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Part 1 of 2 Parts
“The Chernobyl disaster was a nuclear accident that occurred on Saturday 26 April 1986, at the No. 4 reactor in the Chernobyl Nuclear Power Plant, near the city of Pripyat in the north of the Ukrainian SSR in the Soviet Union. It is considered the worst nuclear disaster in history both in terms of cost and casualties and is one of only two nuclear energy accidents rated at seven—the maximum severity—on the International Nuclear Event Scale, the other being the 2011 Fukushima Daiichi nuclear disaster in Japan. The initial emergency response, together with later decontamination of the environment, ultimately involved more than 500,000 personnel and cost an estimated 18 billion Soviet rubles—roughly US$68 billion in 2019, adjusted for inflation.” Wikipedia
When part of the Unit Four reactor’s core melted down, the uranium fuel rods with their zirconium cladding, the graphite control rods and the sand that was dumped on the core in an attempt to quench the fire melted together in a lava. This lava flowed down into the basement rooms of the reactor hall and solidified into formations that were referred to as fuel-containing materials (FCMs). These FCMs contained about one hundred and seventy tons of irradiated uranium representing about ninety five percent of the original fuel load in the reactor.
A concrete and steel sarcophagus called the Shelter was constructed a year after the accident to contain the remains of the Unit Four reactor. Unfortunately, the Shelter allowed rainwater to seep into the ruins. Water acts as a moderator for nuclear process and slows down neutrons. This increases the chances of the neutrons impacting and splitting uranium nuclei. Sometimes, in heavy rainstorms, the emission of neutrons would show a huge increase. A scientist at Chernobyl who risks radiation exposure by entering into the damaged reactor hall is referred to as a “stalker.” After an especially severe storm in June of 1990, a stalker entered the reactor hall and sprayed gadolinium nitrate solution on an FCM to absorb neutrons. He and the other scientists that he worked with were afraid that that FCM might have gone critical (started a self-sustaining nuclear fission process). A few years after that, special sprinklers that sprayed the gadolinium nitrate solution were installed in the roof of the Shelter. Unfortunately, the spray from the sprinklers could not penetrate into some of the basement rooms.
In November of 2016, a massive New Safe Confinement (NSC) was slid over the old Shelter cover. The NSC cost one hundred and eighty billion dollars. It was intended to eliminate the possibility of a criticality and to seal of the Shelter so it could be stabilized and ultimately dismantled. The NSC also keeps out the rain and neutron counts in most parts of the Shelter have been stable or declining since it was installed.
Contrary to expectations, the neutron count began to increase in a few spots. In room 305/2, the neutron count almost doubled in four years. The room contains tons of FCMs buried under debris. The Institute for Safety Problems of Nuclear Power Plants (ISPNPP) modeling suggested that when the fuel in the FCMs dried out, somehow the neutrons bounced around more rather than less and split more uranium nuclei. Neil Hyatt is a nuclear materials chemist at the University of Sheffield. He said, “It’s believable and plausible data. It’s just not clear what the mechanism might be.”
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