• Journal of Korea Water Resources Association
• /
• v.49 no.2
• /
• pp.107-119
• /
• 2016

Since future climate scenarios indicate that extreme precipitation events will intensity, probable maximum precipitations (PMPs) without being taken climate change into account are very likely to be underestimated. In this study future PMPs in accordance with the variation of future rainfall are estimated. The hydro-meteorologic method is used to calculate PMPs. The orographic transposition factor is applied in place of the conventional terrain impact factor which has been used in previous PMPs estimation reports. Future DADs are indirectly obtained by using bias-correction and moving-averaged changing factor method based on daily precipitation projection under KMA RCM (HEDGEM3-RA) RCP 8.5 climate change scenario. As a result, future PMPs were found to increase and the spatially-averaged annual PMPs increase rate in 4-hour and $25km^2$ was projected to be 3 mm by 2045. In addition, the increased rate of future PMPs is growing increasingly in the future, but it is thought that the uncertainty of estimating PMPs caused by future precipitation projections is also increased in the distant future.

• Nuclear Engineering and Technology
• /
• v.53 no.8
• /
• pp.2534-2546
• /
• 2021

Nuclear emergency preparedness and response is an essential part to ensure the safety of nuclear power plant (NPP). Key support technologies of nuclear emergency decision-making usually consist of accident diagnosis, source term estimation, accident consequence assessment, and protective action recommendation. Source term estimation is almost the most difficult part among them. For example, bad communication, incomplete information, as well as complicated accident scenario make it hard to determine the reactor status and estimate the source term timely in the Fukushima accident. Subsequently, it leads to the hard decision on how to take appropriate emergency response actions. Hence, this paper aims to develop a method for rapid source term estimation to support nuclear emergency decision making in pressurized water reactor NPP. The method aims to make our knowledge on NPP provide better support nuclear emergency. Firstly, this paper studies how to build a Bayesian network model for the NPP based on professional knowledge and engineering knowledge. This paper presents a method transforming the PRA model (event trees and fault trees) into a corresponding Bayesian network model. To solve the problem that some physical phenomena which are modeled as pivotal events in level 2 PRA, cannot find sensors associated directly with their occurrence, a weighted assignment approach based on expert assessment is proposed in this paper. Secondly, the monitoring data of NPP are provided to the Bayesian network model, the real-time status of pivotal events and initiating events can be determined based on the junction tree algorithm. Thirdly, since PRA knowledge can link the accident sequences to the possible release categories, the proposed method is capable to find the most likely release category for the candidate accidents scenarios, namely the source term. The probabilities of possible accident sequences and the source term are calculated. Finally, the prototype software is checked against several sets of accident scenario data which are generated by the simulator of AP1000-NPP, including large loss of coolant accident, loss of main feedwater, main steam line break, and steam generator tube rupture. The results show that the proposed method for rapid source term estimation under nuclear emergency decision making is promising.

• Maritime Security
• /
• v.4 no.1
• /
• pp.83-113
• /
• 2022

Although China's maritime militia has not been well known despite its long history, it is recently emerging as a serious threat to maritime security, causing neighboring countries' security concerns due to the growing number of maritime disputes with China. In this regard, it is now time to clearly define the true nature of the Chinese maritime militia. A close look at the organization and roles of the Chinese maritime militia reveals that it is an organization that is systematically managed and operated by the Chinese government and the People's Liberation Army of China. Its role is to serve the purpose of "contributing to the protection and expansion of China's marine interests." In addition, the threat factors of the Chinese maritime militia were analyzed by examining the cases of maritime disputes between the Chinese maritime militia and neighboring countries. First, the Chinese maritime militia has implemented the "Gray Zone Strategy." Second, it is a systematic organization supported by the Chinese government and the People's Liberation Army. Third, it is a maritime power that cannot be ignored as the world's largest militia organization. Fourth, it has a strategic flexibility that enables the execution of the dual mission of working for a living such as commercial fishing and serving in the maritime militia. The threats of the Chinese maritime militia are not limited to Southeast Asian countries located in the South China Sea. This is also the case in Korea as the country cannot avoid maritime disputes with China such as the Ieodo issue and the boundary delimitation of the West Sea. Accordingly, this study was focused on presenting a predictable scenario and countermeasures based on the analysis through a scenario technique with respect to the two cases that are most likely to occur in Korea-China relations. Finally, beyond identifying the nature of the Chinese maritime militia, this study takes a further step to share considerations as to how the organization may operate and develop in the future and how we can cope with its moves.

• Journal of Korea Water Resources Association
• /
• v.57 no.1
• /
• pp.45-58
• /
• 2024

Drought risk is expected to increase as the frequency, intensity, and duration of droughts increase due to climate change. Drought risk is related to not only hydro-meteorological factors, but also water supply and demand. Recently, along with climate change, socioeconomic factors have also been recognized to increase drought risk. Therefore, it is necessary to outlook the drought risk considering various conditions for coping with future extreme droughts in a timely manner. In addition, considering various drought scenarios help reduce the uncertainty in future drought outlook. In this study, drought scenarios considering climate change scenarios, population, and water demand were created to outlook drought risk for 160 administrative districts in Korea, then new levels of drought risk were assigned based on the results of drought risk outlook to suggest drought management measures. The results showed that the drought risk will increase in the future in 2020, 2025, and 2030, compared to past. Especially the drought risk is likely twice as high in 2030 under the baseline and high scenarios. Applying the drought outlook results from this study to the new methodology for setting the risk levels shows that most regions are in Response (V) in 2020 and 2030 for baseline and high scenarios.

• Journal of Korean Society of Disaster and Security
• /
• v.16 no.4
• /
• pp.19-31
• /
• 2023

According to the climate change scenarios, the intensity of typhoons, a major factor in Korea's natural disaster, is expected to increase. The increase in typhoon intensity leads to a rise in wave heights, which is likely to cause large-scale disasters in coastal regions with high populations and building density for dwelling, industry, and tourism. This study, therefore, analyzed observation data of the Donghae ocean data buoy and conducted a numerical model simulation for wave estimations for the typhoon MAYSAK (202009) period, which showed the maximum significant wave height. The boundary conditions for wave simulations were a JMA-MSM wind field and a wind field applying the typhoon central pressure reduction rate in the SSP5-8.5 climate change scenario. As a result of the wave simulations, the wave height in front of the breakwater at Sokcho port was increased by 15.27% from 4.06 m to 4.68 m in the SSP5-8.5 scenario. Furthermore, the return period at the location of 147-2 grid point of deep-sea design wave was calculated to increase at least twice, it is necessary to improve the deep-sea design wave of return period of 50-year, which is prescriptively applied when designing coastal structures.

• Journal of Radiation Industry
• /
• v.17 no.3
• /
• pp.275-282
• /
• 2023

Workers in nuclear power plants are likely to be exposed to radiation from various geometrical sources. In order to evaluate the exposure level, the point-kernel method can be utilized. In order to perform a dose assessment based on this method, the radiation source should be divided into point sources, and the number of divisions should be set by the evaluator. However, for the general public, there may be difficulties in selecting the appropriate number of divisions and performing an evaluation. Therefore, the purpose of this study is to develop an algorithm for dose assessment for arbitrary shaped sources based on the point-kernel method. For this purpose, the point-kernel method was analyzed and the main factors for the dose assessment were selected. Subsequently, based on the analyzed methodology, a dose assessment algorithm for arbitrary shaped sources was developed. Lastly, the developed algorithm was verified using Microshield. The dose assessment procedure of the developed algorithm consisted of 1) boundary space setting step, 2) source grid division step, 3) the set of point sources generation step, and 4) dose assessment step. In the boundary space setting step, the boundaries of the space occupied by the sources are set. In the grid division step, the boundary space is divided into several grids. In the set of point sources generation step, the coordinates of the point sources are set by considering the proportion of sources occupying each grid. Finally, in the dose assessment step, the results of the dose assessments for each point source are summed up to derive the dose rate. In order to verify the developed algorithm, the exposure scenario was established based on the standard exposure scenario presented by the American National Standards Institute. The results of the evaluation with the developed algorithm and Microshield were compare. The results of the evaluation with the developed algorithm showed a range of 1.99×10^-1~9.74×10^-1 μSv hr^-1, depending on the distance and the error between the results of the developed algorithm and Microshield was about 0.48~6.93%. The error was attributed to the difference in the number of point sources and point source distribution between the developed algorithm and the Microshield. The results of this study can be utilized for external exposure radiation dose assessments based on the point-kernel method.

• Journal of the Korean Regional Science Association
• /
• v.35 no.3
• /
• pp.59-76
• /
• 2019

This study aims to develop urban scenarios for future cities and validate the future city scenarios using a Delphi method. The scenarios of future city was derived from urban structure, land use, transportation, and urban infrastructure and development using big data analysis, environmental scanning techniques, and literature review. The Delphi survey interviewed 24 erudite scholars and experts across 6 nations including Korea, USA, UK, Japan, China, Australia and India. The Delphi survey structure was designed to test future city scenarios, verified by the 5-point Likert scale. The survey also asked the timing of each scenario likely happens by the three terms of near-future, mid-future and far-future. Results of the Delphi survey reveal the following points. Firstly, for the future urban structure it is anticipated that urban concentration continues and higher density living in global mega cities near future. In the mid-future small and medium size cities may decrease. Secondly, the land use pattern in the near-future is expected of increasing space sharing and mixed or layered vertical land-use. In addition underground space is likely to be extended in the mid-future. Thirdly, in the near-future, transport and infrastructure was expected to show ICT embedded integration platform and public and private smart transport. Finally, the result of Delphi survey shows that TOD (Transit Oriented Development) becomes a development norm and more emphasis on energy and environment fields.

• Journal of Environmental Impact Assessment
• /
• v.4 no.3
• /
• pp.87-94
• /
• 1995

At both international and national levels, such as in the Rio Declaration and the EU's Fifth Environmental Action Plan, governments have committed themselves to the adoption of the precautionary principle (UNCED 1992, CEC 1992). These commitments mean that the existence of uncertainty in appraising policies and proposals for development should be acknowledged. Uncertainty arise in both the prediction of impacts and in the evaluation of their significance, particularly of those cumulative impacts which are individually insignificant but cumulatively damaging. The EC network of EIA experts, stated at their last meeting in Athens that indirect effects and the treatment of uncertainty are one of the main deficiencies of current EIA practice. Uncertainties in decision-making arise where choices have been made in the development of the policy or proposal, such as the selection of options, the justification for that choice, and the selection of different indicators to comply with different regulatory regimes. It is also likely that a weighting system for evaluating significance will have been used which may be implicit rather than explicit. Those involved in decision-making may employ different tolerances of uncertainty than members of the public, for instance over the consideration of the worst-case scenario. Possible methods for dealing with these uncertainties include scenarios, sensitivity analysis, showing points of view, decision analysis, postponing decisions and graphical methods. An understanding of the development of cumulative environmental impacts affords not only ecologic but also socio-economic investigations. Since cumulative impacts originate mainly in centres of urban or industrial development, in particular an analysis of future growth effects that might possibly be induced by certain development impacts. Not least it is seen as an matter of sustainability to connect this issue with ecological research. The serious attempt to reduce the area of uncertainty in environmental planning is a challenge and an important step towards reliable planning and sustainable development.

• Journal of The Korean Society of Agricultural Engineers
• /
• v.57 no.4
• /
• pp.73-84
• /
• 2015

An embankment raising project on 113 agricultural reservoirs in Korea was implemented in 2009 to increase water supply capacity for agricultural water and instream uses. This study evaluated the future water supply capacity of the Imgo reservoir at which the agricultural reservoir embankment raising project was completed, considering climate change scenarios. The height of the embankment of the reservoir was increased by 4.5 m, thereby increasing its total storage from 1,657.0 thousand to 3,179.5 thousand cubic meters. To simulate the reservoir water storage with respect to climate changes, two climate change scenarios, namely, RCP 4.5 and RCP 8.5 (in which greenhouse gas reduction policy was executed and not executed, respectively) were applied with bias correction for reflecting the climate characteristics of the target basin. The analysis result of the agricultural water supply capacity in the future, after the agricultural reservoir embankment raising project is implemented, revealed that the water supply reliability and the agricultural water supply increased, regardless of the climate change scenarios. By simulating the reservoir water storage considering the instream flow post completion of the embankment raising project, it was found that water shortage in the reservoir in the future is not likely to occur when it is supplied with an appropriate instream flow. The range of instream flow tends to decrease over time under RCP 8.5, in which the greenhouse gas reduction policy was not executed, and the restoration of reservoir storage was lower in this scenario than in RCP 4.5, in which greenhouse gas reduction policy was executed.

• Journal of KIISE
• /
• v.44 no.3
• /
• pp.314-322
• /
• 2017

In MMORPG (Massively Multiplayer Online Role-Playing Game), users advance their own characters to get to the maximum (max) level by performing given tasks in the game scenario. Although it is crucial to retain users with high levels for running online games successfully, little efforts have been paid to investigate them. In this study, by analyzing approximately 60 million in-game logs of over 50,000 users, we aimed to investigate the process through which users achieve the max level and churn of such users since the moment of achieving the max level, and determine possible indicators related to churn after the max level. Based on the result, we can predict churn of the max level users by employing behavioral patterns before the max level. Moreover, we found users who are socially active and communicate with many people before the max level are less likely to leave the service (p<0.05). This study supports that communication patterns are important factors for persistent usage of the users who achieve the max level, which has practical implications to guide elite users on enjoying online games in the long run.