Global donors on Monday pledged additional money to help Ukraine keep Chernobyl safe for generations after causing the world's worst nuclear power disaster 30 years ago.

The 87.5-million-euro ($99 million) commitment toward the construction of a new spent nuclear waste storage facility comes on the eve of the former Soviet republic's commemoration of an accident whose death toll remains in dispute to this day.

Ukraine will still need to find an additional 15 million euros for the underground site to be able to start safely storing the hazardous material in metal caskets by the end of the year.

"It's an important project for the world as well as, of course, for Ukraine and Ukrainians," said Suma Chakrabarti, head of of the European Bank for Reconstruction and Development (EBRD), which is spearheading the project.

Three of Chernobyl's four reactors continued churning out power and creating spent nuclear fuel for 16 years after the April 26, 1986 accident.

An additional 200 tonnes of uranium remain inside the damaged reactor number four, raising fears there could be more radioactive leaks if the ageing concrete structure covering the stricken reactor collapses.

Work began in 2010 on a new 25,000-tonne steel protective barrier that will surround the existing sarcophagus by next year.

Funding for that dome, which costs more than 2.1 billion euros, is mostly in place, although it remains unclear who will pay for its upkeep and operations.

Three decades after the tragedy, which the Soviet authorities spent weeks trying to cover up, the number of people who have died from radiation poisoning remains a matter of intense dispute.

A UN report published in 2005 estimated that "up to 4,000" people could eventually perish from Chernobyl's aftereffects in Ukraine and neighbouring Russia and Belarus.

The following year, the Greenpeace environmental protection group branded the figure a gross underestimate.

The United Nations Scientific Committee on the Effects of Atomic Radiation officially recognised around 30 deaths among those sent to fight and contain the disaster in the days following the blast.