Concrete and/or drainage?

Filling the cavities of the Asse II mine with concrete and flooding them - that was basically the decommissioning concept of the former operator, Helmholtz-Zentrum München (HMGU). From the technical and nuclear law point of view, this concept does no longer present a solution suitable to guarantee the necessary safety for man and environment. The plan is to guarantee safety by retrieving the wastes. This way has been laid down in the so-called Asse law (Article 57b, Atomic Energy Act).

A key prerequisite is, however, that the safety of the miners can be guaranteed over the entire period of time. All experts agree that the mine’s stability can only be achieved by backfilling large cavities where no wastes have been stored with salt concrete as completely as possible. That these measures nevertheless raise scepticism and mistrust, also in the current debates about drainage concepts, is understandable in view of the past.

For this reason, the BfS answers basic questions on this topic.

Is it true that means of access to waste emplacement chambers have recently been filled with concrete, more are to follow and that thus saline water (brine) could subsequently dam up in the chambers?

No.

Already decades ago, all means of access to the emplacement chambers were shut off from the mine openings by up to 20-metre-thick sealing structures. Therefore, nobody can tell the exact situation inside the altogether 13 chambers filled with radioactive wastes. To gain better knowledge of the state of the wastes and the chambers, a drilling programme is currently being carried out at two waste emplacement chambers ("Fact-finding").

Why does the BfS backfill cavities near the emplacement chambers although the radioactive waste needs retrieving?

Meanwhile, the cavities located near the emplacement chambers are up to 100 years old. Over decades, the mine had practically been left to its own devices. When the BfS took over responsibility for the mine from Helmholtz-Zentrum (former GSF) five years ago, it was already in a very bad state. Step by step the BfS has been catching up on measures that would have had to be taken a long time ago: To stabilise the mine, cavities no longer needed are sealed with many thousand cubic metres of salt concrete.

An area that is especially affected by the rock pressure is the level in a depth of 750 metres, one of the oldest mine sections. In that area, where most emplacement chambers are located, stabilisation is urgently required to maintain occupational safety. The stabilisation also reduces the mine’s risk of drowning. Moreover, possible damages and dangers for man and environment can be reduced by the structures, should an uncontrollable inflow of water occur.

Does the backfilling of cavities with concrete not block retrieval?

The measures do not impede retrieval. To recover the wastes, the means of access to the chambers, which have been closed for a long time, need not necessarily be reopened in the same spot. Means of access to the chambers can also be established at other places. It may even be necessary to avoid the old emplacement galleries, part of which may be contaminated and no longer stable. But also areas filled with concrete can be reopened later on, if this is required.

There are warnings that the wastes “are only centimetres away from the brine level” – how does the BfS deal with these warnings?

The people’s concerns about their safety must be taken seriously. However, the BfS will not accept without protest that fears are reinforced on a speculative basis. Since the debate about retrieving the wastes started, it has been known and is therefore not new that we have to expect that drums in individual chambers have become wet because of brines. In today’s debate about a so-called drainage concept, however, one needs to take into account that we take out just 26 litres of brine per day from the area of the waste emplacement chambers. It is therefore not responsible to construct an image suggesting that the stabilising measures currently taken would provoke the drowning of the waste emplacement chambers. The BfS is open for the debate.

The Asse project is a great challenge for all parties involved and there are the most different interpretations and evaluations of many questions. Comparing and discussing these different points of view in order to achieve broad and co-ordinated action, is the aim of the monitoring bodies’ approach and should be dealt with further exactly there. Without prejudice to this, the responsibility for safety is with the mine operator and with the federal state and governmental supervisory authorities.

What does the BfS do with the brine/saline water arising today in a depth of 750 metres?

For many years, a number of so-called collecting points for contaminated brines have been established near the emplacement chambers on the 750-m level. Daily, a total volume of about 26 litres is collected there. On a regular basis, the brines/solutions are monitored, samples are taken and they are pumped into containers. Since these solutions are radioactively contaminated, they are presently stored intermediately underground. Via gaps and clefts in the salt they have collected at special points.

What does the BfS do with the brines after this area has been filled with concrete?

Despite of the backfilling measures, the BfS will maintain the possibility to observe the brines and continue to pump them out, if required. There are completed plans and first constructions for this purpose. There is already evidence of practical experience underground.

In parallel, the BfS has drafted an overall concept for the monitoring and collection of these brines (so-called drainage concept) that has been presented to the Asse-2 Monitoring Group and is being discussed in the specialist board, the Working Group Comparison of Options.