Pumping alone is no solution

The aim of the BfS is the safe decommissioning of the Asse mine. According to the present state of knowledge, this can only be achieved by retrieving the wastes from the mine. At the same time, the BfS is bound by law to arrange for measures to be taken in the event of an emergency, which cannot be ruled out – the so-called drowning of the Asse II mine in case of a design-exceeding inflow of brine. However, in the event of an emergency, the effects on man and environment must be kept as low as possible.

Precautionary and emergency planning of the BfS

The precautionary and emergency planning carried out by the Federal Office for Radiation Protection (BfS) in the past years, has the prime aim to reduce the probability of occurrence of an uncontrollable inflow of water into the mine openings and/or, in the event of an inflow, to keep the effects on man and environment as low as possible. Apart from measures to stabilise the mine, the sealing of the emplacement chambers, this also includes the improvement of the storage and pumping capacities up to – in the event of an emergency – the backfilling of the emplacement chambers’ residual cavities and the counter-flooding of the mine openings with a saturated magnesium chloride solution.

However, implementing the precautionary measures does not prevent the retrieval of the radioactive wastes; it rather creates the prerequisites for retrieval. Because one of the basic requirements for the retrieval of the radioactive wastes is the stabilising effect on the mine openings, which will occur in the context of implementing the emergency measures, in order to enable permanent access to the wastes.

Emergency cannot be controlled by more or larger pumps in the long run

The emergency relating to the Asse mine, the uncontrollable, design-exceeding inflow of brine or solution, however, cannot be controlled by a larger number or larger pumps in the long run. The reasons are:

• Temporal development of the inflow of brine
  
  In the event of brine flowing into a salt mine, it is very probable that the inflow increases until it is design-exceeding and can no longer be controlled. All drowning scenarios of salt mines that have so far been experienced show that the inflow rate always develops exponentially. That means it starts very slowly and can go up to several thousand cubic metres per day after a short time already. An increase in pumping capacity thus only reflects an apparent gain in safety, since the so achieved gain in time for the operational safety of the mine is very limited.
  
  Furthermore, questions need to be clarified as to the environmental impact of the discharge of several thousand cubic metres of influent solution per day into the receiving waters or, respectively, the technical feasibility of the disposal of the chloride-containing influent solutions.

• Spatially limited mine openings
  
  The Asse mine is a spatially limited mine the major part of which has been backfilled. Nor are other places known where solutions might flow into the mine. The pumping capacity and the volume of brines to be collected can thus not be expanded arbitrarily. In the event of an uncontrollable inflow of solutions, the difficulty will be the collection of the solutions in the mine itself. In particular if the solution runs into areas that are inaccessible already today.
  
  The BfS has already increased the pumping capacity to 500 cubic metres per day. That corresponds to more than the 40-fold of the brine volume currently flowing into the mine.

• Increasing inflow rate can change the solution’s chemical composition
  
  All practical examples show that in the event of a dramatic increase in brine inflows, the solutions are no longer saturated with salt but increasingly take on the character of freshwater. As a result the water would dissolve more salt on its way. More and/or larger openings would form through which brine or solution could flow into the mine, flow paths would get bigger, which would again increase the inflow rate. New cavities would form inside the mine as a result of salt dissolving; these new cavities would additionally decrease the mine’s stability.
  
  The basic problem is thus that certain volumes of influent solution would trigger a dynamic process which could no longer be controlled technically, even with an increased pumping capacity. If the influent solution would only be pumped out of the mine in such a case, no hydraulic counter-pressure could be built and the freshwater would practically be "drawn" into the mine and the situation would go worse. The aforementioned change of the influent solution’s chemical composition could also occur at inflow rates of clearly below 500 cubic metres per day already.

• Influent solution may come into contact with radioactive wastes
  
  The situation that the solution flows in the direction of the emplacement chambers and comes into contact with the wastes, cannot be solved by higher pumping capacity either. The collected influent solution must then be treated as radioactive waste and be disposed of. Not just any volume of contaminated solution or brine can be pumped and disposed of. In this case, even an inflow of under 500 cubic metres solution per day may lead to the situation being no longer controllable.

Emergency preparedness: When an inflow of brine is no longer controllable

If an inflow of brine/solution is no longer controllable, the Federal Office for Radiation Protection must ensure that the effects of this event on man and environment are kept as low as possible. Therefore precautionary and emergency measures have been developed in the context of emergency preparedness, which minimise the possible radiological effects in the event of an uncontrollable inflow of water.

The precautionary measures including measures to stabilise the mine, to seal the emplacement chambers and to improve the storage and pumping capacities, are to be implemented as soon as possible. Only after all precautionary measures have been implemented, will the Asse mine have been stabilised to the best possible extent and will the emplacement chambers be best protected from influent solutions.

Contrary to this, emergency measures are only implemented in the event of an emergency, i.e. when the mine is lost. This includes, among others, the backfilling of the emplacement chambers’ residual cavities and the counter-flooding of the mine openings with a saturated magnesium chloride solution. If one did not conduct the counter-flooding, the entire cavity would be filled with the influent solution, which would cause corresponding dissolution and reprecipitation processes, which would then enhance the radionuclides’ mobility. This can only be reduced by discharging saturated magnesium chloride solution. In the event of an emergency, no safety gain can therefore be achieved through pumping.