This study aims to optimize the orifice diameter to reduce pressure hunting in the pilot valves of positioners used in nuclear power plant control systems. Computational Fluid Dynamics (CFD) analysis using ANSYS CFX was conducted to create 3D models with varying orifice diameters (1 mm, 1.5 mm, 2 mm, 2.5 mm, and 3 mm). To enhance the accuracy of the analysis, boundary layer meshing techniques (Inflation) were applied, and the SST k-ω turbulence model was employed. The analysis of pressure variation and pressure hunting over time revealed that larger orifice diameters resulted in reduced pressure hunting, with a 3 mm orifice diameter achieving 0% pressure hunting. Additionally, it was observed that larger orifice radii slightly increased the average outlet pressure. Based on the findings, a 3 mm orifice diameter is recommended to effectively mitigate pressure hunting in pilot valves, contributing to improved system stability in nuclear power plants. Future studies will explore the design of slanted orifices to further analyze fluid flow characteristics.
The reliability of control valves is critical in nuclear power plants to ensure precise fluid regulation and prevent risks associated with overheating or decreased efficiency. Recently, the supply of imported control valves used in these plants has been discontinued, making the development of domestic alternatives an urgent necessity. This study focuses on the design of an orifice in the pilot valve pipe of a positioner to reduce hunting, a key issue that compromises control stability. Fluid analysis was conducted using ANSYS CFX to investigate the fluid behavior in the pipe with the orifice. The analysis methods included enhanced meshing techniques, turbulence models, and residual values to improve convergence and accuracy. To meet the operational requirements of nuclear power plants (outlet pressure: 3.2 bar, inlet pressure: 7 bar), the inlet fluid velocity was determined. The pressure and pressure hunting were analyzed. Results showed that the selected inlet velocity satisfied the operational conditions, and pressure hunting values were measured and analyzed. The findings provide a basis for further optimizing orifice shapes to achieve the target pressure hunting value of 0.5%.
본 논문은 29개국의 ISSP 환경 설문조사 데이터를 이용해 핵발전 위 험에 대한 성별 인식 차이를 계층선형모형(HLM)을 사용하여 개인수준과 국가수준으로 나누어 분석하였다. 개인 수준에서는 기존에 핵발전소 위 험인식에 영향을 미쳤던 변수들의 효과성이 확인되었으며 국가 차원에서 는 국가 차원의 성불평등이 중요한 예측 변수로 나타났다. 구체적인 국 가차원의 변수를 특정하자면 모성 사망률과 청소년 출산율이 핵심 요인 으로 작용하며, 이는 여성의 정치적 대표성이나 고등교육 수준보다 더 큰 변수로 작용한다. 따라서 핵발전소 위험 인식에 있어서는 여성들의 재생산 권리와 건강권에 따른 젠더 격차가 환경인식에 더 중요한 영향을 끼침을 보여준다. 이러한 결과는 핵에너지에 대한 대중 인식을 이해하기 위해 개인적 요인뿐만 아니라 구조적 불평등까지 고려해야 하는 중요성 을 강조하며, 성별에 따른 사회적 건강 격차가 위험 인식 형성에 어떻게 영향을 주는지에 대한 추가 연구의 필요성을 제기한다.
This study investigates the risk reduction effect and identifies the optimal capacity of Multi-barrier Accident Coping Strategy (MACST) facilities for nuclear power plants (NPPs) under seismic hazard. The efficacy of MACST facilities in OPR1000 and APR1400 NPP systems is evaluated by utilizing the Improved Direct Quantification of Fault Tree with Monte Carlo Simulation (I-DQFM) method. The analysis encompasses a parametric study of the seismic capacity of two MACST facilities: the 1.0 MW large-capacity mobile generator and the mobile low-pressure pump. The results demonstrate that the optimal seismic capacity of MACST facilities for both NPP systems is 1.5g, which markedly reduces the probability of core damage. In particular, the core damage risk is reduced by approximately 23% for the OPR1000 system, with the core damage fragility reduced by approximately 72% at 1.0g seismic intensity. For the APR1400 system, the implementation of MACST is observed to reduce the core damage risk by approximately 17% and the core damage fragility by approximately 44% under the same conditions. These results emphasize the significance of integrating MACST facilities to enhance the resilience and safety of NPPs against seismic hazard scenarios, highlighting the necessity for continuous adaptation of safety strategies to address evolving natural threats.
원자력 발전소에 설치되는 안전관련 기기의 손상은 심각한 사고로 이어질 수 있으므로 반듯이 지진안전성을 확보하여야 한 다. MCC, Switchgear, Inverter, Battery charger 등의 전기캐비닛은 대표적인 안전관련 기기이다. 대부분의 실험적 연구는 실험대 상기기의 크기와 실험장비의 성능한계 등으로 인하여 주요부품을 대상으로 하며, 실제 원자력발전소에 납품하는 전기캐비닛을 이용하 여 3축 동시가진에 의한 진동대 실험을 수행한 연구는 많지 않다. 따라서 실제기기를 대상으로 3축 진동대 실험을 통하여 내진성능과 한계상태를 직접적으로 평가하기 위한 연구가 필요하다. 이러한 한계상태평가의 주요 목적은 다양한 부품으로 구성된 캐비닛 단위 실 제기기의 임계 가속도 및 고장 모드를 조사하는 것이다. 본 논문에서는 3축 진동대 실험으로 한계상태 내진성능실험을 수행하여 원자 력발전소에 납품되는 것과 동일한 4종의 전기캐비닛들의 한계상태를 분석하였다.
Kori Unit 1, the first commercial nuclear power plant (NPP) in Korea, was permanently shut down in 2017 and was scheduled for decommissioning. Various programs must be planned early in the decommissioning process to safely decommission NPPs. Radiological characterization is a key program in decommissioning and should be a high priority. Radiological characterization involves determining the decommissioning technology to be applied to a nuclear facility by identifying the radiation sources and radioactive contaminants present within the facility and assessing the extent and nature of the radioactive contaminants to be removed from the facility. This study introduces the regulatory requirements, procedures, and implementation methods for radiological characterization and proposes a methodology to link the results of radiological characterizations for each stage. To link radiological characteristics, this study proposes to conduct radiological characterization in the decommissioning phase to verify the results of radiological characterization in the transitional phase of decommissioning NPPs. This enables significantly reducing the scope and content of radiological characterization that must be performed in the decommissioning phase and maintaining the connection with the previous phase.
Climate change has led to a significant increase in jellyfish populations globally, causing various problems. For power plants that use nearby seawater for cooling, the intrusion of jellyfish into intake systems can block the flow, leading to reduced output or even shutdowns. This issue is compounded by other small marine organisms like shrimp and salps, making it urgent to develop solutions to prevent their intrusion. This study addressed the problem using the BioSonics DT-X 120 kHz scientific fish finder to conduct preliminary tank experiments. We also deployed underwater acoustic and camera buoys around the intake of nuclear power plant, utilizing a bidirectional communication system between sea and land to collect data. Data collection took place from July 31, 2023 to August 1, 2023. While harmful organisms such as jellyfish and salps were not detected, we successfully gathered acoustic data on small fish measuring backscattering strength (SV). Analysis showed that fish schools were more prominent in the evening than during the day. The highest fish distribution was observed at 3:30 AM on July 31 with an SV of -44.8 dB while the lowest was at 12:30 PM on the same day with an SV of –63.4 dB. Additionally, a solar-powered system was used to enable real-time data acquisition from sea buoys with smooth communication between the land server and the offshore buoy located 1.8 km away. This research developed an acoustic-based monitoring system for detecting harmful organisms around the intake and provided foundational data for preventing marine organism intrusion and planning effective measures.