Abstract
The retention and control of iodine is one of the major problems to be solved in the development of processing technology for spent nuclear fuels. In order to achieve a retention of the order required, new and highly reliable systems for removing iodine from a fuel reprocessing plant must be developed. To achieve this goal, we require additional knowledge concerning the aqueous phase chemistry of iodine. Absorption spectra of various species of iodine in aqueous and organic solutions were recorded over the wavelength region 186 to 700 nm. Iodine can be determined by direct spectrophotometry at concentration levels as low as 10-6 M in aqueous solutions and 10 -7 M by concentration through an extraction process. The distribution coefficients were determined at 20 to 50° C in the range 10-2 to 10-7 M iodine. The loss of iodine during the series extraction process was calculated. Several attempts to enrich the concentrations lower than 10-7 M iodine in nitric acid solution by extraction and re-extraction in the presence of reducing and oxidizing agents were unsuccessful. It has been demonstrated that iodine ions can be determined by direct potentiometry to concentration levels as low as 5 x 10-7 M in nitric acid solutions. The effects of 1 to 4 M nitric acid and temperature are examined and discussed. Many useful results were obtained for potentiometric measurements of iodine using buffer solutions. A difference in the behaviour of mixed solutions of iodide, iodine, and iodate with buffer solution is observed. One of the greatest advantages of this method is that the analysis can be carried out within three minutes since the response time of the electrodes is short. This work also summarizes results obtained by earlier studies aiming at the identification of iodine compounds released in solution, and to obtain more information concerning formation mechanisms and kinetics of the iodine exchange reaction.