Optically-Based Array Sensors For Selective In Situ Analysis Of Tank Waste

Abstract

The objective of this research program is to conduct the fundamental research necessary to develop an array of chemically-selective sensors, based on highly selective molecular recognition agents and highly sensitive fluorescence techniques, that can be coupled to fiber optics for remote analytical applications. The ability to detect and measure specific chemicals and radionuclides directly inside a high level waste tank using a remote sensing device could result in considerable benefits with regard to both cost savings and safety issues. An array of fiber optic sensors will be of great value to DOE for the safe and cost-effective in situ characterization of high level waste tanks and other applications where remote sensing will prevent workers from being exposed to chemicals or radiation. In this approach to the design of sensors, agents for selective molecular recognition such as crown ethers are immobilized in an organic polymer matrix that mimics the organic medium in an aqueous-nonaqueous extraction system. The matrix is attached to an optical fiber for remote detection of metal complexation by photonics measurements. Selection of the complexation agent and solvent are derived from our knowledge of metal ion specificity in the analogous aqueous-non-aqueous solvent-extraction chemistry. We additionally utilize our knowledge of synergistic effects for enhancing both the selectivity and the loading in the solvent extraction of alkali metals from tank waste by proper design of the polymeric matrix and by incorporating appropriate co-extractants into the matrix. The objective is to maximize the selectivity for and the degree of binding (loading) of the desired metal ion by the sensor's solid matrix while maintaining stability in the highly alkaline environment of tank waste. This novel approach to the design of photonics-based sensors should result in increased chemical selectivity, which at present is a fundamental limitation of many chemical sensor devices. When fully implemented, this scheme will utilize an array of sensor sites, each with optimized selectivity for one of the components in the analyte.