Radioactivity - The Changing Arctic Environment: The Arctic Messenger - page 66

ter and accumulated large quantities of radionuclides, but as discharge rates later fell from
Mayak, the swamp became a radionuclide source to the river. Between 1951 and 1961, a
system of dams and canals was constructed in the upper part of the Techa River to retain
much of the radioactivity, and after 1951, most waste was discharged into Lake Karachay,
a small lake with no outlet. In 1997, it was reported that the total amount of radioactivity in
the lake was about 4,400 PBq. After discharges to Lake Karachay were terminated, water
levels dropped significantly. In 1997, the lake partially dried out during a summer drought.
Thisresultedinabout22TBqofradionuclides beingredistributed bylocalwindsandledto
more than 1,800 square kilometres of territory receiving deposition of 90 Sr at levels greater
than 3.7 kBq per square kilometre (with 1.0 kBq being equal to 1,000 becquerels).
The incident at Lake Karachay resulted in contamination of parts of the same geo-
graphical area that had occurred following an accident at Mayak in 1957. The latter is now
known as the Kyshtym accident. At this time, a storage tank of high-level radioactive ma-
terial, which was buried more than 8 metres underground, exploded and released about 74
PBq of radioactivity into the atmosphere at up to an altitude of 1.0 kilometre. The domin-
ant long-lived radionuclide released was 90 Sr. For about 11 hours after the explosion, the
radioactive cloud moved north-east for 300-350 kilometres, resulting in a deposition foot-
print of between 800 to 20,000 square kilometres (depending on contours of contamination
criteria). If you do some more reading, you will find this area defined as the East Ural Ra-
dioactive Trace (EURT). Approximately 10,000 people received a collective dose of 1,300
man-Sv and were evacuated for 7-670 days, depending on where they lived. The effective
dose in the most exposed group reached 0.5 Sv. It is possible that a significant proportion
of the 90 Sr derived from the Kyshtym accident may have reached the Arctic Ocean, but the
lack of contemporary measurements does not allow the accident source to be distinguished
from other sources present at the time.
The Tomsk-7 facility is located on the River Tom, shortly before it flows into the Ob
- well upstream of the Ob/Irtysh confluence at Khanty-Mansiysk. It was originally used
for the production of weapons-grade material, but by 1998, the two remaining reactors
were also being used to provide electricity for the town of Tomsk. Radioactive waste from