Chernobyl Disaster
Reactor 4 several months after the disaster. Reactor 3 can be seen behind the ventilation stack.
|
Date
| April 26, 1986
(
1986-04-26
)
|
---|
Time
| 01:23
MSD
(UTC+04:00)
|
---|
Duration
| 1986-Present
|
---|
Location
| Chernobyl Nuclear Power Plant
|
---|
Type
| Nuclear Accident
|
---|
Cause
| Reactor design and operator error
|
---|
Outcome
| INES Level 7
|
---|
Deaths
| 28 from Radiation Posioning, 2 killed in disaster, 15 from terminal thyroid cancer
|
---|
Missing
| 1
|
---|
The
Chernobyl disaster
[1]
was a
nuclear
disaster
. It happened on April 26, 1986 at the
Chernobyl
nuclear power plant
near the town of
Pripyat, Ukraine
. At that time, Ukraine was part of the
Soviet Union
. The station is 110
kilometres
north of the nation's capital,
Kyiv
.
The event was one of the worst
accidents
in the history of
nuclear power
. It was rated level 7, the most severe level, on the
International Nuclear Event Scale
. The only other accident with a level 7 rating is
Fukushima
. The
RBMK
reactors that were used at the plant had no
containment building
to keep the radiation in.
Radioactive
fallout
drifted over parts of the western
Soviet Union
,
Eastern Europe
,
Scandinavia
, the
United Kingdom
, and the eastern
United States
. Large areas of
Ukraine
,
Belarus
, and
Russia
were badly contaminated. About 60% of the radioactive fallout landed in Belarus.
[2]
[3]
About 360,000 people needed to be moved to other places where they could live after the accident. Many people suffered from
acute radiation poisoning
and long-term illnesses such as
thyroid cancer
.
[4]
[5]
On the day of the incident, there was a planned power reduction. By the beginning of the day
shift
, the power level had reached 50%. Then, one of the regional
power stations
went
offline
. On the afternoon of April 25 there was a request that the further power reduction would be postponed. Further power down was allowed after 22:00.
A
turbine
generator
run down test was to take place before the routine shutdown. At 00:05 on April 26, the power was at around 23%. 30 minutes later, the power fell to near zero, probably due to change of regulator. At 01:00 the power stabilized at around 6%. The test would be run at that level. A turbine was switched off and its
oscillations
were measured. Shift foreman A.F. Akimov reported to deputy-chief engineer A.S. Dyatlov (who supervised the power down) that the oscillations were measured. A final
briefing
was given. Everyone went to their instruments and at 01:23:04 the turbine generator run down test began. Everything went completely normally.
The reactor showed a tendency to accelerate as the cooling pumps connected to the turbine generator were slowing, and due to the property called positive void
coefficient
of reactivity; as number of so-called ‘voids’ (e.g. steam bubbles) increases due to increased boiling or loss of coolant, so does the reactivity. But the operators successfully kept the reactor in control and it did not accelerate. At 01:23:40 senior reactor chief control engineer L.F. Toptunov pressed the emergency protection button as planned for the shutdown, at the end of the test. The power was at 7% when the button was pressed. Instead of shutting down the reactor suffered a
power surge
. This was due to the reactor being unstable at low power. The shutdown system had severe design flaws. At 01:23:43 the power jumped to 17%. Due to the power increase, the automatic
control rods
suffered damage and they jammed. Fuel channels ruptured and at 01:23:47 the reactor exploded.
The
explosion
was so powerful that it blew the 1000 ton steel lid off the reactor. The explosion released large amounts of radioactive materials and fuel. This made the
neutron moderator
, made of
graphite
, to start to burn. The fire released more radioactive fallout, which was carried away by the smoke of the fire.
After the accident, Reactor 4 was covered by a "
sarcophagus
" made from
steel
and
concrete
to stop the escape of more radiation from the lost
corium
as well as radioactive dust. The sarcophagus was covered in 2016 with the
New Safe Confinement
structure.
[6]
The accident raised concerns about the safety of the Soviet nuclear power industry. The Soviet Union slowed the process of making its nuclear industry bigger for some time. The government also had to become less
secretive
as a result of the accident. Since 1991, Russia, Ukraine and Belarus have become separate countries. Those countries have continued to pay the high costs for
decontamination
(removing the radioactive material) and
health care
because of the accident. Exposure to radiation leads to a higher risk of getting
cancer
.
It is difficult to count the number of deaths caused by the events at Chernobyl. A 2005
IAEA
report tells of 56 direct deaths. 47 were accident workers, and 9 were children who died of
thyroid cancer
. The report thinks that up to 4,000 people may die from long term diseases related to the accident. However, other
estimates
range from 4,000 to 27,000 by the
Union of Concerned Scientists
.
Greenpeace
estimate that between 93,000 - 200,000 people died as a result of the disaster. Following the disaster, babies and animals born around Chernobyl had defects, such as
cerebrovascular diseases
, physical
deformities
, and
mental disorders.
The animals exposed to high levels of radiation were born with physical deformities and
mutations.
Birds were born with smaller brains and less viable
sperm
.
The other three reactors at Chernobyl continued to operate after the disaster because there were not enough other power plants in Ukraine to meet energy demands. Reactor 2 was permanently turned off and stopped being used in 1991 after a fire in its turbine hall. Reactor 1 was decommissioned in 1996, and reactor 3 was decommissioned in 2000. In 2018, a 3800 panel, 1 megawatt solar plant was opened next to the former nuclear plant.
- ↑
Ukrainian
:
Чорнобильська катастрофа
- ↑
ICRIN Project (2011).
International Chernobyl Portal chernobyl.info
.
- ↑
Environmental consequences of the Chernobyl accident and their remediation: Twenty years of experience. Report of the Chernobyl Forum Expert Group 'Environment'
(PDF)
. Vienna: International Atomic Energy Agency. 2006. p. 180.
ISBN
92-0-114705-8
. Retrieved
13 March
2011
.
- ↑
"Table 2.2 Number of people affected by the Chernobyl accident (to December 2000)"
(PDF)
.
The Human Consequences of the Chernobyl Nuclear Accident
. UNDP and UNICEF. 22 January 2002. p. 32. Archived from
the original
(PDF)
on 1 February 2017
. Retrieved
17 September
2010
.
- ↑
"Table 5.3: Evacuated and resettled people"
(PDF)
.
The Human Consequences of the Chernobyl Nuclear Accident
. UNDP and UNICEF. 22 January 2002. p. 66. Archived from
the original
(PDF)
on 1 February 2017
. Retrieved
17 September
2010
.
- ↑
"As 30th anniversary of Chernobyl nears, giant arch set to encase radiation for next 100 years"
. The Japan Times. 24 March 2016
. Retrieved
27 March
2016
.