Noticeable measurements for krypton-85 in Asse mine
Measurements do not affect protection of workers
The Federal Office for Radiation Protection measured unexpected high levels of krypton-85 in a small shaft of the Asse mine. Near emplacement chamber 1 is located near emplacement chamber 12 the maximum level of the radioactive noble gas is 3,700 becquerel per cubic metre. However, the new results are of no concern with respect to the health and protection of the staff. Under current conditions, the substance does only cause a very low exposure to radiation. Miners working in the repository may handle krypton-85 activities of up to 1 billion Bq when drilling into the emplacement chamber (step 1 of the fact-finding).
In the shaft building on the surface no noticeable concentrations were registered. The level there was 1.5 Bq per cubic metre. That corresponds to the mean atmospheric value in Germany.
The BfS introduced the measurements in the context of the planned trial drillings for the preparation of a possible retrieval of the nuclear waste stored in the Asse mine.
In 1973, 800 krypton-containing specimens of the Federal Armed Forces were emplaced in the Asse mine that had been used in level measurement devices. The specimens were delivered in eight 200-l drums which had previously been welded gas-tight and had additionally been filled with peat and activated carbon. The Federal Office for Radiation Protection assumes that some drums and specimens have already corroded and the krypton-85 is leaking from the drums. However, it cannot be excluded that other waste contains more krypton-85 than stated at the time of emplacement.