Prehistory meets the future when nuclear waste is to be buried for 100 000 years

Sweden is the first country in the world that has decided on a final repository for spent nuclear fuel. The Swedish Government’s decision on 28 January this year means that, most likely, the radioactive waste will be placed in copper cylinders and then buried deep down in the bedrock at Forsmark in the region of Uppland. The waste will be deposited at a depth of 500 meters for 100,000 years, the time during which the uranium must be kept from humans due to its radioactivity.

Linnaeus University researchers Henrik Drake and Cornelius Holtorf have both been engaged in the issues concerning the final repository for over a decade. However, their perspectives differ. We met them to discuss their research in relation to the recently made decision.

Geological studies at Forsmark

Henrik Drake is associate professor of environmental science and well familiar with the bedrock in which the spent nuclear fuel will be stored for a long time ahead. 15 years ago, when he was a doctoral student, he studied the bedrock in Oskarshamn municipality, which, together with Forsmark, has been one of two places that have been of interest for the final repository. When the Swedish Government chose to move ahead with Forsmark in 2009, he continued his geological studies there instead.

Over the years, Henrik Drake has mapped out crack formations and impact from previous ice ages, factors that are important in order to understand how the location may come to change during the long timespan ahead. The issue of a final repository has been an opportunity for Drake to contribute concretely with his geological studies.

“At the time being, we are working on a project with focus on what happens with uranium in the bedrock. For instance, where in the bedrock will the uranium stop if there is a leakage from one of the canisters. We will soon publish a new model for that important process. When you can see that your research is of relevance for the final repository, your driving force becomes bigger than if it was just about studying what has happened to the bedrock”, Drake explains.

Preserve knowledge about the final repository

The link to the final repository looks completely different for Cornelius Holtorf, professor of archaeology with questions relating to heritage futures as his main field of research. Eleven years ago, Holtorf and his colleague Anders Högberg were asked by the Swedish Nuclear Fuel and Waste Management Company, SKB, to look into how knowledge about the final repository can be preserved 100,000 years into the future, to make sure that future generations do not come in contact with the radioactive waste due to lack of knowledge.

“Above all, we have worked with the question of long-term memory. How do you communicate with a person thousands of years into the future who does not know that the nuclear waste is there but who comes across something and wonders what it is? How do you create an awareness of “this place contains something that may be dangerous”? There are a number of proposals for how to express this through writing and symbols”, Holtorf explains.

Relieved by the decision

Both researchers express some relief over the decision to move ahead with the final repository.

“I just felt, ‘finally, it’s time’, as I thought the decision would be made 5–10 years ago. To us, who’ve been working with this, a final repository has never been considered a problem. Instead, it has rather been a competition between Oskarshamn and Östhammar municipalities concerning who gets the final repository, which is very different from the situation in other countries where no one wants to take care of it”, Drake continues.

“The decision on the final repository is important. It makes the use of nuclear power more sustainable as there is a now a clear answer as to what will happen with the waste”, Holtorf adds.

Illustration explaining the final repository that is planned in Forsmark. Svensk kärnbränslehantering, SKB.

500 meters below the ground

Five hundred meters below the ground at Forsmark, it’s like time has stopped. When you talk about changes down here you deal with time periods covering hundreds of millions of years. Drake describes it as a stable environment in a stable period. Thus, conditions are good for keeping the nuclear waste isolated from the surrounding world for 100,000 years, a blink of an eye from a geological perspective.

“It’s important to find out when we have seen large movements in the crust of the Earth to be able to plan what may happen in the bedrock that may affect the final repository. What we have been able to show is that it’s been roughly 400 million years since the latest major events took place. That was when the Scandinavian Mountains formed”, Drake continues.

The temperature is about 15 degrees Celsius year-round. It is a chemically stable environment with no dissolved oxygen and not many nutrients. Despite this, there are traces of life in the cracks in the bedrock.

“This is one of the most extreme systems on Earth from an energy insufficiency point of view.  Despite this, there are living organisms. One can describe these microbes as being in a state of hibernation for long periods of time. And then, when organic material trickles down the cracks in the bedrock, they can restart”, says Drake.

CORE SAMPLE FROM FORSMARK. This is what it looks like 410 meters down into the bedrock at Forsmark, where the future repository is planned. The cylinder-shaped core sample consists mainly of 1.9 billion years old gneiss. The dark stripes are cracks filled with minerals, providing proof of life. “We’ve found traces of life in these cracks. Microbes lived here 400 million years ago”, says Henrik Drake, associate professor of environmental science. Joakim Palmqvist

Microbes will be awakened

When the final repository is to be constructed, these microbes will be awakened again.

“As you drill your way down, oxygen will be introduced into the underground environment. After this, a period will follow when the oxygen is reduced by microbes and by the bedrock itself before, once again, becoming oxygen-free. For most of the time, the environment will be oxygen-free and dark, and the energy that can be found does not offer much to live from. Some chemical reactions will start when you introduce new materials like copper canisters and mud. The environment surrounding the canisters will be warm. Today, there are no copper canisters at 500 meters depth so the environment will change somewhat”, says Drake.

The copper canisters will continue to release heat for as long as the material is radioactive. One benefit with Forsmark in comparison to Oskarshamn is that the bedrock consists to a large extent of quartz, a mineral that effectively leads heat out into the bedrock. Therefore, the canisters can be placed close to each other to save space.

There are cracks in the bedrock, but these serve an important function.

“Forsmark is surrounded by a number of large fracture zones. It’s like a piece of bedrock that floats like a soap between fracture zones. The fracture zones serve as airbags for the final repository by intercepting movement in the bedrock, while the repository volume remains less affected”, Drake explains.

Cornelius Holtorf and Henrik Drake have conducted research linked to the final repository for many years. But their perspectives are completely different. Joakim Palmqvist

Risks with the final repository

The goal with the final repository is to place the spent nuclear fuel in an environment where there is as little activity as possible. It is important that the copper canisters are not exposed to water or oxygen. In that case, they could begin to rust which would shorten their lifespan. In the event of an ice age – we can expect at least one during the time period for the repository – there is a risk that melt water will be pushed down into the bedrock fractures.

“We can see that during the latest ice age, oxygenated water reached roughly ten meters down into the bedrock. This can be seen as a rusty zone in the top 10 to 20 meters”, Drake explains.

In geological contexts, 100,000 years is considered a relatively short period of time and the stable environment at Forsmark offers good conditions for the final repository.

“The repository will be active for such a short period of time in comparison to what I study. The bedrock is about 19,000 times older than that”, Drake continues.

Human impact as a risk

However, there is one risk that has nothing to do with microbes or potential ice ages in the future. Even though 100,000 years is just a brief moment from a geological perspective, such a period of time will bring about enormous changes to human societies. This is where Holtorf comes into the picture.

“The main issue here is how we handle the societal questions. This is what no one has a solution for. We know for a fact that everything can change fundamentally within relatively short periods of time. It is very difficult to predict how people will think and what they will value just 30 years from now”, says Holtorf.

Knowledge about nuclear waste must be kept alive. But a changeable world makes it difficult to design a message that will serve its purpose for many generations.

“There is no reason to believe that one and the same message will work 100,000 years into the future. On the contrary, it will need to be modified quickly. A couple of generations from now, people will have a different understanding of what needs to be communicated relating to the nuclear waste. I don’t know what this will be, but, for instance, one can imagine that it may come to be viewed as a resource instead of as a risk. Therefore, it is important to create a solution that can adapt, by allowing future generations to translate our knowledge to their world and make it part of their knowledge. You can’t create a message based on the knowledge we have today and then expect the matter to be solved for the next 100,000 years”, Holtorf explains.

We can see how quickly society changes also in the changing views of whath should be communicated to future generations in the first place. The message to be send has changed significantly during the last few decades: from a focus on how to deter people from accessing a site by using words and symbols, to describing the site and accounting in detail for what substances are stored there.

SPENT NUCLEAR FUEL AS CULTURAL HERITAGE. “The final repository is a cultural heritage that tells the story of our energy policy since WWII, in which nuclear power has constituted a very important part. But it also tells the story of the development of the environmental movement: resistance to nuclear power was an important part of how the environmental movement started in the 1970s. The final repository as a whole, is an important historical source in the story of an important era of our time”, says Cornelius Holtorf, professor of archaeology.
Joakim Palmqvist

An unusual type of cultural heritage

Holtorf suggests that we view the final repository as a cultural heritage that must be preserved for future generations.

“The final repository is a negative cultural heritage. It means that it is something that we wish to preserve, not necessarily because it’s of benefit to people, but instead one that we must preserve to prevent harm. There are many cultural heritages that are not pleasant, but which must still be preserved”, Holtorf continues.

Last year, he published the book Cultural heritage and the future together with Anders Högberg. It is a book about the role of cultural heritage in the future. On the cover, there is an illustration showing the planned final repository at Forsmark.

Holtorf suggests that the final repository provides an excellent example for discussing the conservation of cultural heritage for the future.

“Nuclear waste is a catalyst. Everyone understands that we must ask ourselves how knowledge about the waste can be preserved 100,000 years into the future”, says Holtorf.

The final repository is an ususual type of cultural heritage.But its meaning will be renegotiated by future generations, precisely as is the case for historical places and objects that we want to preserve. The important thing is that we give those who come after us good conditions for creating their own understanding of the final repository. This we can learn from looking at other cultural heritages that have survived the passage of time.

“Change is a precondition for preservation. There is no way around this. The reason that we have knowledge about the pyramids and appreciate them today, is something completely different than why they were constructed. Unless such change had taken place, the pyramids would not exist today. If they had not become a place for archaeologists and tourists and a source of pride for Egypt, the rocks would have been removed and used for something else a long time ago”, Holtorf concludes.

Mer information

• The research group UNESCO Chair on Heritage Futures which explores questions regarding the preservation of heritages into the future.
• The research project Characteristics and extent of microbial anaerobic methane oxidation and sulfate reduction in the deep terrestrial subsurface over geological time scales.