London, Sep 20: Catastrophic nuclear accidents like Chernobyl disaster in the US that took place in 1986 and the more recent Japan's Fukushima disasters in 2011 may not be relics of the past. But the risk of such disasters are still more likely to occur once or twice per century, a study has warned.
The study found that while nuclear accidents have substantially decreased in frequency, this has been accomplished by the suppression of moderate-to-large events.
The researchers estimated that Fukushima and Chernobyl-scale disasters are still more likely than not once or twice per century, and that accidents like 1979 meltdown at Three Mile Island in the US are more likely than not to occur every 10-20 years.
For the study, a team of international risk experts analysed more than 200 nuclear accidents -- the biggest-ever analysis of nuclear accidents -- which provided a grim assessment of the risk estimated by the nuclear industry.
The "flawed and woefully incomplete" public data from the nuclear industry is leading to an over-confident attitude to risk, the researchers warned.
"We have found that the risk level for nuclear power is extremely high," said lead author Spencer Wheatley, Professor at ETH Zurich in Switzerland.
"The next nuclear accident may be much sooner or more severe than the public realises," added Benjamin Sovacool, Professor at the University of Sussex in Britain.
Further, the standard methodology used by the International Atomic Energy Agency to predict accidents and incidents -- particularly when focusing on consequences of extreme events -- is also problematic, the researchers said.
The study, which put fresh pressure on the nuclear industry to be more transparent with data on incidents, also called for a fundamental rethink of how accidents are rated, arguing that the current method (the discrete seven-point International Nuclear Event Scale or INES) is highly imprecise, poorly defined, and often inconsistent.
For example, the Fukushima accident and the Chernobyl accident are rated 7 -- the maximum severity level -- on the INES scale. However, Fukushima alone would need a score of between 10 and 11 to represent the true magnitude of consequences, the researchers said.
To remove a possibility of such disasters would likely require enormous changes to the current fleet of reactors, which is predominantly second-generation technology, Wheatley noted.
But, "even if we introduce new nuclear technology, as long as older facilities remain operational -- likely, given recent trends to extend permits and relicense existing reactors -- their risks, and the aggregate risk of operating the global nuclear fleet, remain," Sovacool said.
The results were published in the journals Energy Research & Social Scienceand Risk Analysis.