MUPSA. This article provides several detailed approaches that are applicable to multi-unit Level 1 PSA for sites with up to six or more reactor units. To validate the approaches, a multi-unit Level 1 PSA model is developed and the site core damage frequency is estimated for each of four representative multi-unit initiators, as well as for the case of a simultaneous occurrence of independent single-unit initiators in multiple units. For this purpose, an NPP site with six identical OPR-1000 units is considered, with full-scale Level 1 PSA models for a specific OPR-1000 plant used as the base single-unit models.

• Nuclear Engineering and Technology
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• 제44권7호
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• pp.745-754
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• 2012

The correlations between Large Early Release Frequency (LERF) and Early Fatality need to be investigated for risk-informed application and regulation. In Regulatory Guide (RG) -1.174, while there are decision-making criteria using the measures of Core Damage Frequency (CDF) and LERF, there are no specific criteria on LERF. Since there are both huge uncertainties and large costs needed in off-site consequence calculation, a LERF assessment methodology needs to be developed, and its correlation factor needs to be identified, for risk-informed decision-making. A new method for estimating off-site consequence has been presented and performed for assessing health effects caused by radioisotopes released from severe accidents of nuclear power plants in this study. The MACCS2 code is used for validating the source term quantitatively regarding health effects, depending on the release characteristics of radioisotopes during severe accidents. This study developed a method for identifying correlations between LERF and Early Fatality and validates the results of the model using the MACCS2 code. The results of this study may contribute to defining LERF and finding a measure for risk-informed regulations and risk-informed decision-making.

• Nuclear Engineering and Technology
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• 제41권10호
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• pp.1235-1242
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• 2009

Probabilistic seismic hazard analysis (PSHA) is routinely conducted in the US for nuclear plants, for the determination of appropriate seismic design levels. These analyses incorporate uncertainties in earthquake characteristics in stable continental regions (where direct observations of large earthquakes are rare), in estimates of rock motions, in site effects on strong shaking, and in the damage potential of seismic shaking for engineered facilities. Performance goals related to the inelastic deformation of individual components, and related to overall seismic core damage frequency, are used to determine design levels. PSHA has the ability to quantify and document the important uncertainties that affect seismic design levels, and future work can be guided toward reducing those uncertainties.

• Nuclear Engineering and Technology
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• 제53권2호
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• pp.498-508
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• 2021

Micro reactors are increasingly being considered for utilization as distributed power sources. Hence, the probabilistic safety assessment (PSA) of a direct supercritical-CO₂-cooled fast reactor, called micro modular reactor (MMR), was performed in this study; this reactor was developed using innovative design concepts. It adopted a modular design and passive safety systems to minimize site constraints. As the MMR is in its conceptual design phase, design weaknesses and valuable safety insights could be identified during PSA. Level 1 internal event PSA was carried out involving literature survey, system characterization, identification of initiating events, transient analyses, development of event trees and fault trees, and quantification. The initiating events and scenarios significantly contributing to core damage frequency (CDF) were determined to identify design weaknesses in MMR. The most significant initiating event category contributing to CDF was the transients with the power conversion system initially available category, owing to its relatively high occurrence frequency. Further, an importance analysis revealed that the safety of MMR can be significantly improved by improving the reliability of reactor trip and passive decay heat removal system operation. The findings presented in this paper are expected to contribute toward future applications of PSA for assessing unconventional nuclear reactors in their conceptual design phases.

• Nuclear Engineering and Technology
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• 제49권4호
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• pp.710-720
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• 2017

In Korea, many nuclear power plants operate at a single site based on geographical characteristics, but the population density near the sites is higher than that in other countries. Thus, multiunit accidents are a more important consideration than in other countries and should be addressed appropriately. Currently, there are many issues related to a multiunit probabilistic safety assessment (PSA). One of them is the quantification of a multiunit PSA model. A traditional PSA uses a Boolean manipulation of the fault tree in terms of the minimal cut set. However, such methods have some limitations when rare event approximations cannot be used effectively or a very small truncation limit should be applied to identify accident sequence combinations for a multiunit site. In particular, it is well known that seismic risk in terms of core damage frequency can be overestimated because there are many events that have a high failure probability. In this study, we propose a quantification method based on a Monte Carlo approach for a multiunit PSA model. This method can consider all possible accident sequence combinations in a multiunit site and calculate a more exact value for events that have a high failure probability. An example model for six identical units at a site was also developed and quantified to confirm the applicability of the proposed method.

• 한국안전학회지
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• 제38권3호
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• pp.102-109
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• 2023

Following the accident at Fukushima, the true impact of multi-unit accidents came to light. Accordingly, research related to multi-unit accident effect analysis, risk evaluation, and accident prevention/prevention technology has been conducted. Specific examples are mobile/fixed equipment such as multi-barrier accident coping strategy (MACST) and diverse and flexible coping strategies (FLEX), which have been introduced and installed in multi-units for preventing and mitigating multi-unit accidents. These strategies are useful for enhancing the safety of nuclear power plants (NPPs); however, a more efficient strategy is required in terms of the costs of physical and human resources. To effectively and efficiently mitigate an increase in multi-unit accidents, it is necessary to not only to utilize mobile/fixed equipment but to also use crosstie options with resources that already exist at NPPs. Therefore, we analyzed the current international and domestic status of crosstie systems technology and propose a method to evaluate feasibility alongside risk based on a multi-unit probabilistic safety assessment (PSA). To analyze the international and domestic status of crosstie systems technology, actual cases and related research were studied, and a list of potential crosstie safety resources was derived. Additionally, a case study was performed on crosstie cases of two systems within the assumed six units on-site under a multi-unit accident, and a multi-unit PSA-based risk evaluation method is proposed.

• 생명과학회지
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• 제30권6호
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• pp.513-521
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• 2020

Bmi1은 PcG 단백의 일종으로 PRC를 구성하는 성분이다. Bmi1에 관한 초기의 연구는 주로 암세포에서의 역할에 집중되었고, 그 결과 Bmi1은 암세포의 증식과 생존에 중요한 역할을 하는 것으로 받아들여지고 있다. 그러나, 최근의 연구 결과 Bmi1은 퇴행성 신경계 질환이 있는 뇌에서 발현이 감소되어 있고 미토콘드리아의 기능과 활성 산소 수준을 조절하는 것으로 알려져 있다. 본 연구에서는 Bmi1 발현 저하 동물을 이용하여 간질에서 Bmi1의 약물 치료 표적 가능성을 밝히고자 하였다. Bmi1의 발현은 pilocarpine에 의한 경련중첩증 이후 해마의 CA1, CA3 그리고 치상회에서 뚜렷하게 증가하였다. 경련 양상을 볼 때 경련중첩증이 유도되는 비율은 Bmi1^+/+와 Bmi1^+/- 생쥐에서 각각 43.14%와 53.57%로 나타났다. 그러나, 치사율과 해마의 신경세포 손상에는 두 군 간에 통계적으로 유의한 차이를 보이지 않았다. 경련중첩증 유도 2개월 후에 나타난 간질 경련의 빈도수는 통계적 유의성은 없었으나 Bmi1^+/- 생쥐에서 약 50% 낮게 나타났다. 반면, 이끼섬유발아는 Bmi1^+/- 생쥐에서 통계적으로 유의하게 증가하였다. 이러한 결과를 종합하면, Bmi1의 발현이 감소할 때 pilocarpine에 의한 경련 유도와 이끼섬유발아가 증가함을 보여준다.

• 한국조경학회지
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• 제17권3호
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• pp.21-34
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• 1990

팔공산자연공원 동화사지구의 등산로 및 야영장의 훼손실태와 그 주변토양 및 식생환경의 변화를 조사한 결과를 요약하면 다음과 같다. 1. 등산로폭, 나지노출폭, 최대깊이, 등산로물매 및 노면의 토양경도는 이용강도가 높은 바위골등산로가 수수골보다 컸으나 나지노출폭에서만 이용강도의 영향이 인정되어다. 2. 등산로의 훼손형태는 암석노출 42%, 종침식 20% 및 뿌리노출 18% 등의 순으로 토양침식이 상당히 진행되고 있었으며, 건전한 지점은 33%이었다. 3. 등산로경계부에서 임내로 갈수록 토양경도는 데체로 감소하는 경향을 나타냈으나 토양 pH, 토양함수량 및 유기물 함량 등은 변화경향이 일정하지 않았다. 팔공산 자연공원의 등산로주변 토양환경에 대한 이용영향이 아직 심각한 정도는 아니었다. 4. 등산로 주변의 식생구조의 변화는 다양하게 나타났으나 이용형태에 따라 경향을 구분할 수 있었으나, 인위적 간섭이 뚜렷한 조사지에서 종수, 개체수 및 종다양도 등은 영향범위의 파악에 유의한 인자였다. 특히 이용이 통제된 수수골에서는 식생구조가 회복되는 곳도 있었다. 5. 바위골야영장이 수수골야영장보다 파괴정도가 심했고 피해도 3등급 이상의 비율도 각각 91.8%, 44.5%였다. 야영장내 수목훼손형태는 뿌리노출 63%, 수간상처 43% 및 가지손상 30%의 순이었고 훼손목의 거리별 출현빈도는 이용객의 영향범위 파악에 유의한 기준이었다. 6. 생장량비교조사에서 야영장내 수목생장은 비야영장에 비해 적었고 5년전에 비해서도 현재의 생장이 떨어지고 있었다. 7. 야영장주변에서 식생환경에 대한 이용간섭의 범위가 토양환경에 비해 넓었고 이용에 따른 종구성의 이질화가 매우 심하였다. 야영장으로부터 잠재적 영향을 포함한 이용간섭의 영향범위는 바위골 야영장에서 70∼90m, 수수골 야영장에서 20∼30m이었다. 8. 야영장주변에서의 인위적 간섭에 대한 내성수종은 조록싸리, 개옻나무, 산딸기, 노박덩굴, 단풍나무 등으로 파악되었다.