Nuclear Reactions at Chernobyl Are Spiking in an Inaccessible Chamber

Scientists monitoring the ruins of the Chernobyl nuclear power plant in Ukraine have seen a surge in fission reactions in an inaccessible chamber within the complex. They are now investigating whether the problem will stabilise or require a dangerous and difficult intervention to prevent a runaway nuclear reaction. From a report: The explosion at Chernobyl in 1986 brought down walls and sealed off many rooms and corridors. Tonnes of fissile material from the interior of a reactor were strewn throughout the facility and the heat it generated melted sand from the reactor walls with concrete and steel to form lava-like and intensely radioactive substances that oozed into lower floors. One chamber, known as subreactor room 305/2, is thought to contain large amounts of this material, but it is inaccessible and hasn't been seen by human or robotic eyes since the disaster.

Now, researchers have seen a spike in neutron emissions from the room, with levels increasing around 40 per cent since the start of 2016. This points to a growing nuclear fission reaction, so researchers are trying to determine if this surge will fizzle out, as previous spikes in other parts of the ruins have done, or whether they will need to find a way to access the room and intervene. Neil Hyatt at the University of Sheffield, UK, who studies nuclear waste disposal, likens the situation to 'embers in a barbecue pit' and says 'it's a reminder to us that it's not a problem solved, it's a problem stabilised.'

One suggestion for why this is happening is that a new structure placed over the ruined reactor in 2016 is causing the plant to dry out. When uranium or plutonium fuel decay radioactively, they emit neutrons, which can promote a fission reaction if the neutrons are captured by another radioactive nuclei. However, large amounts of water slow these neutrons down, preventing them from being captured. The original shelter, which was hurriedly constructed over the reactor in the months following the accident, was riddled with holes that allowed rainwater and birds inside. If the rainwater was helping to suppress reactions in room 305/2, its absence due to the new structure could mean there is no longer enough water in the room to sufficiently slow neutrons down.

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