May 12, 2021
Nuclear reactions have been discovered smouldering ‘like embers at a barbecue’ in an inaccessible chamber at Chernobyl, according to scientists.
A surge in neutrons have been observed in a chamber known as Subreactor Room 305/2, 35 years after the catastrophic nuclear disaster.
Neutrons are particles in an atom, and are a signal of fission – the splitting of an atomic nucleus resulting in the release of large amounts of energy.
Scientists may be required to intervene at the chamber, which hasn’t been entered since the disaster, to potentially avoid another explosion.
‘We have only assumptions,’ Maxim Saveliev at the Institute for Safety Problems of Nuclear Power Plants (ISPNPP) in Kyiv, Ukraine, told Science Magazine.
‘There are many uncertainties, but we can’t rule out the possibility of an accident.’
Neil Hyatt, a nuclear materials chemist at the University of Sheffield, said the situation was like ‘the embers in a barbecue pit’.
‘It’s a reminder to us that it’s not a problem solved, it’s a problem stabilised,’ he said.
The scientists are using sensors to track a rise in the number of neutrons in the chamber, but they’re rising slowly, suggesting there are still have a few years to figure out how to stifle the threat, according to Science Magazine.
The Chernobyl disaster occurred on April 26, 1986, at unit number four in the Chernobyl Nuclear Power Plant, near the Ukrainian city of Pripyat.
The staff on duty made errors during a safety test that triggered the nuclear reactor’s explosion – a fatal mistake documented in a recent HBO series.
The explosion blanketing the western Soviet Union and Europe with radiation – leading to the largest man-made environmental disaster in history – and the largest ever nuclear disaster.
More than 100,000 people were evacuated and a 20-mile exclusion zone was established that still exists today.
At the time, emergency crews responding to the accident used helicopters to pour sand and boron on the reactor debris to extinguish fires.
The sand melted with uranium fuel rods and their zirconium cladding, as well as graphite control rods, to form a lava.
The lava flowed into the reactor hall’s basement rooms and hardened into highly radioactive formations called lava-like fuel containing materials (LFCMs).
A few weeks after the accident, the crews completely covered the damaged unit in a temporary concrete structure, called the ‘sarcophagus’, to limit further release of radioactive material.
The Soviet government also cut down and buried about a square mile of pine forest near the plant to reduce radioactive contamination at and near the site.
But the problem is the sarcophagus allowed rainwater to seep in, which can send neutron counts soaring.
The plant has since installed sprinklers that emit gadolinium nitrate, which absorbs neutrons – but they can’t penetrate some basement rooms.
In 2016, the New Safe Confinement (NSC) – a massive structure built to confine the remains of the number 4 reactor unit – was installed over the sarcophagus, keeping out rain.
Since then, neutron counts in most areas have been stable or are declining – but not in subreactor room 305/2, where they’ve mysteriously nearly doubled in four years.
‘It’s just not clear what the mechanism might be,’ said Hyatt – but there’s the concern the chamber could become more of a threat as it gets dryer, leading to an uncontrolled release of nuclear energy.
While any explosive reaction would be contained by the NSC, it could threaten to bring down unstable parts of the ageing sarcophagus, filling the NSC with radioactive dust.
There’s no chance of a repeat of the catastrophic explosion, which killed two reactor employees at the scene and hospitalized another 134 with acute radiation poisoning.
But experts are considering sending in a specially-developed radiation resistant robot that could insert boron cylinders, which would sop up neutrons.