The main objective of this research project is to synthesise new macrocyclic compounds (ionizable crown ethers and functionalized calixarenes) capable of decontaminating a selection of real wastes to comply with waste acceptance criteria for a near surface disposal site. The selective cation removal concerns the following radionuclides: the actinides, the caesium and strontium. The second objective of the research is to develop a suitable separation technique enabling the use of low inventory of new macrocyclic compounds while showing potential for subsequent scaling up. These new macrocyclic extractants have to demonstrate significantly higher decontamination and selectivity performances that those already recorded with more conventional ones (e.g. bidentate organophosphorous extractants, DC18C6 crown-ether...) for similar purposes.
The principal aim of this research consists of perfecting the schemes of decontamination of real liquid wastes, medium level reprocessing concentrate and, more generally, liquid wastes arising from reprocessing plants. The objective of this research is to remove selectively actinides, caesium and strontium from high salinity wastes arising from reprocessing operations in order to minimize the volume of wastes to be disposed of in a geological formation. It is intended to investigate the potential of new classes of organic extractants under development in different university laboratories.
Synthesis of macrocycle calixarene compounds from the various p-alkyl-calixarenes has been carried out in order to obtain very strong and selective extractants for long lived radioactive cations such as strontium, caesium and actinides. Crown ethers which possess pendant ionizable groups are also synthesized. Compared with the classical crown ethers, the presence of these groups facilitates the extraction or transport of metal ions.
The tests necessary for determining the effectiveness of macrocycles to remove cations from high sodium content acidic solutions have been prepared.
Gamma spectrometry was used to determine the activities of several nuclides. Inductive coupled plasma mass spectrometry (ICPMS), which enables us to measure a great number of cations simultaneously, was also used.
Several calixarene derivatives (ester, amide) have also been synthesized, in which the residue attached to the phenolic oxygen contains further ligating functions.
This research activity will consist of the implementation of the following items:
- identification of the liquid waste streams to be de-categorised as well as the target decontamination factors;
- synthesis of "tailor-made" macrocyclic compounds capable of performing the desired waste decontamination;
- with the help of the modelling technique, explanation of the selectivity of an extractant and proposal for obtaining the most effective compound;
- setting-up of an experimental screening procedure for selecting the macrocyclic extractants deserving further development and testing;
- determination of the extractive properties of a selection of new macrocyclic compounds (batch experiments);
- development of suitable separation techniques;
- implementation of continuous decontamination experiments with genuine waste;
- appraisal of the results achieved and prospects for future developments and scaling-up
Funding SchemeCSC - Cost-sharing contracts
BT9 5AG Belfast