Since l946 the Soviet \"Mayak\" organization has produced plutonium for nuclear weapons at the Chelyabinsk-40 complex that covers an area of 90 km2 in the Chelyabinsk region of the southern Urals.
From 1949 to 1951 medium- and high-level radioactive waste was discharged directly into the river Techa system, which flows via the river Ob into the Kara Sea.
When this ceased in 1951 the medium- and high-level waste was discharged into a small swampy lake, KARACHAY, covering less than ½ km2 in area, inside the complex. The accumulated amounts of activity are enormous:
3.6 EBq Cs-137 and 0.74 EBq Sr-90.
A twentieth of the activity is in the water phase having a concentration of about 0.5 TBq/m3, whereas the remainder is found in the lake sediments.
In l967 after a drought the borders of the lake were \"relieved\" of about 22 TBq spread by whirlwinds over an area of about 1800 km 2.
1 EBq (EXA = billion billions) is 1018Bq
l TBq (TERA = thousand billions) is 1012Bq