This is not a composite picture, nor is it a film special effect, but a real picture recorded after the explosion of the Chernobyl nuclear power plant. This "elephant foot" thing, which is the material that gathers in the lowest pipe after the furnace core is melted down, has cooled for decades, but it still poses a fatal threat to people.
According to the photographer of this photo, the temperature of the space where the "elephant foot" is located is significantly higher than other places, and the "elephant foot" that has cooled for decades has rekindled?
"Glowing Elephant Feet"
How dangerous is the "elephant foot", why is it rekindled, and what happens after it is rekindled? If it's so dangerous, why not remove it?
<h1 class="pgc-h-arrow-right" > "elephant foot" how did it come from? </h1>
On April 26, 1986, a catastrophic accident occurred at the Chernobyl nuclear power plant near the town of Pripyat in Ukraine. Due to improper operation, the power of Reactor No. 4 surged to about 10 times the maximum design load in a short period of time, resulting in a steam explosion. The explosion tore through the reactor's roof in an instant, and the core rushed straight out of the plant, exposing it to the atmosphere, releasing a large number of radioactive particles and gaseous debris such as cesium-137 and strontium-90.
The Chernobyl nuclear power plant exploded instantly
After the explosion, the high temperature of thousands of degrees in the reactor melted the core fuel, and after 95% of the core was burned by the high temperature, it corroded the ground and pipelines like "strong acid", and continued to spread to the lower layer, and finally condensed in the pipe of corridor 217 on the lowest level, forming this "elephant foot".
How dangerous is < h1 class="pgc-h-arrow-right" > "elephant foot"? </h1>
At the time of the explosion, the irradiation intensity of the roof of the steam turbine reached 20,000 roentgen, the irradiation intensity of the reactor that was blown up was as high as 30,000 roentgen, and the irradiation intensity of the "elephant foot" condensed below also reached 8,000 roentgen.
Roentgen is a unit of irradiation produced by a radioactive substance proposed by the German physicist Wilhelm Roentgen. What is the concept of irradiation for tens of thousands of roentgen? The roentgen measuring instrument has a peak of only 3.6, and once this value is exceeded, it will cause harm to the human body. The intensity of irradiation in a place reaches more than 10,000 roentgen, and people will die after staying here for 3 minutes, and 15,000 röntgen irradiation can kill people invisibly in just 2 minutes. With an irradiation intensity of 8,000 roentgen, people will also die within 4 minutes. Even if you only stand here for a few seconds, it will cause irreversible damage to your body.
The harm of radiation to the human body
So this "elephant foot" is a huge source of radiation. Its main components are silica, as well as trace amounts of uranium, titanium, zirconium, magnesium and graphite. Although uranium-containing particles are unevenly distributed, the mass of radioactivity is evenly distributed.
The person who took the photograph, Artur Konev, was the one who took the picture. Korneyev) was interviewed by The New York Times before retiring. In 1996, he was the chief deputy director of the project to detect "elephant feet", and after entering the room alone, he took this photo of him with "elephant feet" with an automatic camera and flashlight. The ghost flash is shown in the photo because he used long exposure to shoot.
"Elephant Feet"
When Konev tested the elephant's foot, it had cooled down for 10 years, and the irradiation volume was not so high, but it still caused some effect on Konev's body, and when the reporter interviewed him, the 65-year-old looked very weak and had cataracts in his eyes.
What happens if <h1 class="pgc-h-arrow-right" > "elephant foot" rekindles? </h1>
In May 2021, the journal Science published an article that left people to worry.
The article says that the "elephant feet" buried deep under the reactor are once again smoldering, like embers in a barbecue pit. At present, Ukrainian scientists are testing to determine whether the phenomenon will disappear on its own, or to intervene manually to prevent it from burning again and causing an explosion.
Scientists inside the nuclear power plant
Researchers at Ukraine's Kiev Nuclear Power Plant Safety Institute said that when they reported on the dismantling of the reactor, sensors tracked a lot of neutrons, and the number of neutrons is slowly rising, which is the fission signal of nuclear material, which flows from the room where the "elephant foot" is located. The reason for the rise in neutrons is that rainwater seeps into this room.
So the "elephant foot" will be rekindled, which is actually caused by rain. Although engineers likened it to embers in a barbecue pit, it wasn't really like embers, where the rain went out as soon as it was poured. Conversely, the closer the rain gets to it, the easier it is to be rekindled.
Inside the nuclear power plant
The principle is probably that the process of nuclear fission is generally the splitting of heavy nuclei into two or more atoms of less mass. Taking the most common uranium fission in nuclear power plants as an example, after the hot neutron bombards the nuclear raw material uranium-235 atom, it will release 2 to 4 neutrons, and these neutrons will hit other uranium-235, forming a chain reaction.
The neutrons released by nuclear fission move very fast, and it needs to be slowed down to increase the chances of them hitting atoms, which can trigger more nuclear fission. Therefore, nuclear power plants will use moderators to slow down the movement of neutrons, and there are many kinds of moderators, one of which is heavy water.
Nuclear fission process
Heavy water is deuterium oxide, and its relative molecular mass is 11% heavier than water. The chemical properties of heavy water and ordinary water are very similar, and the electrolysis rate is smaller than that of ordinary water. Light water, that is, ordinary water, can also be used as a moderator, but light water will absorb neutrons, so light water reactors can only use enriched uranium, not ordinary uranium.
The uranium-235 used in nuclear power plants is enriched uranium, so it can be used as a slow agent with light water.
After the reactor exploded, the slow agent also no longer continued to provide deceleration "services" for nuclear raw materials, so the high-speed neutrons in the "elephant foot" had lost a lot and could no longer stimulate new chain reactions.
The arrival of the rain is about equivalent to resupplying the "elephant foot" with a slow agent and activating the weak chain reaction again. When the chain reaction is activated, the nuclear fission is restarted, and if the fission reaction is out of control, it will explode again.
The fission reaction is out of control
<h1 class="pgc-h-arrow-right" > how do I get it to go out again? </h1>
If the fission reaction is not out of control, then the nuclear fission will gradually stop after the rain close to the "elephant foot" is dried up. But if there is always water inside, or it rains all the time, the threat will always be there, and human intervention will be required.
The way to intervene manually is to spray the gadolinium nitrate solution inside. Gadolinium nitrate is a monoclinic columnar crystal, easily soluble in water and acetic acid, it has deliquebility, not only can absorb water vapor in the water, but also can absorb water in the air. Simply put, it is sprayed in the reactor, it can play a role in absorbing water, and every time it rains, it can reduce the chance of fission reaction restart.
Gadolinium nitrate
In June 1990, a heavy rain fell on the plant, and a Chernobyl scientist risked radiation to enter the reactor hall and spray gadolinium nitrate. A few years later, an automatic gadolinium nitrate sprinkler was installed here, but because the sprayed solution could not effectively penetrate into the ground, there was still some water in the place where the "elephant foot" was located, and the water inside could not evaporate quickly, mainly because there was a huge sarcophagus above the No. 4 reactor.
The sarcophagus was built a few months after the accident, and in order to prevent further release of radioactive material, the Soviets hastily built a sarcophagus to seal off the 200 tons of high-lying material in reactor 4. But now, due to radiation and other factors, the sarcophagus has aged so badly that even if it was reinforced once in 2008, it will only be used until 2023.
Old Sarcophagus
The current sarcophagus not only has the risk of radiation leakage, but also cannot block the rainwater, and every time it rains, there will be rainwater infiltration, and it also affects the evaporation of water. So the Ukrainian Chernobyl Nuclear Power Plant Company is ready to dismantle this sarcophagus and install a new safety enclosure, the steel coffin.
The steel coffin is a huge grid structure of steel pipes supported by two longitudinal concrete beams. The steel pipe was completed in 2016, commissioning was completed in 2019, and it is expected to dismantle the sarcophagus and install the steel coffin in 2023.
But for now, unstable "elephant feet" will be the most difficult challenge when installing steel coffins in Ukraine. Perhaps they will use some robots that can hold up the radiation to spray gadolinium nitrate at the "elephant's foot", or directly absorb the neutrons in it to reduce its threat.
Steel coffin
The Chernobyl accident was the worst nuclear accident in history, and 35 years ago, it had already buried many lives and normal lives. Now, none of us want the Elephant Foot to be active again, causing a new explosion accident, and hope that Ukraine can successfully solve this crisis.