Co-60 content in the spent graphite masonry of commercial reactors at the Siberian Chemical Combine

Some results of comprehensive investigations of the radioactive contaminati on of graphite masonry from shutdown commercial uranium-graphite reactors a t the Siberian Chemical Combine are reported. The objective of the investig ations was to study the distribution of radionuclides and to determine the contamination level. In the present paper information about Co-60 in the gr aphite of the I-1 and EI-2 reactors is reported. Its content in the samples was measured by gamma-spectrometry. There were about 250 graphite samples from the I-1 reactor and 200 from EI-2. According to the data obtained, the surface contamination level of the blocks can be taken as the same for the entire core within the limits of the errors presented. The average Co-60 c ontamination of the graphite in the surface of blocks from the I-1 core is 5600(-500)(+500) Bq/g and 8400(-1000)(+1200) Bq/g for the EI-2. The Co-60 a ctivity in all blocks from the I-1 core is 1.22.10(12) Bq, and for EI-1 the figure is 2.16.10(12) Bq.