This study proposes a method of separating uranium (U) and minor actinides from rare earth (RE) elements in the LiCl-KCl salt system. Several RE metals were used to reduce UCl3 and MgCl2 from the eutectic LiCl-KCl salt systems. Five experiments were performed on drawdown U and plutonium (Pu) surrogate elements from RECl3-enriched LiCl-KCl salt systems at 773 K. Via the introduction of RE metals into the salt system, it was observed that the UCl3 concentration can be lowered below 100 ppm. In addition, UCl3 was reduced into a powdery form that easily settled at the bottom and was successfully collected by a salt distillation operation. When the RE metals come into contact with a metallic structure, a galvanic interaction occurs dominantly, seemingly accelerating the U recovery reaction. These results elucidate the development of an effective and simple process that selectively removes actinides from electrorefining salt, thus contributing to the minimization of the influx of actinides into the nuclear fuel waste stream.

Two commonly used ceramics in molten salt research are alumina and mullite. The two ceramics were exposed to a combination of rare earth chlorides (YCl3, SmCl3, NdCl3, PrCl3, and CeCl3; each rare earth chloride of 1.8 weight percent) in LiCl-KCl at 773 K for approximately 13 days. Scanning electron microscopy with wave dispersion spectra was utilized to investigate a formation layer or deposition of rare earths onto the ceramic. Only the major constituents of the ceramics (Al, Si, and O2) were observed during the wave dispersion spectra. X-ray fluorescence was used as well to determine concentration changes in the molten salt as a function of ceramic exposure time. This study shows no evidence of ionic exchange or layer formation between the ceramics and molten chloride salt mixture. There are signs of surface tension effects of molten salt moving out of the tantalum crucible into secondary containment.

Molten salt solutions consisting of eutectic LiCl-KCl and concentrations of samarium chloride (0.5 to 3.0 wt%) at 500℃ were analyzed using both cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). The CV technique gave the average diffusion coefficient for Sm3+ over the concentration range. Equipped with Sm3+ diffusion coefficient, the Randles-Sevcik equation predicted Sm3+ concentration values that agree with the given experimental values. From CV measurements; the anodic, cathodic, and half-peak potentials were identified and subsequently used as a parameter to acquire EIS spectra. A six-element Voigt model was used to model the EIS data in terms of resistance-time constant pairs. The lowest resistances were observed at the half-peak potential with the associated resistance-time constant pairs characterizing the reversible reaction between Sm3+ and Sm2+. By extrapolation, the Voigt model estimated the polarization resistance and established a polarization resistance-concentration relationship.

CKD 추출액은 시멘트공정에서 발생한 폐기물인 CKD를 시멘트 원료로 재사용하기 위해 공정 방해물질로 작용하는 KCl을 추출한 폐수이며, 폐수처리시설 증설 등의 문제로 추출액 무방류 및 이를 재이용하고자 하였다. 이온교환법을 적용하여 KCl을 제거한 결과, 이온교환 후 추출액의 pH는 12.7 에서 pH 2 미만으로 감소하였으며 양이온교환수지의 H+가 이온교환을 거쳐 추출액에 용해되었음을 확인하였다. 이온교환의 선택성에 의해 Ca2+, K+ 순서로 제거되었으며, K+ 이온을 제거하기 위해 접촉시 간의 증가가 필요함을 판단하였다. 이온교환수지와 직접접촉시간이 약 6배 높은 접촉시간을 갖는 회분 식장치에서 연속흐름식장치 대비 4배 높은 K+ 제거 효율을, 7배 높은 Cl- 제거 효율을 확인하였다. 양이온교환수지의 H+가 음이온교환수지의 OH- 대비 1.2배 빠른 교환속도를 가짐을 추출액 pH 변화를 통해 확인하였다.