A novel method for detecting salts in nuclear waste melters may enhance cleanup technologies, particularly at the Hanford Site, recognized as one of the world’s largest and most complex nuclear waste cleanup locations. Researchers have utilized two detectors to identify thin layers of sulfate, chloride, and fluoride salts during the vitrification process, which transforms nuclear waste into glass. The creation of these salts can be challenging for the processing and safe storage of waste.
A novel method for detecting salts in nuclear waste melters may enhance cleanup technologies, particularly at the Hanford Site, recognized as one of the world’s largest and most complex nuclear waste cleanup locations.
In a study published in the journal Measurement, researchers from Washington State University employed two detectors to locate thin layers of sulfate, chloride, and fluoride salts formed during vitrification – a process that converts nuclear waste into glass for storage. The buildup of salts poses issues for waste processing and storage.
“We demonstrated a technique to monitor when the salts begin to form,” stated John Bussey, a WSU undergraduate and co-author of the paper. “This allows for the monitoring of the melters to determine if adjustments are needed in the materials being introduced to the melt.”
The vitrification process involves heating nuclear waste in large melters to extremely high temperatures. The resulting glass is then shaped into cylinders and solidified for long-term storage safety.
The U.S. Department of Energy is currently constructing a vitrification facility at the Hanford Site. Due to its history of producing plutonium for the first nuclear bomb, the waste at Hanford is particularly intricate, incorporating almost every element on the periodic table, according to Bussey. Around 55 million gallons of chemical and nuclear waste are stored in 177 tanks at the site.
During the nuclear waste processing, salts can form, which may be corrosive and potentially damage costly vitrification equipment. Additionally, since these salts can dissolve in water, they may lead to leaks and contamination should the waste come into contact with water during storage. The diverse range of waste components at Hanford increases the likelihood of salt formation.
“Salt formation is highly undesirable during the vitrification process,” Bussey noted.
The researchers, using a system developed at Pacific Northwest National Laboratory and the Massachusetts Institute of Technology, applied optical and electrical tools to analyze light emitted within the infrared to microwave spectrum during the melting process. They examined glass melts comparable to those expected at the Hanford site. By employing two types of detectors, they investigated the thermal emissions of the samples and their temporal changes.
“The brightness offers interesting insights into the melting, solidification, and salt formation processes,” remarked Ian Wells, co-lead author and a graduate student in WSU’s School of Mechanical and Materials Engineering. “This approach is unique because it does not require additional lighting or systems; you can gauge the brightness of single-pixel images based purely on the heat emanating from the melt and evaluate what’s occurring.”
The researchers observed significant changes in the melt stage. Whether due to salt formation or shifts between melting and solidification, a distinct change in intensity was evident. They compared various melts and identified behaviors associated with salt presence.
“We can clearly discern what is happening based on these behavioral indicators,” Wells explained. “We were amazed at how sensitive this probe was with even minimal salt presence.”
The system can differentiate between various salt types and can sense them from a distance without needing to be immersed in the radioactive molten glass, thereby reducing complications.
“This advancement moves the monitoring technology significantly closer to practical application within the vitrification plant,” Bussey stated. “This equipment could be directly deployed in the vitrification plant with minimal modifications.”
The researchers also envision potential uses for this technique in molten salt nuclear reactors or in various manufacturing methods, including glass, epoxy, or carbon fiber production, where it is essential to gain insights into phase transitions and the formation of compounds during those stages. They aim to transition from lab-based tests to larger-scale melt tests in the future. This research was supported by the United States Department of Energy Office of Environmental Management.
