Intermediately stored radioactive waste
Apart from the radioactive waste disposed of, waste has also been stored intermediately in the Morsleben repository for radioactive waste. This waste consists of radium-226 waste and of mainly cobalt-60 radiation sources. Measured by volume, the intermediately stored waste covers only a negligible portion of the radioactive waste (less than 0.01 per cent). Still, it represents ca. two thirds of the emplaced activity (182,000 gigabecquerels; as of 2013).
The permanent operating licence which was granted in 1986 and is still effective today does not permit disposal of the intermediately stored waste. However, in the course of decommissioning, the Federal Office for Radiation Protection (BfS) filed an application for its permanent stay – i.e. its disposal – to the Ministry of Agriculture and Environment of the federal state of Saxony-Anhalt (MLU).
Origin of the intermediately stored waste
The data on the intermediately stored waste and the waste disposed of has been documented and archived. All radium-226 radiation sources had been used in the medical field in the former GDR. At the end of the 1960s, the radiation sources were replaced by other radiation sources. Conducted under the auspices of the GDR State Centre for Radiation Protection, the radium radiation sources were collected and at first stored in the Lohmen interim storage facility (Saxony). When Lohmen was closed in 1983, the waste was taken to the Morsleben repository and stored intermediately.
In 1985 and from 1987 to 1990, experiments dealing with the emplacement of heat-generating radioactive waste and its influence on the surrounding salt rock were carried out in the Morsleben repository. In the scope of these tests, five special containers containing mainly cobalt-60 radiation sources were emplaced. Two other special containers contain cobalt-60 radiation sources, the major part of which originates from well irradiation facilities of the former GDR's water management. There, drinking water wells had been equipped with cobalt-60 radiation sources, in order to avoid iron clogging of the well filters (deposition of iron-stone). However, the effect hoped for was not achieved, so that 461 of these radiation sources were taken to Morsleben in 1990 for interim storage. Furthermore, there are six other radiation sources in these containers originating from irradiation facilities of the former Keradenta company for medical and laboratory technology in Radeberg.
Packaging suitable for disposal (conditioning) and emplacement sites
The total mass of the intermediately stored radium-226 is about ten grams. Seven out of altogether eight special containers with an outer volume of ca. five litres contain radium radiation sources. Part of these is leaking. To prevent the discharge of radioactive material, it is incorporated with a synthetic resin and packed into metallic interim storage containers. The eighth special container contains solidified open radium compounds. With the aid of dry cement or gypsum they were solidified inside the special container.
All eight special containers were welded gas-tight and placed together into a 200-l drum. In 1996, it was additionally placed into a 280-l drum. In the scope of relocating the waste to another site on the 4th level in 2006, the drum was additionally provided with a so-called "lost concrete shielding" (VBA). The term "lost concrete shielding" was to express that a further use of the concrete container was not intended (recycling and other use). Since 2006, the radium-VBA has been stored in a bore hole in the ground in the eastern field of the 4th level which has been lined with concrete, where it also is to remain in the course of decommissioning.
The intermediately stored radiation sources (mainly cobalt-60) were placed into sheet steel tins, which again were placed into seven special containers with an outer volume of ca. five litres. Subsequently the special containers were lowered into two bore holes in the so-called underground measuring field (UMF) on the 4th level. Today, two of the special containers are in bore hole A1 at a depth of ca. eight to nine metres. Five special containers are in bore hole A2 at a depth of ca. 9 to 14 metres. There are two other special containers without content between the special containers in bore hole A2. They previously contained material samples for corrosion tests.
Activity of the intermediately stored waste
At the time of its emplacement, the activity of the intermediately stored waste amounted to ca. 2,880,000 gigabecquerels. Due to the radioactive decay, the activity decreased to ca. 170,000 gigabecquerels by 31 December 2014. This means that at this point in time 170,000,000,000,000 (170 trillions) of nuclei had decayed and the activity had decreased to ca. 5.9 per cent of the initial level. For comparison, the activity of the ultimately disposed waste only amounted to 93,000 gigabecquerels on 31 December 2014.
Regular examination of retrievability
In intervals of less than four months, the BfS examines the retrievability of the special containers stored in the UMF. For this purpose, the uppermost special container in the bore holes is gripped with a lifting device, lifted several metres and put down again. With the aid of this procedure, the gripping process and the freedom of movement inside the bore hole are controlled and retrievability is proven.
The competent authority, i.e. the Saxony-Anhalt Ministry for Agriculture and the Environment (MLU), did not make similar arrangements for the lost concrete shielding (VBA) for radium. However, BfS was able to show with the help of model calculations that the lost concrete shielding for radium would be retrievable at least until 30 June 2026. The relevant standard proof of safety is currently being prepared in order to eliminate any residual uncertainties.
Retrievability of the intermediately stored waste
Technically, the intermediately stored waste can be retrieved at any time in principle. However, the Morsleben repository does currently not have a transport container approved for this purpose. With adequate advance notice, however, it can be purchased. Furthermore, a licence for the transport of the intermediately stored waste would have to be applied for. In the unlikely event of an emergency, it would be possible nevertheless to transport the intermediately stored waste to the surface, packed into a transport container available in the repository. To avert hazards, this could be done short-term and without an effective permit.
Current state of approval
By a letter dated 16 December 2014, the MLU, in its capacity as the competent approval authority, approved the extended interim storage of the lost concrete shielding for radium up to 30 June 2026. The approval was granted subject to the additional condition that the submitted standard proof of safety must be completed by 31 December 2016 (1) by providing calculations with respect to existing residual uncertainties or (2) by showing the negligibility of potential interference with the help of a unique visual control. The approval for extended interim storage is bound to the validity of the long-term operating permit. It will only remain valid if the additional condition is fulfilled within the stipulated period of time, i.e. until 31 December 2016.
In its statement of reasons for the additional condition MLU comes to the conclusion that there is no reason to believe the retrievability of the lost concrete shielding for radium will be impeded before 30 June 2026. The additional condition was only stipulated in order to minimise the probability of interference with the lost concrete shielding for radium.
On May, 5 2015, the licence to handle radioactive substances, which are put in interim storage within the underground messauring field (UMF) was extended to June, 30, 2020. The licencing authority responsible for this decision was the Saxony-Anhalt State Office for Geology and Mining (LAGB).
The decommissioning concept provides for disposing of both the radium waste and the radiation sources in the UMF in Morsleben. Calculations on long-term safety have shown that this can be done in a safe way.
State of 2016.04.26