Unlike natural disasters that are caused by extreme environmental conditions, human impact disasters are the product carelessness or mishandling of dangerous equipment. Some examples of these disasters are airplane crashes, chemical disasters and mine collapses.
On 26 April 1986, the Chernobyl nuclear power station, located in Ukraine suffered a major accident, which was followed by a prolonged release of radioactive substances to the atmosphere. This had serious radiological, health and socio-economic consequences for the populations of Belarus, Ukraine and Russia, which still suffer from these consequences. The accident was a product of flawed reactor design that was operated with inadequately trained personnel. It was a direct consequence of Cold War isolation and the resulting lack of any safety culture. Chernobyl is still one of the greatest human impact disasters to occur to date.
TIMELINE OF EVENTS
1986
February – Vitali Sklyarov, Minister of Power and Electrification of Ukraine, in reference to the nuclear reactors quoted,
“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.”
25 April – Friday
The test began. The purpose of the test was to observe the dynamics of the RMBK reactor with limited power flow.
14:00 – Under the normal procedures of the test the reactor would have been reduced to 30% power, however the Soviet electricity authorities refused to allow this as there was apparently need for electricity elsewhere. The reactor remained at 50% power for another 9 hours.
Emergency core cooling system was switched off.
26 April – Saturday
00:28 –The drop in reactor power from 1500 MWt to 30 MWt occurred. Akimov wanted to abort the test, but was over-ridden by Dyatlov and forced to continue.
01:19 – Shutdown signals were blocked from steam-drum separators.
The operator blocked automatic shutdown due to low water levels and the loss of both turbines because of a fear that a shutdown would abort the test.
The operator forced the reactor up to 7% power by removing all but 6 of the control rods. This was a violation of procedure because the reactor wasn’t built to operate at such low power. The RBMK reactor is unstable when its core is filled with water.
01:21 –Valeriy Ivanovich Perevozchenko 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. First stage of the rupture
01:23:40 – All control rods were reinserted for emergency purposes. The reactor started making rumbling noises. The reactor control panel indicated no water flow and failure of pumps.
01:23:44 – Explosion.
The reactor reached 120 times its full power. All the radioactive fuel disintegrated. All the pressure tubes broke due to pressure from excess steam and the explosion started.
01:23:45 – The 1000 ton lid above the fuel elements was lifted by the force of the explosion. Radiation was released into the atmosphere. Air reached the reactor and the oxygen resulted in a graphite fire. The metal of the fuel tubes reacted to the water. This produced hydrogen, and lead to the second explosion.
01:26:03 – fire alarm activated.
Dyatlov (deputy of chief engineer) went to the backup control room, and pressed the emergency button which disconnected power to the control rod servo drives. Although he saw the graphite blocks scattered on the ground outside the plant, he still thought the reactor was intact.
01:28 (approx.) – Fire fighting units under Lieutenant Volodymyr Pravik left the station.
01:35 (approx.) – Firemen fought fires on roof of turbine hall.
02.15 – The Pripyat department of the Ministry of Home Affairs called a crisis meeting. It decided to organize a roadblock in order to prevent cars from entering or leaving the town. Police assistance was requested. Thousands of police arrived and, like the fire fighters, they had no knowledge of radiation, no dosimeters or protective clothing.
05:00 – Militia commander general Berdov arrived from Kiev
06:35 – 37 fire brigades, with a total of 186 fire fighters were called in. All fires extinguished with the exception of the fire contained inside Reactor 4
20.00 –Following the explosion many citizens of Pripyat gathered on a railway bridge to get a view of the nuclear power plant. What they didn’t realize was that the wind that swept over them carried with it a lethal dose of radiation equivalent to 500 Roentgen.
None of the people that stood on the bridge that night survived, it is now often referred to as the “bridge of death”.
27 April – Sunday
Midnight– Buses arrived in Pripyat. They waited for the command to evacuate the city.
10:00 (approx.) – Helicopters made their first drop of sand, boron and lead – Between 27 April and 1 May, about 1800 helicopter flights dropped over 5,000 tons of sand, lead, clay and boron onto the burning reactor. It is now known that none of the neutron absorbers reached the core.
12:00 – radiation levels dropped slightly. However the level of radiation rose again and reached its maximum level.
14:00 – Evacuation of Pripyat began.
27 May
A concrete structure was built; the idea of the sarcophagus was born.
22 December
Soviet scientists announced that the sarcophagus now enclosed the reactor and was designed for a lifetime of 20 to 30 years.
HUMAN, ENVIRONMENTAL AND ECONOMIC IMPACT
Chernobyl was one of the most substantial human impact disasters to occur in history and had some major effects on human, the environment and economy.
The Chernobyl disaster affected lives of about 600,000 people. Evacuation of Pripyat took place the day after the accident, April 27 1986. The inhabitants were allowed to take only necessary items with them. By the time they were evacuated, they were all exposed to large amounts of radiation directly from the radioactive cloud, radioactive materials deposited on the ground, through consuming contaminated food and breathing contaminated air. If the human body absorbs a lethal dose of external radiation, it may cause acute radiation syndrome (ARS). Workers who were near the reactor at the time of the accident and shortly afterwards received high doses of radiation which was fatal to many of them. Children who had consumed milk from that had eaten contaminated grass were particularly affected; this was discovered in a sudden spark in thyroid cancer among children.
For 10 days following the April 26 explosion, the ruptured Chernobyl reactor continued to release large quantities of radioactive substances into the atmosphere. After the accident, the deposition of radioactive iodine contaminated agricultural plants, grazing animals, and thus the milk produced in parts of Belarus, Russia, Ukraine and some other parts of Europe. During the first few years after the accident, the levels of radioactive materials in agricultural plants and animals decreased quickly because of factors such as weathering and decay. Because radioactive caesium is continuously taken up and passed on by organisms in forest ecosystems, the animals and vegetation in affected forests and mountains are particularly contaminated. Forest food products such as mushrooms, berries and game contain the highest recorded levels of caesium-137. Radioactive materials from Chernobyl deposited on rivers, lakes and some water reservoirs both in areas close to the reactor site and in other parts of Europe. The amount of radioactive materials present in water bodies decreased rapidly during the first weeks after the initial deposition because the radioactive materials decayed, were diluted or were absorbed by the surrounding soils.
The costs of the Chernobyl disater can only be estimated however a variety of government estimates put the cost of the accident, at hundreds of billions of dollars. In Ukraine, 5–7 percent of government spending each year is still devoted to Chernobyl-related benefits and programs. Total spending by Belarus on Chernobyl between 1991 and 2003 was more than US $ 13 billion. The local economy was also substantially impacted due to the evacuation of the surrounding cities of Chernobyl and the contamination of agriculture.
FUTURE CHANGES
Since the Chernobyl disaster the international community assessed their readiness and capability to deal with a disaster of this magnitude as the dependency on nuclear energy increases to keep up with the demands of a developing world. Another realization that came from the nature of the accident was on the safety of nuclear power plants. Before the accident, there was a general uneasiness to set safety standards for nuclear facilities beyond recommendatory standards. The most important outcome of the disaster was the Convention on Nuclear Safety which serves as the technical manual for all safety considerations in the building, managing and operation of a nuclear plant. This convention has put out radiation protection plans such as the planned release of radioactive material below prescribed limits and as low as reasonably achievable which will alleviate some radiological consequences in the event of another nuclear disaster.
Conclusion
The Chernobyl disaster was one of the most substantial human impact disasters to occur in history. It affected not only Chernobyl and the cities around it, but the rest of the world also. The human, environmental and economic impacts from the disaster are still seen today with a large amount of money still being put aside for Chernobyl related benefits. The long-term health concerns associated with radiation exposure are just starting to arise amongst affected inhabitants of Pripyat and surrounding cities. Since the disaster extra precautions have been taken to prevent any other nuclear disasters of its magnitude.