The earth trembles, flash floods tear villages away, thick layers of ice deform the world: It is hard to believe that in the face of powerful forces of nature there should be a place where 1900 containers with German nuclear waste can be safely stored for a million years. The soil changes a lot in just 1000 years, not least as a result of climate change, one would think. No wonder, then, that the search for a repository has only recently experienced a setback? A location should not be found by 2031 after all. But that shouldn’t be because there can’t be any safe long-term deposits, if you listen to experts.
According to the Site Selection Act, a location is sought that “guarantees safety for the permanent protection of people and the environment from ionizing radiation and other harmful effects of this waste for a period of one million years”. From a geological point of view, even a million years is not much, says Michael Kühn from the German Research Center for Geosciences (GFZ). “The strata that we’re going to pick out have been lying there unchanged for hundreds of millions of years — and they’re likely to continue to do so.”
Repositories are excluded in seismically active zones
The Federal Office for the Safety of Nuclear Waste Management (BASE) also refers to the “comprehensive understanding of the overall geological situation and the formation of the rocks in the past”. This makes it possible to assess future processes.
Although there are earthquakes in Germany, they are neither very frequent nor very strong. However, they are an important indication of cracks in the rock. “We can say with certainty where there are correspondingly unstable zones,” says the professor. “We can also measure earthquakes that we don’t feel.” If active zones form from cracks in the future, you would almost certainly see it today, he explains.
Regions that are seismically active or that are close to volcanic activity, for example, are excluded anyway, as Horst Geckeis from the Institute for Nuclear Waste Management at the Karlsruhe Institute of Technology (KIT) explains. Again, clay formations selected for a repository in Switzerland are around 175 million years old, and salt deposits in Germany are around 250 million years old. “Over a period of 1000 years, at best, minor changes are to be expected for formations that are assessed as being favorable for disposal.”
The Federal Institute for Geosciences and Natural Resources (BGR) makes it clear: Areas are excluded by law in which a large-scale uplift of more than one millimeter per year is to be expected within a million years or in the past 34 million years fractures in the rock layers of the upper Earth’s crust have taken place. This is called an “active fault zone”.
A million years – that corresponds to eight to ten ice ages
The experts concede that climatic changes also have to be taken into account. However, because the repository is to be located hundreds of meters below the surface of the earth, flooding and heavy rain events will have no effect, according to the BGR. Precautions would be taken to prevent surface water from penetrating into the repository mine during storage of the nuclear waste.
“What we have to take into account when it comes to climate are ice ages,” says GFZ scientist Kühn. In a million years one can count on up to ten ice ages. “Even if global warming continues, there will probably be eight to nine times when we could get huge ice sheets in Germany.” So-called erosion channels must be expected and taken into account. In principle, the icing will be so extensive that large areas of the Federal Republic will sink evenly under the load – and will be lifted again when thawing. However, due to the depth of the repository, the resulting changes in the groundwater did not play a role.
This is also relevant with regard to radioactive radiation. According to Kühn, the gamma radiation, which is the most dangerous, is shielded by just a few meters of rock. Alpha emitters, on the other hand, can be picked up without hesitation, but they should not get into the body. Important fission products such as cesium 137 and strontium 90 with half-lives of around 30 years have almost completely decayed in 1000 years, explains KIT Professor Geckeis.
According to him, the total radioactivity is reduced by a factor of 10 and is determined after 1000 years by long-lived radionuclides such as plutonium and americium. The BASE explains in general terms that the radiation will have decreased significantly after 1000 years. “However, even then, due to the long half-lives of some radionuclides, the radioactive decay of the stored waste is far from complete. The intensity of the radioactivity is still considerable at this point.”
According to Geckeis, formations of mudstone, rock salt or crystalline rock such as granite at a depth of several hundred meters and a repository concept consisting of several barriers will ensure the long-term safety of a repository. Changing the containers is neither necessary nor planned within a million years.
Depending on the concept, thick-walled steel containers with a wall thickness of 30 to 40 centimeters or – as planned in Scandinavia – those with corrosion-resistant coatings made of copper, for example, should be used. “In Swiss safety considerations, it is assumed that a steel container in a repository in the mudstone will remain intact for at least 10,000 years,” explains Geckeis. Any radioactive substances that might escape afterwards are held back by the surrounding clay rock.
According to the site selection law, however, it must be guaranteed that the nuclear waste can be recovered up to 500 years after it has been sealed, as BASE explains. “Should such an undesirable event occur, it could be that the disposal containers for the further process have to be changed again.”
The operators of the nuclear power plants have provided around 24 billion euros for the safe storage of the waste. According to Geckeis, no further costs should be incurred once the camp has been closed, which is currently planned towards the end of this century, and the transfer to the so-called passively safe state.
From a scientific point of view, however, one factor is difficult to calculate, as GFZ researcher Kühn makes clear: “The most insecure thing we have is the human being.” It is impossible to predict what he will do or what new ideas will come up.