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나장환,배연경,이은찬,Na, Jang Hwan,Bae, Yeon Kyoung,Lee, Eun Chan 한국압력기기공학회 2013 한국압력기기공학회 논문집 Vol.9 No.1
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).
격납건물종합누설률시험 주기연장을 위한 웹기반 소외결말분석 프로그램 개발 및 적용
나장환 ( Jang Hwan Na ),황석원 ( Seok Won Hwang ),오지용 ( Ji Yong Oh ) 한국안전학회(구 한국산업안전학회) 2012 한국안전학회지 Vol.27 No.5
For an off-site consequence analysis at nuclear power plant, MELCOR Accident Consequence Code System (MACCS) II code is widely used as a software tool. In this study, the algorithm of web-based off-site consequence analysis program (OSCAP) using the MACCS II code was developed for an Integrated Leak Rate Test (ILRT) interval extension and Level 3 probabilistic safety assessment (PSA), and verification and validation (V&V) of the program was performed. The main input data for the MACCS II code are meteorological, population distribution and source term information. However, it requires lots of time and efforts to generate the main input data for an off-site consequence analysis using the MACCS II code. For example, the meteorological data are collected from each nuclear power site in real time, but the formats of the raw data collected are different from each site. To reduce the efforts and time for risk assessments, the web-based OSCAP has an automatic processing module which converts the format of the raw data collected from each site to the input data format of the MACCS II code. The program also provides an automatic function of converting the latest population data from Statistics Korea, the National Statistical Office, to the population distribution input data format of the MACCS II code. For the source term data, the program includes the release fraction of each source term category resulting from modular accident analysis program (MAAP) code analysis and the core inventory data from ORIGEN. These analysis results of each plant in Korea are stored in a database module of the web-based OSCAP, so the user can select the defaulted source term data of each plant without handling source term input data.
경수로원전의 격납건물종합누설률시험 주기 연장 인허가에 따른 주기적 리스크 재평가
나장환 ( Jang Hwan Na ) 한국안전학회(구 한국산업안전학회) 2013 한국안전학회지 Vol.28 No.7
ILRT Intervals for nuclear power plants in Korea were extended from once in five years to once in ten years. Therefore, it is required to evaluate the risk impact for ILRT interval extensions as a condition of ILRT extensions. In this paper, input data were generated for the reference PWR Plants using the raw data such as meteorological, population distribution and source term data. And the web-based Off-Site Consequence Analysis Program(OSCAP) was used to calculate the effects of extensions based on the two methodologies of NUREG-1493 and NEI Interim Report. The web-based OSCAP was designed based on the MACCS(MELCOR Accident Consequence Code System) Il, which is generally used as a tool for an off-site consequence analysis. The results of periodic risk assessments following ILRT extension were identified not to be significant. It is considered appropriate to apply this study and results in an accident management plan and safety goal, and to the field of public acceptance.
중수로 원자로건물 총누설감시계통 시험 중지에 따른 리스크 영향 평가
배연경 ( Yeon Kyoung Bae ),나장환 ( Jang Hwan Na ),방기인 ( Ki In Bahng ) 한국안전학회(구 한국산업안전학회) 2015 한국안전학회지 Vol.30 No.5
Wolsong Unit 2,3&4 has been performing a containment integrity test during power operation. This test could impact to the safe operation during test. If an accident occurs during pressure dropping phase, reactor trip can be delayed because of the increased pressure difference which causes a time delay to reach the trip set-point. On the contrary, if an accident occurs during pressure increasing phase, reactor trip could be accelerated because the pressure difference to the trip set-point decrease. Point Lepreau nuclear power plant, which installed GCLMS (Gross Containment Leakage Monitoring System) in 1990, has discontinued the test since 1992 due to these adverse effects. Therefore, we evaluated the risk to obviate the GCLMS test based on PWR’s ILRT (Integrated Leak Rate Test) extension methodologies. The results demonstrate that risk increase rate is not high in case of performing only ILRT test at every 5 years instead of doing GCLMS test at every 1.5 years. In addition, the result shows that GCLMS test can be removed on a risk-informed perspective since risk increasement is in acceptable area of regulatory acceptance criteria.