An explosion on September 29, 1957, contaminated an area of 23,000 square kilometers and exposed more than 270,000 people to significant levels of radiation.
It was not until the glasnost era that local residents learned officially about the blast.
The environmental group Greenpeace Russia was to join Chelyabinsk residents in a rally today to call for the relocation of people still living in contaminated areas.
The group has also issued a report criticizing plans by the Russian government to import and reprocess foreign radioactive waste at the Mayak site.
Mayak, which in Russian means "beacon," was secretly built in the late 1940s to produce weapons-grade plutonium. Today, it is the country's largest plant reprocessing nuclear fuel from decommissioned weapons and waste from nuclear reactors.
The Mayak complex is blamed for contaminating the nearby Techa River, the area's only source of drinking water.
The region records high incidences of cancer, sterility, heart diseases, and asthma. But authorities have consistently refused to close down the facility.
Russia plans to build 40 new nuclear reactors in the country by 2030, and hopes to build as many as 60 additional reactors for clients abroad.