Russia’s Production Association Mayak, in the closed city of Ozersk near Chelyabinsk, by the end of the year will complete remediation of reservoir B-9 (Lake Karachai) which contains high level liquid radioactive waste.

PA Mayak, formerly known as the closed city of Chelyabinsk-40 or Chelyabinsk 65, was set up in the late 1940s as part of the nuclear weapons programme to produce plutonium. Today the company produces nuclear weapons components, isotopes, and stores and reprocessed used nuclear fuel.

Like all the nuclear weapons states involved in the post WWII nuclear arms race, little care was taken to deal with radioactive wastes in those early years. High level waste was dumped directly into the river Techa from 1949 to 1951 after which the discharge was stopped and the waste was channelled into a cascade of reservoirs, including Lake Karachai until 1956.

In the 1960s, the lake began to dry out and in 1968, following a drought in the region, the wind carried radioactive dust away from the dried area of the lake, contaminating a large area. Between 1978 and 1986, the lake was filled with almost 10,000 hollow concrete blocks to prevent sediments from shifting.

The Washington, DC-based Worldwatch Institute describes Karachai as the most polluted spot on Earth. The lake accumulated some 4.44 exabecquerels (EBq) of radioactivity over less than 1 square mile of water including caesium-137 and strontium-90. The sediment of the lake bed is estimated to be composed almost entirely of high level radioactive waste deposits to a depth of roughly 3.4 metres. The radiation level in the region near where radioactive effluent is discharged into the lake was approximately 6Sv/h in 1990, according to the Washington, DC-based Natural Resources Defense Council – enough to give a lethal dose to a human within an hour.

Dealing with the lake has been a huge and difficult task, and was part of the federal target programme "Nuclear and Radiation Safety for 2008-2015." Mayak says the danger will finally be eliminated and the pond will be closed completely with rock and concrete blocks in November. Several layers of waterproofing will be placed on top of this over the next few years.

Before the lake was sealed, some 650 cubic metres of special concrete was injected under pressure into the base of the lake through 38 wells in the upper cover. This effectively created a reinforced concrete underwater storage facility for the highly radioactive sediment.

The concrete was developed by scientists of Mayak’s central factory laboratory together with specialists from the radiochemical plant enterprise. The project also includes supporting facilities and communications systems as well as channels to trap and divert upland rainfall.

The project has already been allocated about RUB17bn ($275m). The mothballing of Karachai will be completed before the end of 2015.