The Techa cascade of water reservoirs is the world’s largest open storage facility for liquid low-level radioactive waste. Its capacity is about 360 mln. m3, it occupies an area of more than 65 km2, the total activity accumulated in the water and sediments is about 6·1015 Bq. The major challenge facing the Techa cascade is virtually uncontrollable water level changes. The water level rise can cause significant pollution of the environment. From the late 1990’s onwards, the issue of the Techa cascade safety assurance is considered to be one of the major challenges pertaining to nuclear legacy for «Mayak» and Russia as a whole. Unlike other industrial water reservoirs the Techa cascade liquidation is estimated as highly unrealistic. The main objectives of the paper are:
– brief results summary of the practical works on safety improvement at the Techa cascade carried out over the past decade;
– introduction the works on the Techa cascade performance assessment;
– determination of the existing risks and strategic areas for solving the problem.