Ukraine: Chernobyl power cut could see failure of safety programme says Sheffield expert Claire Corkhill

Professor Claire Corkhill, who is Chair in Nuclear Material Degradation in the University of Sheffield's Department of Materials Science and Engineering, was speaking after Ukrainian authorities said the site of the world's worst nuclear disaster had been knocked off the power grid.

Emergency generators are now supplying back-up electricity as the state communications agency said the outage could put systems for cooling nuclear material at risk.

Prof Corkhill said: "With the electricity supply to the Chernobyl site unavailable there are several areas of concern with regards to the safety of the nuclear material stored there."

She explained that spent nuclear fuel from reactors 1 and 3 requires constant cooling, which is achieved by pumping fresh cool water into the ponds where it is stored.

With no power supply, this water could slowly evaporate, potentially resulting in contamination of the building by low levels of radioactive isotopes.

And, she said, it is essential that radiation monitoring systems are able to monitor the situation inside reactor 4 constantly "so that we can be aware of any potential reasons for concern about the exposed nuclear fuel inside".

Prof Corkhill said: "Another serious concern is the maintenance of the ventilation system in the New Safe Confinement structure.

"This prevents further degradation of Reactor number 4 and the hazardous exposed nuclear fuel within, and is essential to the future decommissioning of the site.

"If there is no power to this structure, we could see the complete failure of the 1.5 billion euro (£1.25 billion) decommissioning programme to make the site safe once and for all."

Prof Corkhill's research focuses on understanding the long-term evolution of radioactive waste material in disposal environments and she provides independent advice to the UK government's radioactive waste management and disposal policies.

She is leading a British team that is making a key contribution to the huge clear-up operation at the stricken Fukushima nuclear power station in Japan after developing material that simulates the most dangerous radioactive debris remaining in the reactors.

The Chernobyl site has been under the control of Russian troops since last week.

The cause of the damage to the power line serving it was not immediately clear

Ukrainian grid operator Ukrenerho said that, according to the national nuclear regulator, all Chernobyl facilities are without power and the diesel generators have fuel for 48 hours.

Without power the "parameters of nuclear and radiation safety" cannot be controlled, it said.

Foreign Minister Dmytro Kuleba said the grid supplying electricity is damaged and called for a cease-fire to allow for repairs.