After 35 years, Chernobyl's underground material has rekindled. Is it going to explode again?

Nuclear power is a technology that makes nuclear fission controllable and used for power generation. Generally speaking, nuclear power is a clean and efficient way to obtain energy, but once an accident occurs, it often brings catastrophic consequences.

According to the severity, nuclear leakage accidents can be divided into seven levels. In human history, there have been two level 7 nuclear leakage accidents, one is the famous Chernobyl nuclear power plant accident, and the other is the Fukushima nuclear power plant accident in Japan. On the surface, the former was caused by human factors, and the latter was caused by natural factors, but in the final analysis, the root cause of both accidents is still human. If it were not for the error in site selection, why would the Fukushima nuclear power plant leak due to the earthquake, and why would it cause such serious consequences after the accident?

The impact of the nuclear power plant accident is far-reaching. To this day, 35 years have passed since the Chernobyl nuclear power plant accident, but it can still be said to be a forbidden zone for life. Moreover, not long ago, Ukrainian scientists discovered through tests that radioactive substances underground in Chernobyl have rekindled.

Where did the radioactive material under the Chernobyl Nuclear Power Plant come from? The nuclear power plant uses controlled nuclear fission technology, and nuclear fission, in simple terms, is to bombard uranium 235 with neutrons. After uranium 235 absorbs a neutron, it will undergo fission to generate new substances and release three neutrons. The released neutrons will combine with other uranium 235 to further trigger fission. This is a chain reaction. So how can nuclear fission be controlled? According to the principle of nuclear fission, the intensity of nuclear fission depends on the number of neutrons, so to control nuclear fission, we must first control the number of neutrons.

Nuclear power plants will insert a control rod into the reactants. This control rod can be used to absorb neutrons. By plugging and pulling out the control rod, the number of neutrons can be controlled, thereby achieving control of nuclear fission.

The Chernobyl nuclear power plant accident was caused by an operational error. The control rods were not inserted in time, which led to overheating and the melting of the fuel rods, which caused the explosion. After the explosion, a large amount of core fuel corroded the ground and pipelines like a strong acid, and finally gathered and condensed in the bottom pipeline, forming what we call a pile of solid radioactive materials. How strong is the radioactivity of this pile of material? Up to 8,000 roentgens. Roentgen is a unit of radiation produced by a radioactive substance.

Generally speaking, the upper limit of unnatural radiation that a person can withstand in a year is 1 roentgen, and the amount of radiation we receive from a CT scan in the hospital is about 6.9 roentgen.

In comparison, we know how terrible 8000 roentgens is. In such an environment of radiation, even if you stay there for just a few seconds, it will cause irreversible damage to your body. This damage may not be noticed immediately, but it will have a long-term impact on your health. If you stay in an environment of 8000 roentgens for 4 minutes, you will die on the spot. Originally, the pile of radioactive materials under Chernobyl has gradually cooled down over the long years, but now it has reignited, and the fission reaction has once again occurred inside the pile of materials. Affected by the reaction, even the temperature of the space where the pile of materials is located is significantly higher than other places.

Why does the cooled material reignite? The reason is actually not that complicated. The culprit is rain.

Water is an indispensable member of nuclear fission reactions, and its role is to act as a moderator. The so-called moderator is used to slow down the speed of reaction neutrons, thereby increasing the probability of neutrons hitting atoms. So when rain comes, it is equivalent to adding a moderator to the already cooled reactants, so the probability of neutrons hitting atoms increases, and the reactants become hot again. Where does the rain come from? After the Chernobyl Nuclear Power Plant accident, the Soviet Union built a sarcophagus above the No. 4 reactor where the accident occurred to seal radioactive materials. However, over time, the sarcophagus aged and rainwater seeped in.

The underground material in Chernobyl has reignited. Is there a possibility of another explosion?

It is hard to say at the moment. Ukrainian scientists are conducting further tests to determine whether there is a risk of explosion. The best way to eliminate the danger is to let the rekindled material cool down again. To this end, two measures have been taken. One is to prepare to absorb moisture by spraying gadolinium nitrate solution to keep the reactants dry, and the other is to build a new steel coffin to replace the dilapidated sarcophagus to prevent rainwater from continuing to seep in. The steel coffin was built in 2016 and is expected to be installed in 2023 to replace the original sarcophagus. Whether it is Chernobyl or Fukushima, the lessons they have brought to mankind are painful. But there is no need for us to talk about nuclear color change, because the two accidents are essentially caused by human factors. As long as humans can learn lessons and continuously improve the construction and management of nuclear power plants, nuclear power will still be a clean and efficient energy source.

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