• 전기화학회지
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• 제5권4호
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• pp.183-188
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• 2002

The structure of species formed in $NbCI_5-I-ethyl-3-methylimidazolium$ chloride (EMIC) room-temperature molten salt (RTMS) was examined with the Raman spectroscopic measurement and ab initio molecular orbital calculation. The equilibrium structures of $NbCl_5,\;NbCl_6^-,\;Nb_2CI_{10},\;Nb_2CI_{11}^-,\;Nb_3CI_6^-,\;NbCI_6^--EMI^+\;(in\;which\;NbCI_6^-$ anion approaches $EMI^+$ cation with strong interaction) and $Nb_2CI_{11}^--EMI^+$ were obtained with the HF/LANL2DZ level of calculation. The harmonic frequencies at each equilibrium structure were compared with Raman spectra. The harmonic frequencies of $NbCI_6^--EMI^+,\; Nb_2CI_{11}^--EMI^+,\;and\;Nb_2CI_{10}$ were in good agreement with the Raman spectra of RTMS melts. In the $NbCI_5-EMIC RTMS$, the main species were $NbCI_6^-\;and\;EMI^+$. In the $NbCl_5-EMIC$ RTMS added $NbCl_5\;over\;50mol\%$, small amount of $Nb_2CI_{11}^-\;and\; Nb_2CI_{10}$ were also formed. The structures of anions and cation in the RTMS distorted from free ions with Coulomb force.

• Journal of Radiation Protection and Research
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• 제41권4호
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• pp.378-383
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• 2016

Background: Radiation dose rates in PRIDE facility is evaluated quantitatively for assessing radiation safety of workers because of large amounts of depleted uranium being handled in PRIDE facility. Even if direct radiation from depleted uranium is very low and will not expose a worker to significant amounts of external radiation. Materials and Methods: ORIGEN-ARP code was used for calculating the neutron and gamma source term being generated from depleted uranium (DU), and the MCNP5 code was used for calculating the neutron and gamma fluxes and dose rates. Results and Discussion: The neutron and gamma fluxes and dose rates due to DU on spherical surface of 30 cm radius were calculated with the variation of DU mass and density. In this calculation, an imaginary case in which DU density is zero was added to check the self-shielding effect of DU. In this case, the DU sphere was modeled as a point. In case of DU mixed with molten salt of 50-250 g, the neutron and gamma fluxes were calculated respectively. It was found that the molten salt contents in DU had little effect on the neutron and the gamma fluxes. The neutron and the gamma fluxes, under the respective conditions of 1 and 5 kg mass of DU, and 5 and $19.1g{\cdot}cm^{-3}$ density of DU, were calculated with the molten salt (LiCl+KCl) of 50 g fixed, and compared with the source term. As the results, similar tendency was found in neutron and gamma fluxes with the variation of DU mass and density when compared with source spectra, except their magnitudes. Conclusion: In the case of the DU mass over 5 kg, the dose rate was shown to be higher than the environmental dose rate. From these results, it is concluded that if a worker would do an experiment with DU having over 5 kg of mass, the worker should be careful in order not to be exposed to the radiation.

• 한국재료학회지
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• 제30권4호
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• pp.176-183
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• 2020

The high-temperature stability of YSZ specimens fabricated by die pressure and cold isostatic press (CIP) is investigated in CaCl₂-CaF₂-CaO molten salt at 1,150 ℃. The experimental results are as follows: green density 46.7 % and 50.9 %; sintering density 93.3 % and 99.3 % for die press and CIP, respectively. YSZ foremd by CIP exhibits higher stability than YSZ formed by die press due to denseness dependency after high-temperature stability test. YSZ shows peaks mainly attributed to CaZrO₃, with a small t-ZrO₂ peak, unlike the high-intensity tetragonal-ZrO₂ (t-ZrO₂) peak observed for the asreceived specimen. The t-ZrO₂ phase of YSZ is likely stabilized by Y₂O₃, and the leaching of Y₂O₃ results in phase transformation from t-ZrO₂ to m-ZrO₂. CaZrO₃ likely forms from the reaction between CaO and m-ZrO₂. As the exposure time increases, more CaZrO₃ is observed in the internal region of YSZ, which could be attributed to the inward diffusion of molten salt and outward diffusion of the stabilizer (Y₂O₃) through the pores. This results in greater susceptibility to phase transformation and CaZrO₃ formation. To use SOM anodes for the electroreduction of various metals, YSZ stability must be improved by adjusting the high-density in the forming process.

• 방사성폐기물학회지
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• 제10권4호
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• pp.229-236
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• 2012

$Li_2O$-LiCl 용융염을 이용한 전해환원기술은 사용후핵연료로부터 우라늄 금속을 회수하기 위해 연구되고 있다. 이 전해환원기술에서는 $Li_2O$가 촉매로 이용되기 때문에 그 농도를 유지하는 것은 매우 중요한 운전인자이다. $ZrO_2$는 피복관의 주성분이 Zr이기 때문에 사용후핵연료에 불가피하게 함유되며, 본 연구에서는 $Li_2O$를 촉매로 이용하는 전해환원공정에서 $ZrO_2$의 거동을 살펴보았다. $Li_2O$와 $ZrO_2$의 화학반응과 전해환원공정 중에서의 생성물을 분석한 결과, $Li_2ZrO_3$와 $Li_4ZrO_4$가 주요하게 관찰되었고, 이는 $Li_2O$의 손실을 가져오는 원인이 된다. 즉, $ZrO_2$는 $Li_2O$를 소모하는 역할을 하며, 반응생성물은 전기화학적으로 안정하기 때문에 $Li_2O$의 손실이 불가피하게 된다.

• 방사성폐기물학회지
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• 제16권2호
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• pp.165-172
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• 2018

용융염-액체금속 추출공정에서 형성되는 액적 크기를 추정하는 방안으로 용융염-액체금속 계를 상온에서 유사한 물-수은 계로 대체하여 액적 형성 실험을 노즐의 종류에 따라 수행하여 Scheele-Meister 모델의 적용성을 평가하였다. 실험에서 액적의 크기 측정은 디지털카메라와 이미지분석 소프트웨어를 사용하였으며 노즐은 0.018 cm과 0.025 cm의 구멍 크기를 가지며 수은의 통과 길이가 1.3 cm인 상용 니들과 두께가 0.5 cm이며 0.0148 cm 구멍 2개, 0.0135 cm 구멍 3개, 0.0135 cm 구멍 4개인 것을 제작하여 사용하였다. 각각의 노즐에서 형성된 액적은 노즐 아래 20 cm까지 안정적인 구형을 유지하였다. 액적 크기의 측정치를 Scheele-Meister 모델의 추정치와 비교하였을 때 10% 오차 범위 안에서 일치하였다. 실험 결과는 물-수은 계에서 액적을 안정적으로 형성시키는 노즐에 대해 액적 크기 추정을 위한 Scheele-Meister 모델이 적용될 수 있음을 보였다.

• Nuclear Engineering and Technology
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• 제56권4호
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• pp.1339-1346
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• 2024

Electrorefining in molten salts is used for purifying actinides. Optimizing electrorefining is key to minimizing processing time and radiological waste. One possible way of improving electrorefining efficiency is using an AC superimposed DC waveform. This waveform has demonstrated potential benefits in aqueous solutions but has never been utilized in a molten metal, molten salt application. This work investigates the effects of using an AC superimposed DC waveform on molten bismuth electrorefining in a molten LiCl-KCl-CaCl2 eutectic. Bismuth has been identified as a potential surrogate for plutonium electrorefining and a potential cathode in electrorefining used nuclear fuel (UNF). All electrorefining runs resulted in a high purity cathode ring and high yield with exception of the run using a low-frequency, high-amplitude superimposed AC waveform, which experienced some contamination and a lower yield. The other three AC superimposed DC runs experienced an average yield 6.7 % higher than the average yield of the DC runs. The electrorefining run using the high-frequency, high-amplitude superimposed AC signal had the highest yield. It is recommended in future studies to investigate the statistical variability of electrorefining yield and current efficiency and the impact of AC superimposed DC waveforms on solidified bismuth anodes.

• 한국세라믹학회지
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• 제38권11호
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• pp.1015-1022
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• 2001

본 연구에서는 용융염법에 의한 Ba-ferrite의 생성기구와 그 자기적특성에 대해 조사하였다. 출발원료 중 BaC $O_3$만이 용융염내에서 용해도를 가졌으며, 이는 용융염내에서는 Ba-ferrite의 생성이 용해된 $Ba^{2+}$가 F $e_2$ $O_3$나 $\delta$-FeOOH의 표면으로 확산하여 표면반응을 통해 일어나는 것으로 보인다. 한편, 출발물질($\delta$-FeOOH와 F $e_2$ $O_3$)에 따라 생성된 Ba-ferrite가 합성되는 온도는 더 낮은 온도에서 생성됨을 알 수 있었다.

• 한국재료학회지
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• 제10권7호
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• pp.471-477
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• 2000

Fe-Ni-Cr 합금의 용융염 부식거동을 $650~850^{\circ}C$ 온도범위에서 조사하였다. 용융염 LiCl에서 Cr을 포함하지 않는 KSA(Kaeri Superalloy)-1 합금은 Fe의 내부산화가 발생하고, Cr을 포함한 KSA-4, Incoloy 800H와 KSA-5는 LiCrO$_2$의 치밀한 보호막이 형성되었다. 혼합용융염 $LiCl-LiO_2$O에서 KSA-1은 Fe의 내부산화, KSA-4는 Cr의 내부산화가 발생하였고, Cr 농도가 높은 Incoloy 800H와 KSA-5는 $LiCrO_2$의 다공성 피 이 형성되었다. 혼합용융염 $LiCl-Li_2$O 에서는 Cr 농도의 증가에 따라 부식속도가 증가하였으며, 부식속도는 시간의존선을 8%Cr 이하의 합금에서는 포물선법칙, 8%Cr 이상의 합금에서는 직선법칙을 나타내었다. 이러한 현상은 Li$_2$O에 의한 보호성 산화물 $Cr_2O_3$의 염기성 용해기구로 설명할 수 있다.

• Nuclear Engineering and Technology
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• 제56권3호
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• pp.1091-1099
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• 2024

Fluoride-salt-cooled High-temperature Reactor (FHR) is a promising nuclear reactor technology. Among many challenges presented by the molten fluoride salts is the corrosion of salt-facing structural components. Higher moisture contents, in the FLiNaK (LiF-NaF-KF, 46.5-11.5-42 mol%) salt, aggravate intergranular corrosion and pitting for the given alloys. Therefore, several thermal dehydration tests of FLiNaK salt were performed with a batch size suitable for thermal-hydraulic experiments. Thermogravimetric Analysis (TGA) was performed for the three constituent fluoride salts individually. Preliminary thermal dehydration plans were then proposed for NaF and KF salts based on the TGA curves. However, the dehydration process may not be required for LiF since its low mass loss (<1.3 wt%). To evaluate the performance of these thermal dehydration plans, a batch-scale salt dehydration test facility was designed and constructed. The preliminary thermal dehydration plans were tested by varying the heating rates, target temperature, and holding time. The sample mass loss data showed that the high temperatures (>500 ℃) were necessary to remove a significant amount of moisture (>1 wt%) from NaF salt, while relatively low temperatures (around 300 ℃) with a long holding time (>10 h) were sufficient to remove most of the moisture from KF salt.

• 한국표면공학회지
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• 제32권3호
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• pp.341-343
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• 1999

The morphology and composition of anodic films, formed on aluminium at various current densities, in the range $1-100{\;}Am^{-2}$, in the molten bisulphate melt at different temperatures (418-498K), have been studied using transmission electron microscopy of ultramicrotomed film sections, and ion beam thinned films. The first sign of incipient breakdown revealed by transmission electron microscopy of stripped films, is always the appearance of dark regions about 1,000 nm in diameter, representing local overgrowth of the film. The breakdown mechanism is closely related to thermal effects, because temperature rises at regions representing local overgrowth in the stripped films were observed at voltages close to the breakdown voltage, likely arising through impact ionization.