A Fiber Optic Multipass Raman Probe and Instrumentation for Monitoring Flammable Gases in High Level Waste Tanks

The Department of Energy (DOE) has 280 underground tanks used to process and store over 90 million gallons of high-level radioactive chemical waste. The conditions in the tanks are conducive to the formation of flammable gases such as hydrogen, ammonia, and methane, as well as fire accelerants (oxidizers) such as nitrous oxide. An accumulation of these flammable gases above their lower flammability limit (LFL) increases the risk of fire and explosion. To mitigate these risks, this project will develop a Raman instrument that can be deployed inside the tanks for monitoring the concentration of these hazardous gases below their lower flammability limit. Phase I showed that flammable gases such as hydrogen and methane can be detected at concentrations below their lower flammability limit in near real time with a multipass retroreflector Raman cell. In its current configuration, the limit of detection of the multipass Raman probe is at 10% of the gases lower flammability limit. Phase II will involve refinements to the multipass Raman gas probe design and the associated Raman instrumentation, in order to permit gas detection at concentrations lower than 10% of the lower flammability limit. A deployable probe and instrument will be developed for field-testing in a high level waste tank at the Savannah River National Laboratory (SRNL). Commercial Applications and other Benefits as described by the awardee: In addition to the application to tank monitoring, the probe could be used by the DOE as an in-line monitor for hydrogen isotopes and other gases in tritium facilities, such as the hydrogen-tritium thermal cycle absorption process. A sensitive Raman probe also could benefit the private sector in relation to: (1) pollutant monitoring, where the probe could be used to monitor the release of hazardous gases from industrial sites for regulatory purposes; and (2) process control, such as in furnace atmosphere control monitoring, where the control and monitoring of such gases as nitrogen, carbon monoxide, hydrogen, ammonia, carbon dioxide, oxygen and other hydrocarbon gases are required