By Jonny Lupsha, Wondrium Staff Writer
Forest fires near the Chernobyl disaster site have spiked local radiation levels, CNN reported. Over 100 firefighters have responded to douse the blazes in the Ukraine near the site of the 1986 nuclear accident. Reactor design attributed to causing the Chernobyl disaster.
According to CNN, the fire that broke out in the Chernobyl exclusion zone spread across 50 acres and increased radiation levels, which are measured in microsieverts per hour (μSv/h). “A total of 124 firefighters, two An-32P planes and an Mi-8 helicopter are battling the largest blazes, and have carried out 42 water drops in the area,” the article said. “The maximum allowable amount of natural background radiation is 0.5μSv/h, the emergency services said, but [head of Ukraine’s ecological inspection service Egor] Firsov’s reported amount was nearly five times that.”
It’s been established that the Chernobyl nuclear accident was the result of a mishandled safety test and that its effects were long-lasting and far-reaching. However, the disaster site was also set up for failure beforehand.
Core Size Design
The nuclear reactor at Chernobyl was built differently and for different purposes than many other nuclear reactors.
“First off, it’s a lot bigger than the submarine-influenced light water reactor designs in the United States, and it was too large for a convenient containment structure,” said Dr. Lawrence Weinstein, Professor of Physics at Old Dominion University. “The core was 46 feet in diameter and 23 feet high; and it’s not just the 23-foot height of the core, but there were 12-foot-long fuel rods that were inserted vertically, so it needed a lot more height than that.”
Dr. Weinstein said that the moderation in the core was mostly done by carbon, leaving the cooling water in the core to absorb neutrons. As the amount of water decreases, there’s less moderation but also less absorption of neutrons.
“That’s positive feedback, which is bad,” he said. “Chernobyl, in fact, had net positive feedback and that’s very bad.”
Control Rod Problems
The overall size of the Chernobyl reactor wasn’t the only problem that led to its catastrophic failure. Additionally, it had a problem related to the vertically-removed fuel rods.
“The control rods were removed by lifting them upwards,” Dr. Weinstein said. “To keep the water from filling the control rod channel—and water, as I said, absorbs neutrons—they had a graphite displacer. So we had this long control rod and underneath it, there was a chunk, another long rod, of carbon, but there was about 1.25 meters, about four feet, of water at the bottom of the control rod channels.”
However, Dr. Weinstein said, as soon as workers pushed in a control rod, it would displace the water. Displacing that water with carbon meant that neutrons that needed to be absorbed by water weren’t being absorbed by carbon.
“The other problem was that the rods moved very slowly,” he said. “It took 18 seconds to insert it, which in a reactor time, is an eternity. It took a very long time for the rods to move all the way in.”
The faulty designs of the reactor and the botched safety test that followed led to the world’s worst nuclear disaster in human history. As we’re seeing nearly 35 years later, fires in the area still cause radiation levels to spike well above safety levels.
Dr. Lawrence Weinstein contributed to this article. Dr. Weinstein is a Professor of Physics at Old Dominion University and a researcher at the Thomas Jefferson National Accelerator Facility. He received his undergraduate degree from Yale University and his doctorate in Physics from the Massachusetts Institute of Technology.