The nearby city of Prypiat

The nearby city of Prypiat was not immediately evacuated after the incident. The townspeople went about their usual business, completely oblivious to what had just happened. However, within a few hours of the explosion, dozens of people fell ill. Sony VAIO VPCS115FG Battery

Later, they reported severe headaches and metallic tastes in their mouths, along with uncontrollable fits of coughing and vomiting.^[50]The general population of the Soviet Union was first informed of the disaster on 28 April, two days after the explosion, with a 20 second announcement in the TV news program Vremya.^[51] At that time ABC released its report about the disaster.^[52] Sony VAIO VPCS117GG Battery

During that time, all radio broadcasts run by the state were replaced with classical music, which was a common method of preparing the public for an announcement of a tragedy that had taken place. Scientist teams were armed and placed on alert as instructions were awaited.

Only after radiation levels set off alarms at the Forsmark Nuclear Power Plant in Sweden,^[53] Sony VAIO VPCS117GGB Battery

over one thousand kilometers from the Chernobyl Plant, did the Soviet Union admit that an accident had occurred. Nevertheless, authorities attempted to conceal the scale of the disaster. For example, after evacuating the city of Prypiat, the following warning message was read on the state TV:

There has been an accident at the Chernobyl Nuclear Power Plant. One of the nuclear reactors was damaged. Sony VAIO VPCS118EC Battery

The effects of the accident are being remedied. Assistance has been provided for any affected people. An investigative commission has been set up.A state commission was set up the same day (26 April) and tasked with investigating the accident. It was headed by Valery Legasov, who arrived at Chernobyl in the evening of 26 April. By the time Legasov arrived, two people had already died and 52 were receiving medical attention in hospital. Sony VAIO VPCS119FJ/B Battery

By the night of 26–27 April – more than 24 hours after the explosion – Legasov's committee had ample evidence that extremely high levels of radiation had caused a number of cases of radiation exposure. Based on the evidence at hand, Legasov's committee acknowledged the destruction of the reactor and ordered the evacuation of Pripyat. Sony VAIO VPCS119GC Battery

The evacuation began at 14:00 on 27 April. An excerpt of the evacuation announcement was translated into English in the program Seconds From Disaster on the National Geographic Channel in 2004.^[54] A translation of the rest of the audio follows.For the attention of the residents of Pripyat! The City Council informs you that due to the accident at Chernobyl Power Station in the city of Pripyat the radioactive conditions in the vicinity are deteriorating. Sony VAIO VPCS11AFJ Battery

The Communist Party, its officials and the armed forces are taking necessary steps to combat this. 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 Oblast. For these reasons, starting from April 27, 1986 2 pm each apartment block will be able to have a bus at its disposal, supervised by the police and the city officials. Sony VAIO VPCS11AGJ Battery

It is highly advisable to take your documents, some vital personal belongings and a certain amount of food, just in case, with you. The senior executives of public and industrial facilities of the city has decided on the list of employees needed to stay in Pripyat to maintain these facilities in a good working order. All the houses will be guarded by the police during the evacuation period. Sony VAIO VPCS11AHJ Battery

Comrades, leaving your residences temporarily please make sure you have turned off the lights, electrical equipment and water off and shut the windows. Please keep calm and orderly in the process of this short-term evacuation.

In order to expedite the evacuation, the residents were told to bring only what was necessary, as the authorities had said it would only last approximately three days. Sony VAIO VPCS11AVJ Battery

As a result, most of the residents left their personal belongings, which are still there today. An exclusion zone of 30 km (19 mi) remains in place today, although its shape has changed and its size has been expanded.

As the plant was run by authorities in Moscow, the government of Ukraine did not receive prompt information on the situation at the site, according to the former chairman of Presidium of Verkhovna Rada of Ukrainian SSR, Sony VAIO VPCS11J7E/B Battery

Valentyna Shevchenko.^[55] In her recollections she stated that she was at work when at 09:00Vasyl Durdynets who performed duties of the Minister of Internal Affairs at the time (as the First Deputy Minister) called in with a report on the recent situation, adding at the end that there was a fire at the Chernobyl AES (AES – an abbreviation for a nuclear power plant), which was extinguished and everything was fine (see Fire containment). Sony VAIO VPCS11M1E/W Battery

When Shevchenko asked "How are the people?", he replied that there was nothing to be concerned with: "some are celebrating a wedding, others are gardening, and others are fishing in the Pripyat River".^[55]

On 25 April 2011 the President of Ukraine Viktor Yanukovych awarded Durdynets the "Distinguished Juror of Ukraine" as an advisor of the Ministry of Internal Affairs, Sony VAIO VPCS11V9E Battery

a participant in the liquidation of consequences of Chernobyl disaster, and a general of Internal Service of Ukraine.^[56] After the report Shevchenko called in to Volodymyr Shcherbytsky (Head of the Central Committee of CP(b)U, de facto – a head of state).^[55] Shcherbytsky stated that he anticipated a delegation of the state commission headed by the deputy chairman of the Council of Ministers of USSR.^[55] Sony VAIO VPCS11V9E/B Battery

Among the delegation's officials were academic Evgeny Velikhov, a leading nuclear specialist in the Soviet Union; a head of Hydro-Meteorologic Service of USSRYuriy Izrael; a chief radiologist of the country Leonid Ilyin; and others. From the Boryspil International Airport the delegation drove to the power plant, realised the seriousness of the situation that night, and decided to evacuate the residents of Prypiat.^[55] Sony VAIO VPCS11X9E/B Battery

On 26 April 2011 Velikhov was awarded Order of Meritof the III degree from the President of Ukraine Viktor Yanukovych for his contributions in the liquidation of consequences of the Chernobyl disaster.^[57]

By the morning of 27 April, buses arrived in Prypiat to start the evacuation at 11:00. By 15:00, 53,000 people were evacuated to various villages of Kiev region.^[55] Sony VAIO VPCS123FGB Battery

At first it was decided to evacuate the population temporarily for three days, however later it was postponed permanently. Many took only the most necessary items and their documents leaving all the rest behind.^[55] The next day, talks began for evacuating people from the 10 km zone.

Shevchenko was the first of the Ukrainian state top officials to arrive at the disaster site early on 28 April. Sony VAIO VPCS125EC Battery

There she spoke with members of medical staff and people, who were calm and hopeful that they could soon return to their homes. Shevchenko returned home near midnight, stopping at a radiological checkpoint in Vilcha, one of the first which were set up soon after the accident.^[55]

There was a notification from Moscow that there was no reason to postpone the 1 May celebrations (including the annual parade), Sony VAIO VPCS128EC Battery

but on 30 April a meeting of the Political bureau of the Central Committee of CP(b)U took place to discuss the plan for the upcoming celebration. Scientists were reporting that the radiological background in Kiev city was normal. At the meeting, which was finished at 18:00, it was decided to shorten celebrations from the regular 3.5–4 to under 2 hours. Sony VAIO VPCS129GC Battery

Two floors of bubbler pools beneath the reactor served as a large water reservoir for the emergency cooling pumps and as a pressure suppression system capable of condensing steam in case of a small broken steam pipe; the third floor above them, below the reactor, served as a steam tunnel. The steam released by a broken pipe was supposed to enter the steam tunnel and be led into the pools to bubble through a layer of water. Sony VAIO VPCS12C7E/B Battery

After the disaster, the pools and the basement were flooded because of ruptured cooling water pipes and accumulated firefighting water, and constituted a serious steam explosion risk.The smoldering graphite, fuel and other material above, at more than 1200 °C,^[59] started to burn through the reactor floor and mixed with molten concrete from the reactor lining, creating corium, a radioactive semi-liquid material comparable tolava. Sony VAIO VPCS12L9E/B Battery

If this mixture had melted through the floor into the pool of water, it was feared it could have created a serious steam explosion that would have ejected more radioactive material from the reactor. It became necessary to drain the pool.The bubbler pool could be drained by opening its sluice gates. Volunteers in diving suits entered the radioactive water and managed to open the gates. Sony VAIO VPCS12V9E/B Battery

These were the engineers Alexei Ananenko (who knew where the valves were) and Valeri Bezpalov, accompanied by a third man, Boris Baranov, who provided them with light from a lamp, though this lamp failed, leaving them to find the valves by feeling their way along a pipe. All of them returned to the surface and according to Ananenko, their colleagues jumped in joy when they heard they had managed to open the valves. Sony VAIO VPCY115FGS Battery

Despite their apparently good condition after completing the work, all three suffered from radiation sickness and later died.^[62] Some sources claim incorrectly that they died in the plant.^[63] It is likely that intense alpha radiation hydrolyzed the water, generating a low-pH hydrogen peroxide (H₂O₂) solution akin to anoxidizing acid.^[64] Sony VAIO VPCY115FX/BI Battery

Conversion of bubbler pool water to H₂O₂ is confirmed by the presence in the Chernobyl lavas of studtite and metastudtite,^[65][66] the only minerals that contain peroxide.^[67]

Fire brigade pumps were then used to drain the basement. The operation was not completed until 8 May, after 20,000 metric tons of highly radioactive water were pumped out. Sony VAIO VPCY115FXBI Battery

With the bubbler pool gone, a meltdown was less likely to produce a powerful steam explosion. To do so, the molten core would now have to reach the water tablebelow the reactor. To reduce the likelihood of this, it was decided to freeze the earth beneath the reactor, which would also stabilize the foundations. Usingoil drilling equipment, the injection of liquid nitrogen began on 4 May. Sony VAIO VPCY118EC Battery

It was estimated that 25 metric tons of liquid nitrogen per day would be required to keep the soil frozen at −100 °C.^[19]:59 This idea^[68] was soon scrapped and the bottom room where the cooling system would have been installed was filled with concrete.

The worst of the radioactive debris was collected inside what was left of the reactor, Sony VAIO VPCY118GX/BI Battery

much of it shoveled in by liquidatorswearing heavy protective gear (dubbed "bio-robots" by the military); these workers could only spend a maximum of 40 seconds at a time working on the rooftops of the surrounding buildings because of the extremely high doses of radiation given off by the blocks of graphite and other debris. The reactor itself was covered with bags of sand, lead and boric acid dropped from helicopters: Sony VAIO VPCY119FJ/S Battery

some 5,000 metric tons of material were dropped during the week that followed the accident.

At the time there was still fear that the reactor could re-enter a self-sustaining nuclear chain-reaction and explode again, and a new containment structure was planned to prevent rain entering and triggering such an explosion, and to prevent further release of radioactive material. Sony VAIO VPCY11AFJ Battery

This was the largest civil engineering task in history, involving a quarter of a million construction workers who all reached their official lifetime limits of radiation.^[46] By December 1986, a large concretesarcophagus had been erected to seal off the reactor and its contents.^[69] A unique "clean up" medal was given to the workers.^[70]

Many of the vehicles used by the "liquidators" remain parked in a field in the Chernobyl area.^[71] Sony VAIO VPCY11AGJ Battery

During the construction of the sarcophagus, a scientific team re-entered the reactor as part of an investigation dubbed "Complex Expedition", to locate and contain nuclear fuel in a way that could not lead to another explosion. These scientists manually collected cold fuel rods, but great heat was still emanating from the core. Rates of radiation in different parts of the building were monitored by drilling holes into the reactor and inserting long metal detector tubes. Sony VAIO VPCY11AHJ Battery

The scientists were exposed to high levels of radiation and radioactive dust.^[46]

After six months of investigation, in December 1986, they discovered with the help of a remote camera an intensely radioactive mass in the basement of Unit Four, more than two metres wide and weighing hundreds of tons, which they called "the elephant's foot" for its wrinkled appearance. Sony VAIO VPCY11AVJ Battery

The mass was composed of sand, glass and a large amount of nuclear fuel that had escaped from the reactor. The concrete beneath the reactor was steaming hot, and was breached by solidified lava and spectacular unknown crystalline forms termed chernobylite. It was concluded that there was no further risk of explosion.^[46] Sony VAIO VPCY11M1E/S Battery

There were two official explanations of the accident: the first, later acknowledged to be erroneous, was published in August 1986 and effectively placed the blame on the power plant operators. To investigate the causes of the accident the IAEA created a group known as the International Nuclear Safety Advisory Group(INSAG), which in its report of 1986, INSAG-1, Sony VAIO VPCY11S1E Battery

on the whole also supported this view, based on the data provided by the Soviets and the oral statements of specialists.^[72] In this view, the catastrophic accident was caused by gross violations of operating rules and regulations. "During preparation and testing of the turbine generator under run-down conditions using the auxiliary load, Sony VAIO VPCY11V9E/S Battery

personnel disconnected a series of technical protection systems and breached the most important operational safety provisions for conducting a technical exercise."^[73]:311

The operator error was probably due to their lack of knowledge of nuclear reactor physics and engineering, as well as lack of experience and training. Sony VAIO VPCY218EC/BI Battery

According to these allegations, at the time of the accident the reactor was being operated with many key safety systems turned off, most notably the Emergency Core Cooling System (ECCS), LAR (Local Automatic control system), and AZ (emergency power reduction system). Personnel had an insufficiently detailed understanding of technical procedures involved with the nuclear reactor, and knowingly ignored regulations to speed test completion. Sony VAIO VPCY218EC/G Battery

The developers of the reactor plant considered this combination of events to be impossible and therefore did not allow for the creation of emergency protection systems capable of preventing the combination of events that led to the crisis, namely the intentional disabling of emergency protection equipment plus the violation of operating procedures. Sony VAIO VPCY218EC/L Battery

Thus the primary cause of the accident was the extremely improbable combination of rule infringement plus the operational routine allowed by the power station staff.

In this analysis of the causes of the accident, deficiencies in the reactor design and in the operating regulations that made the accident possible were set aside and mentioned only casually. Sony VAIO VPCY218EC/P Battery

Serious critical observations covered only general questions and did not address the specific reasons for the accident. The following general picture arose from these observations. Several procedural irregularities also helped to make the accident possible. One was insufficient communication between the safety officers and the operators in charge of the experiment being run that night. Sony VAIO VPCY21S1E/L Battery

The reactor operators disabled safety systems down to the generators, which the test was really about. The main process computer, SKALA, was running in such a way that the main control computer could not shut down the reactor or even reduce power. Normally the reactor would have started to insert all of the control rods. The computer would have also started the Sony VAIO VPCY21S1E/P Battery

"Emergency Core Protection System" that introduces 24 control rods into the active zone within 2.5 seconds, which is still slow by 1986 standards. All control was transferred from the process computer to the human operators.This view is reflected in numerous publications and also artistic works on the theme of the Chernobyl accident that appeared immediately after the accident,^[19]and for a long time remained dominant in the public consciousness and in popular publications. Sony VAIO VPCY21S1E/SI Battery

In 1991 a Commission of the USSR State Committee for the Supervision of Safety in Industry and Nuclear Power has reassessed the causes and circumstances of the Chernobyl accident and came to new insights and conclusions. Based on it, in 1992 the IAEA Nuclear Safety Advisory Group (INSAG) published an additional report, INSAG-7,^{[23] Sony VAIO VPCCW1S1E/R Battery}

which reviewed "that part of the INSAG-1 report in which primary attention is given to the reasons for the accident." and included the USSR State Commission report as Appendix I.^[23]

In this INSAG report, most of the earlier accusations against staff for breach of regulations were acknowledged to be either erroneous, based on incorrect information obtained in August 1986, or less relevant. ^{Sony VAIO VPCCW1S1E/W Battery}