Russian authorities have confirmed reports of a spike in radioactivity in the air over the Ural Mountains.

But the suspected source of the leak, a nuclear fuel processing plant, denied it was the source of contamination.


The Russian Meteorological Service said in a statement on Tuesday it recorded the release of ruthenium-106 in the southern Urals in late September and classified it as "extremely high contamination".


Russian authorities insisted, however, that the contamination posed no health risks.


France's nuclear safety agency earlier this month said it recorded radioactivity in the area between the Volga River and the Ural Mountains from a suspected accident involving nuclear fuel or the production of radioactive material.


It said the release of the isotope posed no health or environmental risks to European countries.


Last month, when reports of a trace of ruthenium over Europe first appeared, Russia's state-controlled Rosatom corporation denied any leak.


Rosatom reaffirmed on Tuesday that the ruthenium emission registered by the state meteorological service had not come from any of its facilities.


The corporation said it was working closely with international organisations to identify the potential source of the emission.


The Russian meteorological office's report, however, noted high levels of radiation in residential areas near Rosatom's Mayak plant.


The Mayak plant reprocesses nuclear fuel and produces radioactive material for industrial and research purposes. It accounts for half of Russian exports of radioactive isotopes.


Air samples in the town of Argayash in late September-early October, for example, showed levels nearly 1,000 times higher than those recorded in the previous months.


Mayak said it had not conducted any work on extracting ruthenium-106 from spent nuclear fuel "for many years".


'No major health threat', scientists say

Western scientists said the ruthenium-106 levels disclosed did not by themselves indicate any major health threat.


"Ruthenium is very rare and hence its presence may suggest that an event of some nature has occurred," Malcolm Sperrin, director of the Department of Medical Physics and Clinical Engineering at Oxford University Hospitals in England, said.


"That being said, the natural abundance is so low that even a factor of 900 up on natural levels is still very low."


Professor Paddy Regan at the University of Surrey said the fact that the ruthenium was found in isolation, rather than with other radioactive materials "suggests a leak from a fuel/reprocessing plant or somewhere they are separating the ruthenium" rather than a bigger nuclear accident.


"If it was a reactor leak or nuclear explosion, other radioisotopes would also be present in the plume and from the reports, they are not," he said.


He added any health effect would be negligible.
Poor record of nuclear disasters

Mayak, in the Chelyabinsk region, saw one of the world's worst nuclear accidents on September 29, 1957, when a waste tank exploded, contaminating 23,000 square kilometres and prompting authorities to evacuate 10,000 residents from neighbouring regions.


Some details of the disaster were first released to the public in 1989 as part of former Soviet leader Mikhail Gorbachev's openness campaign, but the exact scope of its impact on the local population has remained unclear.


In 2004, it was confirmed that waste was being dumped in the local Techa River. Nuclear regulators say that no longer happens, but anti-nuclear activists say it is impossible to tell given the level of state secrecy.


In 2016, Associated Press reporters visited a village downstream from Mayak where doctors have for years recorded rates of chromosomal abnormalities, birth defects and cancers vastly higher than the Russian average.


A Geiger counter at the riverbank in the village of Muslyumovo showed measurements 80 to 100 times the level of naturally occurring background radiation.


A decades-long Radiation Research Society study of people living near the Techa River, conducted jointly by Russian and American scientists, linked radiation particularly to higher rates of cancer of the uterus and oesophagus.


The Nuclear Safety Institute at the Russian Academy of Sciences, which oversees safety standards for the country's nuclear industry, has insisted Mayak's nuclear waste processing system presents no danger to the surrounding population.


Environmental pressure group Greenpeace said in a statement it would petition the Russian Prosecutor General's office to investigate "a possible concealment of a radiation accident" and check whether public health was sufficiently protected.

Russia admits spike in radioactive ruthenium-106 over Ural Mountains amid fears of nuclear accident - ABC News (Australian Broadcasting Corporation)