The ageing nuclear waste facility in the Asse II salt mine near Wolfenbüttel in Lower Saxony is facing a growing problem of water penetration. The mine, which holds some 126,000 barrels of low- and intermediate-level radioactive waste, is operated by Germany’s Federal Association for Final Storage (BGE – Bundesgesellschaft für Endlagerung), a federally owned company within the remit of the Federal Environment Ministry. In April 2017, BGE took over responsibility as operator of the Asse II mine and the Konrad and Morsleben repositories from the Federal Office for Radiation Protection. Salt water has been entering the facility for decades, increasing concern about the stability of the 13 chambers filled with waste.

From 1967 to 1978, around 47,000 cubic metres of low- and intermediate-level radioactive waste were emplaced in the mine according to information from former operator, the Association for Radiation Research (now known as Helmholtz Zentrum München, HMGU). Some 67% of the waste originated from NPPs. Typical waste included: filters, scrap metal, paper, laboratory waste, building rubble, wood, slurries and mixed waste. Other waste was delivered by research institutes, the nuclear industry and other waste producers such as the medical industry.

Records show how many drums are stored in the Asse mine, but there is some uncertainty as the radionuclide and substance inventory as the waste declaration at the time does not meet current standards. The radioactive waste was emplaced in 13 former mining chambers Two chambers are located in the central section and 10 in the southern flank of the mine at depths of 725 and 750 metres. A further chamber is located at the 511-metre level.

At the start of emplacement, the waste containers were stacked in an upright position. In order to make better use of the space, the former operator subsequently began stacking them on their sides. From 1971 onwards, the waste was primarily dumped using a wheel loader. The simultaneous handling of multiple drums led to lower costs and lower radiation exposure for staff. There were no plans for retrieval, and possible damage to the waste containers was disregarded. The surrounding rock salt was intended to provide long-term protection.

According to current laws and state of the art of science and technology, the final disposal of radioactive waste in the manner employed at the Asse II mine would not be eligible for a licence although no laws were broken based on the legislation in force at the time. If the waste were to remain in the mine, it would not be possible to demonstrate that the legal safety objectives would be met and the intention is for the waste to be retrieved. So far, none of the barrels have been removed and is not expected to start before 2033 as scientific methods to do it safely are still being investigated. It’s estimated it will cost at least €4.7bn ($5.1bn).

So far, the water penetrating the salt dome from the outside – some 12 cubic metres a day – has been mostly absorbed and pumped to the surface. However, the infiltration patter has changed, BGE head Iris Graffunder recently told the environmental committee of the Bundestag. Graffunder earlier pointed out the deteriorating situation. “Due to this strong change in water access, we are alarmed” she tolkd Braunschweig newspaper. According to the BGE, the amount of water at the main collection point has been decreasing for several months. “This means that the water is collecting somewhere else. That worries us,” she said.

Experts warn that is the partly torn and rusted barrels mix with the water this could eventually contaminates groundwater. The inventory reportedly consists of 104 tonnes of uranium, 81 tonnes of thorium and 29 kilograms of plutonium. There are also toxins such as arsenic, mercury and banned pesticides, which were also disposed of in the mine.

The BGE has applied for the complete renovation of the main collection point, which is located at the 658-metre level in the mine. Experts are currently trying to find and repair possible damaged areas. According to the BGE, the water infiltration has increased from 0.8 to three cubic metres on the lower 725-metre level. At the even lower collection points directly in front of the nuclear waste chambers at the 750-metre level no increase in the salt water level has so far been observed.

Federal Environment Minister Steffi Lemke (Greens) has expressed concern about the situation “I take the situation in the Asse II nuclear waste warehouse in Lower Saxony very seriously,” she said. She added that, in her view, the recovery of the waste was the safest option and “should remain our top priority”.