Chernobyl Timeline

Chernobyl Timeline

Chernobyl is one of only two level 7 nuclear under classification of the International Nuclear Event Scale. The other been Fukushima Daiichi Nuclear Power Plant in Ōkuma, Fukushima Prefecture which is primarily initiated by the tsunami following the Tōhoku earthquake on 11 March 2011.

26th September 1977 :
Located approximately 65 miles to the north of Kyiv, Ukraine (which was then part of the Soviet Union), the plant begins supplying power to the grid.

February 1986 :
A Soviet official is quoted as saying that the odds of a nuclear meltdown are “one in 10,000 years”. At this time, there are four 1,000 megawatt reactors, with two further ones under construction.

25th April 1986 – 1 am :
Operators begin reduction of power at reactor No. 4 in readiness for a safety test. This was timed to coincide with a routine maintenance shutdown. The test was to determine whether in the event of a power failure, the plant’s still spinning turbines can produce enough electricity to keep coolant pumps running during the short timespan before the emergency generators kick in. This safety test was to bring about the destruction of the reactor.

25th April 1986 – 2 pm :
The emergency core cooling system for reactor No. 4 is disabled. This was done to avoid it interfering with the test. This does not actually cause the accident, it does however worsen the impact. 

25th April 1986 – 2pm :
The tests and shutdown are delayed temporarily to accommodate the region increased power requirement.

25th April 1986 – 11:10pm :
Permission is granted for the operators to continue with the test and shutdown. The night shift are now on duty. It is alleged that they never received the correct instruction on performing the required test procedure.

26th April 1986 – 12:28am :
The power falls too far below the level where the reactor is considered stable. Operators respond to the situation by initiating the removal of the control rods. This was in violation of the plants safety guidelines. This still does not resolve problem, and they where still unable to raise the power, due in part to xenon buildup in the reactor core.

26th April 1986 – 1 am : With the power stabilised (although at a lower than preferred level) the plant supervisors order the test to proceed. Subsequently the automatic emergency shutdown system and other safety features are turn off.

26th April 1986 – 1:23:04 am :
The test officially commences, and an unexpected power surge occurs.

26th April 1986 – 1:23:40 am :
The emergency shutdown button is pressed by one of the operators. The control rods jam as they entered the reactor core.

26th April 1986 – 1:23:58 am :
The first explosion occurs, this was followed by at least one more, which blows the 1,000 ton roof off the reactor, shooting a fireball in the night sky. The air fills with dust and graphite chucks. Radiation begins to spew out. Numerous fires start, including one on top of the neighbouring reactor No. 3. Despite all evidence to the contrary, the nuclear engineer in charge insists that reactor No. 4 is still intact. He was later to die from radiation poisoning.

26th April 1986 – 1:28 am :
The first firefighters arrive. They have no knowledge of the radiation leaking out and wear no protective clothing.

26th April 1986 – 2:15 am :
Local Soviet officials hold an emergency meeting. They decided to stop vehicles from entering or exiting Pripyat, the nearby city built to house workers at the power plant. Roadblocks where manned by Police officers who had no knowledge of the radiation and wear no protective clothing.

26th April 1986 – 5 am :
Reactor No. 3 is shut down by operators. This will be followed the next morning by reactor Nos. 1 and 2. They are re-opened months later.

26th April 1986 – 6:35 am :
All of the fires have been extinguished except for a blaze in the reactor core, which will burn for days.

26th April 1986 – 10 am :
In an attempt to slow radioactive emissions escaping, helicopters begin dumping sand, clay, boron, lead and dolomite into the burning core.

27th April 1986 – 2 pm :
Although the residents had been told nothing about the disaster for some 36 hours, Soviet officials finally begin evacuating roughly 115,000 people from towns and villages in the surrounding area, including approx 47,000 from Pripyat alone. Residents are informed it will be temporary and that they should pack only vital documents and belongings, plus some food. Shortly after their departure, however, an exclusion zone is set up preventing their return.

28th April 1986 :
Air monitoring at a Swedish nuclear power plant detect a large amount of radiation in the atmosphere. They quickly establish the source was not local, and it is traced back to the USSR. When challenged Soviet officials admit that there’s been an accident, but they falsely state the situation is under control. 

29th April 1986 :
Spy satellite photos provide U.S. officials with their first glimpse of the devastation brought about by the disaster.

1st May 1986 :
Soviet officials refuse to cancel the May Day festivities in Kyiv. This was even though radiation continues to be released from the exposed core unabated. 

2nd May 1986 :
Background radiation levels in Kyiv are recorded as 200 times greater than normal.

4th May 1986 :
Liquid nitrogen is pumped underneath the damaged reactor in order to cool it. Other aspects of the cleanup operation, which is recorded as involving up to 800,000 workers, include bulldozing contaminated villages, shooting contaminated pets and livestock, and burying huge amounts of contaminated topsoil. 

6th May 1986 :
Radioactive emissions drop sharply. This is quite probably due to the fire in the core having burned itself out. Meanwhile, Soviet officials finally take the decision to close schools in Kyiv and residents are advise to stay inside and not to eat leafy vegetables.

8th May 1986 :
Workers finish draining about 20,000 tons of radioactive water from the basement under the core.

9th May 1986 :
Workers begin pouring concrete under the reactor. Later, this is encased in an enormous concrete and metal structure. This is known as the sarcophagus.

14th May 1986 :
Soviet leader Mikhail Gorbachev speaks publicly about the incident for the first time, saying on state TV that “the worst is behind us.”

25th-29th August 1986 :
The International Atomic Energy Agency (IAEA) hosts a conference. Scientists at this blame the accident not just on human error and a low safety culture, but also on Soviet reactor design flaws. 

15th December 2000 :
Reactor No. 3, the last working reactor, is shut down. Reactors No. 1 and No. 2 had been shut down in 1996 and 1991, respectively.

April 2006 :
Gorbachev writes that the Chernobyl disaster, “even more than my launch of perestroika, was perhaps the real cause of the collapse of the Soviet Union.”