Eung-Ho Kim

A NEW APPROACH TO MINIMIZE PYROPROCESSING WASTE SALTS THROUGH A SERIES OF FISSION PRODUCT REMOVAL PROCESS

Abstract In this work, a new approach to remove fission products including decay heat elements was proposed. This study aims at providing a new way to minimize the amount of waste salt for a repository, while removing the high decay heat fission products [Cs, Sr, Ba, and Y including other rare earth (RE) elements] from the waste salts generated during a chloride pyroprocessing procedure. These elements were removed in consecutive order from the pyroprocessing units. First, Cs could be released in the form of an oxide gas during voloxidation of UO2 and captured by a fly-ash filter. Then, Sr was recovered in the form of carbonate precipitates from the LiCl waste salt generated during the course of an electoreduction process, by using Li2CO3. Finally, RE elements plus yttrium in the spent LiCl-KCl waste salt generated during electrorefining were removed in the form of oxides (or oxychlorides) by using an oxygen sparging method. It was confirmed that the removal yields of each element were ~90% for Cs at ~1473 K, >99% for Sr at a molar ratio of [Li2CO3/SrCl2 = 3], and >99% for the RE elements plus yttrium. Using these successes as a basis, a reference flow sheet for removing the high decay heat elements from pyroprocessing units is presented in this work. Also, a salt regeneration system to minimize the amount of waste salt is proposed in this study.

Concentrations of CsCl and SrCl2 from a Simulated LiCl Salt Waste Generated by Pyroprocessing by Using Czochralski Method

Separation of CsCl and SrCl2 from LiCl was carried out by using a separation technology, the Czochralski crystallization method. It was experimentally confirmed that Cs as well as Sr could be separated simultaneously from a LiCl molten salt by the suggested crystallization process without any additive or adsorption medium. The concentrations of Cs and Sr in LiCl decreased from 1.81 and 4.18 wt% in the initial salt to minimum values of 114 and 36 ppm in the grown LiCl crystal, respectively. The separation mechanism of Cs and Sr is described by the solubility difference of the solutes between the molten and solid states. It is expected that the total amount of salt waste will decrease drastically, because most of LiCl could be recovered by recycling with an electroreduction process.

Destruction of chlorobenzene and carbon tetrachloride in a two-stage molten salt oxidation reactor system.

Molten salt oxidation (MSO) is one of the promising alternative destruction technologies for chlorinated organics, because it is capable of trapping chlorine during organic destruction. This study investigated the characteristics of a two-stage MSO reactor system for the destruction of CCl(4) and C(6)H(5)Cl. Investigated parameters were the MSO reactor temperature (from 1023 K to 1223 K) and the excess oxidizing air feed rate (50% and 100%). The destruction of chlorinated solvents is substantial in the Li(2)CO(3)-Na(2)CO(3) eutectic molten salt, irrespective of the tested condition. However, further oxidation of CO, which is found to be the major destruction product, is not substantial due to the limited temperature and gas residence time in the MSO reactor. Increases in the reactor temperature as well as those in the oxidizing air feed rate consistently lead to decreased emissions of carbon monoxide. No significant influence of the MSO reactor operating condition on the chlorine capturing efficiency was found. Over 99.95% and 99.997% of the chlorine was captured in the hot MSO reactors during the C(6)H(5)Cl and CCl(4) destructions, respectively. This result suggests a relatively low potential of the MSO system in the recombination of chlorinated organics, when compared to a conventional incineration system.

Phosphorus removal characteristics in hydroxyapatite crystallization using converter slag.

This study was performed to investigate the phosphorus removal characteristics in hydroxyapatite (HAP) crystallization using converter slag as a seed crystal and the usefulness of a slag column reactor system. The effects of alkalinity, and the isomorphic-substitutable presence of ionic magnesium, fluoride, and iron on HAP crystallization seeded with converter slag, were examined using a batch reactor system. The phosphorus removal efficiencies of the batch reactor system were found to increase with increases in the iron and fluoride ion concentrations, and to decrease with increases in the alkalinity and magnesium ion concentration. A column reactor system for HAP crystallization using converter slag was found to achieve high, stable levels of phosphorus elimination: the average PO4-P removal efficiency over 414 days of operation was 90.4%, in which the effluent phosphorus concentration was maintained at less than 0.5 mg/L under the appropriate phosphorus crystallization conditions. The X-ray diffraction (XRD) patterns and Fourier transform infrared (FTIR) spectra of the crystalline material deposited on the seed particles exhibited peaks consistent with HAP. Scanning electron micrograph (SEM) images showed that finely distributed crystalline material was formed on the surfaces of the seed particles. Energy dispersive X-ray spectroscopy (EDS) mapping analysis revealed that the molar Ca/P composition ratio of the crystalline material was 1.72.

Carbonate Reaction of Alkaline-Earth Element by Carbonate Agent Injection Method

The carbonate reaction of some alkaline-earth chlorides was investigated by a carbonate agent injection method in LiCl-KCl eutectic salts containing both SrCl2 and BaCl2 and LiCl molten salts containing SrCl2. The effects of the injected molar ratio of a carbonate agent (Li2CO3 or K2CO3) and the temperature (450–750°C) on the conversion efficiencies of the strontium and barium chloride to their carbonates were determined. The forms of strontium and barium carbonate resulting from the carbonate reaction with carbonate agents were identified by XRD and SEM-EDS analyses. In these experiments, the carbonate agent injection method can carbonate strontium and barium chlorides effectively at over 99% under LiCl-KCl eutectic and LiCl molten salt conditions. For LiCl-KCl eutectic molten salts, carbonation efficiency was more favorable in the case of K2CO3 injection than in the case of Li2CO injection, where strontium and barium were carbonated in the form of Ba0.5Sr0.5CO3. For LiCl molten salts, strontium was carbonated in the form of SrCO3 by Li2CO3 injection.

Removal of alkaline-earth elements by a carbonate precipitation in a chloride molten salt

Separation of some alkaline-earth chlorides (Sr, Ba) was investigated by using carbonate injection method in LiCl-KCl eutectic and LiCl molten salts. The effects of the injected molar ratio of carbonate ([K2 (or Li2 )CO3 /Sr (or Ba)Cl2 ]) and the temperature (450–750 °C) on the conversion ratio of the Sr or Ba carbonate were determined. In addition, the form of the Sr and Ba carbonate resulting from the carbonation reaction with carbonates was identified via XRD and SEM-EDS analysis. In these experiments, the carbonate injection method can remove Sr and Ba chlorides effectively over 99% in both LiCl-KCl eutectic and LiCl molten salt conditions. When Sr and Ba were co-presented in the eutectic molten salt, they were carbonated in a form of Ba0.5 Sr0.3 CO3 . And when Sr was present in LiCl molten salt, it was carbonated in the form of SrCO3 . Carbonation ratio increased with a decreasing temperature and it was more favorable in the case of a K2 CO3 injection than that of Li2 CO3 . Based on this experiment, it is postulated that carbonate precipitation method has the potential for removing alkali-earth chlorides from LiCl-KCl eutectic and LiCl molten salts.Copyright