When the Chernobyl Nuclear Power Plant in Ukraine caught fire 35 years ago, it caused the world’s worst nuclear accident, spreading fallout as far afield as Northern Ireland, Wales, Scotland, and northern England.
Desperate Soviet officials encased the ruined reactor in a thick concrete “sarcophagus” to prevent more radioactive contamination spreading from the wreckage of the power plant’s No. 4 reactor. In 2010, a second shield was built around the reactor to prevent deadly leakage.
But now, it appears that nuclear reactions are starting up spontaneously inside the containment shield.
The fire is restarting “like the embers in a barbecue pit,” says Neil Hyatt, a nuclear materials chemist at the University of Sheffield.
A sealed room deep within the reactor is putting out a small, but steadily increasing stream of neutrons, a tell-tale sign that nuclear fission is taking place within the reactor.
One of the most significant issues for scientists trying to contain the radioactive contamination is rainwater. During heavy storms the water penetrates the shielding, causing deadly radioactivity to leach into groundwater.
In June 1990 one scientist risked his life by dashing into the reactor hall and spraying radiation-absorbing gadolinium nitrate solution onto part of the reactor that threatened to go critical.
But beyond these desperate fire-fighting measures, the Ukrainian authorities have no clear plan on how to prevent a new meltdown.
There has been a long-standing plan to remove the reactor’s fuel cells, FCMs, and store them deep underground.
The European Bank for Reconstruction and Development has offered to finance the complex and hazardous procedure – but as long as the “embers” of the fire continue to heat up, the operation is on hold.
Maxim Saveliev, from Ukraine’s Institute for Safety Problems of Nuclear Power Plants, told Science magazine that it would be dangerous to try to dismantle the sealed reactor to establish exactly what’s happening.
“There are many uncertainties,” he said, “but we can’t rule out the possibility of [an] accident.”
Worst of all, scientists still aren’t quite sure why the nuclear reaction is restarting: “It’s just not clear what the mechanism might be,” says Hyatt.