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Is Chernobyl core still hot?

The Chernobyl nuclear disaster that occurred in 1986 was one of the worst nuclear accidents in history. On April 26, 1986, a safety test gone wrong led to an explosion and fire at reactor 4 of the Chernobyl Nuclear Power Plant in Pripyat, Ukraine. This caused a massive release of radioactive material into the environment that spread across Europe.

So even over 35 years later, a common question is – is the Chernobyl core still hot with radiation? Let’s take a deeper look at what’s happened at the Chernobyl site since the fateful disaster.

What was the extent of the Chernobyl disaster?

The Chernobyl accident was catastrophic and had far-reaching effects. The explosion and subsequent fire released large amounts of radioactive material like iodine-131, cesium-137, strontium-90, and plutonium isotopes into the atmosphere for over 9 days until the fire was contained.

The radioactive cloud spread over Europe, contaminating areas over 150,000 square km in Belarus, Russia and Ukraine. Over 300,000 people were evacuated from within an 18 mile radius of the plant. 31 deaths are directly attributed to the disaster, with estimates of further premature deaths ranging into the thousands.

The intense radiation damaged reactor 4 beyond repair. The damage also included the reactor core where the nuclear fuel rods were housed. Dealing with the damaged reactor core that was still highly radioactive would prove to be one of the major challenges in the aftermath.

What happened to the reactor core after the Chernobyl disaster?

The reactor core contained about 180-190 metric tons of uranium fuel as well as fission products with substantial radioactivity. The explosions had damaged the core, scattering fuel and radioactive material into the reactor and surrounding areas.

Initially, firefighters were able to contain the blaze and began cleanup. But the core itself remained extremely hot both thermally and radioactively. Within a couple of days, the core melted through the concrete floors and mixed with molten concrete, producing radioactive lava-like material now known as Corium.

This highly radioactive Corium accumulated in the basement underneath the reactor. If it reached groundwater, it could have triggered another steam explosion which would have released more radiation.

By May 10, over 5000 metric tons of materials like sand, boron, clay, and lead had been air dropped into the reactor in an effort to stop Corium from spreading. By December that year, a concrete slab was built under the reactor to contain the Corium.

Was the Chernobyl reactor entombed?

By late 1986, it was clear reactor 4 could not be salvaged. In fact it was so dangerously unstable, that collapsing the rest of the building could trigger another catastrophic release of radioactive dust.

It was decided that the best course of action was to seal off and contain the reactor by building an impenetrable cover around it. This protective structure is referred to as the Object Shelter or the Sarcophagus.

Built between May 1986 and November 1986, this giant steel and concrete structure was designed to stop additional radioactive material from escaping as well as protect the reactor from external damage. By December, the reactor was effectively entombed within the Sarcophagus.

Issues with the original Sarcophagus

While the Sarcophagus met the objective of containing the radioactive materials and isolating the remains of reactor 4, it was only designed to last for around 30 years. However, it had some serious issues right from the start:

  • It was hastily built in very hazardous conditions, with high radiation hampering construction.
  • Water leaks allowed rainwater into the structure, causing corrosion and rust over the years.
  • The Sarcophagus was not covered, allowing debris like bird excrement or dust to accumulate inside over time.
  • Some experts warned that its unstable parts could collapse, causing the release of up to 200 tons of radioactive dust.

By the late 1990s, there was global concern about the deteriorating Sarcophagus and the need for a more permanent solution was apparent.

The New Safe Confinement (NSC)

Also called the New Shelter, the NSC is an immense steel structure designed to replace the hastily built Sarcophagus. Built with state of the art engineering, this giant arch would seal in the radioactive remains of reactor 4 for the next 100 years. Construction began in 2010 with coordination between over 100 companies from countries like Ukraine, Germany, the United States and Russia.

Some key facts about the NSC:

  • Half as tall as the Eiffel Tower, the NSC is the largest movable land-based structure ever built, with a span of 257m, a length of 162m and a height of 108m
  • The arch frame structure was built away from the reactor and later slid into place over the existing Sarcophagus in November 2016.
  • Weighing 36,200 metric tons, the NSC was designed to withstand tornado winds up to 206 mph.
  • Its special cranes allow for remote handling of radioactive debris inside the structure.

In July 2019, the European Bank of Reconstruction and Development declared the NSC officially completed. With this modern shelter now containing the entirety of reactor 4, the risks of additional radioactive release have been dramatically reduced.

What is happening inside the remains of reactor 4?

Inside the remains of reactor 4, which the NSC now safely contains, temperatures have cooled significantly compared to 1986 but radioactivity levels are still high:

  • The Corium lava flow remnants still buried deep under the reactor have cooled but likely remain at levels where exposure would be fatal.
  • Temperature of the core now estimated to be between 40-90 degrees Celsius, much lower than the thousands of degrees during meltdown.
  • Radiation levels inside various areas of the shelter vary from around 5 Roentgen per hour in the least contaminated areas to thousands of Roentgen in the fuel containing compartments.

Ongoing work includes monitoring to ensure containment, stabilizing unstable structures, dismantling unstable parts and reducing water infiltration. Techniques like using robots help minimize risks to human workers.

Waste management efforts are focused on clearing radioactive debris inside the shelter and decontaminating the existing structure. The ultimate goal is to eventually dismantle the unstable Sarcophagus. This will only happen once radiation inside has decayed to safer levels and the NSC is deemed stable. But full dismantling is likely decades away.

Is the Chernobyl core still reacting?

The destroyed Chernobyl reactor is no longer undergoing nuclear fission reactions, so there is no active ‘critical’ core. However, the remaining radioactive fuel still generates heat and radiation through other processes:

  • Radioactive decay – Heavy unstable isotopes like cesium-137 and strontium-90 decay into more stable atoms, releasing energy.
  • Absorbed neutrons – Nuclei that absorbed neutrons during the reaction continue to decay and release energy.

So while the periods of intense heat from uncontrolled reaction and meltdown are gone, radioactive decay continues and will keep releasing heat for many more years, necessitating constant cooling efforts.

How much radiation is being released from Chernobyl now?

Ongoing containment efforts have dramatically reduced the radiation still being released from the Chernobyl site compared to 1986. Monitoring data shows:

  • Radiation emissions reduced from initial peak of 50 million Curies in 1986 to about 5 million Curies in subsequent years.
  • Levels today average around 10,000 Curies per year, dominated by cesium-137 and strontium-90.
  • For perspective, a typical functional commercial reactor releases 400-500 Curies per year.

The vast scale of the original disaster and radioactive inventory means Chernobyl will remain a radiation hazard for some time. But modern engineering provides effective containment, allowing only minimal emissions within regulatory limits.

Has radiation decreased since the disaster?

Yes, radiation levels have decreased substantially since 1986 due to natural decay processes:

  • Half life of release isotopes – iodine-131 half life is 8 days, cesium-137 is 30 years.
  • Dispersion and deposition – Radioactive materials dispersed around the region have decayed.
  • Decay of shorter lived isotopes – For instance, iodine-131 decayed faster than cesium-137.

Measurement data shows radiation levels in worst hit areas down from 10-15 Rontgen per hour in 1986 to around 0.5 per hour today. But some localized spots of high contamination still remain dangerously radioactive.

Ongoing efforts continue to decontaminate the surrounding region. Over 1000 sq miles of forests and floodplains remain under restriction to allow for further decay before they can be deemed safe again.


While almost 4 decades have passed since the catastrophic disaster, the destroyed Chernobyl reactor core remains highly radioactive and will be so for many more years to come. But modern engineering like the New Safe Confinement provides an effective barrier between the contaminated reactor and the outside world.

This allows the remaining radioactive materials to decay under controlled conditions rather than posing an active hazard. So while the Chernobyl core remains ‘hot’, it is now part of an isolated zone where radiation levels continue to decrease over time.