In the beginning of April, 1998, Belgoprocess started the large scale decommissioning of shutdown facilities at the former waste treatment department of the Belgian Nuclear Research Centre (SCK•CEN).

In the second half of 2000, the decommissioning of a former open concrete storage pond was started. It has two parts, one with a volume of 200 m3, the other has a volume of 2 000 m3. In the past, the tanks were used as open cooling reservoir for the scrubber water of an incinerator for low level beta-gamma wastes. As a result, it contained some 126 Mg of sludges that were treated in a bituminisation facility.

After emptying and rinsing of the tanks, samples were taken from the inner (brick) and the outer (concrete) wall to define the contamination levels in the material. It was found that the first layer of about one centimetre of the brick wall showed some radium contamination. Samples taken from the outer wall showed no contamination, which does not mean that the entire outer wall should be free of contamination. It was seen that the outer wall had some cracks, and there was no guarantee that a layer of bitumen in between the two walls was still in good condition. Also the top layer of the concrete bottom proved to be radium contaminated.

The outer walls of the storage pond were supported by a thick layer of soil, which proved to contain some spots of contamination. The contaminated soil was segregated and evacuated, the remaining part was removed to a temporary storage area, waiting to be monitored for final unconditional release.

The paper gives an overview of the decommissioning activities relating to the open concrete storage pond at the former waste treatment department of the Belgian Nuclear Research Centre (SCK•CEN).

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