MAYAK, a nuclear energy facility in theformer Soviet Union that remainedshrouded in secrecy for over 40 yearsnow, has been identified as perhaps themost disastrous, according to a recentresearch report. Though not as well-known as the nuclear power plant atChernobyl, the Mayak complex isresponsible for a comparable environ-mental legacy: more than twice theamount of radioactive material releasedin the accident at Chernobyl has beendumped in a nearby lake since 1951(Environment, Vol 39, No 1).
A relatively small lake, one kmlong and half a kin wide, with a maximum depth of only six metres, LakeKarachay is probably the largest openaccumulation of nuclear waste in theworld. According to measurements, thelevel of radioactivity in the lake is as highas 120 million curies (curie is thestandard measurement of radioactivity,equal to the number of disintegrations(3.7 x 1010) undergone by one grammeof radium in one second).
The vast complex of Mayak, createdin the late 1940s to produce plutoniumfor nuclear weapons, is situated nearthe city of Ozersk in the southernUral mountains. It became operationalin 1948 and continued producingplutonium for nuclear weapons until1990. Since then, Mayak has been usedto reprocess fuel from nuclear reactorsand to produce special radionuclides.Although current operations are on amuch lower scale, radio -contaminationproblems remain.
The complex was a disaster from thestart. A design flaw in its radiochemicalplant forced workers to clean filters usedto separate the plutonium and uraniumby hand, exposing them to very highlevels of radiation.
Disposing of the plant's radioactivewastes was also a major problem. The easiest wayout was to dump them in a lake, the Techa river, which river flows through the area. From March 1950 to November 1951, approximately 2.5 million curies of radioactive waste was released into the river.
From 1949 to 1956, at Mayak released approximately 76 million cubicmetres of waste with atotal radioactivity of 2.86million curies into theTecha. As a result, 28,000people living along theriver were exposed to substantial doses of radiation.Even now, a number of large reservoirsand dams along the Techa houselow-level nuclear refuse.
As many as 20 serious accidents areknown to have occurred at Mayak,including seven 'criticality events'.Criticality events, in which a spontaneous chain reaction releases lethalneutrons and gamma radiation, arerelatively rare. Only 13 such eventsoccurred in the Soviet Union during the40 years in which it was producingnuclear weapons. In comparison, eightsuch events took place in the us.
On September 29, 1957, a majoraccident took place when a storage tankcontaining high-level radioactive wasteexploded with a force equivalent to70 tonnes of TNT. Approximately 90 per cent (18 million curies) of the radioactive material released by the explosion settled in the immediate vicinity of the tank.
The level of wastes dumped into Lake Karachay exceeds those released into the Techa. These can pose a hazard in the surrounding area by either 'resuspension' in the air or by contaminating groundwater. On windy days, large amounts of radionuclides are lifted from the surface of the lake in the form of mist, which can travel long distances before settling down. To prevent this, Russian authorities are now covering the entire surface of the lake with hollow concrete blocks. The project should be completed within a few years, and will eliminate one source of contamination. But groundwater contamination is amore serious problem.