The Chernobyl Nuclear Power Plant sarcophagus, completed in December 1986, reduced the spread of radioactive contamination and provided radiological protection for the crews of the undamaged reactors.

Nearly all of the 211 control rods had been extracted, and excessively high coolant flow rates meant that the water had less time to cool between trips through the core, therefore entering the reactor very close to the boiling point.

One such survivor, Alexander Yuvchenko, said that once he stepped out and looked up towards the reactor hall, he saw a "very beautiful" laser-like beam of blue light caused by the ionized-air glow that appeared to be "flooding up into infinity".

[18]: 73 It was thought by some that the core fire was extinguished by a combined effort of helicopters dropping more than 5,000 tonnes (11 million pounds) of sand, lead, clay, and neutron-absorbing boron onto the burning reactor.

It was headed by Valery Legasov, First Deputy Director of the Kurchatov Institute of Atomic Energy, and included leading nuclear specialist Evgeny Velikhov, hydro-meteorologist Yuri Izrael, radiologist Leonid Ilyin, and others.

Nevertheless, with the view to keep people as safe and healthy as possible, the children being top priority, we need to temporarily evacuate the citizens in the nearest towns of Kiev region.

The mention of a commission also indicated to observers the seriousness of the incident,[69] and subsequent state radio broadcasts were replaced with classical music, which was a common method of preparing the public for an announcement of a tragedy in the USSR.

[74][76] It was feared that if this mixture melted through the floor into the pool of water, the resulting steam production would further contaminate the area or even cause another explosion, ejecting more radioactive material.

During the construction of the sarcophagus, a scientific team, as part of an investigation dubbed "Complex Expedition", re-entered the reactor to locate and contain nuclear fuel to prevent another explosion.

[54] In December 1986, after six months of investigation, the team discovered with the help of a remote camera that an intensely radioactive mass more than 2 metres (6 ft 7 in) wide had formed in the basement of Unit Four.

Crane operators worked blindly from inside lead-lined cabins taking instructions from distant radio observers, while gargantuan pieces of concrete were moved to the site on custom-made vehicles.

The purpose of the sarcophagus was to stop any further release of radioactive particles into the atmosphere, isolate the exposed core from the weather and provide safety for the continued operations of adjacent reactors one through three.

[111][112] Prior to the completion of the New Safe Confinement building, rainwater acted as a neutron moderator, triggering increased fission in the remaining materials, risking criticality.

The fluctuations have led to fears that a self-sustaining reaction could be created, which would likely spread more radioactive dust and debris throughout the New Safe Confinement, making future cleanup even more difficult.

"[137][138] Dr. T. Steen, a microbiology and immunology teacher at Georgetown's School of Medicine, recommends that tourists wear clothes and shoes they are comfortable throwing away and to avoid plant life.

[133] Tourism rebounded after COVID in 2021, but the Russian invasion of Ukraine in early 2022 meant the Chernobyl area saw active fighting and the exclusion zone closed to all visitors.

Rain was deliberately seeded over 10,000 square kilometres (3,900 sq mi) of Belarus by the Soviet Air Force to remove radioactive particles from clouds heading toward highly populated areas.

[64]: 64–65 [better source needed] Meanwhile, massive silt traps were constructed, along with a 30-metre (98 ft) deep underground barrier to prevent groundwater from the destroyed reactor entering the Pripyat River.

Most domestic animals were removed from the exclusion zone, but horses left on an island in the Pripyat River 6 km (4 mi) from the power plant died when their thyroid glands were destroyed by radiation doses of 150–200 Sv.

[169][better source needed] Subsequent research on microorganisms, while limited, suggests that in the aftermath of the disaster, bacterial and viral specimens exposed to the radiation underwent rapid changes.

[179] Of the 440,350 wild boar killed in the 2010 hunting season in Germany, approximately one thousand were contaminated with levels of radiation above the permitted limit of 600 becquerels of caesium per kilogram, of dry weight, due to residual radioactivity from Chernobyl.

The Norwegian Agricultural Authority reported that in 2009, a total of 18,000 livestock in Norway required uncontaminated feed for a period before slaughter, to ensure that their meat had an activity below the government permitted value of caesium per kilogram deemed suitable for human consumption.

[196] However, childhood thyroid cancer increased, with about 4,000 new cases reported by 2002 in contaminated areas of Belarus, Russia, and Ukraine, largely due to high levels of radioactive iodine.

[197] Psychosomatic illness and post-traumatic stress, driven by widespread fear of radiological disease, have had a significant impact, often exacerbating health issues by fostering fatalistic attitudes and harmful behaviors.

[203]: 42 The mutation rates among animals in the Chernobyl zone have been a topic of ongoing scientific debate, notably regarding the research conducted by Anders Moller and Timothy Mousseau.

[206][207] In 1996, geneticist Ronald Chesser and Robert Baker published a paper[208] on the thriving vole population within the exclusion zone, in which the central conclusion was essentially that "The mutation rate in these animals is hundreds and probably thousands of times greater than normal".

[220] Studies on regions of Ukraine and Belarus suggest that around 50 children exposed in utero during weeks 8 to 25 of gestation may have experienced an increased rate of intellectual disability and lower verbal IQ.

"[256] Numerous structural and construction quality issues, as well as deviations from the original plant design, had been known to the KGB since at least 1973 and passed on to the Central Committee, which took no action and classified the information.

In direct response to the Chernobyl disaster, a conference to create a Convention on Early Notification of a Nuclear Accident was called in 1986 by the International Atomic Energy Agency.

[267][268] The documentary The Battle of Chernobyl (2006) shows rare original footage a day before the disaster in the city of Pripyat, then through different methods goes in depth on the chronological events that led to the explosion of the reactor No.