Scientists recorded nuclear reactions occurring under a new confinener, which isolates the destroyed reactor of the Chernobyl NPP. Potential danger is a buried uranium fuel mass, and researchers are trying to establish whether the reaction will be ceased by itself or urgent measures will be required. This is reported in an article published in the SCIENCE journal.
According to Anatoly Doroshenko from the Institute for the Safety Problems of Nuclear Power Plants, the sensors track the growing amount of neutrons indicating the flow of nuclear fission reactions. Experts cannot exclude a new accident, but the neutron flux grows slowly, and may pass for several years before the worst scenario can be realized. During this time, scientists hope to come up with measures to counteract the threat.
April 26, 1986, when part of the active zone of the fourth block was melted, uranium fuel rods, their zirconium sheath, graphite regulating rods and sand used to extinguish the fire, formed Corimon – lavetling fuel-containing material (TCM) or “Nuclear Lava” . It is a passage to the basement rooms of the reactor hall, where he froze, forming a “elephant leg” – an extremely radioactive mass, the presence next to which for 10 minutes may be fatal. In general, Chernobyl Corimary contains 170 tons of radioactive uranium, but with time, radioactivity decreases.
The problem is that the first insulating structure, called “shelter”, allowed rainwater to seep inside. Water slows down neutrons, increasing the likelihood of their interaction with uranium nuclei, which led to a sharp increase in the neutron flow as a result of decay. At first they coped with this, spraying the nitrates of the gadolinium, absorbing neutrons, but the spray could not penetrate the basement. It was believed that the new safe confinement stabilizes the situation, but in some places the stream of neutrons continued to grow. For example, indoors 305/2, where tons of TSM are buried under the rubble, the neutron flux has doubled in four years.
Models have shown that radioactivity growth is associated with TCM drying, which is a paradoxical method increases the likelihood of absorption of uranium nuclei of free neutrons. Experts fear that the fission reaction will accelerate exponentially. What will lead to uncontrolled release of nuclear energy. It threatens the collapse of the “shelter” and filling the space under confinement with radioactive dust.
One of the ideas is to develop a robot that can withstand intensive radiation long enough to drill holes in TSM and insert cylinders with boron that will absorb free neutrons.