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The Chernobyl Nuclear Disaster

The Chernobyl nuclear disaster began early in the early hours of Saturday 26 April 1986 within the Chernobyl Nuclear Power Plant. An explosion and fire released large quantities of radioactive particles into the atmosphere, which spread over much of Western USSR and Europe. It is considered the worst nuclear power plant accident in history and is one of only two classified as a level 7 event on the International Nuclear Event Scale (the other being the Fukushima nuclear disaster in 2011).

The disaster began during a system test at reactor number four of the Chernobyl plant. There was a sudden surge of power output, and when an emergency shutdown was attempted a more extreme spike in power output occurred, which led a reactor vessel to rupture and a series of explosions. These events exposed the graphite moderator of the reactor to air, causing it to ignite. The resulting fire sent a plume of highly radioactive smoke into the atmosphere and over an extensive geographical area. The plume went on to drift over large parts of the western Soviet Union and Europe. According to official post-Soviet data about 60% of the radioactive fallout landed in Belarus.

The battle to contain the contamination and avert a greater catastrophe ultimately involved over 500,000 workers, known as liquidators, and cost an estimated 18 billion Rubles.
Only after the level of radiation set off alarms at the Forsmark Nuclear Power Plant in Sweden, over one thousand kilometers from the Chernobyl Plant, did the Soviet Union publicly admit that an accident had occurred. The true scale of the disaster was concealed. After evacuating the nearby city of Pripyat, the following warning message was read on state TV:

There has been an accident at the Chernobyl Nuclear Power Plant. One of the nuclear reactors was damaged. The effects of the accident are being remedied. Assistance has been provided to any affected people. An investigative commission has been set up.”
– 28 April 1986, 21:00

From 1986 to 2000, over 350,000 people were evacuated and resettled from the most severely contaminated areas of Belarus, Russia, and Ukraine.
Thirty one deaths are directly attributed to the accident, all among the reactor staff and emergency workers. Estimates of the number of deaths potentially resulting from the accident vary enormously. A UNSCEAR report places the total confirmed deaths from radiation at 64 as of 2008. The World Health Organization (WHO) suggests it could reach 4,000 civilian deaths, a figure which does not include military clean-up worker casualties. A 2006 report predicted 30,000 to 60,000 cancer deaths as a result of Chernobyl fallout. A Greenpeace report puts this figure at 200,000 or more. The Russian publication, Chernobyl, concludes that 985,000 premature cancer deaths occurred worldwide between 1986 and 2004 as a result of radioactive contamination from Chernobyl.

Nearly 400 million people resided in territories that were contaminated with radioactivity at a level higher than 4 kBq/m2 (0.11 Ci/km2) from April to July 1986. Nearly 5 million people (including, more than 1 million children) still live with dangerous levels of radioactive contamination in Belarus, Ukraine, and European Russia.”
- From Chernobyl: Consequences of the Catastrophe for People and the Environment.

A massive concrete and metal structure, a sarcpphagus, was hastily constructed to encase Unit 4 as an emergency measure to halt the release of radiation into the atmosphere following the 1986 disaster.

Timeline of the disaster


Construction of the town of Pripyat, one of 9 “atom towns” begins, to be inhabited by future employees of the nuclear power plants.
March – Construction of the Chernobyl Nuclear Power Plant begins (ChNPP).

Construction of Chernobyl Nuclear Power Plant. ©


Discussions take place in Kiev about the type of nuclear plant to be built at Chernobyl. Chernobyl’s director, Bryukhanov, proposes construction of Pressurized Water Reactors (PWRs). He informs the Ukraine Minister of Energy, Aleksei Makukhin, that an RBMK (a boiling water reactor) releases forty times more radiation than a PWR. The scientist Alekzandrov opposes this, saying that the RBMK- 1000 was not only the safest reactor, but it also produced the cheapest electricity as well. For this reason it was decided to build the RBMK pressure tube reactors.


October – Filling of the cooling water reservoir for the Chernobyl Power Plant begins.


The first of the Chernobyl Nuclear Power Plants four reactors is ready to operate followed by number 2 in 1978.
According to data held by the KGB, design deviations and violations of construction and assembly are occurring in the construction of the 2nd generating unit.


Pripyat officially proclaimed as a city.
April – The Chernobyl Atomic Power Station reaches its first 10 billion kilowatt-hours of electical output.

Night time shot of Pripyat


A partial core meltdown occurs in reactor No. 1. The extent of the accident was not made public until 1985.  The reactor was repaired and put back into operation within months.


December – The construction of Unit 4 at Chernobyl is completed and the plant becomes operational on the 20th. This news was reported by the media on 22 December, a festive day for workers in the energy industry. In the Soviet Union it was customary for all sections of public employment to have their own special day, when they receive public acclaim for their work and are given extra bonuses.


April – The Minister of Energy, Anatoly Mayorets, decrees that information on any adverse effects caused by the functioning of the energy industry on employees, inhabitants and the environment, were not suitable for publication by newspapers, radio or television.


February – Vitali Sklyarov, Minister of Power and Electrification of Ukraine, in reference to the nuclear reactors in Ukraine, is quoted in Soviet Life magazine as saying:

“The odds of a meltdown are one in 10,000 years. The plants have safe and reliable controls that are protected from any breakdown with three safety systems.”

27 March – Literaturna Ukraina (Ukrainian Literature) publishes an article written by Ms Lyubov Kovalevska (believed to be a senior manager at Chernobyl Nuclear Power Plant (NPP)) in which she writes that substandard construction, workmanship and concrete, along with thefts and bureaucratic incompetence are creating a time bomb “The failures here will be repaid, repaid over the decades to come”.

25 April – Friday

The test begins.

01:00 – The reactor was running at full power with normal operation. Steam power was directed to both turbines of the power generators. Slowly the operators began to reduce power for the test. The purpose of the test was to observe the dynamics of the RMBK reactor with limited power flow.

13:05 – Twelve hours after power reduction was initiated the reactor reached 50% power. Now only one turbine was needed to take in the decreased amount of steam caused by the power decrease and turbine #2 was switched off.

14:00 – Under the normal procedures of the test the reactor would have been reduced to 30% power, but the Soviet electricity authorities refused to allow this because of an apparent need for electricity elsewhere, so the reactor remained at 50% power for another 9 hours.

Emergency core cooling system switched off.

26 April – Saturday

00:00 – Aleksandr Akimov, the unit shift chief in charge of the test takes over from Tregub, who stays on-site.

00:28 – Control rods transferred from local to global control: Power plummets in the reactor; further rods withdrawn.

The drop in reactor power from 1500 MWt to 30 MWt is disconcerting; Akimov wants to abort the test, but is over-ridden by Dyatlov and forced to continue.

Anatoly Dyatlov, the deputy chief engineer, supervised the test. At the moment reactor power slipped to 30 MW thermal, he insisted the operators continue the test. He overrode Akimov’s and Toptunov’s objections, threatening to hand the shift to Tregub (the previous shift operator who had remained on-site), intimidating them into attempting to increase the reactor power. The power stabilized at 200 MWt at around 1:00 am  and did not rise further, due to continued xenon poisoning of the core.

01:03 – Fourth cooling pump connected to right loop.

01:19 – Shutdown signals blocked from steam-drum separators.

The operator blocks automatic shutdown due to low water level and the loss of both turbines because of a fear that a shutdown would abort the test.

The operator forces the reactor up to 7% power by removing all but 6 of the control rods. This was a violation of procedure as the reactor was never built to operate at such low power. The RBMK reactor is unstable when its core is filled with water. The operator tried to take over the flow of the water which was returning from the turbine manually which is very difficult because small temperature changes can cause large power fluctuations. The operator was not successful in getting the flow of water corrected and the reactor was getting increasingly unstable.

01:19 – Control rods raised.

01:21 – Caps to fuel channels on charge face seen jumping in their sockets.

Valeriy Ivanovich Perevozchenko, the reactor section foreman, was present on the open platform at Level +50 shortly before the explosion. He witnessed the 350 kg blocks atop the fuel channels of the Upper Biological Shield jumping up and down and felt the shock waves through the building structure; the rupture of the pressure channels was in progress. He started to run down the spiral staircase to Level +10, through the deaerator gallery and the corridor heading to the control room, to report his observations.

01:21:50 – Pressure falls in steam drums.

01:23:40 – Emergency reinsertion of all control rods.

As the temperature of the water became too high Cavitation (bubbles) reached the main circulation pumps. The coolant started boiling in the reactor, and the reactor power slowly increased. Toptunov reports a power issue to Akimov. Akimov presses the AZ-5 button, class-5 emergency. The control rods, according to the synchro indicators, seized at a depth of between 2 and 2.5 meters instead of inserting to their full depth of 7 meters. Akimov disconnected the clutches of the control rod servos to let the rods descend into the core under their own weight, but the rods did not move. The reactor was now making rumbling noises. Akimov was confused. The reactor control panel indicated no water flow and failure of pumps.

01:23:44 – Explosion.

The reactor reaches 120 times its full power. All the radioactive fuel disintegrates, and pressure from all of the excess steam which was supposed to go to the turbines broke every one of the pressure tubes leading to an explosion.

01:23:45 – The 1000 ton lid above the fuel elements is lifted by the first explosion. The release of radiation starts. Air reaches the reactor and the oxygen results in a graphite fire. The metal of the fuel tubes reacts to the water. This is a chemical reaction which produces hydrogen, and this hydrogen explodes: the second explosion. Burning debris flies into the air and lands on the roof of Chernobyl Unit 3. (There was barely any attention paid to this hydrogen explosion in the Soviet report about the accident. In studies commissioned by the US government however, it was concluded that the second explosion was of great significance, and that the original explanation of the accident was incorrect. Richard Wilson of the Harvard University in the US said this second explosion was a small nuclear explosion.)Cross section of Reactor Four

The explosion occurred, the air filled with dust, power went out, and only battery-powered emergency lights stayed in operation.

The night shift main circulating pump operator, Valery Khodemchuk, was likely killed immediately; he was located in the collapsed part of the building, in the far end of the southern main circulating pumps engine room at level +10. His body was never recovered and is entombed in the reactor debris.

Perevozchenko, the reactor section foreman,  ran into the control room, reporting the collapse of the reactor top. Brazhnik ran in from the turbine hall, reporting fire there. Brazhki, Akimov, Davletbayev, and Palamarchuk ran into the turbine hall, having seen scattered debris and multiple fires on Levels 0 and +12.

01:26:03 – fire alarm activated.

Akimov called the fire station and the chiefs of electrical and other departments, asking for electrical power for coolant pumps, removal of hydrogen from hydrogen generators, and other emergency procedures to stabilize the plant and contain the damage. Internal telephone lines were disabled; Akimov sent Palamarchuk to contact Gorbachenko. Kudryavtsev and Proskuryakov returned from the reactor and reported its state to Akimov and Dyatlov. Insisting the reactor was intact, Akimov ordered Stolyarchuk and Busygin to turn on the emergency feedwater pumps. Davletbayev reported a loss of electrical power, torn cables, and electric arcs. Akimov sent Metlenko to the turbine hall to help with the manual opening of the cooling system valves, which was expected to take at least four hours per valve. Perevozchenko returned and reported that the reactor was destroyed, but Akimov insisted it was intact.

Dyatlov ordered reactor cooling with emergency speed, assuming the reactor was intact and the explosion had been caused by hydrogen accumulating in the emergency tank of the safety control system. Other employees went to the control room, reporting damage. Dyatlov went to the backup control room, pressing the AZ-5 button there and disconnecting power to the control rod servo drives; despite seeing the graphite blocks scattered on the ground outside the plant, he still believed the reactor was intact. Kudryavtsev and Proskuryakov returned to report the reactor damage they had seen, but Dyatlov insisted what they had seen was the results of an explosion of the emergency tank, claiming the explosion of the 110m³ tank at Level +71 was sufficient to destroy the central hall roof. Dyatlov reported his assumptions as reality to Bryukhanov and Fomin, the higher-level managers. In the corridor, he met Genrikh and Kurguz and sent them to the medical station. He ran to the control room of Block 3, ordered Bagdasarov to shut down Reactor 3, then returned to control room 4 and ordered Akimov to call the daytime shift and get people to the affected unit; namely Lelechenko, whose crew had to remove hydrogen from the Generator 8 electrolyzer.

Aleksandr Kudryavtsev and Viktor Proskuryakov, the SIUR trainees from other shifts, were present to watch Toptunov and learn. After the explosion they were sent by Dyatlov or Akimov to the central hall to turn the handles of the system for manually lowering of the presumably seized control rods. They ran through the deaerator gallery to the right to the VRSO unit elevator, found it destroyed, so climbed up the staircase instead, towards Level 36; they missed Kurguz and Genrikh, who used another stairwell. Level 36 was destroyed, covered with rubble. They went through a narrow corridor towards the central hall, entered the reactor hall, and found it blocked with rubble and fragments; dangling fire hoses were pouring water into the remains of the reactor core, the firemen not there anymore. The Upper Biological Shield was slanted, jammed into the reactor shaft; a blue and red fire raged in the hole. The minute the two stood above the reactor was enough to darken their bodies with “nuclear tan” and give them a fatal radiation dose. They returned to Level 10 and to the control room, reporting the situation; Dyatlov insisted they were wrong, the explosion had been caused by hydrogen-oxygen mixture in the 110m³ emergency tank and the reactor itself was intact.

Valeriy Ivanovich Perevozchenko, the reactor section foreman arrived at the control room shortly after the explosions, then returned to search for his comrades. He witnessed the destruction of the reactor building from the broken windows of the deaerator gallery. With his face already tanned by the radiation, he went to the dosimetry room and asked Gorbachenko for radiation levels; Gorbachenko left with Palamarchuk to rescue Shashenok while Perevozchenko went through the graphite and fuel containing radioactive rubble on Level 10 to the remains of Room 306 in an unsuccessful attempt to locate Khodemchuk, close to debris emitting over 10,000 roentgens per hour (90 µA/kg). He then went to the control room of Genrikh and Kurguz and found it empty; vomiting and losing consciousness, he returned to the control room to report on the situation.

01:28 (approx) – Fire fighting units under lieutenant Lieutenant Volodymyr Pravik leave the station.

Vyacheslav Brazhnik, the senior turbine machinist operator, ran into the control room to report the fire in the turbine hall. Pyotr Palamarchuk, the Chernobyl enterprise group supervisor, together with Razim Davletbayev, followed him back to the turbine room. They witnessed fires on Levels 0 and +12, broken oil and water pipes, roof debris on top of turbine 7, and scattered pieces of reactor graphite and fuel, with the linoleum on the floor burning around them. Palamarchuk unsuccessfully attempted to contact Sashenok in Room 604, then ran around the turbogenerator 8, down to Level 0 and urged the two men from the Kharkov mobile laboratory, assigned to record the turbine 8 vibrations, to leave; they, however, had both already received a lethal radiation dose. Akimov asked Palamarchuk to look for Gorbachenko and then rescue Sashenok as the communication with the dosimetry room was cut. Palamarchuk met Gorbachenko by the staircase on Level +27, then they together found and recovered Shashenok’s unconscious body.

Alexander Yuvchenko was located in his office between reactors 3 and 4, on Level 12.5; he described the event as a shock wave that buckled walls, blew doors in, and brought a cloud of milky grey radioactive dust and steam. The lights went out. He met a badly burned, drenched and shocked pump operator, who asked him to rescue Khodemchuk; that quickly proved impossible as that part of the building did not exist anymore. Yuvchenko, together with the foreman Yuri Tregub, ran out of the building and saw half of the building gone and the reactor emitting a blue glow of ionized air. They returned to the building and met Valeri Perevozchenko and two junior technicians, Kudryavtsev and Proskuryakov, ordered by Dyatlov or Akimov to manually lower the presumably seized control rods. Tregub went to report the extent of damage to the control room. Despite Yuvchenko’s explanation that there were no control rods left, the four climbed a stairwell to Level 35 to survey the damage; Yuvchenko held open the massive door into the reactor room and the other three proceeded in to locate the control rod mechanism; after no more than a minute of surveying the reactor debris, enough for all three to sustain fatal doses of radiation, they returned, their skin darkened with “nuclear tan” in reaction to the high dose of radiation. The three were the first to die in the Moscow hospital. Yuvchenko meanwhile suffered serious beta burns and gamma burns to his left shoulder, hip and calf as he kept the radioactive-dust-covered door open. It was later estimated he received a dose of 4.1 Sv. At 03:00, he began vomiting intensely; by 06:00, he could no longer walk. He later spent a year in the Moscow hospital receiving blood and plasma transfusions and received numerous skin grafts.

01:35 (approx) – Firemen fight fires on roof of turbine hall. Arrival of firefighters from Pripyat, Kibenok’s guard

Grigorii Khmel, the driver of one of the fire engines, later described what happened:

We arrived there at 10 or 15 minutes to two in the morning… We saw graphite scattered about. Misha asked: “Is that graphite?” I kicked it away. But one of the fighters on the other truck picked it up. “It’s hot,” he said. The pieces of graphite were of different sizes, some big, some small, enough to pick them up…

We didn’t know much about radiation. Even those who worked there had no idea. There was no water left in the trucks. Misha filled a cistern and we aimed the water at the top. Then those boys who died went up to the roof – Vashchik, Kolya and others, and Volodya Pravik…. They went up the ladder … and I never saw them again.

However, Anatoli Zakharov, a fireman stationed in Chernobyl since 1980, offers a different description:

I remember joking to the others, “There must be an incredible amount of radiation here. We’ll be lucky if we’re all still alive in the morning.”

Twenty years after the disaster, he said the firefighters from the Fire Station No. 2 were aware of the risks.

Of course we knew! If we’d followed regulations, we would never have gone near the reactor. But it was a moral obligation – our duty. We were like kamikaze.

01:56 – Major Telyatnikov takes command of fire fighting units

02:00 – Dyatlov, deputy chief engineer, ordered Akimov, unit shift chief, to feed water to the reactor, and together with Gorbachenko, a radiation monitoring technician, went to survey the plant from the outside. Despite seeing the fuel and graphite scattered around, he still believed the reactor was intact. They then returned to the control room. At 05:00, he got sick and together with Gorbachenko went to the medical unit. Fomin replaced him at his post with Sitnikov.

02.15 – The Pripyat department of the Ministry of Home Affairs calls a crisis meeting. It is decided to organize a road block in order to prevent cars from entering or leaving the town. Police assistance is requested. Thousands of police arrive; and, as with the fire fighters, they have no knowledge of radiation, no dosimeters or protective clothing.

02:30 – Brukhanov, the plant manager, arrives at the bunker under the administrative block

Akimov reports a serious radiation accident but that the reactor is intact, fires are in the process of being extinguished, and a second emergency water pump being readied to cool the reactor. Due to limitations of available instruments, they seriously underestimate the radiation level.

03:00 – Bryukhanov called Maryin, the deputy secretary for the nuclear power industry, reporting Akimov’s version of the situation. Maryin sent the message further up the chain of command, to Frolyshev, who then called Vladimir Dolgikh, who called Gorbachev and other members of the Politburo. At 04:00, Moscow ordered feeding of water to the reactor.

03:30 – Telyatnikov contacted Akimov, asking what was happening to his firemen; Akimov sent him a dosimetrist.

04:00 – Further fire fighting units arrive from Chernobyl, Polesskoe and Kiev

04:30 – Chief engineer Fomin arrived in the Block 4 control room

Akimov reported an intact reactor and damage to the emergency water feed tank. Fomin ordered continuous feeding of water into the reactor, which was already in progress by emergency pump 2 from the deaerators (a device that is widely used for the removal of oxygen and other dissolved gases from the feedwater to steam-generating boilers). Fomin kept pressing the staff to feed water to the reactor and transferred more people to Unit 4 to replace those being disabled by radiation. After Dyatlov left, Fomin ordered Sitnikov, his replacement, to climb to the roof of Unit C and survey the reactor; Sitnikov obeyed and received a fatal radiation dose there; at 10:00 he returned and reported to Fomin and Bryukhanov that the reactor was destroyed. The managers refused to believe him and ordered that water continued to be fed into the reactor; the water however, flowed through the severed pipes into the lower levels of the plant, carrying radioactive debris and causing short circuits in the electric cableways common to all four of the blocks.

05:00 – Militia commander general Berdov arrives from kiev

06:00 – Akimov, already nauseous, was replaced at 06:00 by the unit chief Vladimir Alekseyevich Babychev, but together with Toptunov stayed in the plant. Believing the water flow to the reactor to be blocked by a closed valve somewhere, they went to the half-destroyed feedwater room on Level +24. Together with Nekhayev, Orlov, and Uskov, they opened the valves on the two feedwater lines, then climbed over to Level +27 and almost knee-deep in a mixture of fuel and water, opened two valves on the 300 line; due to advancing radiation poisoning they did not have the strength to open the valves on the sides. Akimov and Toptunov spent several hours turning valves; the radioactive water in Room 712 was half submerging the pipeline. Smagin went in to open the third valves, spent 20 minutes in the room, and received 280 rads.

Vladimir Sashenok, the automatic systems adjuster from Atomenergonaladka (the Chernobyl startup and adjustment enterprise), was supposed to be in Room 604, the location of the measurement and control instruments on the upper landing across from the turbine room, on level +24, under the reactor feedwater unit; he was reporting the states of the pressure gauges on the multiple forced circulation circuit to the computer room by telephone. The communication lines were cut during the explosion. Shashenok received deep thermal and radiation burns over his entire body when the overpressure spike destroyed the isolation membranes and the impulse pipes of the manometers in his instrument room just before the explosion, which then demolished the room itself. The landing was found damaged, covered with ankle-deep water, and there were leaks of boiling water and radioactive steam. Sashenok was found unconscious in Room 604, pinned under a fallen beam, with bloody foam coming out of his mouth. His body was severely contaminated by radioactive water. He was carried out by Gorbachenko and Palamarchuk and died at 06:00 in the Pripyat hospital under care of the chief physician, Leonenko Vitaliy, without regaining consciousness. Gorbachenko, a radiation monitoring technician, suffered a radiation burn on his back where Sashenok’s hand was located when he helped carry him out. Khodemchuk and Sashenok were the first two victims of the disaster.

Nikolai Gorbachenko, having found Sashenok, returned to his post and changed clothes and shoes. He was then ordered to look for Khodemchuk, but the search was unsuccessful. He went to the control room and with Dyatlov went outside to survey the reactor building. At 05:00, he began feeling weak and vomiting and was transported to hospital, from where he was released on 27 October.

Volodymyr shashenok

06:35 – 37 fire brigades, with a total of 186 fire fighters, have by now been called in. All fires extinguished with the exception of the fire contained inside Reactor 4

08:00 – New shift clocks on at all four units

286 men continue to work on the construction of 5th and 6th reactors

20.00 – A government committee is established, led by Valery Legasov. They are surprised by the bits of graphite they see lying around when they arrive. None of them suspect a graphite fire.

Following the explosion many inhabitants of Pripyat gather on a railway bridge just outside of the city that provides a view of the nuclear power plant. They spoke of beautiful flames in all the colours of the rainbow (the burning graphite) and how the flames reached higher than the pillars of smoke.  Sadly what they didn’t konw, was that the wind that swept over them carried with it a dose of radiation equivalent to 500 Roentgen (exposure to 750 Roentgen/h, 7,5 Sv, is deemed a lethal dose).

Of the people standing on the bridge that night no one survived, it is now often referred to as the “bridge of death”.

Lyubov’ Kovalevskaya was in Pripyat the night of the accident. When she woke up late the next morning, her mother had reported strange sounds coming from the power station during the night. In an interview layer published in June 1987, Kovalevskaya told of what she saw when she went outside that Saturday:

“All the roads were covered in water and some white liquid. Everything was white, foamy, all the curbs…I walked further and saw a policeman here, another there, I had never seen so many policemen in the town. They weren’t doing anything, just sitting in various places, at the post office, the Palace of Culture. As if there was martial law. It was quite a shock. But people were walking about normally, there were children everywhere. It was very hot. People were going to the beach, to their country cottages, many people were already there, or sitting by the stream next to the cooling reservoir. That’s an artificial water reservoir next to the nuclear power station.

Anya, my daughter, had gone to school. I went home and said, ‘Mama, I don’t know what has happened, but don’t let Natasha (my niece) out of the house, and when Anya returns from school, take her straight into the house’. But I didn’t tell her to close the window…I went back to the central square…The reactor was quite visible, one could see that it was burning and that its wall was broken. There were flames above the hole. That chimney between the third and fourth blocks was burning hot, it looked like a burning column… We knew nothing all day. Nobody said anything. Well, they said there was a fire. But about radiation, that radioactivity was escaping, there was not a word. Anya came back from school and said, ‘Mama, we had physical exercise outside for almost a whole hour.’ Insanity.”

27 April – Sunday

Midnight– Buses begin to arrive in Pripyat. They wait for the command to evacuate the city, spending the entire night in a state of alert.

01.13 – The operation of Units 1 and 2 is stopped at 01.13 and 02.13 hours respectively, twenty-four hours after the start of the accident at Block 4.

07.00 – General Pikalov sets out in a truck fitted out with radiation apparatus. He rams through the closed gates and stops at the plant to measure the radiation. He establishes that the graphite in the reactor is burning, and that an enormous amount of radiation and heat is being given off.

10:00 (approx) – Helicopters make first drops of sand, boron and lead

Between 27 April and 1 May, about 1800 helicopter flights deposit over 5,000 metric tons of sand, lead, clay, and neutron absorbing boron onto the burning reactor. It is now known that virtually none of the neutron absorbers reached the core.

Helicopter dropped sand, lead, clay, and neutron absorbing boron.

Helicopters dropped sand, lead, clay, and neutron absorbing boron (

The Ukrainian filmmaker Vladimir Shevchenko captured film footage of an Mi-8 helicopter as its main rotor collided with a nearby construction crane cable resulting in the death of its four-man crew. The photo of the helicopters crew shown in the video clip below was taken by Igor Kostin the day before the crash.

12:00 – radiation levels drop slightly. There was briefly hope that no evacuation would be necessary. However the level of radiation rises again and reaches its maximum level.

14:00 – Evacuation of Pripyat begins.

Residents were given two hours to gather their belongings. The evacuation of Pripyat’s 43,000 residents took 3.5 hours, using 1,200 buses from Kiev. Residents remember that everyone was in a hurry, but nobody was panicking. The residents of Pripyat were asked to carry with them only what was required for two or three days, some food, a change of underwear, and their identity papers. Dosimeters are confiscated.

“Queues of jammed buses left the city. One after the other, like giant beetles, kilometre after kilometre. The traffic was insane. Only a Second World War survivor can imagine a similar scene.” – Resident of Pripyat

Of those who tried to return later, having realised that Pripyat was lost forever, to fetch belongings of affection, some succeeded but many more encountered alarm wired buildings and armed military.
An excerpt of the evacuation announcement:

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

The population of Pripyat are evacuated

The population of Pripyat are evacuated (Igor Kostin).

28 April – Monday

09:30 – Staff at the Forsmark Nuclear Power Plant, Sweden, detect a dangerous surge  in radioactivity. Initially picked up when a routine check reveals that the soles shoes worn by a radiological safety engineer at the plant were radioactive.

21:02 – Moscow TV news announce that an accident has occurred at the Chornobyl Nuclear Power Plant.

“Measures are being taken to eliminate consequences of the accident. Aid is being given to those affected. A government commission has been set up”.

All radio broadcasts run by the state were then 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.

23:00 – A Danish nuclear research laboratory announces that an MCA (maximum credible accident) has occurred in the Chernobyl nuclear reactor. They mention a complete meltdown of one of the reactors and that all radioactivity has been released.

29 April – Tuesday

The sixth item on the main television evening news program, Vremya, says that 2 people died during the accident, a portion of the reactor building was destroyed, and residents of Pripyat and three nearby towns were evacuated.

The first real information in the western world came on Tuesday morning, when a powerful American reconnaissance satellite provided Washington analysts with photos of Chernobyl. They were shocked to see the roof blown off above the reactor and the glowing mass still smoking.

The first Soviet photos of the Chernobyl accident were censored by removal of the smoke before being printed in the newspapers.

Polish authorities decide to distribute iodine tablets in the north-east of the country to infants and children to protect them from thyroid cancer.

30 April – Wednesday

Tass carries a government statement denying western reports on mass casualties. The statement repeats the earlier assertion that only two people died during the accident and that 197 have been hospitalised and levels of radiation are decreasing

Damaged Unit 4 as seen from ground level. ©

1 May – Thursday

The wind has changed direction and is now blowing in the direction of Kiev.
Annual May Day parades held in the Ukrainian capital Kiev and the Byelarus capital Minsk to emphasize that all was “normal”.
The Soviet bureaucrats removed their children from Kiev and other threatened areas immediately after the accident.
A week after the Chernobyl tragedy all the children’s playgrounds in the town of Wiesbaden, south west Germany, were closed due to the level of radiation.

Playground closed due to radiation

German playgrounds closed in south west Germany due to radiation levels (AP Photo/Frank Rumpenhorst).

2 May

Two floors of bubbler pools beneath the reactor served as a large water reservoir for the emergency cooling pumps. After the disaster, the pools and the basement were flooded because of ruptured cooling water pipes and accumulated firefighting water.

The smoldering graphite, fuel and other material above at a temperature of more than 1200 °C,started to burn through the reactor floor and mixed with molten concrete from the reactor lining, creating corium, a radioactive semi-liquid material comparable to lava. If this mixture had melted through the floor into the pool of water, it was feared it would create a serious steam explosion that would eject even more radioactive material from the reactor. It was therefore necessary to drain the pool.

Three engineers volunteered, Alexei Ananenko (who knew where the valves were), Valeri Bezpalov, and, Boris Baranov, whose job was to hold a submersible light. Their light failed almost immediately, and they were forced to proceed in darkness, often underwater, to find the valves. The sluice gates opened, and the water was drained. All of them returned to the surface and according to Ananenko, their colleagues jumped for joy when they heard they had managed to open the valves. Despite their good condition after completion of the task, all of them suffered from radiation sickness, and later died. Some sources claim incorrectly that they died at the plant.

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 table below the reactor. To reduce the likelihood of this, it was decided to freeze the earth beneath the reactor, which would also stabilise the foundations. Using oil drilling equipment, the injection of liquid nitrogen began on 4 May. It was estimated that 25 metric tons of liquid nitrogen per day would be required to keep the soil frozen at −100 °C. This idea was soon scrapped and the room where the cooling system would have been installed was filled with concrete.

Miners and Metro construction workers start tunnel under Unit 3 to construct heat exchanger under No.4 reactor (shown 3.09 minutes in to clip below).

A 30 kilometre zone around the reactor is designated for evacuation (90.000 people).

5 May

An embankment begins to be constructed on the Pripyat River to try and prevent it from being contaminated.

6 May

Emissions of radionuclides drop from 8 million to 150,000
Fluid nitrogen is pumped from along pipes from Unit 1 to freeze the earth under the reactor and prevent a steam explosion.
The first extensive report on the situation appears in Pravda.
Schools in Gomel and Kiev are closed, all children are sent elsewhere. Bringing the total number of people forced to leave to 500.000. 140.000 of which are not allowed to return home.
Kiev radio finally, eleven days late, warns its audience not to eat leafy vegetables and to stay indoors as much as possible.

7 May

Fire brigade pumps drain the basement under the core of water. The operation was not completed until 8 May, after 20,000 metric tons of highly radioactive water were pumped out.
As a reward, the fire fighters receive 1000 rubles each (approximately 2000 US dollars).
The first extensive report on the situation appears in Pravda.
Schools in Gomel and Kiev are closed, all children are sent elsewhere. Bringing the total number of people forced to leave to 500.000. 140.000 of which are not allowed to return home.
Kiev radio finally, eleven days late, warns its audience not to eat leafy vegetables and to stay indoors as much as possible.

8 May

In an interview with Izvestiya, Academician Yevgeny Velikhov, vice-president of the Soviet Academy of Sciences and chief scientist sent to Chernobyl, says the disaster is “without precedent”.

9 May

Lieutenant Volodymyr Pravik, Hero

Lieutenant Volodymyr Pravik, Hero

Lieutenant Volodymyr Pravik, one of the first fireman at the scene, dies of acute radiation sickness a few days before his 24th birthday in Hospital No.6 Moscow. His body laid to rest in a sealed zinc coffin in the Mitinskoe cemetary, Moscow. He posthumously received the medals of the Order of Lenin and hero of the Soviet Union.





IAEA states that Moscow started to encapsulate the reactor, especially pouring concrete under the reactor, preventing it from reaching groundwater.


Residents of Kiev line up to get forms filled out prior to radiation checks for everyone possibly exposed to radioactive fallout, May 9, 1986

Residents of Kiev line up to get forms filled out prior to radiation checks for everyone possibly exposed to radioactive fallout, May 9, 1986

10 May

Aleksandr Akimov dies having received radiation burns to 100% of his body. A senior reactor operator, at the controls in the control room at the time of the explosion; received fatal dose during attempts to restart the feed water flow into the reactor; posthumously awarded the Order “For Courage” of third degree.

According to the IAEA the fire is extinguished, but the temperature in the reactor is still rather high. Meanwhile a Ukrainian government official states: reactor is still burning and fire fighters are continuously trying to put the fire out.


Liquidators wash down Pripyat

Liquidators wash the radioactive dust off the streets using a product called “bourda”, meaning molasses. May 1986.

22 May

Russian First Deputy Health Minister denies popular believe that vodka (& red wine) is a good cure for radiation exposure.

23 May

A Soviet government committee orders the distribution of iodine preparations. At this point it is of no medical value. Radioactive iodine is only active for ten days, and will already have accumulated in the thyroid glands of the inhabitants of the contaminated territories.

27 May

A month after the accident the danger is not yet over. A concrete structure will be built, the idea of the sarcophagus is born.

15 June

Almost the complete management team of the reactor has been dismissed for ‘irresponsibility and lack of control’, Pravda announces. Amongst them Chernobyl Director Victor Bryukanov and deputies (senior engineer) Nikolai Fomin who will be brought on trial a year later.

3 July

Viktor Petrovich Bryukanov imprisoned

Viktor Petrovich Bryukanov imprisoned

The Politbyuro to sentence Viktor Petrovich Bryukanov, the director of the Chernobyl plant at the time of the incident, to 10 years of imprisonment for “serious errors and shortcomings in the work that lead to the accident with severe consequences.” Bryukhanov was also expelled from the communist party.

Having been exposed to large doses of radiation Bryukhanov was suffering from radiation sickness and due to bad health he was released in 1991, having served five years of his sentence. Bryukhanov to this day claims that there was nothing wrong with the reactors themselves and that there was a technical error with the fourth reactor only. He was considered a scapegoat by many.

According to the World Health Organisation, 240,000 recovery workers were called upon between 1986 and 1987 . Altogether, special certificates were issued for 600,000 people between 1986 – 1992 recognizing them as liquidators. Many liquidators were praised as heroes by the Soviet government and the press, while some struggled to have their participation officially recognized for years.

After the explosion the the remaining three reactors were shut down. However even during the reactors’ suspension it was necessary to ensure their maintenance and monitoring.

20 August

A full report on the cause of the accident was submitted (in Russian) to the International Atomic Energy Agency (IAEA). It states there was an extraordinary sequence of carelessness, mismanagement and violations of safety codes leading to the accident.

18 September

Galsjo Forest elk hunters fill a quarry in Northern Sweden with carcasses contaminated with radioactivity

20 September

The Soviet Union has paid out $3 billion, mainly for relocation, compensation and loss of power.

Barbed wire fence around Pripyat, 1986. ©

29 September

Reactor 1 restarts and is connected to the grid on October 1

10 October

Construction work on reactors 5 & 6 is resumed.


October 1st – Work is carried out on the sarcophagus over reactor 4. Construction of reactors 5 and 6, in the background, is soon to resume. (ZUFAROV/AFP/Getty Images)

9 November

Reactor 2 restarts

November – Hans Blix (centre), the director of the International Atomic Energy Agency, watches a video detailing the clean-up operations with members of a government commission.Blix became a central figure of the disaster clean-up , visiting the Chernobyl site several times and overseeing the building of the sarcophagus.

Hans Blix, Director of the International Atomic Energy Agency, visits Chernobyl

Hans Blix, Director of the International Atomic Energy Agency, visits Chernobyl.

14 December

A concrete roof (“sarcophagus”) is completed over the fourth reactor. It is built to protect the environment from radiation for at least 30 years. 300,000 tons of concrete and 6,000 tons of metal constructions were utilised.

construction of the "sarcophagus".

Construction of the “sarcophagus” (

We estimated the situation and saw that the reactor core fragments were scattered over a wide area. Add to that atmospheric movement. So, we realised that there was every reason to cover whatever could be the source of further radioactive discharges. A shelter had to be built. It was another matter, what kind of shelter. But covering it was a must.

It was decided that after a sarcophagus was built, people would be able to come close to it and that radiation measurements on its surface shouldn’t exceed one roentgen an hour. That was unattainable, I regret to say. But the walls did show something near it. Where we failed was the roof.

The work was on the edge of what was possible in engineering terms. You had to have intuition and an immense amount of courage.

The situation began to change and that enabled helicopters to fly at lower altitudes for better observation. We developed specialized bathyscaphe tanks, inside which people were lowered. Every day we gained new knowledge, every day we introduced certain modifications and, as a result, it became possible to do it within a brief period.

Evgeny Akimov, a nuclear engineer from the Chernobyl rescue operation –

One of the specialised bathyscaphe tanks, inside which people were lowered.

One of the specialised bathyscaphe tanks, inside which people were lowered (

22 December

Soviet scientists announce that the sarcophagus now enclosing the reactor was designed for a lifetime of only 20 to 30 years.


March – Vladimir Chevchenko, a Russian filmmaker who documented much of the early response to the disaster dies due to radiation sickness.

21 April

Reactor 3 restarts supplying electricity.

24 April

Construction work on blocks 5 and 6 halted. On May 23, 1989 it is decided not to complete the reactors.

16 September

The Chernobyl disaster has cost the Soviet Union the equivalent of 200 billion UK Pounds, a senior Moscow official discloses.


Norway increases the limit for caesium in reindeer meat for consumption to 6000 Bq/kg. This is extremely high. Sweden also increases their limit to 1500Bq/kg from 300Bq/kg in May 1987. Most countries have a limit of 600 Bq/kg. And even this figure is heavily criticised. But due to this limit much of the reindeer meat can be sold in Scandinavian countries.


October 11

A fire breaks out in the turbine hall of Reactor 2. The fire began in Turbine 4 while it was idle for repairs. A faulty switch caused a surge of current to the turbine, igniting insulating material on some electrical wiring.This subsequently led to a leak of hydrogen, used as a turbine coolant, into the turbine hall which created the conditions for fire to start in the roof and for one of the trusses supporting the roof to collapse.

1991 turbine hall fire

Aftermath of the 1991 turbine hall fire


The Ukraine Government hold an international competition for proposals to replace the hastily constructed sarcophagus over reactor 4.
394 entries are received however only one proposes a sliding arch approach.

A subsequent study confirms that by using this method there is much less chance of the construction workers receiving a harmful dose of radiation.


15 December

Reactor 3, the last functioning reactor, is shut down.


17 September – The project contract for the New Safe Confinement (shelter over reactor 4) is finally signed, with French consortium Novarka constructing the 150 by 257 meter arched structure. Construction costs are estimated at 432 million euros with a project time of five years.

A computer-simulated image of the construction of the New Safe Confinement

A computer-simulated image of the construction of the New Safe Confinement(Image courtesy of NOVARKA)




On October 31, 2008, four residents of the Kyiv region were found guilty of trying to removed 15 tons of contaminated, radioactive scrap metal from the Chernobyl Exclusion Zone. A judge in the Ivankov District Court of Kyiv found the individuals in violation of the requirements of radiation safety. Radiation from this scrap was found to be hundreds of times higher than permissible limits.

Prosecutors in the Kyiv region and the General Directorate had begun investigating organised crime and corruption in the Ukrainian Security Service. The task force found that two of the people involved in the crime were members of the police force.

The verdict, announced on October 31, found all four guilty of the crimes and imprisoned.

Around that time two residents of the Ivankiv District were also arrested while trying to remove the metal from the Chernobyl Exclusion Zone without proper documentation.

Metal theft within the zone

Metal theft within the zone

Looting has always been an issue in the zone. Most valuable articles, such as cars and electrical appliances were deliberately crushed or broken after the accident to prevent theft but many former residents believe a considerable amount of their belongings were in fact stolen. “Even if we considered it, we were too busy and too scared to do it” reports a former liquidator but in the early to mid nineties it was not uncommon for buyers to check the radiation level of household goods for sale at markets.

Sergey Chernenky was stationed in the zone soon after the accident and was responsible for catching looters, who were numerous. These people wanted to make money selling contaminated goods in the markets of Kiev. Sergey recalls that two people once tried to steal a car from the zone. They were able to drive a short distance before they died. The contaminated car had a radiation reading of 6000 roentgen.



Ukraine’s Emergencies Ministry officially began licensing tourist trips . More than 10,000 tourists visit Chernobyl and its surroundings each year. Forbes magazine even names the dead zone one of the world’s most exotic tourist destinations.

20 June

The zone is closed to tourists as trips are suspended.

The prosecutor general’s office conducts checks and rules that the Emergencies Ministry has broken the law by operating trips as well as making an unhealthy profit. With every tourist to the zone paying around a US $100 for entry the Ministry has a turnover of millions dollars every year.

“We urge the ministry to inform the government of every dollar earned by these trips. We know that a lot of money has been made – but we have no idea in whose pockets it ended up. Why not put the money into the budget and use it to solve the zone’s problems?” Alexander Ampleev, a spokesman for Ukraine’s Prosecutor General’s Office.

The Emergencies Ministry files a lawsuit in a bid to resume tours to the contaminated zone.

25 November

A Kiev court officially bans tours to Chernobyl and its surroundings.
Officials rule that the Emergencies Ministry does not have the right to authorise trips to Chernobyl without permission from the Interior Ministry.


19 January

Pripyat is re-opened to tourists. The dispute is resolved, but the cost of entry is raised $130.

13 February

A section of power plant roof collapses after heavy snowfall. The “sarcophagus”, 50 metres away, is unaffected.

A section of power plant roof collapses

A section of power plant roof collapses


Estimated completion date of the New Safe Confinement Shelter over reactor 4.

New Safe Confinement Shelter over reactor 4

Model depicting the completed New Safe Confinement over reactor 4 (image courtesy NOVARKA)

What is the Exclusion Zone?

The “Chernobyl Nuclear Power Plant Zone of Alienation” is the officially designated exclusion area around the site of the Chernobyl nuclear reactor disaster. It is commonly known as the “Chernobyl Exclusion Zone” or simply “The Zone”.

Established soon after the disaster by the Russian military to cover the areas worst affected by radioactive contamination it was initially an area of 30 kilometer (19 mile) radius from the Chernobyl Nuclear Power Plant designated for evacuation and placed under military control. Its borders have since been expanded to cover a larger area of the territory of Ukraine, approximately 2,600 km2.

The purpose of the Exclusion Zone is to restrict access to the most hazardous areas, reduce the spread of radiological contamination and conduct radiological and ecological monitoring activities. Today, the Exclusion Zone is one of the most radioactively contaminated areas in the world and draws significant scientific interest due to the high levels of radiation exposure in the environment, as well as an increasing interest from tourists.

The Chernobyl Exclusion Zone is managed by an agency of the State Emergency Service of Ukraine whilst the power plant itself and its sarcophagus (and replacement) are administered separately.

The Exclusion Zone that surround the power plant. ©

Looking south east across the Zone from the roof of Reactor 5.

Looking south east across the Zone from the roof of Reactor 5

What is Pripyat?

Named after the nearby Pripyat River, Pripyat was founded on 4 February 1970 in northern Ukraine. Built to house the employees of the Chernobyl Nuclear Power Plant 4 kilometres away it became the ninth nuclear city in the Soviet Union. It was officially proclaimed a city in 1979, and had grown to a population of roughly 49,400 before being evacuated in the days following the nuclear disaster in 1986. Pripyat now lies within the Exclusion zone and remains uninhabited due to the high levels of radiation. Along with being a home to the nuclear power plant’s employees, Pripyat was also a major railroad and river cargo port. It was a young and prosperous city with the average age of the population approximately 26 years old.

The evacuation of Pripyat

The population of Pripyat, over 49,000 people, were not immediately evacuated after the explosion at the nuclear power plant in the early hours of Saturday the 26th April 1986. The majority of people, unaware of the explosion or its scale, went about their usual business the following day. Weddings were held, children played outside and gardeners worked on their plots. The smoke rising from the Power Plant, a highly radioactive plume, was explained away by officials as a routine steam discharge.

However, within hours of the explosion, dozens of people began to fall ill. Later, reporting severe headaches and metallic tastes in their mouths, along with uncontrollable fits of coughing and vomiting. A few residents gathered on bridges and rooftops in order to view the burning reactor exposing themselves, in some cases, to doses of radiation that would later prove fatal.

In the early hours of Sunday 27th the first of over 1200 buses began to arrive in Pripyat in preparation for a possible evacuation. Trains at the Yanov railway station were also prepared.
At a meeting between 10:00-12:00 on Sunday morning the chairman of the Governmental Commission provided the local party and Soviet authorities with an update and the evacuation order for Pripyat was announced (the official time and date of the announcement is considered be 12.00, midday, on the 27 April).

At the same time radiation levels began to drop and there was briefly hope that an evacuation would not be necessary. But just two hours later radiation levels rose to what would later be recognised as their highest ever level.

Local radio reported the order to evacuation to residents just after 1pm as police began to work their way from house to house. Residents gathered at the entrances to their homes at 1.50pm and the official evacuation began at 2pm when the first buses and trucks collected the residents and their belongings.

The residents of Pripyat were asked to carry with them only what was required for two or three days away, some food, a change of underwear, and their identity papers. Dosimeters were confiscated.
The evacuation of Pripyat’s residents took 3.5 hours and used all 1,200 buses. Residents recall that everyone was in a hurry, but nobody was panicking. No one would live in Pripyat again.

In the weeks following the evacuation most valuable articles, such as cars and electrical appliances were deliberately crushed or broken to prevent looting but many former residents believe a considerable amount of their belongings were in fact stolen.

Later that year the city of Slavutich was constructed, 45 kilometres, from Pripyat to house the personnel of the Chernobyl nuclear power plant and their families, evacuated from Pripyat. As of 2005 Slavutych had about 25,000 inhabitants with its economic and social situation remains closely linked to the decommissioning of power plants and other facilities within the Zone. Once a year, close to the disasters anniversary, former residents are allowed to return to Pripyat.

The sarcophagus 

The sarcophagus that currently encases Unit 4 of the Chernobyl Nuclear Power Plant is a giant metal concrete and structure quickly constructed as an emergency measure in 1986 to halt the release of radiation into the atmosphere following the explosion. The official Russian name is “Obyekt Ukrytiye” which means shelter or covering.

It is estimated that within the shelter there is 200 tons of radioactive corium, 30 tons of contaminated dust and 16 tons of uranium and plutonium. In 1996 it was considered impossible to repair the sarcophagus as radiation levels within it were as high as 10,000 röntgens per hour (background radiation in cities is around 20-50 microröntgens per hour, a lethal dose being 500 röntgens over five hours). A decision to replace the sarcophagus with a “New Safe Containment” was taken and construction of the new structure is now well underway. Originally planned to be in place by 2005, the New Shelter is expected to be completed by the French consortium Novarka in 2015.

Construction of the sarcophagus

The sarcophagus was constructed under extremely dangerous conditions, with very high levels of radiation, and severe time constraints. Design of the sarcophagus started on May 20 1986, a little over three weeks on from the disaster. The construction lasted for 206 days, from June to late November of the same year. It was first necessary to build a cooling slab under the reactor to prevent the hot nuclear fuel from burning through the foundations. Four hundred coal miners were called upon to dig the required tunnel below the reactor and by June 24 the necessary 168 metre long tunnel was in place.

More than 400,000 m3 of concrete and 7,300 tons of metal framework were used during construction with the building ultimately enclosing 740,000 m3 of heavily contaminated debris and soil inside. The high levels of radiation made it immensely dangerous for humans to carry out work on the sarcophagus and robots were used for joining and welding where possible. The extreme conditions made it impossible to completely seal the seams of the sarcophagus.

The sarcophagus has over 60 bore holes to allow observation of the interior of the core. In places the structure incorporated ventilation shafts to allow for some convection inside. Filtration systems were put in place to prevent radioactive material escaping through these holes.

The construction process consisted of eight stages:

  1. Clearing and concreting the area surrounding reactor unit 4
  2. erection of initial reinforced concrete protective walls around the perimeter
  3. construction of separation walls between units 3 and 4
  4. cascade wall construction
  5. covering of the turbine hall
  6. construction of a high-rise buttress wall
  7. erection of supports and installation of a reactor compartment covering
  8. installation of the ventilation system.

The existing Object Shelter is primarily supported by the damaged remains of the Unit 4 Reactor Building, which are largely considered to be structurally unsound as a result of explosive forces caused by the accident. Three major structural members support the roof of the Object Shelter. Two beams, usually referred to as B-1 and B-2, run in an east-west direction and support the roof beams and panels. A third, more massive member, the “Mammoth Beam”, spans the largest distance across the roof from east to west and assists in supporting the roof beams and panels. The roof of the shelter itself consists of 1 metre diameter steel pipes laid horizontally north to south and steel panels that rest at an angle, also in the north-south direction.

The south wall of the Object Shelter is formed by the steel panels of the roof as they make an angle of approximately 15 degrees from vertical. The east wall of the shelter is formed by the reactor building itself, and the north wall by a combination of the reactor building and concrete segments. The west wall is constructed of large concrete sections reinforced by buttresses. The complexity of the segments of the west wall necessitated their construction off-site; they were then lifted into place by a remotely operated tower crane. It is these buttressed sections of the Object Shelter that are most often recognized in photographs of the sarcophagus.

Inside the sarcophagus

On December 22 1988, Soviet scientists announced that the sarcophagus would only last 20–30 years before requiring restorative maintenance work. The Object Shelter was never intended to be a permanent containment structure. Its continued deterioration has increased the risk of its radioactive contents leaking out. In 2010 it was revealed that water leaking through the sarcophagus roof was becoming radioactively contaminated before seeping through the reactor’s floor into the soil.

Designed Stabilisation Steel Structure

The Designed Stabilisation Steel Structure (DSSS) is the yellow metal work that can be seen against the sarcophagus. It is 63 metres tall and has a series of cantilevers that extend through the western buttress wall, and is intended to stabilise the sarcophagus. This DSSS was put in place because if the wall of the reactor building or the roof of the shelter were to collapse, then large amounts of radioactive dust and particles would be thrown into the atmosphere. In December 2006 the “Designed Stabilisation Steel Structure” (DSSS) was extended until 50% of the roof load (about 400 tons) was transferred from the axis 50 wall to the DSSS.

Upper Biological Shield

A further threat is the concrete slab that formed the “Upper Biological Shield” (UBS), situated above the reactor prior to the accident. This concrete slab was thrown upwards by the explosion in the reactor core and now rests at approximately 15° from vertical. The position of the upper bioshield is considered inherently unsafe, as only debris supports it in its nearly upright position. If the bioshield were to move it would disturb the radioactive dust, resulting in a release of material, and could potentially damage the shelter itself. The UBS is a circle 15 meters in diameter, weighing 1000 tons and consisting of 2000 cubes, each located above a fuel channel. The shield, called Pyatachok (“five kopek coin”) before the disaster, was afterwards named Component “E” and nicknamed “Elena”; the twisted fuel bundles still attached to it are called “Elena’s hair.

The recent collapse

On Tuesday 12 February 2013 a 600 m2 section of the roof of the turbine-building, adjacent to the sarcophagus, collapsed. Initially it was assumed that the roof collapsed because of the weight of the snow on it. However the amount of snow was not exceptional, and the report of a Ukrainian fact-finding panel concluded that the part collapse of the turbine-building was the result of sloppy repair work and aging of the structure. Experts such as Valentin Kupny, former deputy director of the nuclear plant, did warn that the complex was on the verge of a collapse, leaving the building in an extremely dangerous condition. After the 12 February incident, radiation levels were up to 19 becquerels per cubic meter of air: 12 times normal. The report assumed radioactive materials from inside the structure spread to the surrounding area after the roof collapsed. All 225 workers employed by the Chernobyl complex and the French company, Novarka, that is building the new shelter were evacuated shortly after the collapse. The managers of the complex stated that radiation levels around the plant were at normal levels (between 5 and 6 mS/h) and should not affect workers’ health. According to Valentin Kupny the situation was underestimated by the Chernobyl nuclear complex managers and information was kept secret.

New Safe Confinement

The New Safe Confinement (NSC or New Shelter) is the structure, paid for by the Chernobyl Shelter Fund, intended to fully contain the damaged nuclear reactor and prevent the reactor complex from leaking further radioactive material into the environment for the next 100 years. The confinement is expected to be completed by the French consortium Novarka in 2015.

Photographs of construction progress can be seen at

The word “confinement” is used rather than the traditional “containment” to emphasize the difference between the “containment” of radioactive gases that is the primary focus of most reactor containment buildings, and the “confinement” of solid radioactive waste that is the primary purpose of the New Safe Confinement.
Objectives of the NSC:

  • Make the destroyed ChNPP Unit 4 environmentally safe (i.e. contain the radioactive materials at the site to prevent further environmental contamination)
  • Reduce corrosion and weathering of the existing shelter and the Unit 4 reactor building
  • Mitigate the consequences of a potential collapse of either the existing shelter or the Unit 4 reactor building, particularly in terms of containing the radioactive dust that would be produced by such a collapse.
  • Enable safe deconstruction of unstable structures (such as the roof of the existing shelter) by providing remotely operated equipment for their deconstruction.

International competition

In 1992, the Ukraine Government held an international competition for proposals to replace the existing sarcophagus. Of the 394 entries 19 entries were examined in detail, with only the British submission proposing a sliding arch approach. There was no overall winner with the French submission came 2nd with the UK and German proposals coming joint 3rd.

Subsequently, a pan-European study (the TACIS programme) re-examined the proposals of the top three finalists of the competition and the study selected the sliding arch proposal as the best solution for their further investigations and recommendations. By using the sliding method there is much less chance of the construction workers receiving a harmful dose of radiation.
The advantages of a sliding arch include:

  1. Off site construction limits the radiation doses of the construction workers to a minimum.
  2. An arch fits snugly over the damaged reactor (minus its chimney).
  3. An arch is easier to slide than a square box.

The arch-shaped steel structure will have an internal height of 92.5 metres (303.5 ft) and the internal span of the arch is to be 245 metres (803.8 ft). The dimensions of the arch were determined based upon the need to operate equipment inside the new shelter and decommission the existing shelter. The overall length of the structure is 150 metres (492.1 ft). The ends of the structure will be sealed by vertical walls assembled around, but not supported by, the existing structures of the reactor building.

The NSC is to being constructed 180 metres (590 ft) west of unit four and slid into place. The final phase of construction of the NSC involves the deconstruction of the unstable structures associated with the original Object Shelter. The goal of deconstruction has imposed significant requirements upon the load carrying capacity of the arches and foundation of the NSC, as these structures must carry the weight of not only the suspended cranes to be used in deconstruction, but also the loads of those cranes. The NSC design includes two bridge cranes suspended from the arches. These cranes travel east to west on common runways and each has a span of 84 metres (276 ft).

Workers carry two dosimeters, one showing real-time exposure and the second recording information for the worker’s dose log. Workers have a daily and annual radiation exposure limit. Their dosimeter beeps if the limit is reached and the worker’s site access is cancelled.

Project status

The New Safe Confinement (NSC) was originally intended to be completed in 2005, but the project has gone through several delays. In June 2003 the projected completion date was slated for February 2008. In 2009, planned completion was projected for 2012; the same year, progress was made with stabilisation of the existing sarcophagus, which was then considered stable enough for another 15 years. On February 2010 the reported completion date of the NSC was pushed back to 2013, then summer 2015. The estimated completion date is now estimated to be 2017.

30 September 2013 – The international team of engineers completes the first stage of the protective sarcophagus.

24 July 2015 – The ‘western’ and ‘eastern’ halves of the arch of the New Safe Confinement (NSC) are joined together.