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Two phase (air-molten carbonate salt) flow characteristics in a molten salt oxidation reactor
Yung-Zun Cho,양희철,강용 한국화학공학회 2009 Korean Journal of Chemical Engineering Vol.26 No.3
Molten salt oxidation process is one of the most promising alternatives to incineration that can be used to effectively destroy the organic components of mixed and hazardous wastes. To detect the flow characteristics of the molten salt oxidation process (air-molten carbonate salt two-phase flow), differential pressure fluctuation signals from a molten salt oxidation process have been analyzed by adopting the stochastic methods. Effects of the input air flow rate (0.05-0.22 m/sec) and the molten salt temperature (870-970℃) on the phase holdup and flow characteristics are studied. The gas holdup increases with an increasing molten salt temperature due to the decrease of the viscosity and surface tension of the molten carbonate salt. It is found that a stochastic analysis of the differential pressure signals enables us to obtain the flow characteristics in the molten salt oxidation process. The experimentally obtained gas holdup data in the molten salt reactor were well described and characterized by means of the drift-flux model.
Minimization of Eutectic Salt Waste from Pyroprocessing by Oxidative Precipitation of Lanthanides
CHO, Yung-Zun,PARK, Gil-Ho,YANG, Hee-Chul,HAN, Dae-Seok,LEE, Han-Soo,KIM, In-Tae Atomic Energy Society of Japan 2009 Journal of nuclear science and technology Vol.46 No.10
<P>A lab-scale lanthanide precipitation apparatus, which has a 4 kg/batch size, was installed and tested. By using this lab-scale apparatus, cooxidative precipitation experiments of lanthanides were carried out. As lanthanides, 8 rare-earth elements (Y, La, Ce, Pr, Nd, Sm, Eu, and Gd) were used. By a reaction with oxygen, La, Pr, Nd, Sm, Eu, and Gd were converted to their oxychloride form (REOCl) and Ce, Pr, and Y to their oxide form (REO<SUB>2</SUB>, RE<SUB>2</SUB>O<SUB>3</SUB>). Since these lanthanide oxides or oxychlorides are nearly insoluble to eutectic salt, they were all precipitated by a free settling at the bottom, where about 7 h of precipitation time was required. It was found that under the conditions of 750°C salt temperature, a 12 h sparging time, and 5 L/min oxygen sparging rate, all the used rare-earth elements showed over 99% oxidation efficiency. However, in the case of 800°C temperature, they show over 99% conversion efficiency only after 6 h.</P>
EUTECTIC(LiCl-KCl) WASTE SALT TREATMENT BY SEQUENCIAL SEPARATION PROCESS
Cho, Yung-Zun,Lee, Tae-Kyo,Choi, Jung-Hun,Eun, Hee-Chul,Park, Hwan-Seo,Park, Geun-Il Korean Nuclear Society 2013 Nuclear Engineering and Technology Vol.45 No.5
The sequential separation process, composed of an oxygen sparging process for separating lanthanides and a zone freezing process for separating Group I and II fission products, was evaluated and tested with a surrogate eutectic waste salt generated from pyroprocessing of used metal nuclear fuel. During the oxygen sparging process, the used lanthanide chlorides (Y, Ce, Pr and Nd) were converted into their sat-insoluble precipitates, over 99.5% at $800^{\circ}C$; however, Group I (Cs) and II (Sr) chlorides were not converted but remained within the eutectic salt bed. In the next process, zone freezing, both precipitation of lanthanide precipitates and concentration of Group I/II elements were preformed. The separation efficiency of Cs and Sr increased with a decrease in the crucible moving speed, and there was little effect of crucible moving speed on the separation efficiency of Cs and Sr in the range of a 3.7 - 4.8 mm/hr. When assuming a 60% eutectic salt reuse rate, over 90% separation efficiency of Cs and Sr is possible, but when increasing the eutectic salt reuse rate to 80%, a separation efficiency of about 82 - 86 % for Cs and Sr was estimated.
Simulation of Chlorination Process for Spent Nuclear Fuel Partitioning
Jinmok Hur,Yung-Zun Cho,Chang Hwa Lee 한국방사성폐기물학회 2023 한국방사성폐기물학회 학술논문요약집 Vol.21 No.2
This study investigated the effectiveness of various chlorinating agents in partitioning light water reactor spent fuel, with the aim of optimizing the chlorination process. Through thermodynamic equilibrium calculations, the effects of using MgCl2, NH4Cl, and Cl2 as a single chlorinating agent or applying MgCl2, NH4Cl, and Cl2 sequentially for spent fuel chlorination were evaluated Furthermore, in this study, assuming the actual process operation situation, where only a part of the semi-volatile nuclides is removed during the heat treatment process, and including the process of precipitating the molten salt from the chlorination process with K3PO4 and K2CO3 precipitants, the percentage distribution of 50 nuclides in the light water reactor spent fuel into each process stream was quantitatively calculated using the simulation function of the HSC program and tabulated for intuitive viewing. Compared to a single chlorinator, sequential chlorination more effectively separated the heat and radioactivity of the spent fuel from the uranium-dominated product solids. Specifically, the sequential application of the chlorinating agents following heat treatment led to a final solid separation characterized by 93.1% mass retention, 5.1% radioactivity, and 15.4% decay heat, relative to the original spent fuel. The findings underscore that sequential chlorination can be an effective method for spent fuel partitioning, either as a standalone approach or in combination with other partitioning processes such as pyroprocessing.
Ju Ho Lee,Yung-Zun Cho 한국방사성폐기물학회 2018 방사성폐기물학회지 Vol.16 No.4
공기 분위기하 UO2의 독특한 산화거동을 모사하기 위해 기존 Crackling Core Model (CCM)을 개선하였다. UO2가 U3O8으로 전환될 때 시간-전환율 곡선에서 나타나는 실험적 sigmoid 거동을 근사하게 재현할 수 있도록 모델 개선에 파편화 효과로 인한 반응 표면적 증대 및 결정립 가변 전환시간 개념을 고려하였다. UO2는 U3O7을 거쳐 U3O8으로 전환되며 최종 결정립 산화 소요 시간은 초기 결정립 산화 소요 시간의 10배에 해당한다는 가정을 도입했을 때, 개선된 모델은 599 - 674 K에서의 UO2 구 형 입자의 실험적 산화거동과 근사한 계산결과를 나타내었으며 핵종성장모델(Nucleation and Growth Model) 및 자촉매반응모델(AutoCatalytic Reaction Model)과 비교할 때 가장 작은 오차를 보여주었다. 개선된 모델을 통해 U3O8으로의 100% 전환시 계산된 활성화에너지값은 57.6 kJ·mol-1로 자촉매반응모델로 계산된 값인 48.6 kJ·mol-1보다 크며, 외삽에 의해 결정된 실험값에 더 근사함이 밝혀졌다. This study presents a revised crackling core model for the description of UO2 sphere oxidation in air atmosphere. For close reproduction of the sigmoid behavior exhibited in UO2 to U3O8 conversion, the fragmentation effect contributing to the increased reactive surface area and the concept of variable grain conversion time were considered in the model development. Under the assumptions of two-step successive reaction of UO2 → U3O7 → U3O8 and final grain conversion time equivalent to ten times the initial grain conversion time, the revised model showed good agreement with the experimental data measured at 599 – 674 K and a lowest deviation when compared with Nucleation and Growth model and AutoCatalytic Reaction model. The evaluated activation energy at 100% conversion to U3O8, 57.6 kJ·mol-1, was found to be closer to the experimentally extrapolated value than to the value determined in AutoCatalytic Reaction model, 48.6 kJ·mol-1.