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THE APPLICATION OF PSA TECHNIQUES TO THE VITAL AREA IDENTIFICATION OF NUCLEAR POWER PLANTS
HA JAEJOO,JUNG WOO SIK,PARK CHANG-KUE Korean Nuclear Society 2005 Nuclear Engineering and Technology Vol.37 No.3
This paper presents a vital area identification (VAI) method based on the current fault tree analysis (FTA) and probabilistic safety assessment (PSA) techniques for the physical protection of nuclear power plants. A structured framework of a top event prevention set analysis (TEPA) application to the VAI of nuclear power plants is also delineated. One of the important processes for physical protection in a nuclear power plant is VAI that is a process for identifying areas containing nuclear materials, structures, systems or components (SSCs) to be protected from sabotage, which could directly or indirectly lead to core damage and unacceptable radiological consequences. A software VIP (Vital area Identification Package based on the PSA method) is being developed by KAERI for the VAI of nuclear power plants. Furthermore, the KAERI fault tree solver FTREX (Fault Tree Reliability Evaluation eXpert) is specialized for the VIP to generate the candidates of the vital areas. FTREX can generate numerous MCSs for a huge fault tree with the lowest truncation limit and all possible prevention sets.
The Influence of Source Term Release Parameters on Health Effects
Jeong, Jongtae,Ha, Jaejoo Korean Nuclear Society 1999 Nuclear Engineering and Technology Vol.31 No.3
The influence of source term release parameters on offsite health effects was examined for the YGN 3&4 nuclear power plants. The release parameters considered in this study are release height, heat content, and release time. The effects of core inventory change as a function of fuel burnup was also examined. The health effects by the change of release parameters are early fatalities, cancer fatalities, and early fatality distance. The results showed that early fatalities and early fatality distance decrease as release height increases, although it does not have significant influence on cancer fatalities. The values of both early and late health effects decrease as heat content increases. As release time increases, health consequence shows maximum value in 2 hours of release time and then decreases rapidly. As fuel burnup increases, early fatalities decrease rapidly, while cancer fatalities increase rapidly. Both cases show little variation afterward. Early fatality distance is almost same in all fuel turnup history. The information obtained through this research is very useful in developing strategies for reducing offsite consequences when combined with the influence of weather conditions on offsite risks.
A Probabilistic Risk Assessment for Inorganic Arsenic
Yu, Donghan,Ha, Jaejoo 한국환경독성학회 1998 환경독성보건학회지 Vol.13 No.2
확률론적 해석방법은 환경독성물질에 의한 인체위해도 평가시 사용된 각 입력인자들의 불확실성까지 고려하는 방법론이다. 기존의 위해도평가방법론은 불확실성을 고려하지 않고 단순히 결과치의 포인트 값만을 제공하는데 비해 이러한 확률론적 해석방법은 입력인자들의 불확실성이 고려되고 결과치에 대한 이들의 중요도가 산출될 수 있는 등 더 많은 정보를 제공하므로써 환경위해도를 기반으로 한 환경정책 결정시 용이하게 사용될 수 있다. 본 논문은 현재 미국에서 음용수 기준설정시 논란이 많은 무기비소에 대해 확률론적 평가방법론을 적용하였다. 우선 인체위해도평가에 필요한 무기비소의 각종 자료들을 수집, 정리하고 이를 바탕으로 각 인자들의 불확실성을 파악하였다. 최종적으로 이들로부터 무기비소가 포함된 음용수를 마신 일반인의 피부암 위해도를 확률적으로 계산하였다. 또한 계산된 결과치의 여러 위해도기준치를 비교하여 정책결정에 필요한 의사결정에 대해서도 살펴보았다. 계산결과에 의하면 다수의 일반인들이 무기비소를 함유한 음용수섭취를 통해 현재 위해도설정치 (10^(-6)) 보다 높은 피부암 위해를 입고 있는 것으로 나타나 이에 대한 규제가 필요하다고 본다. When one uses the conventional approach using conservative point-estimated values, results usually show the bounding estimates. This approach, however, does not lead to realistic estimates of health risks nor can it consider the uncertainty of its input values. In order to overcome these problems, this pa-per introduces the concept of probabilistic analysis. The probabilistic approach uses a distribution of key variables (chemical concentrations, frequency, and body weight, etc.) to represent their uncertainty. This method provides considerable useful information to the risk manager because it can identify the uncertainty of the results. This paper has evaluated a probabilistic skin cancer risk associated with inorganic arsenic exposure by drinking water ingestion as the selected case study. Based on the results, the current level of inorganic arsenic in drinking water indicates that the majority of the general population exceeds the cancer risk criterion (10^(-6)) set by the EPA in the United States. Hence, it appears that measures to reduce arsenic levels in water supplies should be considered. The approach provides a more realistic evaluation of cancer from inorganic arsenic by considering the variation of its input parameters. Based on enough information from the analysis, risk managers would be able to make a wise decision regarding the cancer risk associated with inorganic arsenic.
Jung, Wondea,Park, Jinkyun,Kim, Jaewhan,Ha, Jaejoo IEEE 2007 IEEE transactions on nuclear science Vol.54 No.5
<P> With a scarcity of empirical data, much of the input regarding a human reliability analysis (HRA) is dependent on an analysts' subjective judgment, which is one of the major causes of a high uncertainty in the results of an HRA. When considering that risk-informed activities require the probabilistic safety assessment (PSA) quality to be as high as possible, an HRA should be performed by using a systematic method with realistic plant specific data to meet the established requirements for risk-informed applications. In order to obtain more objective HRA results, data extracted from real experiences or simulators is essential. This paper presents a human performance analysis of the emergency tasks for nuclear power plants (NPPs) to support an HRA. Using the full-scope simulator of a reference plant, more than 110 simulator records with six emergency scenarios were gathered and analyzed to generate an operators' performance time such as the time taken to diagnose what event has occurred, and the time to execute a procedural step or a task. A sensitivity analysis for an HRA has also been performed by using an operators' performance time. </P>