Part 2 of 2 Parts (Please read Part 1 first)
Thirty-five years after the accident at Chernobyl, nuclear fission reactions are smoldering in the buried FCMs inside of room 305/2. Neil Hyatt said that “It is like embers in a barbecue pit.” Ukrainian scientists are working hard to determine whether the reactions will quench themselves or whether extraordinary interventions will be needed to prevent another nuclear accident.
Sensors are tracking a rising number of neutrons which is a signal of nuclear fission in room 305/2 which is currently inaccessible. Anatolii Doroshenko works at the Institute for Safety Problems of Nuclear Power Plants (ISPNPP) in Kyiv, Ukraine. He reported the growing neutron flux problem at discussions last week about plans to dismantle the Unit Four reactor. Maxim Saveliev also works at the ISPNPP. He said, “There are many uncertainties. But we can’t rule out the possibility of [an] accident.” Saveliev says that the neutron count is rising slowly and he feels that the managers of Chernobyl have a few years to figure out how to deal with the threat. Japan is watching the activities at Chernobyl with great interest because they are currently coping with the aftermath of the Fukushima nuclear disaster in 2011. Hyatt said that “It’s a similar magnitude of hazard.”
The threat of another disaster at Chernobyl cannot be ignored. As water in the ruins continues to recede, Hyatt says that “the fission reactions accelerate exponentially,” leading to “an uncontrolled release of nuclear energy.” Fortunately, there is no chance of a repeat of 1986 when the explosion and fire sent a cloud of radioactive particles over Europe. If a runaway fission reaction started in an FCM, it could sputter out after the heat generated by fission boils off the remain water. Saveliev notes that although any explosive reaction would be contained, it could still cause the collapse of unstable parts of the decrepit Shelter which would fill the NSC with radioactive dust.
Dealing with the new threat at Chernobyl is a serious challenge. The high radiation levels in room 305/2 prevent the installation of sensors. Spraying the gadolinium nitrate solution is not possible because the FCSs in the room are entombed under concrete. One suggestion is to construct a robot that is able to withstand the intense radiation long enough to drill holes in the FCMs and insert boron cylinders. These cylinders would act like control rods and absorb neutrons. Before any such steps are taken, the ISPNPP intends to increase monitoring of two other areas where the FCMs have the potential of criticality.
The possibility of critical fission reactions are not the only challenge facing the managers of Chernobyl. Attacked by intense radiation and high humidity, the FCM are disintegrating. This is generating more radioactive dust that complicates plans to dismantle the old Shelter. Early in the work on FCMs, a formation called the Elephant’s Foot was found to be so hard that scientists had to use the fire from a Kalashnikov rifle to break off a piece for analysis. Saveliev says that that sample now has the consistency of sand.
Ukraine has long held the intention to remove the FCMs and store them in a permanent geological repository. With assistance of from the European Bank for Reconstruction and Development, Ukraine hopes to have a comprehensive plan for Chernobyl by September of this year. However, with fission still flickering inside the Shelter, it may be harder than ever to bury the reactor’s active remains.