About 90 minutes north of Stockholm lies an ancient defensive hillfort called Broborg. Northwest scientists are digging up and studying pieces of the ancient Swedish fort and trying to figure out how the structure has lasted around 2,000 years.
The ancient Swedes built it by piling up rocks in a wooden frame and then put other rocks between those boulders. Then they piled up charcoal around the whole thing and lit it off. They would keep the fires burning for months.
Some of the rocks would melt into glass—sticking the other rocks together. It’s really strong glass, just like scientists want to make at Hanford.
“It is very reassuring to find samples of nearly the identical material that have aged naturally,” said Albert Kruger, a top glass scientist with the U.S. Department of Energy at Hanford.
Standing the test of time
One of Kruger's main projects is to figure out how to take millions of gallons of low-activity radioactive liquids out of aging underground tanks, and turn them into big glass blocks.
For decades scientists had made different types of glass themselves, and then tried to simulate the ravages of time in labs.
“Up until now, the bulk of the tests have been grinding these sections of monoliths of glass that we’ll produce into very fine powders and testing the powders in very high temperatures and burying them in water if you want or immersing them in water,” Kruger said.
But Kruger said there’s no better test for how Hanford glass will last over time, than time itself.
Back in 2012 at a science conference in France, Kruger heard about this giant fort with glass mortar that’s lasted thousands of years. Since then, he’s been studying the work of the ancient Swedes. And bringing pieces back to Richland.
Ancient ideas, modern goals
In a highly-secure part of the Pacific Northwest National Laboratory, Carolyn Pearce has pieces of the Swedish fort glass in neat artifact boxes.. She scans them with all sorts of machines before making a few exacting cuts on these valuable artifacts.
They look like pumice stone or lava rock. And on the outside is a fine layer of sandy crud and dust.
“That dusty exterior is really important to us,” Pearce said. “Because these materials have been exposed to near-surface conditions. So, soil, moisture, changes in weather—it’s Sweden, so it’s very cold in winter and warmer in summer. And so these materials have been put through the tests for over periods of hundreds of years. And so we can look at how the material has responded to those conditions.”
Basically, she is investigating the crud.
“Yes, we are indeed, the crud and the glass that’s next to the crud,” Pearce added.
That crud tells them how the glass is breaking down over time into the environment. Better understanding how the water chemistry and microbes disrupt the glass can help them formulate stronger Hanford glass. And a better shot at keeping radioactive waste locked away from the environment for as long as possible.
Pearce said the old fort glass is special. A gift to future generations from the glass-making know-how of the past.
“They had all of that knowledge and they built a structure that lasted hundreds and hundreds of years after they did,” Pearce said. “And it’s still there for us to find today.”
Pearce and Kruger will have to work fast to suss out the strongest waste glass possible. The huge glass-making plant is under construction now in Hanford’s desert. The plan is to make “hot” glass in just five years.
* Editor's note: As this story was being prepared for publication the reporter learned some analysis of the Swedish glass would be conducted by a family member.
Jessica Robinson contributed to this report.