Investigations on measurement and methodology for dielectric constant of solvents used for actinide separations in nuclear fuel cycle

Abstract

PUREX (Plutonium uranium reduction extraction) is a versatile reprocessing method being employed in nuclear fuel cycle to separate U/Pu from the spent fuel present in 4 M nitric acid medium. The process is carried out by using 1.1 M tributyl phosphate (TBP)/n-DD (dodecane) as the extractant. High aqueous solubility and radiological and chemical degradation followed by retention of actinides are major disadvantages. However, to overcome certain demerits encountered by TBP and other alkyl phosphate-based extractants, organic phosphonate-based extractants have been developed and used to extract actinide.

Various organophosphorous based solvents are synthesized to develop better extractants for separation and recovery of actinides by solvent extraction in nuclear reactor/allied facilities. The polarity of the organic phase in the solvent extraction is a key parameter, which determines the amount of metal that can be loaded in the organic phase. The dielectric constant is an admissible ability to dissolve common ionic compounds. Typically, the dielectric constant of a solvent is evaluated for polarity. Higher dielectric constant is a measure of higher polarity, and greater is the capability of the solvent to hold the steady charges. The instrumentation setup is devised and developed for the measurement of the dielectric constant of solvents in a given medium The challenge in the setup is developing a dielectric sensor and instrumentation, that is compatible with sophisticated solvents possessing wide dynamic response with high accuracy, stability and precision. The investigations of the sensor, measurement methodology and estimation of the dielectric constant with various known and unknown solvents for the separation and recovery of actinides in the nuclear fuel cycle and nuclear waste treatment of the fast breeder test reactor were carried out and studied in detail. The dielectric constant of various standard solvents lying in the range 1–40 was measured and validated from literature values with an accuracy of ±1 %. Subsequently, the measurement of dielectric constant was carried out over different solvents such as Di-iso-amyl-iso-amyl phosphonate (DiAiAP), Di-iso-amyl-butyl phosphonate (DiABP), Di-sec-amyl-hydrogen phosphonate (DsAHP) and Di-sec-butyl-hydrogen phosphonate (DsBHP) synthesized in our laboratory.