• Nuclear Engineering and Technology
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• 제55권6호
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• pp.2011-2017
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• 2023

Gas submerged jet is an outstanding thermohydraulic phenomenon in pool scrubbing of fission products during a severe nuclear accident. Experiments were performed on the hydraulic characteristics in the ranges of air mass flux 0.1-1400 kg/m²s and nozzle diameter 10-80 mm. The results showed that the dependence of inlet pressure on the mass flux follows a power law in subsonic jets and a linear law in sonic jets. The effect of nozzle submerged depth was negligible. The isolated bubbling regime, continuous bubbling regime, transition regime, and jetting regime were observed in turn, as the mass flux increased. In the bubbling regime and jetting regime, the air volume fraction distribution was approximately symmetric in space. Themelis model could capture the jet trajectory well. In the transition regime, the air volume fraction distribution loses symmetry due to the bifurcated secondary plume. The Li correlation and Themelis model showed sufficient accuracy for the prediction of jet penetration length.

• Nuclear Engineering and Technology
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• 제56권2호
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• pp.568-574
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• 2024

The development of radiation-tolerant radio-frequency (RF) systems can be a solution for applications in extreme radiation environments, such as nuclear power plant monitoring and space exploration. Among the crucial components within an RF system, the low noise amplifier (LNA) stands out due to its vulnerability to TID effects, mainly relying on transistors as its main devices. In this study, the TID effects in the LNA using standard 0.18 ㎛ complementary metal oxide semiconductors (CMOS) technology are estimated and analyzed. The results show that the LNA can withstand absorbed radiation up to 100 kGy. The S₂₁, S₁₁, noise figure (NF), stability (K), and linearity of the third input intercept point (IIP3) slightly shifted from the initial values of 0.8312 dB, 0.793 dB, 0.00381 dB, 1.34406, and 2.36066 dBm, respectively which are still comparable to the typical performances. Moreover, the standard 0.18 ㎛ technology has demonstrated its radiation tolerance, as it exhibits negligible performance degradation in the conventional LNA even when exposed to radiation levels up to 100 kGy. In this context, simulation approach offers a means to predict the TID effects and estimate the radiation exposure limit for electronic devices, particularly when transistors are used as the primary RF components.

• Nuclear Engineering and Technology
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• 제56권3호
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• pp.873-879
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• 2024

A sodium-cooled fast reactor (SFR) core has a potential of prompt criticality due to a change of core material distribution during a severe accident, and the resultant energy release has been one of the safety issues of SFRs. In this study, the safety assessment of an unprotected loss-of-flow (ULOF) in a small SFR (SSFR) has been performed using the SIMMER-IV computer code, which couples the models of space- and time-dependent neutronics and multi-component, multi-field thermal hydraulics in three dimensions. The code, therefore, is applicable to the simulations of transient behaviors of extended disrupted core material motion and its reactivity effects during the transition phase (TP) of ULOF, including a potential of prompt-criticality power excursions driven by fuel compaction. Several conservative assumptions are used in the TP analysis by SIMMER-IV. It was found out that one of the important mechanisms that drives the reactivity-inserting fuel motion was sodium vapor pressure resulted from a fuel-coolant interaction (FCI), which itself was non-energetic local phenomenon. The uncertainties relating to FCI is also evaluated in much conservative way in the sensitivity analysis. From this study, the ULOF characteristics in an SSFR have been understood. Occurrence of recriticality events under conservative assumptions are plausible, but their energy releases are limited.

• Nuclear Engineering and Technology
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• 제55권11호
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• pp.4120-4124
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• 2023

High-level radioactive waste produced by nuclear power plants are disposed subterraneously utilizing an engineered barrier system (EBS). A gap inevitably exists between the disposal canisters and buffer materials, which may have a negative effect on the thermal transfer and water-blocking efficiency of the system. As few previous experimental works have quantified this effect, this study aimed to create an experimental model for investigating differences in the temperature changes of bentonite buffer in the presence and absence of air gaps between it and a surrounding stainless steel cell. Three test scenarios comprised an empty cell and cells partially or completely filled with bentonite. The temperature was measured inside the buffers and on the inner surface of their surrounding cells, which were artificially heated. The time required for the entire system to reach 100℃ was approximately 40% faster with no gap between the inner cell surface and the bentonite. This suggests that rock-buffer spaces should be filled in practice to ensure the rapid dissipation of heat from the buffer materials to their surroundings. However, it can be advantageous to retain buffer-canister gaps to lower the peak buffer temperature.

• Nuclear Engineering and Technology
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• 제55권12호
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• pp.4477-4490
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• 2023

Fuel locking mechanisms (FLMs) are essential in upward-flow research reactors to prevent accidental fuel separation from the core during reactor operation. This study presents a novel design concept for a remotely controlled plate-type nuclear fuel locking mechanism. By employing electromagnetic field analysis, we optimized the design of the electromagnet for fuel unlocking, allowing the FLM to adapt to various research reactor core designs, minimizing installation space, and reducing maintenance efforts. Computational flow analysis quantified the drag acting on the fuel assembly caused by coolant upflow. Subsequently, we performed finite element analysis and evaluated the structural integrity of the FLM based on the ASME boiler and pressure vessel (B&PV) code, considering design loads such as dead weight and flow drag. Our findings confirm that the new FLM design provides sufficient margins to withstand the specified loads. We fabricated a prototype comprising the driving part, a simplified moving part, and a dummy fuel assembly. Through basic operational tests on the assembled components, we verified that the manufactured products meet the performance requirements. This remote-controlled micro locking mechanism holds promise in enhancing the safety and efficiency of plate-type nuclear fuel operation in upflow research reactors.

• Nuclear Engineering and Technology
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• 제55권12호
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• pp.4335-4349
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• 2023

Nuclear marine propulsion has been emerging as a next generation carbon-free power source, for which proper passive residual heat removal systems (PRHRSs) are needed for long-term safety. In particular, the characteristics of unlimited operation time and compact design are crucial in maritime applications due to the difficulties of safety aids and limited space. Accordingly, a compact and long-term-operable PRHRS has been proposed with the key design concept of using both air cooling and seawater cooling in tandem. To confirm its feasibility, this study conducted system design and a transient analysis in an accident scenario. Design results indicate that seawater cooling can considerably reduce the overall system size, and thus the compact and long-term-operable PRHRS can be realized. Regarding the transient analysis, the Multi-dimensional Analysis of Reactor Safety (MARS-KS) code was used to analyze the system behavior under a station blackout condition. Results show that the proposed design can satisfy the design requirements with a sufficient margin: the coolant temperature reached the safe shutdown condition within 36 h, and the maximum cooling rate did not exceed 40 ℃/h. Lastly, it was assessed that both air cooling and seawater cooling are necessary for achieving long-term operation and compact design.

• Nuclear Engineering and Technology
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• 제56권5호
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• pp.1698-1711
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• 2024

Heat pipe cooled reactors have gained attention as a potential solution for nuclear power generation in space and deep sea applications because of their simple design, scalability, safety and reliability. However, under complex operating conditions, a control strategy for variable load operation is necessary. This paper presents a two-dimensional transient characteristics analysis program for a heat pipe cooled reactor and proposes a variable load control strategy using the recuperator bypass (CSURB). The program was verified against previous studies, and steady-state and step-load operating conditions were calculated. For normal operating condition, the predicted temperature distribution with constant heat pipe temperature boundary conditions agrees well with the literature, with a maximum temperature difference of 0.4 K. With the implementation of the control strategy using the recuperator bypass (CSURB) proposed in this paper, it becomes feasible to achieve variable load operation and return the system to a steady state solely through the self-regulation of the reactor, without the need to operate the control drum. The average temperature difference of the fuel does not exceed 1 % at the four power levels of 70 %,80 %, 90 % and 100 % Full power. The output power of the turbine can match the load change process, and the temperature difference between the inlet and outlet of the turbine increases as the power decreases.

• Nuclear Engineering and Technology
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• 제56권5호
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• pp.1754-1761
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• 2024

In hadrontherapy, secondary fragments are generated by nuclear interactions of the incident heavy ion beam with the atomic nuclei of the target. It is important to determine the yield of production and the dose contribution of these secondary fragments in order to determine the radiobiological effectiveness more accurately. This work aims to fully identify the secondary fragments generated by nuclear interactions of proton and helium (⁴He) ion beams in a High-Density Polyethylene (HDPE) target and to investigate the dose contributions by secondary fragments. Incident protons with energies of 55.90 MeV and 105.20 MeV and helium ions with energies of 52.55 MeV/u and 103.50 MeV/u in the HDPE phantom have been investigated by the means of Geant4 Monte Carlo (MC) simulations. Simulated results were validated using NASA Space Radiation Laboratory (NSRL) Bragg curves experimental data. The results showed that the dose contribution of secondary fragments deriving from helium ion beams is three times higher than in the case of proton beams. This is due to a higher production of nuclear fragments in the case of helium ion beams. This work contributes to a better understanding of secondary fragments generated by protons and helium ions in the HDPE target.

• Nuclear Engineering and Technology
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• 제56권6호
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• pp.2428-2435
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• 2024

Training for radiation protection and control requires a visual understanding of radiation, which cannot be perceived by the human senses. Trainees must also master the effective use of measuring instruments. Traditionally, such training has exposed trainees to radiation sources. Here, we present a novel e-training strategy that enables safe, exposure-free handling of a radiation measuring tool called a survey meter. Our mixed reality radiation-training system merges the physical world with a digital one. Collaborating with a mixed reality headset (HoloLens 2), this system constructs a mock-up of a survey meter in real-world space. The HoloLens 2 employs a browser-based application to visualize radiation and to simulate/share the use of the survey meter, including its physical movements. To provide a dynamic learning experience, the system adjusts the survey-meter mock-up readings according to the operator's movements, distance from the radiation source, the response time of survey meter, and shielding levels. Through this approach, we expect that trainees will acquire practical skills in interpreting survey-meter readings and gain a visual understanding of radiation in real-world situations.

• 정보관리학회지
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• 제31권3호
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• pp.29-63
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• 2014

본 연구에서는 Y세대의 특징을 밝히고 Y세대가 요구하는 차세대디지털도서관서비스를 도출하고자 하였으며, 이들의 요구가 베이비붐세대와 어느 정도 차이를 보이는지를 비교하고자 하였다. 연구결과, 첫째, Y세대가 가장 많이 이용하는 디지털기기는 휴대폰 또는 스마트폰으로 나타났고, 다음으로 데스크탑 PC, 노트북 PC, 디지털 카메라 순으로 나타났으며, 사용비율에 있어서 약간의 차이는 있지만 그 순위는 베이비붐세대와 거의 유사하게 나타났다. 둘째, 이용하는 디지털서비스에 있어서 Y세대와 베이비붐세대는 상당한 차이를 보이고 있는 것으로 분석되었으며, Y세대는 인터넷 포털을 가장 많이 이용하고 베이비붐세대는 이메일서비스를 가장 많이 이용하는 것으로 나타났다. 셋째, Y세대와 베이비붐세대가 차세대디지털도서관에 요구하는 서비스를 클라우드서비스, 무한창조공간, 빅데이터, 증강현실, 구글글래스, 상황인식기술, 시맨틱서비스, SNS서비스, 디지털교과서서비스, RFID 및 QRCode 서비스, 도서관공간구성, 최첨단디스플레이기술, 기타 획기적인 서비스로 구분하여 조사한 결과, Y세대가 가장 높은 요구도를 보인 서비스는 빅데이터서비스였고, 베이비붐세대는 디지털교과서서비스였다.