The Chernobyl dissidents or how the Soviet nuclear disaster shaped opposition within the communist bloc

Forty years after the explosion of the Chernobyl nuclear power plant, the disinformation policy carried out by the USSR and its “satellites” – notably Bulgaria – shows how secrecy fueled suspicion while mobilizing scientists and activists. Their actions contributed to the emergence of environmental movements that supported the democratic opposition across the entire communist bloc of that era.

At 1:23 a.m., on April 26, 1986, reactor No. 4 of the Chernobyl nuclear power plant, then under USSR, experienced a catastrophic failure before exploding, blowing apart part of the facilities and leaving the site scarred. The reactor core, left exposed, releases large quantities of radioactive substances into the atmosphere. In the following months, more than 200,000 people were evacuated from the surrounding areas.

Carried by the winds, the radioactive cloud contaminated large regions of Europe, with particularly significant fallout in Ukraine, in Belarus and in Russia. The emissions continued until May 5, forming clouds of cesium-137 and other isotopes, whose concentration decreases with distance but still affects very large territories. The cloud reached the Balkans on May 1.

At the time, Dimitar Vatsov was a 15-year-old high school student in Sofia. “Right after the radioactive rains, the Komsomol [the youth organization of the Soviet Communist Party] sent my class to work in the fields,” he recalls. “Every morning, a bus would come to pick us up to harvest spinach and chives.”

Until May 7, Bulgarian authorities made no public announcement regarding the disaster. According to later official statements, environmental contamination was minimal and required no special measures. Yet, four of Vatsov’s classmates died of cancer in the years that followed.

This experience profoundly affected him. Today, a philosopher and professor at the New Bulgarian University in Sofia, he launched last fall a seminar entirely dedicated to the consequences of the Chernobyl disaster in Bulgaria, bringing together historians, journalists, and nuclear physicists.

"Bulgaria was the only country in the socialist bloc to take no measures after the disaster,” he explains. Although the country ranks only eighth among the most radiation-exposed countries according to a UN report, it recorded the highest rate of thyroid cancers among children outside the former USSR. “As a philosopher, this singularity led me to reflect on truth, the ethics of political discourse, and more broadly, on the cynicism of the communist regime of that time.”

The Bulgarian black-out

After the Chernobyl accident, information was tightly filtered in Eastern Bloc countries to minimize contamination risks while preserving the USSR’s prestige. In Czechoslovakia, the word katastrofa was carefully avoided in the early phases, replaced by the term havárie (“accident”), used without qualification. Official reports highlighted Soviet expertise and heroism, the quick control of the incident, and the supposed exaggeration of facts by the “Western imperialist media.” However, Bulgaria stood out as the country with the strictest censorship and where no significant action was taken.

“Ceaușescu – one of the most authoritarian dictators of the time – warned the Romanians as early as May 2 about the contamination risk. In Yugoslavia, pregnant women and children were asked to stay indoors, and basic precautions like washing fresh foods were recommended. In Bulgaria, it was a total black-out,” recounts Vatsov.

We weren’t told anything, we just had to obey. It was only years later that I understood the true extent of the disaster – Petko Kovatchev

Nuclear physicist Gueorgui Kaschiev, then employed at the Kozloduy plant in northwestern Bulgaria, vividly remembers those days: “The only information we received was that there was a fire at Chernobyl and that it had been extinguished.”

Through a large antenna installed on his building, Kaschiev was able to pick up Yugoslavian television. “Information from Sweden and from Finland quickly made it clear that the incident was much more serious than officially acknowledged. Western media broadcast satellite images showing the destroyed reactor, maps tracing the radioactive cloud, and reports indicating that Yugoslavia had sent planes to evacuate its citizens studying in Kiev.”

By the end of April, Kaschiev and his colleagues understood that the cloud was heading toward Bulgaria. Between May 1 and 2, radiation levels reached up to ten times the natural background, especially after rains. Faced with the persistent silence of authorities, information spread informally: engineers warned their relatives to take basic precautions, often met with disbelief. Subsequent analyses of food samples, including milk from nearby farms, confirmed extreme contamination.

Archives accessible today show that the Bulgarian government closely monitored the evolution of the disaster and the extent of contamination across Europe and Bulgaria, analyzing foreign press, intelligence reports, and daily radiation measurements across the country. For Vatsov, the Bulgarian Communist Party’s Politburo feared that revealing the true scale of contamination would cause panic and political unrest, as had happened in Poland: “Beyond this initial explanation, I can only describe this attitude as a moral failure on the part of the ruling elites, who showed deep contempt for the rest of the population.”

Petko Kovatchev, an environmental activist doing his mandatory military service at the time, recalls that the army reacted quickly: “From one day to the next, we stopped consuming fresh products and only ate canned foods in the canteen. Outdoor activities were canceled, and we were ordered to measure radiation levels around the base with Geiger counters.”

However, these measures were not accompanied by any explanation. “We weren’t told anything, we just had to obey. It was only years later that I understood the true extent of the disaster.”

The cynicism of the nomenklatura

The management of the consequences of Chernobyl in Bulgaria revealed glaring inequalities in access to information and health protection. At the top was the nomenklatura – senior party officials, secret police, administrative cadres, and military officers. During the crisis, they benefited from privileged access to meals and supplies distributed via the Rila State Hotel, in the center of Sofia. The Politburo received bottled water from deep sources and imported foods – Australian lamb, vegetables from Egypt and from Israel – to avoid contamination.

According to Vatsov, the elite of this nomenklatura – about 300 people – was never in danger, as special measures were taken to ensure their safety and well-being: “The army applied less strict measures, but enough to reduce exposure. The rest of the population, however, was kept in total ignorance.”

The decision to proceed with the May 1, 1986 parade – during which many children paraded in the streets of Sofia despite the threat of radioactive rains – symbolizes this cynicism. Fortunately, the demonstration started at 11 a.m., while the radioactive cloud only reached Bulgarian territory in the afternoon, at the earliest around 2 p.m.

Many propaganda sporting events were also organized across the country, as well as forced labor projects supervised by youth brigades, mainly composed of young people aged 15 to 25. These “volunteers” were required, at least twice a year, to perform physically demanding tasks such as agricultural or construction work. It is estimated that about 365,000 young people were exposed in this way.

On May 10, after a meeting at the Ministry of Energy in Sofia, Kaschiev visited his sister-in-law. Children played outside in front of the building, while adults discussed calmly. When he urged them to keep children indoors and not to let them play in the sandbox, his warning was rejected. “I was accused of trying to spread panic,” he recounts. “Someone even implied I was probably a Western agent and threatened to report me to the authorities.”

In all Eastern Bloc countries, despite often insufficient measures, the May 1 parades were maintained. In Poland also, celebrations took place as planned, while the government publicly denied any health risk. Meanwhile, Polish authorities distributed iodine tablets and limited milk sales. The rapid distribution of iodine, started on the afternoon of April 29, is often cited as an exemplary response to a radioactive emergency: within three days, 18.5 million people – adults and children – received an iodine pill.

Scientists and environmental activism

Right after the fall of the regime, Kovatchev learned more about the Chernobyl disaster and its consequences through an exhibition organized by physicists from Sofia University. Even under communism, some of them were part of informal environmental networks that would later become Ecoglasnost, an organization Kovatchev joined as a student.

Founded in spring 1989, a few months before the fall of communism, Ecoglasnost was a civic movement focused on environmental protection, born from the political liberalization climate inspired by Soviet glasnost. In autumn, Ecoglasnost organized petitions and public demonstrations, including the gathering on November 3 in Sofia, considered one of the first open civic mobilizations against the communist regime. The movement quickly expanded its demands to civil liberties and democratic reforms.

In December 1989, it became the first officially recognized non-communist political organization in Bulgaria. It then played a key role in structuring the democratic opposition by joining the Union of Democratic Forces. It also initiated the first inspections of the Kozloduy plant.

The engagement of the scientific community in environmental struggles contributed to weakening the regime in its final years. This involvement had already manifested in 1987 in Ruse, in the north of the country. At that time, atmospheric pollution from a chemical factory across the Romanian border had triggered widespread protests. From this movement arose the Ruse Public Council for Environmental Protection, the first informal organization tolerated under communism, which played a decisive role in early national mobilizations and the democratic transition.

At the same time, the discovery of radioactive “hot particles” in Bulgaria – evidence of the extent of the Chernobyl catastrophe – prompted several physicists to closely monitor the crisis and study its consequences. The Sofia University exhibition visited by Kovatchev in December 1989 was the result of this work.

Similar movements emerged in other socialist countries, such as Hungary and Czechoslovakia, combining scientific engagement with ecological and democratic awareness.

Environmental concerns became a driving element, expressing demands for responsibility and transparency. This phenomenon fueled reformist networks that later contributed to shaping Hungary’s negotiated transition to democracy.

As radiation levels increased at the end of April and early May 1986, Hungarian scientists and health professionals documented contamination and exchanged information informally, while official communication remained limited and reassuring. The growing gap between expert knowledge and public discourse created a moral dissonance among these professionals, torn between scientific integrity and loyalty to the state. In this context, environmental concerns became a driving element, expressing demands for responsibility and transparency. This phenomenon fueled reformist networks that later contributed to Hungary’s negotiated transition to democracy.

In former Czechoslovakia, the Chernobyl disaster also helped galvanize environmental movements, which subsequently became key actors in the Velvet Revolution of 1989. Although the regime was one of the most repressive in the Eastern Bloc, it tolerated more environmental activism than open political dissent, considering concerns about pollution, water contamination, or landscape degradation as relatively harmless and difficult to censor.

The second wave of contamination

Due to the lack of measures taken by Bulgarian authorities, cows, sheep, and goats continued grazing on contaminated pastures and consuming radioactive fodder until spring 1987. Dairy products from this food chain remained in circulation, causing a “second wave” of contamination estimated at nearly 30% of the total exposure. This situation – unique in the history of Chernobyl – partly explains the exceptionally high thyroid cancer rates among very young children in Bulgaria.

Retired physicist Liliana Prodanova, then a researcher at the Solid State Physics Institute, only learned of the severity of the situation in mid-May. “My husband was vice-rector of Sofia Technical University. I myself specialized in silicon research, so we understood perfectly the implications of this contamination. We took discreet precautions, like thoroughly washing foods. We also removed contaminated soil around our country house. That year, we planted nothing.”

She recalls that friends often asked them to measure the radioactivity of yogurts intended for children, using institute instruments. “We did it discreetly, without official permission.”

In contrast, the nomenklatura was fully aware of the risks. They tested the dairy products they consumed and imported the rest from abroad. On the outskirts of Sofia, the pastures around the royal palace of Vrana – then occupied by party officials – were mowed in May to prevent contamination. The hay was then redistributed to livestock cooperatives supplying the capital, which produced contaminated dairy products.

The physicists at Kozloduy plant used one of their laboratories to develop their own measuring instruments, Kaschiev recalls. They designed a device to evaluate thyroid radiation exposure. “Those who took no precautions at the beginning of May, especially those who went on vacation at that time, were exposed to contamination levels up to 10,000 times higher than ours. In early May, I stocked up on cheese and powdered milk. That probably protected us from the second wave,” he explains.

The dissenters of Chernobyl

There were no dissidents in Bulgaria before the Chernobyl accident, asserts Vatsov. “The awareness of being deceived by authorities and exposed to serious health risks shaped the political engagement of an entire generation, especially within the scientific community.”

Kaschiev, whose political engagement and professional path were shaped by the disaster, is a prime example. His anger at the moral and political failures of the regime led him to specialize in nuclear safety. From the late 1980s, he transitioned from reactor physics to risk assessment, first as an employee inside the plant, then as a university teacher and nuclear inspector. In 1997, he was appointed director of Bulgaria’s national nuclear regulation laboratory.

In other socialist countries, the Chernobyl disaster also became a catalyst for opposition to the regime. In Poland, it gave rise to a powerful anti-nuclear movement. Fears related to the disaster quickly turned into opposition to the Żarnowiec nuclear power plant project, sparking nationwide protests involving environmental groups, local activists, and dissidents such as Lech Wałęsa, future democratically elected president of the country.

During a referendum in 1990 held alongside local elections, over 86% of voters rejected the Żarnowiec project, leading to its definitive abandonment. As political scientist Kacper Szulecki notes, these mobilizations both reflected and accelerated profound social and generational transformations, while further undermining Moscow’s legitimacy in Poland.

If the disaster left a lasting mark on Bulgarian society, it did not lead to a broad anti-nuclear movement. The Kozloduy plant, modernized and still operational, is widely seen as a source of national pride and a guarantee of energy independence. The disastrous management of Chernobyl mainly highlighted the indecency and cynicism of the communist regime, as well as the irrationality of its ideology.

In December 1991, after the fall of the regime, the Sofia Supreme Court convicted former Health Minister Lyubomir Shindarov and former Deputy Prime Minister Grigor Stoichkov, accused of deliberately misleading the population, for criminal negligence. After a lengthy appeal process, their sentences were reduced to two and three years in prison respectively. They remain the only senior Bulgarian officials truly prosecuted and convicted for the management of the Chernobyl disaster.

For nuclear physicist Atanas Krastanov, a young researcher in the 1980s and witness to the regime’s mishandling of the disaster, nuclear energy itself is not the problem. “The Chernobyl accident was primarily the result of human error,” Krastanov estimates, clarifying, “it was not originally a nuclear explosion, but a thermal explosion caused by pressure buildup.” Today, Krastanov works as an expert at the Sofia City Emergency, Disaster, and Crisis Prevention Center. He recently participated in writing a documentary on the subject, scheduled for release in fall 2026.

What future for nuclear power?

Environmental activist Petko Kovatchev, close to the NGO Za Zemiata and anti-nuclear networks, disputes this interpretation: “The argument of human error is not valid,” he affirms, because “most industrial and nuclear accidents originate from human error. That does not mean nuclear power is safe.” He adds that popular support for nuclear energy in Bulgaria mainly relies on concerns about energy independence and low electricity costs, rather than scientific or ethical considerations.

In this context, the construction of a new nuclear power plant at Belene, in northern Bulgaria, could still happen. Despite strong opposition from environmental organizations and local populations, a national referendum held in 2013 approved the project. Abandoned and then revived several times – mainly for geopolitical reasons, the initial plan involving a Russian third-generation reactor – it could now be entrusted to the French company Framatome and the American General Electric.

The project to sell the already built reactors at Belene to Ukraine, aiming to replace the Zaporijjia plant currently under Russian control, was ultimately abandoned. The last government even considered making this plant a source of electricity for future data centers.

The disastrous management of Chernobyl mainly highlighted the indecency and cynicism of the communist regime, as well as the irrationality of its ideology.

Furthermore, two new reactors are planned at Kozloduy, built by Canadian companies. Commissioned in 1970, the plant now operates only its two most recent reactors, from 1988 and 1993. The older units were shut down in the 2000s under EU pressure, which conditioned Bulgaria’s accession to their closure.

Once described as one of the most dangerous nuclear plants in the world, Kozloduy now meets all safety requirements of the International Atomic Energy Agency (IAEA). The site also hosts a nuclear waste storage facility, scheduled to start operation in 2027. Environmental activists regularly denounce the lack of transparency surrounding industrial decisions, incidents, and accidents affecting the plant.

Gueorgui Kaschiev is very critical of Bulgaria’s nuclear governance. For him, the Belene project is a “financial catastrophe” and a vehicle for embezzlement of public funds. At Kozloduy, he points to deteriorating conditions: rising costs of spare parts and maintenance, reduced energy output below international recommendations, and technical failures such as leaks in the steam generator of reactor No. 6. “The safety culture is clearly deteriorating,” he warns.

This article was produced as part of the PULSE project, a European initiative supporting transnational journalistic collaborations. Andrea Braschayko, Martin Vrba, and Daniel Harper contributed to it.