In the abandoned iron ore mine KONRAD a wide range of geo-mechanical and geophysical investigations are being performed to prove the deformation characteristics and integrity of the rock masses. On the basis of the mining experiences and the scientific results, a conceptual design for an underground repository for radioactive wastes was developed in accordance with the requirements set by the technical necessities of waste handling, the mining safety regulations and the high standards for radiological safety.

INTRODUCTION

In the Federal Republic of Germany the national programme for radioactive waste disposal is based on the principle of underground storage of all waste categories. As salt domes are found in numbers in the northern part of Germany and as rock salt has excellent thermal conductivity as well as rock mechanical properties, the salt formation is the first choice for the disposal of high active wastes (HAW) from the fuel element reprocessing cycle. Other wastes such as low active wastes (LAW) from nuclear research centres and operating and decommissioned nuclear power stations may well be disposed in other geological formations with different petrophysical and rock mechanical properties. Despite favourable hydrogeological features such rock formations must allow for the construction of suitably sized rooms and galleries. Under the aspect of full operational and long time rock mechanical safety, the final disposal rooms have to be designed huge enough for the extensive transport and disposal techniques which are in many ways different from a conventional mining operation. The intensive utilization of the disposal formation is most important in view of a favourable cost-price relation not only for the disposal operation but also for the low production costs for nuclear energy. In Germany the abandoned iron ore mine KONRAD in the vicinity of Salzgitter (Lower Saxony) is at present being investigated on its feasibility and its storage potential with respect to the disposal of LAW in drums and as large components.

TECHNICAL AND GEOLOGICAL REVIEW OF THE MINE

The KONRAD mine, put into operation between 1958 and 1965, its.shafts, headgear and hoisting equipment are of modern design. The two shafts measure 7 m in diameter each. The hoists and cages of the production shaft have a hauling capacity of up to 20 Mg. Large size cages measuring 2.4 × 2.4 m2 and up to 6 m in height can be installed. The underground travel ways on three mine levels 1000m, 1100 m and 1200 m below surface are accessible by diesel engine driven machines with pay loads of app. 20 Mg. The now abandoned mining operation was undertaken initially in the way of room and pillar mining and later, along with the adaptation of the LHD-technique, as pillar caving within a system of sublevels. Until 1976, when the production was terminated, about 6.6 Tg of ore were hauled and about 2.5 Mm2 of total cavity volume were opened. The sedimentary oolitic iron ore (Minette type) being of Jurassic age appears in the so-called Gifhorner Trough, a synsedimentary geological structure which has been cut by the Lower cretaceous transgression and which is covered by younger rock formations, mainly clay- and marlstones.

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