Non-intrusive seismic monitoring of high-level radioactive waste repositories

High-level radioactive waste needs to be isolated from the biosphere for ~1 million years. This can be achieved by embedding the waste in appropriate sealing material and then burying it within a suitable geological formation at considerable depth. Monitoring of disposed high-level radioactive waste requires non-intrusive methods to be applied. We have investigated the possibilities and limitations of seismic tomography for such a monitoring task. Changes within a repository are expected to produce subtle but measurable variations of the seismic waveforms when a high-quality sparker source and firmly grouted multi-component geophones are employed. Traveltime tomography is not expected to be particularly useful, but full-waveform inversions have the potential of characterizing changes within a repository. Application of the acoustic approximation proved to be unsuitable, but elastic inversions could provide useful diagnostic information.