On-Line Monitoring of Gas-Phase Molecular Iodine Using Raman and Fluorescence Spectroscopy Paired with Chemometric Analysis

Abstract

Molten salt reactors (MSRs) have the potential to safely support green energy goals while meeting baseload energy needs with diverse energy portfolios. While reactor designers have made tremendous strides with these systems, licensing and deployment of these reactors will be aided through the development of new technology such as on-line and remote monitoring tools. Of particular interest is quantifying reactor off-gas species, such as iodine, within off-gas streams to support the design and operational control of off-gas treatment systems. Here, the development of advanced Raman spectroscopy systems for the on-line analysis of gas composition is discussed, focusing on the key control species I2(g). Signal response was explored with two Raman instruments, utilizing 532 and 671 nm excitation sources, as a function of I2(g) pressure and temperature. Also explored is the integration of advanced data analysis methods to enable real-time and highly accurate analysis of complex optical data. Specifically, the application of chemometric modeling is discussed. Raman spectroscopy paired with chemometric analysis is demonstrated to provide a powerful route to analyzing I2(g) composition within the gas phase, which lays the foundation for applications within molten salt reactor off-gas analysis and other significant chemical processes producing iodine species.

Leveraging Multiple Raman Excitation Wavelength Systems for Process Monitoring of Nuclear Waste Streams

“…Monitoring approaches based on optical spectroscopy are uniquely suited to providing detailed chemical composition information on a process batch or stream. − Optical approaches can provide a range of chemical information, including identification and quantification of elemental and molecular species. ,− Optical approaches are also generally mature and can be flexibly integrated into a variety of process types. ,, As an example, optical spectroscopy probes can be plumbed into hazardous environments and are robust enough to withstand radiation dose, corrosive media, high temperatures, and wide ranges of pressures. ,− Most beneficially, for several optical approaches such as Raman, instrumentation and control equipment can be located in remote, safe locations with only fiber optics traversing the space between detectors and probes.…”

“…9,13−16 Optical approaches are also generally mature and can be flexibly integrated into a variety of process types. 13,17,18 As an example, optical spectroscopy probes can be plumbed into hazardous environments and are robust enough to withstand radiation dose, corrosive media, high temperatures, and wide ranges of pressures. 7,17−19 Most beneficially, for several optical approaches such as Raman, instrumentation and control equipment can be located in remote, safe locations with only fiber optics traversing the space between detectors and probes.…”

H-Canyon Dissolver Offgas Monitoring Using Raman Spectroscopy

“…Fiber compatibility permits a more advantageous location for the instrument and reduces potential worker exposure to hazardous conditions. These advantages have been recognized by other DOE laboratories that have demonstrated the suitability of Raman-based gas monitoring in applications such as measurement of I2 gas emitted from molten salt reactors 7 and trace gas detection in natural gas streams. 8 Raman spectroscopy has also been used for long term monitoring of hydrogen isotope distributions in the Karlsruhe Tritium Neutrino project.…”

“…The offgas is next directed through a heated reactor containing silver nitrate coated berl saddles, which trap radioactive iodine. A probable reaction is thought to be 10 : 6 AgNO3 + 3 I2 + 3 H2O  5 AgI + AgIO3 + 6 HNO3 (7) with the reactor maintained between 175 -190 o C. Finally, the offgas passes through a particulate filter (steam-heated glass wool) before being emitted from the stack.…”

Raman Spectroscopy Coupled with Chemometric Analysis for Speciation and Quantitative Analysis of Aqueous Phosphoric Acid Systems

“…In order to effectively reprocess the hazardous materials in these tanks, methods of accurate characterization are necessary, allowing for a more permanent disposal . Offline lab analyses take hours to days to complete, have limited accuracy in dynamic solution environments, and require extraction and handling of hazardous samples. − Fortunately, there now exists remote, immediate, online, and nondestructive analyses using optical spectroscopy. ,, Raman spectroscopy has been employed for accurate quantification of various analytes in complex systems for waste reprocessing and other areas of the nuclear cycle. ,− Raman probes are particularly desirable due to their ability to function in harsh environments without the need for frequent calibration. − Robust detection methods for uranium, plutonium, neptunium, aqueous nitrate, gaseous iodine, and other relevant species have also been established. ,,− Raman and UV–vis microprobes have been used to extend applications to the microscale, further reducing researcher exposure to hazardous materials. ,− Phosphoric acid and its three deprotonated species are Raman active, allowing for the application of Raman spectroscopy to phosphate systems. In our application, a Raman probe is inserted within the fuel reprocessing and related waste streams in direct contact with the solution, allowing in situ measurement.…”