139 Fun Facts About Chernobyl

On what date did reactor 4 at Chernobyl explode?

Reactor 4 exploded at 01:23 on 26 April 1986, a Saturday, with the night shift at the controls; the blast tore off the reactor's 1,000-tonne upper lid.

Which numbered unit at the Chernobyl plant blew up in 1986?

Unit 4 was the reactor that exploded; its twin, Unit 3, shared the same building and kept generating electricity until it was finally shut down in December 2000.

Besides Chernobyl, which accident is the only other one rated at Level 7, the maximum on the International Nuclear Event Scale?

Fukushima, after Japan's 2011 earthquake and tsunami, joined Chernobyl as the only Level 7 events on the International Nuclear Event Scale.

What was the reactor crew attempting when the accident happened?

The idea was to see whether the coasting turbine could power the coolant pumps until the diesel generators kicked in.

What type of Soviet reactor was used at Chernobyl?

Chernobyl's four units were RBMK reactors, a graphite-moderated, water-cooled Soviet design with individual pressure tubes instead of a single pressure vessel.

The RBMK design flaw known as a positive void coefficient meant that steam voids in the coolant did what?

Steam voids increased core reactivity: in an RBMK the water absorbed more neutrons than it moderated, so boiling removed an absorber and power rose, a positive feedback loop with little to restrain it.

Which fission by-product 'poisoned' the reactor, dragging power far below the test plan?

Xenon-135, a strong neutron absorber, accumulates when power falls; after the reactor slumped to about 30 MW thermal, it held output far below the 700 MW the test plan required.

What was the designation of the emergency shutdown button pressed at 01:23:40?

AZ-5 was the RBMK's emergency protection button; pressing it drove every control rod into the core at once, and within seconds power surged instead of falling.

What was on the tip of each RBMK control rod, displacing water and briefly boosting power?

Each rod ended in a graphite extension, or displacer; on insertion the graphite displaced water at the bottom of the channel, briefly adding reactivity, the 'positive scram effect' INSAG-7 highlighted.

Which deputy chief engineer was on hand to direct the fatal test?

Anatoly Dyatlov, the plant's deputy chief engineer, supervised the test in person and survived acute radiation sickness; shift supervisor Akimov and operator Leonid Toptunov, at the controls, both died within weeks.

How long after the accident did the Soviet government establish the initial 10-kilometre exclusion zone?

The 10-km zone came 36 hours after the explosion, when the evacuation of Pripyat began at 14:00 on 27 April; the whole city was emptied by late afternoon.

Radiation from Chernobyl was first detected outside the USSR at a nuclear plant in which country?

Sweden raised the alarm: on the morning of 28 April workers at a Swedish nuclear plant some 1,100 km away set off contamination alarms, and by evening Moscow had admitted an accident.

The Soviet Union first acknowledged the accident on which TV news programme?

The 20-second statement was read on Vremya, Soviet television's main evening news, at 21:02 on 28 April, two days after the explosion.

What was dropped from helicopters onto the burning reactor in the days after the explosion?

Helicopter crews dropped some 5,000 tonnes of sand, lead, clay and boron onto the ruin in the fortnight after the blast; later analysis suggested very little of it reached the core.

Until what date did the fire inside reactor 4 keep burning?

Possibly more than half of the reactor's graphite burned away in those two weeks.

Engineer Oleksiy Ananenko volunteered to open the sluice gates and drain what beneath the reactor?

The three volunteers drained the bubbler pools, the pressure-suppression pools beneath the reactor; officials feared molten corium reaching that water would trigger a steam explosion, but it dripped in harmlessly.

Coal miners were brought in to dig a tunnel under the reactor to install what?

The miners were to install a cooling system, a nitrogen-fed heat exchanger beneath the reactor to stop a meltdown reaching the groundwater; it was never switched on and the cavity was filled with concrete.

Roughly what share of the debris on the reactor roof was cleared by robots before humans took over?

Robots managed only about 10% of the roof debris before radiation crippled their electronics; some 3,828 men, nicknamed 'biorobots', shovelled the rest by hand before the sarcophagus was sealed.

What name was given to the hundreds of thousands of clean-up workers?

Liquidators was the collective name for the soldiers, miners, pilots and workers who contained the disaster; they received a special medal and certificate but often worked with little protection.

Which Soviet scientist led the commission and presented its findings to the IAEA in 1986?

Valery Legasov, an inorganic chemist rather than a reactor specialist, delivered the five-hour Soviet report that August; he later said 'I did not lie in Vienna, but I did not tell the full truth'.

What happened to the scientist who led the Chernobyl commission on 27 April 1988, a day after the second anniversary?

He had recorded audio tapes, The Legasov Testament, describing the liquidation and the reactor's flaws.

Which deputy chairman of the Council of Ministers headed the government commission sent to Chernobyl?

Boris Shcherbina, a deputy chairman of the Council of Ministers, reached the plant on the evening of 26 April and ran the commission on site; he died in 1990, aged 70.

What was the population of Pripyat when it was evacuated the day after the explosion?

About 49,000 people lived in Pripyat, a young city of plant workers with an average age of about 26, when it was emptied on 27 April 1986.

Pripyat's famous abandoned Ferris wheel had been due to open officially for which holiday?

The amusement park, Ferris wheel included, was scheduled to open officially on 1 May 1986 for the May Day holiday, five days after the disaster.

Which purpose-built city replaced Pripyat as home for the plant's workers?

Slavutych, begun in late 1986 and occupied from 1988, sits some 45 km east of the plant across the Dnieper; a rail line through Belarusian territory linked it to the plant.

The pine woodland near the Chernobyl plant whose trees died after absorbing high levels of radiation became known as what?

The Red Forest takes its name from the ginger-brown colour its pines turned as they died; it lies just west of the plant, directly under the path of the first plume.

What is the 'Elephant's Foot'?

It was once so hard that an armour-piercing AK-47 round was needed to chip a sample; it has since softened to a sand-like texture.

Which of Chernobyl's neighbouring Soviet republics got about 60% of the fallout on the USSR?

Belarus, whose border lies only about 16 km from the plant, took the brunt when the first plume drifted north; roughly a fifth of Belarusian territory was contaminated.

Which two isotopes were most responsible for radiation doses to the general population?

Iodine-131 has an eight-day half-life and drove the surge in childhood thyroid cancers; caesium-137 still keeps the zone closed.

Movement restrictions on sheep from contaminated British uplands were lifted in which year?

The final controls, on farms in North Wales and Cumbria, were lifted in 2012, 26 years after the accident; as late as 2009 some 369 farms were still under restrictions.

As of 2005, roughly how many cases of childhood thyroid cancer had occurred in the affected populations?

UNSCEAR counted more than 6,000 thyroid cancers diagnosed by 2005 among people who were children or adolescents in 1986; fifteen had proved fatal, and 'a large fraction' were attributed to the accident.

How many of the 134 workers with acute radiation syndrome died within three months?

Of the 134 workers with confirmed acute radiation syndrome, 28 died within the first months, most of them firefighters and plant staff; two more workers had been killed by the explosion itself.

The New Safe Confinement, the arch slid over the old sarcophagus, was designed to last how long?

French consortium Novarka built it with firms from 24 nations; a Russian drone damaged it in February 2025.

Ukraine's decommissioning plan targeted completion of the reactor clean-up by which year?

Ukraine's decommissioning plan set 2065 as the target for finishing the clean-up of reactor 4's debris; the New Safe Confinement was assembled beside the reactor from 2010 and slid into place in 2016.

Which Soviet over-the-horizon radar near Chernobyl was nicknamed the 'Russian Woodpecker'?

Duga, the giant over-the-horizon radar whose antenna array rises about 150 m near the plant, earned the 'Russian Woodpecker' nickname from the sharp tapping it put onto shortwave bands worldwide.

Which endangered wild equine was introduced to the exclusion zone in 1998?

Thirty-one Przewalski's horses were released in the zone in 1998 to graze the abandoned farmland; despite poaching losses, the herd later grew to well over a hundred.

Which two video games are credited with boosting tourism to Pripyat and the exclusion zone?

S.T.A.L.K.E.R.: Shadow of Chernobyl and Call of Duty 4: Modern Warfare, both released in 2007 and both set partly in Pripyat, were widely credited with drawing gamers to the zone; the 2019 HBO series gave another boost.

Russian troops occupied the Chernobyl plant during the Ukraine invasion from 24 February until when?

Russian forces pulled out on 31 March 2022 after five weeks, having formally handed control back to the plant's staff; during the occupation they had dug trenches in the Red Forest.

The Chernobyl plant originally carried the name of which Soviet leader?

The 'V. I. Lenin' was dropped from the name after Ukrainian independence.

Who created and wrote the 2019 HBO/Sky miniseries Chernobyl?

Craig Mazin, until then best known for comedies such as The Hangover Part II, created and wrote every episode; he won the 2019 Emmy for writing a limited series.

In the miniseries, Emily Watson's scientist Ulana Khomyuk is what?

Jared Harris played Legasov and Stellan Skarsgard played Shcherbina.

The miniseries shot its reactor scenes at the decommissioned Ignalina plant in which country?

Ignalina, in Lithuania, had two RBMK reactors, the only ones built outside Russia and Ukraine; its last unit was shut down in 2009 as a condition of EU membership.

Which two RBMK plants entered service before Chernobyl, the USSR's third?

Leningrad (1973) and Kursk (1976) were the first RBMK stations; Chernobyl's unit 1 followed in 1977, while Smolensk and Ignalina only started up in the 1980s.

Roughly how far is the Chernobyl plant from Kyiv?

The plant lies about 100 km north of Kyiv on the Pripyat River; the capital's May Day parade went ahead on 1 May 1986 despite elevated radiation in the city.

Between which years did the plant's four reactors enter commercial operation?

Unit 1 entered commercial service in 1978 and unit 4 in 1984; units 5 and 6 were still under construction when the accident halted work for good.

The plant's cooling pond lay 5 km from the Pripyat River's junction with which river?

The pond lay about 5 km from the river's junction with the Dnieper.

Which Soviet pressurised-water reactor design is contrasted with the RBMK as safer?

The VVER, a pressurised-water reactor with a steel pressure vessel and a negative void coefficient, became the USSR's export design; the RBMK was cheaper to build but had no full containment.

What does the RBMK acronym translate to in English?

RBMK stands for Reaktor Bolshoy Moshchnosti Kanalnyy, 'high-power channel-type reactor': the fuel sits in individual pressure channels running through a large graphite moderator block.

Which RBMK unit was the only one built to the revised post-1986 OPB-88 safety standards?

Smolensk-3, the last RBMK ever completed, was the only unit built to the OPB-88 rules adopted after the accident, which earned it the 'third generation' label.

On what date was Pripyat founded?

It was proclaimed a city in 1979 and grew to 49,360 people.

Which Russian oblast received the heaviest Chernobyl fallout of any region in Russia?

Bryansk Oblast, bordering both Belarus and Ukraine, took the heaviest fallout in Russia; rain brought the caesium plume down over its south-western districts in the last days of April 1986.

Why was access to Pripyat unrestricted before the disaster, unlike military towns?

Pripyat was a model 'atomograd', an atomic city.

What radius did the Soviet authorities set for the full exclusion zone in May 1986?

The 30 km radius, set in early May 1986 after the first 10 km zone proved inadequate, gave the area its lasting name, the 30-Kilometre Zone; it was evacuated and placed under military control.

Roughly how large is the Ukrainian part of the Chernobyl exclusion zone?

The Ukrainian zone covers about 2,600 square kilometres, roughly the size of Luxembourg; across the border it adjoins Belarus's Polesie State Radioecological Reserve, which adds some 2,100 more.

What are the returnees who illegally live inside the exclusion zone called?

Samosely, 'self-settlers', are mostly elderly villagers who returned illegally within months of the evacuation; their numbers dwindled from over a thousand to a couple of hundred by the 2010s.

In which year was Chernobyl's Unit 1 permanently shut down?

Unit 1 was shut down on 30 November 1996 under a 1995 memorandum with the G7 and the European Union that traded closure for Western aid; unit 3 ran on until 2000.

US scientist Jim Beasley, who studies the zone's wolves, is based at which university?

Jim Beasley is a wildlife ecologist at the University of Georgia's Savannah River Ecology Laboratory; his team has collared wolves and camera-trapped other mammals across the zone.

Who directed the HBO/Sky miniseries Chernobyl?

Johan Renck, a Swedish director who had worked on Breaking Bad and David Bowie's 'Blackstar' video, directed every episode and won the 2019 Emmy for directing a limited series.

How many episodes did the miniseries Chernobyl have?

The five episodes ran weekly from 6 May 2019 on HBO, with Sky Atlantic airing each a day later in the UK; the finale, 'Vichnaya Pamyat', aired on 3 June.

How many Primetime Emmy nominations did the miniseries receive?

Chernobyl received nineteen Primetime Emmy nominations in 2019 and won ten, including Outstanding Limited Series, Directing and Writing.

Which actor won a Golden Globe for playing Soviet official Boris Shcherbina in the 2019 miniseries Chernobyl?

Stellan Skarsgård took Best Supporting Actor at the 77th Golden Globes, where Chernobyl also won Best Miniseries; Jared Harris played Valery Legasov.

Which Icelandic composer wrote the miniseries' score?

Cinematographer Jakob Ihre drew on Soviet films like Stalker and Come and See.

Which Vilnius district stood in for Pripyat in the miniseries?

Fabijoniškės, a 1980s Soviet-built housing district of Vilnius, doubled for Pripyat; filming began there on 13 May 2018.

Which Russian culture minister called the miniseries 'masterfully made'?

Vladimir Medinsky, Russia's culture minister from 2012 to 2020, praised the series as 'masterfully made'; his father had been one of the liquidators.

Which French consortium designed and built the New Safe Confinement?

Novarka was a joint venture of Vinci Construction Grands Projets and Bouygues Travaux Publics; the arch it built weighs some 36,000 tonnes and spans 257 metres.

Roughly what was the estimated total cost of the Shelter Implementation Plan?

The Shelter Implementation Plan was costed at around €2.15 billion, of which the New Safe Confinement itself accounted for about €1.5 billion.

Which institution managed the international Chernobyl decommissioning funds?

The EBRD managed the Chernobyl Shelter Fund on behalf of dozens of donor governments and organisations, and in 2015 committed extra money of its own to cover the remaining shortfall.

Between which months of 1986 was the original Shelter Structure built?

It was an emergency measure to confine reactor 4's radioactive material.

About how many tons of radioactive corium did the sarcophagus lock in?

The shelter sealed in about 200 tons of radioactive corium, along with 30 tons of highly contaminated dust and 16 tons of uranium and plutonium.

What is the Ukrainian name of the sarcophagus?

Officially the Shelter Object (Ob'yekt Ukryttia), the structure was built so hastily that by 1996 its roof and walls needed stabilisation work; it was never expected to last more than about 30 years.

Valery Legasov was first deputy director of which atomic energy body?

Legasov was first deputy director of the Kurchatov Institute of Atomic Energy in Moscow from 1983, under Anatoly Aleksandrov, despite being an inorganic chemist rather than a reactor physicist.

Which honorary title did Boris Yeltsin posthumously give Legasov in 1996?

Yeltsin named Legasov a Hero of the Russian Federation on 20 September 1996, eight years after his death; in 1986 Gorbachev had reportedly struck him from the list for Hero of Socialist Labour.

In which city was Valery Legasov born?

Valery Legasov was born in Tula on 1 September 1936, the son of a Communist Party official; he went on to study chemical technology at Moscow's Mendeleev Institute.

Anatoly Dyatlov was released from prison in 1990 for what reason?

He died in 1995, most likely from radiation exposure.

Dyatlov received what sentence at the 1987 trial?

Dyatlov, Bryukhanov and Fomin each got the maximum ten years in a labour camp at the July 1987 trial held in the town of Chernobyl; all six defendants were found guilty.

Where did Dyatlov graduate with honours in 1959?

Dyatlov graduated with honours from the Moscow Engineering and Physics Institute (MEPhI) in 1959, then spent years fitting reactors into submarines at a shipyard in Komsomolsk-on-Amur.

Plant director Viktor Bryukhanov was born in which city?

Viktor Bryukhanov was born in Tashkent, Uzbek SSR, on 1 December 1935 and trained as an engineer there before a career at thermal power plants; he directed the Chernobyl plant from 1970 until 1986.

Which chief engineer refused to shut down reactor 3 on the night of the accident?

Chief engineer Nikolai Fomin refused; night-shift chief Yuri Bagdasarov wanted to shut reactor 3 down at once and finally did so on his own initiative that morning as coolant reserves ran low.

At what exact time did the fatal test begin?

The rundown test began at 01:23:04, when steam to the turbine was shut off; the emergency shutdown button was pressed 36 seconds later, at 01:23:40.

Radiation alarms first sounded on 28 April 1986 at which Swedish plant?

Forsmark, north of Stockholm, lies more than 1,000 km from Chernobyl; a worker's shoes set off a contamination monitor on the morning of 28 April, and staff first suspected a leak at their own plant.

Roughly how many personnel did the Soviet response involve?

More than 500,000 personnel took part in the Soviet response, at an estimated cost of 18 billion rubles.

Chernobyl released roughly how many times more radioactive material than the Hiroshima bomb?

Chernobyl released about 400 times as much radioactive material as the Hiroshima bomb, because a reactor core holds far more accumulated fission products than a single weapon produces.

Which Ukrainian president ordered the final shutdown of reactor 3 in December 2000?

Leonid Kuchma gave the order by video link from Kyiv on 15 December 2000, and the reactor 3 operator pressed the shutdown button, ending electricity generation at the site.

By 2000, roughly how many people had been permanently resettled from the worst-hit areas?

About 350,000 people had been resettled by 2000: some 116,000 evacuated in 1986 and a further 220,000 or so moved out of the worst-hit districts in the years that followed.

In which year did the UN create the Chernobyl Trust Fund for victims?

The UN Chernobyl Trust Fund was set up in 1991, five years after the accident, to channel aid to the affected regions; coordination of UN Chernobyl work passed to the UN Development Programme in 2004.

The name Chornobyl comes from the Ukrainian word for which plant?

Chornobyl is the Ukrainian name for Artemisia vulgaris, the mugwort or common wormwood; the link to the 'Wormwood' star of Revelation became a popular apocalyptic motif after 1986.

Roughly how many square kilometres were contaminated by caesium-137 above 555 kBq/m2?

Cs-137 and I-131 caused most of the population's radiation dose.

In which year did Ukraine designate most of the exclusion zone a biosphere reserve?

The Chornobyl Radiation and Ecological Biosphere Reserve was created by presidential decree in April 2016, covering about 2,270 square kilometres of the zone.

Roughly how many residents lived in the town of Chernobyl before the 1986 evacuation?

Its 2020 population was estimated at just 150 people.

In which year is Chernobyl first mentioned, as a ducal hunting lodge?

Chernobyl is first recorded in 1193 in the Hypatian Codex, as a hunting lodge of Prince Rostislavich, almost eight centuries before the nuclear plant.

Which Hasidic family made Chernobyl a major religious centre in the 18th century?

Jews began moving into the town in the 16th century.

Between which years did the Duga radar system operate?

Duga operated from July 1976 to December 1989; two operational systems were built, one near Chernobyl and one near Komsomolsk-on-Amur in the Russian Far East.

What NATO reporting name was given to the giant Duga antenna?

NATO called the array Steel Yard; the larger of the two antennas near Chernobyl stands about 150 m tall, and its beams were aimed over the pole towards North American missile fields.

At what frequency did the Duga 'woodpecker' tapping sound repeat?

The signal pulsed at 10 Hz, ten taps a second, which gave it the woodpecker sound; it disrupted broadcasts so badly that some receivers added 'Woodpecker Blanker' circuits.

Which firm, based in Yeysk, manufactured the rides of Pripyat's amusement park?

The Yeysk-based Attraktsion plant was the Soviet Union's main maker of Ferris wheels and park rides, supplying 'Parks of Culture and Rest' like Pripyat's across the country.

Until what year did liquidators keep using Pripyat's Azure swimming pool?

The Azure (Lazurny) pool stayed in use until 1998, a dozen years after the evacuation, because liquidators working in the zone needed somewhere to keep fit; it is one of Pripyat's best-known ruins.

Roughly how many people lived in Slavutych in the 2020s?

Slavutych's population stayed in the low twenty-thousands from the 1990s, about 24,000 at the 2001 census; administratively it is an exclave of Kyiv Oblast inside Chernihiv Oblast.

How large is the Red Forest area around the plant?

The Red Forest covers about ten square kilometres immediately west of the plant, where the pines absorbed the highest doses from the first plume.

Why is none of today's Red Forest woodland the pine that was irradiated in 1986?

The young forest now shelters wolves, lynx, bison and brown bears.

In which month was the Elephant's Foot discovered?

It sits in a maintenance corridor beneath the ruined reactor.

Which isotope released at Chernobyl has a half-life of about 24,000 years?

Plutonium-239 has a half-life of about 24,100 years; together with its decay products it leaves the most contaminated ground near the plant hazardous for tens of thousands of years.

How many UN organisations make up the Chernobyl Forum?

The Chernobyl Forum brought together eight UN bodies, the IAEA, WHO, UNDP, FAO, UNEP, UN-OCHA, UNSCEAR and the World Bank, plus the governments of Belarus, Russia and Ukraine.

Where was the Chernobyl Forum founded in February 2003?

The Forum was founded at the IAEA's headquarters in Vienna at a meeting on 3-5 February 2003; its main report, released on 5 September 2005, put eventual deaths at up to 4,000 among the most exposed.

Where was firefighter Vasily Ignatenko buried after dying of radiation sickness?

Ignatenko and the other first responders who died of radiation sickness in Moscow were buried at Mitinskoe Cemetery in sealed zinc coffins, where a memorial to them now stands.

Ignatenko's widow Lyudmilla told her story to which Nobel-winning author?

Svetlana Alexievich, the Belarusian journalist who won the 2015 Nobel Prize in Literature, opened her 1997 oral history of the disaster with Lyudmilla Ignatenko's monologue.

Ignatenko served with which numbered Pripyat brigade of paramilitary firefighters?

Ignatenko was a senior sergeant in Pripyat's Paramilitary Fire Brigade No. 6 (SVPCh-6), which reached the burning reactor within minutes alongside the plant's own fire crew.

Fire commander Leonid Telyatnikov was awarded which top honour in September 1986?

Telyatnikov, the plant's fire chief, was made a Hero of the Soviet Union on 25 September 1986, together with two lieutenants honoured posthumously; he survived his dose and died of cancer in 2004.

Under what title was Alexievich's oral history of the disaster published in the UK?

Penguin published Anna Gunin and Arch Tait's translation as Chernobyl Prayer in 2016, a literal rendering of the Russian Chernobylskaya molitva; the earlier US edition was called Voices from Chernobyl.

Which US prize did the American translation of Voices from Chernobyl win in 2005?

Keith Gessen's translation, Voices from Chernobyl, won the National Book Critics Circle Award for general nonfiction for 2005, the year Dalkey Archive Press published it in the US.

Which Paranormal Activity creator co-wrote and produced the 2012 film Chernobyl Diaries?

It grossed $37 million on a $1 million budget.

Which 1971 novella lent its background and terminology to the S.T.A.L.K.E.R. game?

Tarkovsky's 1979 film Stalker also inspired it.

Which Ukrainian studio developed S.T.A.L.K.E.R.: Shadow of Chernobyl?

GSC Game World, founded in Kyiv by Sergiy Grygorovych, developed the game over some six years before THQ published it in March 2007.

How many endings does S.T.A.L.K.E.R.: Shadow of Chernobyl have?

The player is the amnesiac Marked One hunting the mysterious Strelok.

In which Oscar category did the 2003 film Chernobyl Heart win?

Chernobyl Heart, directed by Maryann DeLeo, won the Academy Award for Documentary Short Subject at the 2004 ceremony; its title refers to the heart defects seen in children of the region.

Which Irish charity founder appears in Chernobyl Heart?

Adi Roche, who founded Chernobyl Children's Project International in Cork in 1991, guided the filmmakers through Belarusian hospitals and orphanages.

Which 1988 disaster was Boris Shcherbina put in charge of after Chernobyl?

He retired in 1989 and died in 1990.

Shcherbina was influential in developing which industry in Siberia's Tyumen Oblast?

As Tyumen party boss from 1961 to 1973 Shcherbina drove the opening of the West Siberian oil and gas fields, then ran the ministry that built oil and gas facilities before his 1984-1989 stint as deputy premier.

Which actor directed and starred in the 2021 Russian film Chernobyl: Abyss?

Danila Kozlovsky directed and starred in Chernobyl: Abyss, released in Russia in April 2021 and sold abroad as Chernobyl 1986; he plays a Pripyat firefighter drawn into the clean-up.

What colour are the gondolas of Pripyat's abandoned Ferris wheel?

The wheel's yellow gondolas, faded and rusting, became the zone's most photographed image; it stands in the amusement park beside the Palace of Culture Energetik.

How old was senior reactor control engineer Leonid Toptunov on the night of the accident?

Leonid Toptunov, born in August 1960, was 25 when he sat at the controls of Unit 4; he died of radiation sickness in a Moscow hospital on 14 May 1986.

In which town did senior reactor engineer Leonid Toptunov study nuclear engineering?

Toptunov graduated from the Obninsk Institute for Nuclear Power Engineering in 1983, in the town that housed the world's first grid-connected nuclear plant, and joined Chernobyl the same year.

Which safety system did the operators switch off before starting the rundown test?

The emergency core cooling system was switched off so that it would not flood the core with water during the rundown; the disconnection had been written into the test programme itself.

Photographer Igor Kostin worked for which Soviet press agency when he covered Chernobyl?

Igor Kostin was the Kyiv-based photographer of the Novosti Press Agency (APN); his famous first image of the ruined reactor, taken on 26 April, came out grainy and fogged because radiation had damaged the film.

How did Igor Kostin reach the plant to take his first photograph of the ruined reactor?

Kostin flew over the plant in a helicopter on 26 April after a pilot friend tipped him off; he shot through an open window, and radiation ruined nearly all of the film.

Which 1957 accident is the only one rated Level 6 on the INES scale?

The Kyshtym disaster of 29 September 1957 was a chemical explosion in a tank of liquid nuclear waste at the Mayak plutonium plant; it was kept secret in the USSR for decades.

Which closed city, now Ozyorsk, was the site of the 1957 Mayak waste-tank explosion?

Mayak's closed city was Chelyabinsk-40, later renumbered Chelyabinsk-65 and renamed Ozyorsk in 1994; the plume contaminated the strip known as the Eastern Ural Radioactive Trace.

In which year did the IAEA introduce the International Nuclear Event Scale?

The IAEA and the OECD Nuclear Energy Agency introduced INES in 1990, four years after Chernobyl; each level is roughly ten times as severe as the one below.

What INES level was the 1979 Three Mile Island accident given?

Three Mile Island was rated Level 5, an 'accident with wider consequences': the core partly melted but releases beyond the site were small; the 1957 Windscale fire received the same rating.

In which year was Belarus's Polesie State Radioecological Reserve established?

The Polesie State Radioecological Reserve was created in 1988 in the most contaminated part of Gomel Oblast, two years after the accident, and was enlarged in 1993.

Roughly what area did the Polesie State Radioecological Reserve cover when established?

The reserve covered about 1,300 square kilometres at its creation and was later enlarged to some 2,160; it encloses the Belarusian territory worst affected by fallout.

What nickname did plant workers give reactor 4's upper biological shield?

The upper biological shield, 'Structure E', was nicknamed Elena; the explosion flipped the roughly 1,000-tonne disc, which came to rest tilted on edge inside the reactor shaft.

Who commanded the first firefighter brigade on the scene, dying of radiation sickness two weeks later?

Lieutenant Volodymyr Pravyk led the plant's own fire brigade onto the roofs within minutes; he died in Moscow on 11 May 1986, and his crew had no idea the scattered graphite was lethal.

When buses arrived to evacuate Pripyat on 27 April 1986, how long were residents told they would be away?

Residents were told to bring documents and food and to expect about three days away; a column of more than a thousand buses emptied the city by late afternoon, and most belongings were never recovered.

Roughly how many Soviet pilots flew helicopter drops of sand, lead, clay and boron onto the reactor?

More than 600 Soviet pilots flew the thousands of sorties needed to smother reactor 4, several taking lethal doses; a Mi-8 crashed in October 1986 when its rotor clipped a crane cable, killing four.

How long did Chernobyl's backup diesel generators take to reach full load, a gap the turbine run-down test was meant to bridge?

The diesels needed 60-75 seconds to generate the 5.5 MW that runs one main pump; bridging that gap was the point of the test, with pump inertia providing coolant meanwhile.

At Chernobyl, how long did the RBMK reactor's control rods take to travel the full 7-metre height of the core?

The rods crawled at 0.4 m/s, taking 18 to 20 seconds to travel the core, and their graphite tips first displaced neutron-absorbing water, briefly boosting reactivity.

The last reading on reactor 4's control panel showed output jumping to roughly how many megawatts thermal?

The final control-panel reading was 33,000 MW thermal, roughly 30,000 MW and about ten times the reactor's rated 3,200 MW; some later estimates put the true spike ten times higher still.

How many control rods did the RBMK-1000 have, nearly all of which had been withdrawn before the explosion?

The RBMK-1000 had 211 control rods; by the start of the test the equivalent of fewer than eight remained in the core, against a minimum of fifteen required by the operating rules.

On the day of the Chernobyl accident, to which airport did the government commission that included Valery Legasov fly?

Boryspil International Airport, near Kyiv, received the commission, which included nuclear specialist Evgeny Velikhov, hydro-meteorologist Yuri Izrael and radiologist Leonid Ilyin.