The transparency failure left a legacy of mental as well as physical problems, a lesson that Japan must learn as it battles the risk of radiation at its Fukushima nuclear power plant, Russian and Ukrainian psychologists said.
Those most at risk are those sent in to clean up the contaminated areas -- the liquidators who in the former Soviet Union suffered from severe mental problems as they balanced the information they were given with reality.
"Insufficient information (on the risks after a nuclear accident) can generate tensions that destroy the health of people submitted to extreme conditions," said Valery Krasnov, director of a psychological institute in Moscow.
"The authorities must not hide information," said Krasnov, the author of a book entitled "Psychological Problems for Liquidators after the Chernobyl Catastrophe".
The USSR sent in tens of thousands of liquidators into Chernobyl in the immediate aftermath and subsequent months. Those who survive have long complained they were given no idea of the scale of the calamity.
The sheer notion that the authorities can hide part of the truth "creates a sentiment of vulnerability in the population which translates into different kinds of psychosomatic problems," Krasnov said.
Observers have criticised Japan for giving incomplete and sometimes contradictory information about the true situation at Fukushima, amid fears the plant is at risk of a full nuclear meltdown.
"Japan is keeping information back just like we did at Chernobyl. It's 1986 all over again," Krasnov said, while acknowledging that this time "the situation is not of the same magnitude".
"The liquidators are still suffering psychological problems. These kind of consequences can be felt for years afterwards. We are talking about depression and anxiety," he added.
"The authorities must act so that people can offer hands to each other and help others. To be in a situation of passive waiting is the worst outcome of all," Krasnov said.
Tetyana Sochko, who works at the Borodianka centre outside Kiev for helping victims overcome the psychological effects of Chernobyl, recalled that at the time of the Chernobyl disaster, neither the liquidators nor their families were given reliable information.
"The dominant feeling then was fear. They did not know what would be awaiting them, and their loved ones, in the future," she said.
Sochko said many of the victims who seek help at the centre have succumbed to a "victim syndrome" as they believe they sacrificed their health in the Chernobyl zone and then received nothing in return.
Vladimir Bondarenko, himself a former liquidator who worked at Chernobyl, said that there had been a large number of suicides amongst his fellow workers.
"They felt their only option was to hang themselves. Their wives left them and they became convinced that being exposed to radiation simply meant death," he added.
He noted however that Japan appeared far more cautious in exposing its nuclear workers, pointing to how it had held back on helicopter water dumping operations due to high radiation.
"Back then we used helicopters and planes and we were working right on top of the reactors," he added.
Psychologist Georgy Sytin, who has looked after former liquidators for the last 15 years, said that an important problem for the veterans after the disaster had been impotence, meaning they could not father children.
"I helped 80 percent (of those treated) recover. This 80 percent were paralysed by fear," he said.
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