Radiological States around the Kraton-4 Underground Nuclear Explosion Site in Sakha

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A radiological survey around the site of Kraton-4, an underground nuclear explosion (Yield of 20 kt, depth of 560 m, 1978) in Sakha was carried out in March 1998. Gamma survey and in-situ spectroscopy on the ground exhibited quite normal levels: a dose rate of 0.022 mSv/h and Cs-137 surface contamination of less than 1.1 kBq/m^2 around the hypocenter. The results suggested no remarkable leakage of radioactivity from the epicenter to the ground surface at least not for non-rare gas elements as of 1998. Twelve underground nuclear explosions (UNEs) with industrial applications were conducted in the Sakha republic of the Russian Federation between 1974 and 1987. Figure 1 shows a schematic time-table of the UNEs with information of output in kilotons and underground depth, taken from Yakimets (1996)1). Most of the UNEs were carried out at a depth of 500 to 1500 m. The maximum yield was 20 kt. Four UNEs were conducted for a geological study of deep seismic waves of the earth crust, six UNEs to intensify oil recovery and gas inflow, one UNE to obtain underground crude oil, and one UNE (named Crystal) for the building of a dam for the storage of waste after the extraction of useful components from ore. However two UNEs, Crystal (2 kt, -100 m, 1974) and Kraton-3 (20 kt, -525 m, 1978) failed, with radioactive releases to the environment.
日本放射線影響学会の論文