Preliminary geotechnical investigations are described in view of selecting a site for disposal of radioactive wastes in geological formations.

INTRODUCTION

The peaceful use of nuclear energy for industrial electricity production has been ruled out in Austria by the popular referendum of November 5, 1978. However, prior to that date extensive work on radioactive waste management and particularly on waste disposal has been carried out in Austria by various organizations. The work reported here refers to projects which were executed by the Austrian Electricity Generating Board.

In connection with granting the operational licence for Austria's first 722 MWe boiling water reactor at Zwentendorf the utility has been requested by the licencing authorities to satisfactorily demonstrate, that is to prove, the Capability to close the nuclear fuel cycle. Thus, according to the "polluter pays principle" the Austrian electricity utilities carried out extensive projects for the disposal of radioactive wastes which included both non-site specific as well as site specific geotechnical investigations.

GENERAL

The principle geotechnical efforts were mainly concentrated on the northern parts of Austria being one of the geologically most suitable areas for radioactive waste disposal-which even preliminary geotechnical surveys had already shown. LANDSAT-satellite imagery of the chosen area has been studied and evaluated. More detailed magnetic measurements were carried out with distances of 50 m between the single stations. The rock itself being granodiorite turned out to be coarse-grained with porphyric texture.

Lately, acoustic emission analyses were conducted to investigate rock-mechanic properties in view of establishing thermal load criteria as a consequence of high level waste disposal.

SITE INVESTIGATIONS

The geophysical site investigations (Holzer, 1979) included amongst others, magnetic measurements, hydrological surveys and a morphological analysis of the environment. The Bohemian Massif in which the detailed site investigations were performed consists dominantly of medium- to high-grade metamorphic suites which in Hercynian times were intruded by widespread granitic to granodiorite plutons. The general seismotectonic situation is such that the central part can be considered as seismically inactive and tectonically stable.

According to the utilitie's reprocessing contract with COGEMA, conditioned vitrified high-level waste of about 3–4 m3 /a depending on the fission product concentration and resulting from the operation of the first nuclear power plant should have eventually been deposited.

It was intended to dispose of high-level, medium-level and low-level radioactive waste at one site (Held, 1978). The different emplacement levels are connected by two shafts, A and B. Disposal of the low-level' and medium-level wastes was planned at a depth of about 100 - 130 m, whereas the -bearing medium level and high-level waste was to be emplaced at a depth of about 500 m.

It is evident that the site evaluation for a waste repository is a multivariable problem. The choice of the weights associated with the individual site parameters is one of the most difficult tasks. Moreover, it is also import to realize that besides the safety related aspects for site selection other aspects may also be important such as socio-political, economic and other factors.

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