What does the nuclear half-life refer to?

Nuclear power: 6 facts about our nuclear waste and its disposal

Why does nuclear waste have to go to the interim storage facility?

After several years of burning, spent fuel elements from nuclear power plants still radiate extremely strongly and generate a lot of heat. They consist of a wide mixture of the most varied, but all of them radioactive substances. Such fuel rods first have to decay in water-filled decay basins for a long time until the short-lived radionuclides have emitted and the heat build-up subsides. The fuel elements are then packed into so-called Castor casks, where they continue to die down for several decades thanks to air cooling. Only then are they cool enough - below 100 degrees Celsius on the surface - to be able to store them in the rock.

Until then, highly radioactive waste poses particularly great dangers, because large amounts of radioactivity could be released into the environment in the event of fires, plane crashes or terrorist activities. At present, however, many Castor casks are not adequately protected at nuclear power plants for logistical reasons, instead of decaying in central interim storage facilities.

How does the final disposal work?

The final disposal concept envisages enclosing the Castor containers completely in rock at a depth of a few hundred meters. It is extremely important that no water can get into the containers. Firstly, water massively increases corrosion; secondly, the radioactively contaminated water could end up in the groundwater, exposing the nearer region to increased radiation in the long term. A repository should therefore be far enough below the groundwater. But it mustn't be too deep either, because below about 1000 meters below ground the rock is already very hot.

In Germany, the Bundestag has commissioned a repository search commission to search for a suitable repository that meets the requirements. This currently comes to the conclusion that the task may not be fully completed until the middle of the next century: According to estimates by the experts, the last nuclear waste containers can be stored "between 2075 and 2130" and the repositories finally closed after another 20 to 40 years become.

The host rock for the repository sought is currently mainly clay, salt and granite. Clay and salt have the advantage of high plasticity: At greater depths, the pressure is so great that any gaps that may arise in the rock close by themselves. However, some degree of corrosion can never be avoided. After a few thousand to ten thousand years, the containers and their contents dissolve and mix with the surrounding rock. Then it is no longer the containers, but the host rock that ensure the closure of the highly radioactive waste. Depending on the storage time, however, many radionuclides with a shorter half-life have already decayed by this point in time, and the total radioactivity has decreased significantly. However, other substances such as plutonium are still largely preserved.

What could transmutation bring?

The handling of the long-lived nuclear waste in particular poses fundamental ethical problems, because its storage duration is beyond the human imagination. Nobody can know what the world will look like in a few hundred, thousand, let alone hundreds of thousands of years and in what number and at what technological level of civilization people will then live. There are approaches to convert some of the long-lived substances into more short-lived ones with the help of radiation called transmutation. Then at least these would no longer need to be stored for more than a million, but only for millennia. However, these concepts are not yet able to transmute all permanently dangerous substances. In addition, they are facing enormous technical difficulties and will make the disposal of nuclear waste significantly more expensive than the final disposal favored by politics and the energy industry. Ethically, it has some merits, at least on paper. However, some critics consider it to be the wrong path to distract the public from the difficulties of high-level radioactive waste. Perhaps only future technologies will offer satisfactory options here.