Carolyn Pearce is busy digging up, cutting up and even x-raying ancient glass across the globe for study. Why? She’s trying to figure out the properties of the strongest glass on earth today, ones that have survived for thousands of years. That way the U.S. Department of Energy can be confident in its science to bind up radioactive wastes for thousands of years to come. Some of the glass she’s working with is from a Swedish hillfort, some from glass beads from a burial site in Poland and some from the Newberry volcano in Oregon. We sit down with her at our remote studio on the Washington State University Tri-Cities campus.
Note: The following transcript was created by a computer and edited by a volunteer.
Dave Miller: This is Think Out Loud on OPB. I’m Dave Miller, coming to you from Washington State University Tri-Cities. We are here all week, in partnership with Northwest Public Broadcasting, to talk about the legacy and the future of the Hanford Nuclear Reservation. We’re going to start today with that future.
The English writer Robert Macfarlane in his book, [“Underland”], laid out the problem with his customary clarity and elegance: “For as long as we have been producing nuclear waste,” he wrote, “we have been failing to decide how to dispose of it … Slowly, expensively, miraculously, injuriously, we have learned how to convert uranium into power and into force. We know how to make electricity from uranium and we know how to make death from it, but we still do not know how best to dispose of it when its work for us is done.”
Carolyn Pearce is one of many people who came here to wrestle with those questions. She’s a chemist at the Pacific Northwest National Lab and the director of a program called IDREAM that stands for [Interfacial] Dynamics in Radioactive Environments and Materials. Among her tasks right now: to explore the properties of ancient glass substances that have survived for thousands of years so that the US Department of Energy can be more confident in its plan to bind up radioactive waste in solid form deep into the future. Carolyn Pearce, welcome to Think Out Loud.
Carolyn Pearce: Thank you for having me.
Miller: Let’s start with the real basics. What is the overall problem that you’re a part of trying to solve?
Pearce: So here at the Hanford site, we have a legacy from plutonium production for the US Department of Energy Weapons Program, where we have about 56 million gallons of liquid waste that’s historically been stored in 177 underground tanks out here at the Hanford site. And it’s the mission of the Department of Energy to convert that liquid waste into a safe form for disposal. And the way that they’re going to do that is by turning it into a glass, by vitrification.
Miller: Why was vitrification chosen? And this has been a project that’s been going on now for decades. The plan to vitrify, to glassify, to solidify this stuff – why was this chosen?
Pearce: It’s a mature technology and has been used around the world for encapsulating radioactive materials. And it’s basically because glass is by definition amorphous, so it doesn’t have a crystalline structure. And so it is very accommodating for other elements within its structure. Elements like technetium and iodine that are radioactive can sit inside that glass structure and that makes it a much more robust waste form.
Miller: Am I right that it’s incredibly hard to even know exactly what’s in these tanks?
Pearce: We have an idea of what’s in the tanks based on the inventory of what went into them, and there have been sampling campaigns to analyze the constituents. But the problem is that they’re in a radiation field – a continuous radiation field – generating reactive species that continue to change and generate new chemistries within the waste. And so that is our problem. We know we have a snapshot of what the waste is now, but we have to know how it’s going to change as we move forward into the future. And that’s something that we’re still learning about.
Miller: How do you do that? I mean, if it’s always changing, how do you know what it’s going to be like an hour from now or 100,000 years from now?
Pearce: There have been efforts made to monitor over time. We know that radiation will consume certain chemicals and generate others, so we can make predictions and models based on radiation chemistry. But there is also investment still in fundamental science through the Office of Science, through IDREAM, to really look at how radiation in these low-water, very alkaline environments changes the chemistry. So we’re still learning to get that predictive understanding for years to come.
Miller: You mentioned that vitrification is not new and that it’s already been used for nuclear waste?
Pearce: Yes.
Miller: So what’s different about Hanford? I mean, we’re talking about a project that has had some stops and starts, some huge red flags, reports a decade ago saying there are a lot of issues with this. If it’s already been done, what’s different about what you’re trying to do here?
Pearce: I think that two of the things that are different about Hanford are just the scale – no one has built a waste treatment plant on this scale for vitrification before – and then also the variability of the chemistry. Even within the US, at Savannah River, the chemistry is not as complex as here at Hanford. So, whereas they have a vitrification program there, and we can learn a lot from that, the difference in chemistry here in the different tanks causes more technological challenges.
Miller: And just to be clear: vitrification, it doesn’t change anything about the radioactivity of this waste, right?
Pearce: Correct.
Miller: It just immobilizes it?
Pearce: Yes.
Miller: Why is that so important? I mean, if it’s still going to be radioactive, why is turning it into a solid such an important thing to do?
Pearce: That’s a great question. So, right now, the waste is in a liquid form. And there are sort of different forms of the waste within the tanks: it’s present as a sludge; and a supernatant, which is liquid; and then a salt cake which precipitated out of the liquid. But with it being in a liquid form, there is a potential for those tanks to leak, and some of the single shell tanks – so they only have one shell of steel – have already leaked waste into the subsurface. And they’ve all now been emptied of all that liquid waste, and it’s all now in double-shell tanks, but they have also a finite lifetime. And so if we can convert it into a vitrified waste form, where we have been able to model the performance over hundreds of thousands of years, it’s a much safer alternative to leaving it in the liquid form that it’s in now.
Miller: You mentioned hundreds to thousands of years. What is the time frame that you’re thinking about?
Pearce: So we’re really thinking about the time frame of the performance assessment for the disposal facility where that low-activity waste glass will end up. And the time frame for that is being able to predict performance over about 1,000 years. But we do want to understand much longer time frames because the major radionuclides in the low activity waste are technetium-99 and iodine-129 that have half-lives of around 2,000 and then 2 million years, respectively. And so we do want to understand the behavior on much longer time scales.
Miller: How do you wrap your head around a half-life of 2 million years?
Pearce: It’s very challenging. And I think that’s why these analogs are just so important because we can look into the past millions of years, right? We have examples of natural obsidian glass that has been in the environment for millions of years. And we can look at how that has changed over time. And that’s what’s going to give us confidence – looking ahead to those millions of years that the waste will be disposed in a glass form.
Miller: All right. So let’s talk about that sort of historical work that you’re doing to think about the deep future, how the deep past can inform the deep future. So obsidian is one example you’re talking about and people all around Oregon, and I think in Washington, too, can see that from volcanoes. What have you learned from obsidian?
Pearce: We’ve been taking samples with a permit from the Deschutes National Forest from the Newberry volcano just outside Bend. And that’s of interest to us because, actually the big obsidian flow – the last major event – was on the order of 1,500 years ago, so it’s in the right time regime for us to look at with regards to the disposal facility.
Miller: A baby in terms of geological time, but helpful for you.
Pearce: Yes, absolutely. And so what we’ve learned from that is that the glass is incredibly durable. We’ve been able to look and quantify the alteration layers that are on the order of microns – so, you know, the thickness of human hair – over those time scales. But we’ve also learned, through looking at multiple analog sites, that the surface of the glass can be colonized by the local microbial community. Understanding that interaction is also part of our work in these natural environmental settings.
Miller: What does that mean? So microbes or bacteria – they could basically live their lives and in a sense, eat the rock. What does that mean if the rock, or glass in this case, is highly radioactive waste?
Pearce: That’s what we’ve been working to understand. Now, the low-activity waste that will be disposed of in the integrated disposal facility at Hanford will not have a significant heat associated; it’s not heat-generating waste because it’s low-activity waste. And the radionuclides that are present – the type of radiation that they emit, their beta emitters – that won’t necessarily be able to reach the exterior of the waste form. And so the organisms could potentially colonize the outer surface and not be significantly impacted by radiation fields, which would be the case with high-level waste, which is heat generating and has radionuclides that have the potential to emit radiation that could reach that biofilm on the surface.
Miller: Before we hear more about other places you’ve gone to look for analogs, as I’ve been thinking about the problem you’re trying to solve, an analogy I came up with is car manufacturers or tire manufacturers who are trying to simulate wear and tear. So they can just have a tire do the equivalent of 100,000 miles while it’s not going anywhere. Are there ways that you can do the same: approximate the passage of time very quickly?
Pearce: Yes. Yes, absolutely. And so that is in fact what is done; there are accelerated aging tests that are conducted on these glass waste forms in the laboratory, where we use things like temperature as a proxy for time frames. And that is how the glass compositions are formulated: based on the performance of the glasses in some of these accelerated aging tests. But of course, that’s not representative of the actual disposal environment. So we need to combine what we learn from those accelerated aging tests and understand the mechanisms of alteration and then verify that with what we actually see from samples that have sat in a relatively constant temperature in the environment for thousands of years.
Miller: Can you tell us about a trip you took to a hillfort in Sweden?
Pearce: Yes, absolutely. This program is supported by Department of Energy Office of River Protection, and the glass program is led by Albert Kruger. And he met, at a conference, a gentleman called Rolf Sjöblom, who actually worked on Swedish nuclear waste disposal. And they discussed this material that’s present at the hillfort as a potential analog for low activity waste glass. Because at the hillfort, the ancient people – pre-Viking people around 1,500 years ago – had the technology to take the granitic boulders, which was the local geology, and then pack a different type of rock, amphibolite, between them and set fires to make temperatures high enough – around 1100 degree C – to actually melt that amphibolite and fuse the granite blocks together to fortify hillfort. And so it’s actually a glassy material that’s holding together those granitic boulders.
Miller: And what did you learn when you looked at that early human glass-like substance?
Pearce: So what we learned was, it was incredibly durable, because it was the part of the wall that had been vitrified that still remains and you can still see today. Once again, we got a permit from the Uppsala County Council to work with the Swedish archaeologists and actually do an excavation of the wall of the hillfort to take samples. And when they got to the vitrified region, they had to use sledgehammers and pickaxes to try and get through that material because it was so durable, holding the wall together. And that was just a really visual example of glass doing its job over a very long period of time.
Miller: It’s interesting to think that – assuming that the archaeologists are right – the reason for that glass was defense, which is in a sense, in a roundabout way, the same reason for the work you’re doing now – I mean, the clean-up after an enormous World War II and then Cold War build-up of these weapons. What was it like to be there and to be touching or seeing this old human technology as you’re trying to figure out a very new human technology?
Pearce: It was a fascinating experience, and I would certainly encourage anyone to visit the site; it’s called Broborg in Sweden. And it has a very particular atmosphere. It feels like many things took place in that space, and that there was just a lot of history – and history that we don’t know, because the hillfort was built before written word. And so there’s no record of why the hillfort was built. There’s still debate in the literature as to why they vitrified the walls. Could it just have been an accident [like] a lightning strike or a cooking fire? But I think if you go there and see the very deliberate way in which these box-like structures were created around the circumference of the fort and just the strength of this vitrified wall, it’s certainly – based on our findings – suggest that it was intentional to support the defense of the hillfort.
Miller: And as many mysteries as there are there, that was only, in quotes, what, “3,500 years ago” or so, right?
Pearce: 1,500.
Miller: Only 1,500 years ago. I mean, but we’re talking about half-lives in the tens or hundreds or millions of years. I know you’re a chemist, you’re not an archaeologist or a linguist or a graphic designer, but those kinds of people have all been brought in to think about signage or symbols to tell future humans, future whoevers, who most likely are not going to speak any languages or reading languages that we know of now. The message that we want those future creatures to understand is: do not enter, do not touch, do not eat, go away, this is a place of danger and will be a bad place forever – essentially, in terms of the way our brains think. How do you do that in a way that those creatures will understand?
Pearce: Well, I think that’s a fascinating question, and I certainly don’t have the answer. But I can say that we did learn a lot from the hillfort because it was abandoned for many years, and no one really visited it or knew of its existence. And part of that was because of folklore. There were all these tales of trolls and monsters that guarded this site. So people stayed away from it until very recently. I think we can learn from that; that there’s this generational storytelling that we could pass on, perhaps not even through the written word but through spoken word as …
Miller: Taboo.
Pearce: Yes. To explain why it’s not appropriate to be in this site.
Miller: It’s not treasure here; it’s death.
Pearce: It’s death, yeah.
Miller: How do you think about the work that you’re doing in the context of climate change? Because we’re talking here about disposing of waste from a production of plutonium for bombs, but there is a lot of waste from existing power plants, and there would be more if there were more nuclear power.
Pearce: I absolutely think nuclear power is part of the solution to the climate problem and to our mixed energy sources of the future. But we do have to solve this problem, and I’m passionate about that. I’ve worked here, I’ve worked at the University of Manchester in the UK on deep geological disposal facilities for that waste. So I think it’s a problem that we have to solve, and that’s going to require not just scientists but also real community engagement and an understanding of the benefits of safely disposing of these materials so that we can have a clean energy future.
Miller: What’s at stake in the work you’re doing right now?
Pearce: I think, what we can learn from the work that we’re doing right now, we’ll learn from it at Hanford. That’s the main thing that I think we can take away from what has happened here, is learn about the decisions that were made and the implications for the future. And then use that knowledge that we’re developing about the different waste forms to help inform disposal of other waste from energy production around the world.
Miller: Maybe this is not exactly the way engineers and scientists thought about this in the ‘40s, and ‘50s, and even the decades after that, but the sense I get is that relatively early on, they knew that the disposal systems they had in place were inadequate. But they were working with urgency that they, especially in ‘44 and ‘45, saw a kind of existential threat – and certainly, that was the feel in the Cold War as well.
So, in the sense, it seems like the idea was: engineers or scientists will have a better solution in the future, but we have to do what we have to do right now. There were a ton of ramifications that came from that, many of them negative. I’m wondering if you have that same thought, or if you see yourself and the hundreds of other scientists all around here as being a permanent solution? Or if you’re also hoping that humans that follow will figure out a better way?
Pearce: I always hope that the humans that follow will find a better way. And I believe that they will. But, I really believe that we have so much to learn from the technologies that have developed, not just to vitrify the waste, but also to remove radionuclides from the groundwater through the pump-and-treat facilities. There’s just a massive knowledge base that’s developed here. And I think we need to use that going forward for things like generating new energy sources, and understanding how we can generate energy from different materials, and improve our nuclear power plants to reduce the burden on the waste. And I think that’s our duty: to really learn from that and make that happen.
Miller: Carolyn Pearce, thanks very much.
Pearce: Thank you.
Miller: Carolyn Pearce is a chemist at the Pacific Northwest National Lab.
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