• Nuclear Engineering and Technology
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• v.55 no.3
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• pp.927-938
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• 2023

The blanket plays an important role in fusion reactor and stands extremely high thermal and electromagnetic loads during operation situation and plasma disruption event, brings the need for precise thermal and electromagnetic analysis. Since the thermal field and EM field interact with each other nonlinearly, we develop a method of electromagnetic-thermal two-way coupling by using finite element software COMSOL. The coupling analyses of blanket under steady state and MD event are implemented and the results are analyzed. For steady state, the influences of coupling effects are relatively small but still recommended to be considered for a high precision analysis. The influence of thermal field on EM field can't be ignored under MD events. The variation of force density could cause a significant change in stress in certain parts of blanket. The influence of Joule heat during MD event is negligible, yet the potential temperature rise caused by induced current after MD event still needs to be researched.

• Proceedings of the Earthquake Engineering Society of Korea Conference
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• 1998.10a
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• pp.421-435
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• 1998

An empirical formula for estimating duration magnitude(MD)is determined by analyzing 619 epicentral distance-duration data set, obtained from earthquakes of 1989-1998 recorded at the KMA network. Based on two assumptions: 1) observed signal duration decreases with increasing epicentral distance, and 2) seismographs of KMA are set at low-gain and therefore inclusion of sensitivity correction term in the equation is not necessary, scaling predicted duration at epicenter to Tsuboi's local magnitude yielded the duration magnitude equation: MD =2.0292$\times$log$\tau$＋0.00123Δ-1.4017 for 1/0$\leq$ML$\leq$5.0, where $\tau$is total signal duration(sec)and Δis epicentral distance(km). Event by event comparison of ML values against MD estimates for t152 events shows that for events having a same ML the difference in MD estimates reaches as high as 1.1 magnitude units. So, to test the usefulness of the duration magnitude equation, we have calculated ML-MD relations by which duration magnitude estimates are converted to local magnitudes ("predicted" ML, say) which are then compared with the directly determined local magnitude values. Except for events with stations where duration is anomalously reestimates(predicted ML) which are in an agreement within a 0.2 magnitude units with the corresponding ML values. Although this study could gain some insights into magnitudes of the past events, we still need to re-examine all the observables in order to obtain more reliable and precise information about magnitude and hypocenter location. So we will pursue a new local-magnitude scaling, as well as refinement of the duration magnitude equation, starting soon with re-reading the amplitudes-arrival time records of (and hence relocating) 250+earthquakes of 1979-present recorded at the KMA network. Thus, with more reliable and precise earthquake parameters determined we would better understand the recent seismicity and related tectonic process within and adjacent region to the Korean peninsula.peninsula.

• Proceedings of the Korea Information Processing Society Conference
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• 2007.05a
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• pp.1288-1290
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• 2007

Congestion in WSN increases energy dissipation rates of sensor nodes as well as loss of packets and thereby hinders fair and reliable event detections. We find that one of the key reasons of congestion in WSN is allowing sensing nodes to transfer as many packets as possible. This is due to the use of CSMA/CA that gives opportunistic media access control. In this paper, we propose an energy efficient congestion avoidance protocol that includes source count based hierarchical and load adaptive medium access control. Our proposed mechanism ensures load adaptive media access to the nodes and thus achieves fairness in event detection. The results of simulation show our scheme exhibits more than 90% delivery ratio with retry limit 1, even under bursty traffic condition which is good enough for reliable event perception.

• The Journal of Asian Finance, Economics and Business
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• v.7 no.7
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• pp.131-137
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• 2020

The research investigates the impact of the lockdown period caused by the COVID-19 to the stock market of India. The study examines the extent of the influence of the lockdown on the Indian stock market and whether the market reaction would be the same in pre- and post-lockdown period caused by COVID-19. Market Model Event study methodology is used. A sample of 31 companies listed on Bombay Stock Exchange (BSE) are selected at random for the purpose of the study. The sample period taken for the study is 35 days (24 February-17 April, 2020). An event window of 35 days was taken with 20 days prior to the event and 15 days during the event. The event (t1) being the official announcement of the lockdown. The results indicate that the market reacted positively with significantly positive Average Abnormal Returns during the present lockdown period, and investors anticipated the lockdown and reacted positively, whereas in the pre-lockdown period investors panicked and it was reflected in negative AAR. The study finds evidence of a positive AR around the present lockdown period and confirms that lockdown had a positive impact on the stock market performance of stocks till the situation improves in the Indian context.

• Nuclear Engineering and Technology
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• v.55 no.2
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• pp.696-706
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• 2023

Consequences of an anticipated Beyond Design Basis Accident (BDBA) Long-Term Station Blackout (LTSBO) event with complete loss of grid power in the VVER-1200 reactor of Rooppur Nuclear Power Plant (NPP) of Unit-1 are assessed using the RASCAL 4.3 code. This study estimated the released radionuclides, received public radiological dose, and ground surface concentration considering 3 accident scenarios of International Nuclear and Radiological Event Scale (INES) level 7 and two meteorological conditions. Atmospheric transport, dispersion, and deposition processes of released radionuclides are simulated using a straight-line trajectory Gaussian plume model for short distances and a Gaussian puff model for long distances. Total Effective Dose Equivalent (TEDE) to the public within 40 km and radionuclides contribution for three-dose pathways of inhalation, cloudshine, and groundshine owing to airborne releases are evaluated considering with and without passive safety Emergency Core Cooling System (ECCS) in dry (winter) and wet (monsoon) seasons. Source term and their release rates are varied with the functional duration of passive safety ECCS. In three accident scenarios, the TEDE of 10 mSv and above are confined to 8 km and 2 km for the wet and dry seasons, respectively in the downwind direction. The groundshine dose is the most dominating in the wet season while the inhalation dose is in the dry season. Total received doses and surface concentration in the wet season near the plant are higher than those in the dry season due to the deposition effect of rain on the radioactive substances.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.11 no.5
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• pp.1029-1036
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• 2007

State explosion is a well-known problem that impedes analysis md testing of discrete event systems, thus making the verification of large systems intrinsically difficult job. This paper suggests a hierarchical verification methodology of untimed DEVS model which can alleviate the state explosion problem. The method is a repetitive procedure of designing and verifying between the upper level and the lower level models abstracting away the unnecessary information with respect to a given verification task. A small example was employed to show our suggested method in detail.

• Nuclear Engineering and Technology
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• v.50 no.6
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• pp.860-868
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• 2018

This article presents a new design of earthquake instrumentation that is suitable for quick decision-making after the seismic event at the nuclear power plant (NPP). The main objective of this work is to ensure more availability of the NPP by expediting walk-down period when the seismic wave is incident. In general, the decision-making to restart the NPP after the seismic event requires more than 1 month if an earthquake exceeds operating basis earthquake level. It affects to the plant availability significantly. Unnecessary shutdown can be skipped through quick assessments of operating basis earthquake, safe shutdown earthquake events, and damage status to structure, system, and components. Multidecision parameters such as cumulative absolute velocity, peak ground acceleration, Modified Mercalli Intensity Scale, floor response spectrum, and cumulative fatigue are discussed. The implementation scope on the field-programmable gate array platform of this work is limited to cumulative absolute velocity, peak ground acceleration, and Modified Mercalli Intensity. It can ensure better availability of the plant through integrated decision-making process by automatic assessment of NPP structure, system, and components.

• The Journal of the Korea Contents Association
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• v.6 no.2
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• pp.17-26
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• 2006

SIP(Session Initiation Protocol)-based centralized conference service model has advantage of easiness in conference management and service as compared to other models. However when media server which is one of the components of conference server is included in the conference server, this model shows disadvantage of high server work load with increasing numbers of conferences and participants. In this paper, to improve this problem, we have suggested and implemented a new conference service model in which an UA(User Agent) who first make the conference acts as a media server instead of conventional conference server and, the conference server with conference event package takes only part of management of the conference and its participants. Therefore, many more conferences can be held and managed compared to the conventional centralized conference service model because load of the conference server decreases in our suggested model md, furthermore the participants needs only make SIP call connections to the UA who first make the conference for establishing media session.

• Proceedings of the Korean Vacuum Society Conference
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• 1999.07a
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• pp.42-42
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• 1999

본 연구에서는 극 저 에너지 이온 주입에 관한 연구를 위하여 새로이 제안된 PLDAM(phenomenological local damage accumulation model)을 효과적인 분자동역학 이온 주입 분포 계산 방법(highly efficient molecular dynamics (MD) schemes)에 적용하여 극 저 에너지 이온 주입에 관하여 연구하였다. PLDAM은 셀에 축적된 에너지와 이온 발생 순서(history of recoil event) 및 열 전도를 고려하여 실리콘 자기 이완과 재결합을 고려하고 있다. 효과적인 분자동역학 이온 주입방법으로는 MDRANGE code를 사용하였다. 국부적인 격자결함을 고려하지 않은 MDRANGE의 결과는 불순물 분포의 실험치와 꼬리 부분에서 많은 차이를 보여주었다. 그러나 본 연구에서 사용된 국부적인 격자결함 축적을 고려한 MDRANGE의 결과는 극 저 에너지 이온 주입 실험치와 잘 일치하였다. 또한 본 연구에서는 <100> 실리콘 기판 위의 0.1$\mu\textrm{m}$$\times$0.1$\mu\textrm{m}$ 영역에 도즈에 해당하는 이온만큼을 주입하여 불순물 분포를 계산하였다. 붕소와 비소의 경우에, 도즈와 이온주입 에너지가 증가하에 따라서 국부적으로 축적된 격자결함이 불순물의 분포에 미치는 영향이 커지는 것을 알 수 있었다. 특별히 이온 주입 에너지와 함께 무관하게 도즈 1014/cm2 이상에서는 국부적으로 축적된 격자 결함이 불순물의 분포에 크게 영향을 미치는 것으로 나타났다.

• Transactions of the Korean Society of Pressure Vessels and Piping
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• v.9 no.1
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• pp.15-19
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• 2013

The auxiliary feedwater is an important to remove the heat from the reactor core when the main feedwater system is unavailable. In most initiating events in Probabilistic Safety Assessment(PSA), the operaton of this system is required to mitigate the accidents. For one of domestic nuclear power plants, a design change of a turbine-driven auxiliary feedwater pump(TD-AFWP), pipe, and valves in the auxiliary system is implemented due to the aging related deterioration by long time operation. This change includes the replacement of the TD-AFWP, the relocation of some valves for improving the system availability, a new cross-tie line, and the installation of manual valves for maintenance. The design modification affects the PSA because the system is critical to mitigate the accidents. In this paper, the safety effect of the change of the auxiliary feedwater system is assessed with regard to the PSA view point. The results demonstrate that this change can supply the auxiliary feedwater from the TD-AFWP in the accident with the motor-driven auxiliary feedwater pump(MD-AFWP) unavailable due to test or maintenance. In addition, the change of MOV's normal position from "close" to "open" can deliver the water to steam generator in the loss of offsite power(LOOP) event. Therefore, it is confirmed that the design change of the auxiliary feedwater system reduces the total core damage frequency(CDF).