By Stephen Eke
BBC Russian affairs analyst
A report of radiation levels 58,000 times higher than normal at a Chechen chemical plant has renewed international fears about the poor storage and handling of radioactive materials in the former Soviet Union.
The Soviet Union scattered nuclear weapons across its territory
The main worry is that nuclear material could fall into the hands of militants, who might use it to build a so-called "dirty bomb". But the problems go beyond that.
The Soviet Union, whose leaders had little regard for the environment, left an enduring legacy of radioactive pollution on a massive scale.
A huge swathe of Kazakhstan was contaminated by open-air explosions conducted at its nuclear test site during the Cold War.
Ukraine and Belarus still suffer from the radioactive fallout from the Chernobyl nuclear power station.
And Lake Karachay, near the Russian Urals city of Chelyabinsk, home to a nuclear fuel facility, is said to be the most radiation-polluted place on earth.
Just three examples of what resulted from the Soviet state's total disregard for safety and the health of its own people.
In addition, nuclear facilities in the post-Soviet countries have often fallen into disrepair.
With the collapse of the Soviet Union, the problem of radioactive pollution - and what to do with very considerable amounts of leftover radioactive material - took on extra dimensions.
The gravest fear - that of a nuclear bomb falling into the wrong hands - has not been realised.
The nuclear weapons the Soviet Union dispersed around its territory were surrendered by the newly independent countries like Ukraine and Belarus.
And international funding programmes have helped keep them safely protected in Russia.
But the threat of lower-lever nuclear material being traded on the black market is still taken seriously.
It may come from old medical equipment, or any number of former research centres that closed amid economic chaos.
The US and UN say that most of the nuclear material in the former Soviet Union can be traced.
But Russia's customs authorities say they still detect hundreds of attempts every year to smuggle radioactive materials across the country's borders.