• Nuclear Engineering and Technology
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• 제53권1호
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• pp.61-68
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• 2021

Experiments of vertically upward steam-water two-phase flow have been carried out in single-side heated narrow rectangular channel with a gap of 3 mm. Flow patterns were identified and classified through visualization directly. Slug flow was only observed at 0.2 MPa but replaced by block-bubble flow at 1.0 MPa. Flow pattern maps at the pressure of 0.2 MPa and 1.0 MPa were plotted and the difference was analyzed. The experimental data has been compared with other flow pattern maps and transition criteria. The results show reasonable agreement with Hosler's, while a wide discrepancy is observed when compared with air-water two-phase experimental data. Current criteria developed based on air-water experiments poorly predict bubble-slug flow transition due to the different formation and growth of bubbles. This work is significant for researches on heat transfer, bubble dynamics and flow instability.

• 한국분말재료학회지
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• 제12권6호
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• pp.422-427
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• 2005

The $Al_2O_3$ with various phases were prepared by simple ex-situ hydrolysis and spark plasma sintering (SPS) process of Al powder. The nano bayerite $(\beta-Al(OH)_3)$ phase was derived by hydrolysis of commercial powder of Al with micrometer size, whereas the bohemite (AlO(OH)) phase was obtained by hydrolysis of nano Al powder synthesized by pulsed wire evaporation (PWE) method. Compaction as well as dehydration of both nano bayerite and bohemite was carried out simultaneously by SPS method, which is used to fabricate dense powder compacts with a rapid heating rate of $100^{\circ}C$ per min. under the pressure of 50MPa. After compaction treatment in the temperature ranges from $100^{\circ}C\;to\; 1100^{\circ}C$, the bayerite and bohemite phases change into various alumina phases depending on the compaction temperatures. The bayerite shows phase transition of $Al(OH)_3{\to}{\eta}-Al_2O_3{\to}{\theta}-Al_2O_3{\to}\alpha-Al_2O_3$ sequences. On the other hand, the bohemite experiences the phase transition from AlO(OH) to ${\gamma}-Al_2O_3\;at\;350^{\circ}C.$ It shows AlO(OH) ${\gamma}-Al_2O_3{\to}{\delta}-Al_2O_3{\to}{\alpha}-Al_2O_3$ sequences. The ${\gamma}-Al_2O_3$ compacted at $550^{\circ}C$ shows a high surface area $(138m^2/g)$.

• 과학기술학연구
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• 제12권1호
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• pp.107-144
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• 2012

2011년 3월에 일본 후쿠시마에서 발생한 핵사고의 영향 때문에 최근 한국 사회에서도 에너지 미래에 대한 관심이 높아지고 있다. 한국 정부는 에너지 수요가 계속 증가할 것이라는 전제 하에 원자력 발전 확대 정책을 고수하는 반면, 한국의 시민사회와 진보정당들은 핵발전소를 단계적으로 폐지하자는 탈핵 주장을 잇달아 내놓고 있다. 최근 시민사회 쪽 연구자들에 의해 정부의 공식적인 시나리오와는 다른 대안적인 에너지 시나리오들이 발표되면서 앞으로 정부 쪽의 주류 시나리오와 시민사회 쪽의 대안적 시나리오 사이에 경합이 불가피한 상황이다. 이 글은 2008년에 결정된 제1차 국가에너지기본계획에 포함된 에너지 시나리오와 2012년에 발표된 시민사회단체들의 에너지 시나리오들의 내용을 인식론적이고 방법론적인 기반, 가치 지향성, 제도적 기반, 그리고 시나리오 등장의 사회적 배경 등의 측면에서 비교함으로써 한국의 에너지 시나리오를 둘러싼 '전문성의 정치'를 분석하고 있다. 전문성의 정치란 누구의 지식과 전문성을 정당한 것으로 인정할 것인지 혹은 어떤 지식과 접근법을 가치 있고 믿을만한 것으로 여겨야 하는가를 둘러싸고 사람들 사이에서 형성되는 갈등적 경합과정이다. 분석 결과, 정부의 에너지 시나리오는 과학주의적 인식론과 포캐스팅 방법론에 기반하고 있고, 가치중립성에 의거한 전문가주의를 표방하고 있으며, 에너지 수급에 대한 기존 추세를 전제로 주로 정부연구소의 신고전파 경제학자들에 의해 작성되었음을 알 수 있었다. 반면에 시민사회의 대안 시나리오는 구성주의적인 인식론과 백캐스팅 방법론에 기반하고, 시민참여와 같은 적극적인 가치개입을 주장하고 있으며, 후쿠시마 핵사고를 직접적인 계기로 하여 대학과 시민사회의 다양한 학문적 배경을 지닌 연구자들에 의해 작성되었다는 점을 발견할 수 있었다.

• 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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• 제32권2호
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• pp.128-141
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• 2000

The critical heat flux (CHF）experiments have been carried out in a wide range of pressures for an internally heated vertical annulus. The experimental conditions covered ranges of pressures from 0.57 to 15.01 MPa, mass fluxes of 0 kg/$m^2$s and from 200 to 650 kg/$m^2$s, and inlet subcoolings from 85 to 413 kJ/kg. The characteristics of the present data and the effect of pressure on CHF are discussed. Most of the CHFs were identified to dryout of the liquid film in the annular or annular-mist flow. For the mass flux of 200 kg/$m^2$s, there were the indications that the CHF occurred at the transition from annular to annular-mist How in the pressure range of 3~10 MPa. For the mass fluxes of 550 and 650 kg/$m^2$s, the CHFs had a maximum value at a pressure of 2~3 MPa, and the pressure at the maximum CHF values had a trend moving toward the pressure at the peak value of pool boiling CHF as the mass flux decreased. The CHF data under a zero mass flux condition indicate that both the effects of pressure and inlet subcooling on the CHF were smaller, compared with those on the CHF with net water upward flow.