A nuclear waste canister, made from copper, will be used at Finland’s nuclear waste repository at the Olkiluoto nuclear power plant. Credit: Courtesy of Posiva Oy
Over the next several decades, the amount of United States nuclear waste is expected to be more than 150,000 tons, and the proposed containers to hold the waste might fall apart.
Ohio State researchers suggest the canisters proposed to be used to store nuclear waste will corrode faster than originally thought, releasing highly toxic radioactive material into the environment, according to a study published Jan. 27 in Nature Materials.
Xiaolei Guo, a research associate in the materials science and engineering department, said previous models for predicting corrosion were incomplete because they didn’t take into account how the rusting canisters would interact with high-level nuclear waste.
“None of the previous studies considered this kind of corrosion interactions,” Guo said. “They have not considered the waste package as an entire system.”
High-level waste is the most toxic radioactive waste and the byproduct of the U.S. nuclear weapons program, according to the websites of the U.S. Government Accountability Office and the Department of Energy. The U.S. has more than 100,000 tons of nuclear waste that need to be disposed of safely, and about 15,000 tons are high level.
Most of the waste — including spent nuclear fuel used at power plants — is stored where it was generated, according to the GAO website. In 1987, the U.S. began looking at a mountain 100 miles northwest of Las Vegas, as a place to store the country’s nuclear waste, but a facility has not been completed.
Stainless steel canisters containing the waste would be mined into tunnels 1,000 feet below the Yucca Mountain top, according to the Environmental Protection Agency’s website.
The nuclear waste would be processed and mixed with glass or ceramics to make “waste forms” before being placed into the canisters, Guo said. The corrosion-resistant glass and ceramic materials would prevent the release of radioactive elements into the environment.
When the packages go into the ground, heat from the waste forms would dry the water up around the tunnels, but thousands of years later, the water will return when the forms cool down, Guo said. Each part of the waste package, by itself, would take hundreds of thousands of years to corrode; however, when these parts are pressed against each other, corrosion accelerates.
The water will corrode the canister first, releasing metal ions and protons that create an acidic environment between the stainless steel and the waste forms. Guo said because the space between the forms and the canister is so small, the concentration of ions and protons “can increase very fast.”
The waste forms will begin to corrode more rapidly than normal conditions when exposed to this environment, and Guo said this corrosion will release the embedded radioactive nuclear waste into the surrounding area.
Over a month, the research team, which included scientists at Ohio State, Penn State University, Rensselaer Polytechnic Institute, University of North Texas, the French Alternative Energies and Atomic Energy Commission and the Pacific Northwest National Laboratory simulated the corrosion of the materials together and used computers to project expected corrosion over thousands of years, according to a press release from PNNL.
“We can’t just do a test on a material and say, ‘That material corroded this much in 30 days and extrapolate that to a million years.’ It doesn’t work that way,” Joseph Ryan, a materials scientist at PNNL and co-author of the study, said in a press release. “At the most basic level, we try to understand the underlying chemistry of corrosion. Then, we feed that information into computer models to calculate the expected release over time.”
According to the release, the researchers pressed stainless steel against glass materials and placed them into a sodium chloride solution kept at 194 degrees Fahrenheit. After 30 days, they noticed differences between the experimental and control materials, which indicated the simulation caused higher rates of corrosion.
Aside from Finland, no country has begun to build a storage site for high-level nuclear waste. The Finnish site will use canisters made from copper and cast iron, according to the website of Posiva Oy, the company tasked with building the storage facility under the Olkiluoto Nuclear Power Plant in Finland.
According to Posiva Oy’s website, the Finnish canisters will protect the nuclear waste forms from the “corrosive effects of groundwater,” and their corrosion models take into account “unfavorable conditions for hundreds of thousands of years.”
Guo said the current U.S. model for storing nuclear waste is not totally insufficient, but incomplete.
“The final plan for the disposal has not been finalized yet,” Guo said. “We still have time — have [the] capability to improve it to ensure safety.”
