Ukraine's President Petro Poroshenko placed flowers at a memorial in Kyiv Tuesday honoring the "Heroes of Chernobyl" following the 1986 nuclear power station disaster (photo).

Church bells rang and mourners laid flowers at Chernobyl's memorial square as the clock turned 1:23 am, the time when the plant's reactor number four exploded in April 1986.

"There was crying and screaming," local pensioner Maria Urupa told AFP as she recalled the terror that struck locals as they watched poisonous clouds of radiation waft in from the plant thirty years ago.

A UN report in 2005 estimated that "up to 4,000" people could eventually perish from the invisible poison in Ukraine and neighboring Russia and Belarus.

The exact number of dead remains a subject of intense debate because the Soviet authorities kept most of the information about the disaster hidden.

Global donors

The EU was among the global donors that promised an additional 87.5 million euros ($99 million) to help secure the Chernobyl nuclear power plant, as the Ukrainian government began marking 30 years since the disaster.

The money will go toward the construction of a new spent nuclear waste storage facility, adding to the 2 billion euros already donated to helping clean up and secure the site. Ukraine still needs 15 million additional euros to be able to safely store hazardous materials underground.

"It's an important project for the world as well as, of course, for Ukraine and Ukrainians," said Suma Chakrabarti, chief of the European Bank for Reconstruction and Development (EBRD), the organization in charge of the project.

A tragic anniversary

The announcement came as Ukraine commemorated the worst nuclear disaster in history. On April 26, 1986, a failed test triggered a nuclear meltdown that sent atomic radiation billowing into the atmosphere and forced tens of thousands from their homes.

The then Soviet-Ukraine government tried to behave as if nothing had happened in the immediate aftermath, worried that a disaster might tarnish its image. People in the vicinity of the reactor were not even told to evacuate until 36 hours after the meltdown.

The immediate meltdown and long-term impact radioactive exposure left an unknown number of people dead and sick. A controversial UN report published in 2005 put the number of dead at around 4,000.

The Soviet government drafted around a half a million civilian and military personnel, so called "liquidators," to respond and clean up the disaster. A UN Scientific Committee on the Effects of Atomic Radiation later reported that nearly 30 percent of those people died from radiation exposure.

Structure to prevent leaks

The anniversary comes as a new giant 1.5 billion euro ($1.7 billion) steel structure is set to be placed over the nuclear reactor this year to prevent leaks. The old structure was hastily put together after the meltdown, prompting concern its collapse could create another disaster.

More than 40 governments contributed to the giant steel dome, which will protect the 2000 tons of radioactive uranium inside the reactor for the next 100 years.

The dome, even if it lasts a century, is a temporary solution in terms of radioactive half-lives. A 2,600 square km (1,000 square miles) radioactive no-go zone remains around Chernobyl.

The Chernobyl disaster sparked an entire anti-nuclear and environmental movement, while leading to a halt in new nuclear power construction in many countries. As a result, some current nuclear power plants have aging nuclear reactors built in the 1960s and '70s.

The UN atomic watchdog used the anniversary to warn of "complacency" in nuclear safety. Even after improvements in safety following the 2011 Fukushima disaster in Japan, IAEA head Yukiya Amano said on Tuesday that the take away from both disasters "is that safety can never be taken for granted."

Another scare

Ukrainian President Petro Poroshenko claimed Tuesday that Russia nearly caused a new disaster reminiscent of Chernobyl by waging war near a power plant in eastern Ukraine.

"Let us not forget that hostilities were held several hundred kilometres from the power plant in Zaporizhia," Poroshenko said in his speech Tuesday.

Moscow has repeatedly denied Kyiv's accusations that it has provided active troops or weapons to the rebels.

blc/cw/jr/jbh (dpa, AFP, Reuters)