The question of what exactly is hidden under the massive concrete and steel structures of the Chernobyl nuclear power plant has haunted the minds of scientists and the public for decades. After the 1986 disaster, the fourth power unit was mothballed, but the processes inside it did not stop immediately. Reactor core underwent enormous changes, turning into a complex mixture of molten fuel, graphite and structural materials.
Today, almost 40 years later, processes that require constant monitoring continue under the “New Safe Shelter” (NBU). Chernobyl sarcophagus It not only covers the destroyed reactor, it isolates a gigantic volume of radioactive dust and debris that has accumulated over the years of operation and accident. Understanding what's going on underneath the surface is critical to assessing long-term risks.
Many people think of a reactor as just a hot pile of metal, but the reality is much more complex. Inside are corium arrays - radioactive lava that burned through the concrete and froze in bizarre shapes. The study of these structures makes it possible to predict the behavior of radioactive materials in the future and plan the final liquidation of the consequences of the accident.
The structure of the destroyed reactor and the "Elephant's Foot"
Directly under the arches of the old sarcophagus, built in 1986, is what remains of the RBMK-1000 reactor hall. The explosion tore off the reactor cover and scattered graphite blocks throughout the station. The bulk of the fuel was thrown out, but a significant part melted and flowed down, forming complex geological structures.
The most famous object inside is a formation called the "Elephant's Foot". This is a frozen stream of corium that resembles the leg of a giant animal. Chernobyl corium is a eutectic mixture of uranium dioxide, zirconium oxide, molten concrete and reaction products with stainless steel. The melting point of this mixture reached 2000 degrees Celsius and higher.
What is the Elephant's Foot made of?
The formation is based on uranium dioxide, zirconium oxides, graphite, molten concrete and products of thermal decomposition of carbides. The radioactivity of this object in the first years after the accident was so high that a person received a lethal dose within a few minutes of being nearby.
It is important to understand that the Elephant's Foot is not the only object. Other lava-like formations were also discovered in the basements of the reactor block. They are highly dense and contain significant amounts of uranium. Radioactive isotopes in these masses continue to decay, although their activity has decreased significantly compared to the first years after the accident.
The problem of fuel containing materials (FCM)
Under the sarcophagus there are huge volumes of so-called fuel-containing materials. This is not only molten fuel, but also dust containing microparticles of uranium and plutonium, settled on all surfaces of the block. TSM are distributed unevenly: somewhere they are dense pieces of ceramics, and somewhere they are fine dust, which easily rises into the air at the slightest movement.
Scientists classify these materials according to their origin and physical state. The main danger is dust, since it can be carried outside the shelter if the seal is broken or strong winds inside the unit. Dust control is one of the main tasks of the ventilation systems of the old sarcophagus.
Over time, the properties of FCM change. Under the influence of their own radiation and moisture, they are destroyed and their chemical composition changes. Silicate glasses, formed as corium cools, can crack and crumble, increasing the surface area and potential release of radionuclides.
Fuel-containing materials under the sarcophagus remain a source of increased radiation hazard for thousands of years, requiring constant isolation.
Groundwater and the risk of soil contamination
One of the most alarming questions is what is happening under the foundation of the reactor, in the ground. Immediately after the accident, there was a real risk that molten fuel would burn through the concrete slab and reach groundwater. This could lead to catastrophic pollution of Europe's water resources. To prevent this, a complex cooling and soil freezing system was built under the reactor.
Fortunately, the corium froze before reaching the aquifers. However, the problem of interaction of radioactive materials with water remains relevant. Groundwater around the station are under constant monitoring. Although there is no direct contact with fuel, migration of radionuclides through the soil is possible, especially in areas of old liquid waste disposal areas.
There is also moisture inside the block itself. Condensate formed due to temperature changes and precipitation penetrating through cracks interact with FCM. This leads to the washing out of radioactive isotopes and their redistribution within the shelter volume. Drainage system the old sarcophagus collects these waters so that they do not spread beyond the structure.
To reduce the risk of dust formation inside the sarcophagus, special binders are used to cover surfaces with radioactive dust.
The New Safe Shelter: Protection and the Future
The old sarcophagus, built in haste, had a limited service life and did not provide complete sealing. To solve this problem, an international project was implemented to build a “New Safe Shelter” (NSH). This is a giant arched structure that was placed over the old sarcophagus in 2016-2019.
NBU is not just a roof, it is a complex engineering complex. Bridge cranes are installed inside the arch, which allow you to safely dismantle the structures of the old sarcophagus and remove fuel-containing materials. NBU tightness prevents the release of radioactive dust into the atmosphere even in the event of the collapse of old structures.
The service life of the new shelter is designed for 100 years. During this time, it is planned to completely remove the remaining fuel and dismantle the reactor. This is an unprecedented task that has no analogues in world practice. Robotic systems will operate in high radiation conditions, controlled by operators from protected areas.
Excess pressure is maintained inside the arch so that air escapes only through filtration systems. Monitoring systems monitor the slightest changes in the condition of structures and background radiation. Any accident within the perimeter will be localized.
Radiation conditions and isotopic composition
Under the sarcophagus is a mixture of many radioactive isotopes. In the first days after the accident, the main danger was represented by short-lived isotopes of iodine and xenon. Now, decades later, the main sources of radiation are cesium-137, strontium-90 and isotopes of plutonium.
Cesium-137 has a half-life of about 30 years, meaning its activity has decreased by about four times since the accident. However, plutonium-239 will remain dangerous for tens of thousands of years. Alpha radiation Plutonium does not pass through the skin, but is deadly if ingested through dust.
The pattern of radiation distribution under the sarcophagus is extremely heterogeneous. There are “hot spots” where the fuel concentration is maximum, and areas with a relatively low background. Dosimetric monitoring is carried out continuously, and data is transmitted in real time.
| Isotope | Half-life | Type of radiation | Main danger |
|---|---|---|---|
| Cesium-137 | 30 years old | Beta, Gamma | External irradiation, contamination of territories |
| Strontium-90 | 29 years old | Beta | Accumulation in bones |
| Plutonium-239 | 24,000 years | Alpha | Internal exposure (dust) |
| Americium-241 | 432 years | Alpha, Gamma | Plutonium decay product, growing over time |
☑️ Risk factors under the sarcophagus
Fuel recovery plans and final disposal
The ultimate goal of all work is the complete removal of fuel-containing materials from under the sarcophagus. This process will take decades. First, it is necessary to dismantle the unstable structures of the old sarcophagus, which could collapse at any moment. For this, special manipulators are used.
After clearing the space, crushing and packaging of corium into special containers will begin. Transportation These containers will be transported along protected routes for long-term storage or processing. Given the volume of materials, this is a logistical challenge of colossal proportions.
⚠️ Attention: Any work to remove fuel must be carried out remotely. It is impossible for a person to be in close proximity to a SCI without protection due to the high level of gamma radiation.
In parallel, work is underway to stabilize the foundation and the fuel masses themselves. If corium begins to crumble or change properties, the extraction technology must be adapted. Scientists continue to study the behavior of materials to avoid unexpected reactions.
Where will the seized fuel go?
The extracted fuel-containing materials are planned to be processed or preserved in special storage facilities on the territory of the Exclusion Zone. Complete disposal in other types of reactors is currently considered a less likely scenario due to the complex composition of the mixture.
Environmental monitoring and long-term forecasts
The impact of objects under the sarcophagus on the environment is minimized thanks to the NBU, but monitoring does not stop for a minute. Sensors record radiation levels, temperature, humidity and seismic activity. Environmental control applies not only to the station itself, but also to the perimeter of the Exclusion Zone.
Scientists' forecasts agree that if all security measures are observed, the object does not pose a threat to the rest of the world. However, nature can make its own adjustments. Earthquakes, hurricanes or man-made disasters - all these risks are taken into account when designing safety systems.
The Chernobyl accident became a lesson for all humanity. What is under the sarcophagus is a reminder of the power of the atom and the responsibility for its use. Elimination of consequences is a century-long marathon that has already begun.
Is the sarcophagus dangerous for tourists visiting the Chernobyl nuclear power plant?
For organized tourist groups, visiting the Exclusion Zone is safe, since the routes are laid away from dangerous zones, and the time of stay is limited. The new sarcophagus is completely sealed, and the radiation background near it (at a distance from hiking trails) does not significantly exceed the natural background, although at certain points there may be local excesses. The main rule is not to touch objects and not to go off the route.
Could a new nuclear reaction begin under the sarcophagus?
Spontaneous resumption of a nuclear chain reaction under modern conditions under a sarcophagus is excluded. The fuel has burned out heavily, its concentration has dropped, and the geometry of the debris is not conducive to the development of a chain reaction. However, in 2021, a slight increase in the neutron flux was recorded in one of the rooms, which is associated with the drying out of moisture and a change in the conditions for the passage of neutrons, but it was very far from criticality.
How long will the New Safe Shelter last?
The design life of the New Safe Shelter is 100 years. During this time, it is planned to completely dismantle the old sarcophagus and remove all fuel-containing materials. After completion of the work, the NBU will also be dismantled or mothballed, depending on the chosen strategy for the final decommissioning of the facility.
Is it true that there is a radioactive lake flowing under the reactor?
This is a common myth. Immediately after the accident, there was a real threat of melt penetration into the aquifers, but thanks to the heroic efforts of the miners and engineers who laid a cooling system under the reactor, this was avoided. Groundwater in the area of the plant is monitored, and although it may contain traces of radionuclides, there is no “lake” under the reactor.