An engineering professor at Texas A&M University has developed a quick test for determining the permeability of material used in storage of nuclear waste by the Department of Energy. The process, which takes minutes, can determine the potential for nuclear waste to reach the environment from storage, according to a March 22 A&M press release.
The process of grouting — combining nuclear waste with a cement mixture for stable storage — has been tested and used at multiple locations in the DOE complex. That includes the Savannah River Site in South Carolina, where salt waste that makes up about 90 percent of 35 million gallons of Cold War-era waste in storage is separated from other material, grouted at the Saltstone Production Facility, and then pumped into concrete vaults for permanent on-site storage.
On behalf of the Savannah River National Laboratory, A&M civil engineering associate professor Zachary Grasley evaluated the permeability of grout mixtures and the potential for nuclear waste to flow through the solid material.
His advanced testing method involved hollow and solid cylinders of different grout samples from the lab, saturating them with water, and placing them in a pressure vessel which put the material at high levels of water pressure, the release says.
“Immediately after, the pressure on the surface of the sample equalizes to the pressure the vessel was subjected to, causing the material to contract. The pressure level inside the sample remains much lower, however, because the solid structure of the grout is bearing most of the pressure,” according to the release. “Because liquids flow from high pressure areas to lower pressure areas, water will begin to flow into the pore network of the sample if the pressure is sustained. As water permeates the material, it begins filling the pores in the sample, causing it to expand and regrow. This expansion rate is measured, allowing for flow rate and permeability to be quantified.”
Grasley noted the importance of determining the speed at which nuclear materials might flow through grout in storage. Even minimal tweaks to the mix can produce major changes in permeability, he said in the release. That, in turn, has a significant impact on how long it takes for material to leak out of the grout.
