The effect of radiolysis of BTBP type molecules on distribution ratios

Licentiate thesis, 2008

Partitioning and transmutation of spent nuclear fuel enables a decrease in the long term radiotoxicity and volume of the waste to be disposed. By transforming the long-lived nuclides into shorter-lived or even stable ones, the time required for a final repository to be regarded safe for the environment can decrease from 100,000 years to less than 1,000 years. To enable these transformations, the elements with long-lived nuclides need to be separated from the rest of the fuel, and possibly also from each other. One way to perform this separation is solvent extraction and one type of organic ligands developed to be used in the separation process is the BTBP (6,6’ bis(5,6 dialkyl [1,2,4-]triazin 3 yl) 2,2’-bipyridine) family. This work aims at investigating how organic solvents containing BTBP type molecules are affected when exposed to irradiation. In an industrially implemented process the feed streams can contain many highly radioactive nuclides and the radiation will be extensive, and it is thus important that the radiolytic stability of the solvent is well known. It was shown that γ irradiation may increase or decrease both distribution ratios and separation factors for solvents containing BTBP ligands. The behaviour depends on both the type of BTBP molecule and the diluent. The effect of varying the dose rate was also investigated, and a number of future studies are suggested.