Going deeper underground

What happens to the thousands of tons of radioactive waste generated every year at our nuclear power plants? Some of the used nuclear fuel can technically be reused in weapons, but the process is inherently dangerous, so this is not common practice. Some waste can be burned, producing additional energy. But there’s still a lot left over to dispose of. And with regulators like the US Environmental Protection Agency (EPA) setting a 10,000-year minimum time for waste to be looked after, this can be challenging.

The answer is deep geological disposal – literally burying the waste deep underground, often in shale or salt mines. This brings yet more concerns, such as the potential contamination of groundwater and even earthquakes, so it’s vital that the waste is packaged carefully and safely, in a way that ensures no radiation leaks out.

In Germany, the authorities have decided to stop the operation of nuclear power plants, which means many plants will be decommissioned, producing an enormous volume of radioactive waste that needs disposing. The Gesellschaft für Nuklear-Service mbH (GNS) provides solutions for nuclear disposal during decommissioning and is responsible for the disposal of almost all of Germany’s radioactive waste in federal storage facilities. The waste is handed over to the German authorities.

The disposal process

Almost 90 percent of Germany’s radioactive waste is medium-level and low-level radioactive waste (MAW and LAW). The country’s final repository for MAW/LAW has been established for some time, and the Konrad mine (near Salzgitter) is expected to go into operation in 2022 after extensive construction work, with a storage potential of approximately 300,000 m³.

The waste is usually packaged in steel barrels, which are then packed into steel containers, often with concrete inliners. The empty cavities between the barrels are filled with concrete; there are no gaps allowed in the containers, and the concrete has to meet certain requirements, including a pressure of less than 0.2 bar in the container during its storage and a compressive strength of more than C20/25. When radioactive waste is involved, there is no room for nonconformity, as the packing cannot be removed and redone safely. This means the concrete must meet the rigorous standards every time.

Kiwa has been working with the GNS for two years, having developed a quality management system for them. The Kiwa team tests the properties of the concrete, examining its thermal conductivity and capacity, permeability and porosity, but also shrinkage and strength properties under real storage conditions.

Kiwa also inspected and certified the first practical processes, including checking that staff were competent in handling the concrete, as well as looking at the planning, execution, documentation and archiving information about the quality of the concreting.

As more and more waste is produced during decommissioning of the nuclear power in Germany, there will be a need to produce the high-performance concrete more quickly and reliably on-site. There is already a scientific and practical foundation, but narrow space conditions, including the inclusion of high-security control areas, variation of the available machines or mixing technology and the type of waste, provide recurring challenges. Today’s requirement profiles and knowledge levels can be supplemented or adapted in the future, if needed to meet these challenges.

Kiwa Germany has successfully mastered another task, also in the field of concrete technology for radioactive waste disposal, and has been involved in the decommissioning of nuclear power plants. The procedure will be accredited by the German Accreditation Body (DAkkS) to meet Kiwa’s quality standards.

More information: Ronny.Stadie@kiwa.de