Expert report on chamber 4 in the Asse repository: Structural collapse would not release radioactivity

Even if pieces of rock fallen down destroyed the drums containing low-level radioactive waste stored in chamber 4 of the Asse II repository, no radioactivity would be released into the mine. The already existing sealing of chamber 4 would not be damaged by the increased air pressure. This proves a rock-mechanic expert report developed by the Institute of Rock Mechanics (IFG Leipzig) on behalf of the Federal Office for Radiation Protection (BfS).

For reasons of precaution, BfS nevertheless plans to install an additional protection and to enforce the sealing of chamber 4 with an additional concrete plug. The Repository Surveillance unit responsible for nuclear surveillance has already given its consent to the measure and does not consider it necessary to immediately carry out a danger prevention measure. Whether long-term processes may lead to a gradual release of radionuclides at other places in the chamber, is currently being examined in another radiological expertise. Results are expected to be presented in February.

To be able to erect the additional barrier, BfS filed a corresponding application at the Landesamt für Bergbau, Energie und Geologie Niedersachsen (LBEG), which has not been granted so far. Also for precautionary reasons, BfS installed a monitoring system in front of the chamber with which the radioactivity in this area is continuously monitored.

Background

Since the beginning of the year, BfS has been the new operator of the facility. Rotational monitoring measurements carried out by the former operator Helmholtz Zentrum München (HMGU) showed at the end of 2008 that parts of the roof in emplacement chamber 4 on the 750-m level could loosen and fall on the low-level radioactive waste stored in the chamber. In the opinion of the new operator, BfS, and the regulatory authorities, it is currently not necessary to implement danger prevention measures. Nevertheless, measures are considered to prevent a dispersion of radioactively contaminated dusts and mine air from the emplacement chanber into the mine and into the exhaust air in case of a piece of rock falling from the roof, which cannot be excluded. Therefore, it is intended to enforce the sealing of the damaged chamber as a precautionary measure. In doing so, BfS pursues the objective of not impairing decommissioning options for Asse through these measures.