Published August 12, 2011
RICHLAND, Wash. – A shipwreck 1,800 years ago in the Adriatic Sea might give scientists at Pacific Northwest National Laboratory better information about how well modern glass might work to contain radioactive waste.
The Department of Energy is building a $12.2 billion vitrification plant at the Hanford nuclear reservation to glassify radioactive waste before it is buried deep in the ground.
The glass, formed from the waste and glass-forming materials, is planned to keep the radioactive waste secure for thousands of years. But until recently, the longest test on a piece of man-made glass holding simulated radioactive waste has been about 25 years.
Thanks to the shipwreck "we can use data points Romans thoughtfully started for us hundreds of years ago," said Joseph Ryan, a senior scientist at the Department of Energy national laboratory in Richland.
He and scientist Denis Strachan, a laboratory fellow, are taking an atom-by-atom look at ancient glass to see how the glass has held up to corrosion.
Thursday, the two held up a chunk of green glass, marbled with iridescent streaks, that once was the handle of a jar.
It was among the glass that archaeologists believe was carried on the merchant ship Iulia Felix 1,800 years ago. The ship, which measured about 50 feet long, sank six miles off the coast of Grado, scattering glass at the bottom of the Adriatic Sea.
The Iulia Felix is believed to have carried containers of oils and spices, but also a barrel of glass pieces that may have been bound for the port of Aquileia, a center of Roman glass making. The glass pieces would have been recycled there.
Strachan and Ryan also have obtained glass from an archaeological dig at the ancient ruins of Aquileia. The glass is not as well dated, but also could be about 1,800 years old.
The most likely way for modern glass incorporating radioactive waste to corrode and dissolve after it is buried, contaminating the environment, is by exposure to water.
In the Iulia Felix sample, the scientists have pieces of glass that have been sitting in water for 1,800 years. The glass also has some chemical similarities to the glass that will be produced using Hanford's radioactive waste. Both should contain about 20 percent to 25 percent sodium.
Strachan traveled to Italy to get the glass from the Aquileia archaeological excavation. He didn't want just another piece of ancient glass, but glass still buried in the soil so researchers could look at how the glass dissolved and material from the glass moved into and through the soil.
The PNNL researchers have used a focused ion beam to machine minute cones out of the iridescent streaks in the glass from the Iulia Felix to look at samples measuring about 20 nanometers, or a ten-thousandth the diameter of a human hair. The iridescent streaks are caused by the reflection of light off the areas where the glass has corroded at the points the handle was attached to the jar.
The samples are being studied with an atom probe at the Environmental Molecular Sciences Laboratory on the PNNL campus, which can show an atom-by-atom picture of the structure of the iridescent glass. Images show individual atoms arranged in layers of magnesium and oxygen.
The ancient glass wasn't designed to be durable over 1,800 years, but it has held up well, Strachan said. And the glass planned to incorporate nuclear waste can be designed to be even more durable, he said.
But the study will put data to that assertion. It will provide a mathematical look at how glass dissolves that can be used to confirm and refine computer models now used to predict the performance of glass.
"We want to show if we put (waste) glass underground and let it sit for millions of years, the public will be safe," Strachan said.
The study, which is part of international research on glass corrosion, is being paid for by the Department of Energy.
In addition to information about glassified waste from national defense projects, such as plutonium production at Hanford, DOE also is interested in information that could be useful if the nation decides to reprocess commercial nuclear fuel and then glassify the waste from reprocessing.
The project also could help archaeologists. By learning more about the rate of glass corrosion, archaeologists may be better able to date ancient glass.