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  • Author or Editor: Hwan-Seo Park x
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Summary  

Amorphous zirconium phosphate (Zr(HPO4)2 .nH2O, AM-ZP) has been investigated as a material for selective removal of Cs or Sr from molten salt waste at aqueous state and its ceramic waste form. NZP (MZr2P3O12, M=Li, Na, Cs, and Sr), was synthesized by three methods and evaluated their durability by the Product Consistency Test (PCT) method. AM-ZP has a high selectivity on Cs and Sr even in the presence of Li with high concentration. From the leaching data, the leached fractions (LF) of each product at a given time in infinite leachate volume can be calculated by a semi-empirical equation. The LF of Li, Na, Cs and Sr on the product prepared by composition-adjusting process were 0.143, 0.078, 0.017, and 0.034, respectively. It can be concluded that AM-ZP is an effective material for selective removal of radionuclides from molten salt waste and its metal-loaded ZP can be changed into a durable waste form close to NZP structure by a composition-adjusting process.

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Abstract  

A new two-step process was investigated to treat LiCl molten salt waste containing volatile radionuclides generated from an electro-metallurgical processing (pyro-processing) of spent oxide fuels. First, the chemical form of the soluble LiCl waste was transformed into a chloride-free and less soluble hydroxide compound by an electrochemical method, where an electrolytic de-chlorination was performed without adding any chemical salt. Then, a gelation process of the chemical form-changed Li compound, named gel-route stabilization/solidification (GRSS) system aimed to reduce the volatility of the radionuclides greatly, was introduced to stabilize/solidify the hydroxide salt wastes. The application of the electrochemical dechlorination/transformation process and the subsequent gel-route stabilization process to treat the soluble LiCl salt wastes was found to be effective.

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Abstract  

Radioactive molten salt generated from a pyrochemical process to separate reusable U and TRU elements is one of problematic wastes to manage for a final disposal. For the minimization of final waste, it is desirable to selectively remove radionuclides from the waste salts. In this paper, structural change of some zeolites in a series of molten salt systems and its removal behavior of CsCl was investigated. Zeolite-4A(LTA) was transformed into LiAlSiO4 and Li-sodalite with the mol-fraction of LiCl in LiCl–KCl system at 650 °C while it was not changed in NaCl–KCl at 750 °C, regardless of mol-fraction of metal chloride. Other commercial zeolite with specific structure (FAU) had the same trends on the structural stability in molten salt system. From the Cs removal experiments, the decomposed zeolitic materials in molten salt lost their removal ability of Cs. In conclusion, a new selective material or method should be investigated or developed for obtaining the validity on the separation of group I and II radionuclides from a molten waste salt because the zeolite 4A is unstable in the LiCl system and it also showed a low capacity in the LiCl–KCl phase. This paper gives basic information on the removal of radionuclides from molten systems by using zeolitic materials.

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