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1. What caused the Chernobyl accident?
On April 26, 1986, the Number Four RBMK reactor at the nuclear power plant at Chernobyl, Ukraine, went out of control during a test at low-power, leading to an explosion and fire that demolished the reactor building and released large amounts of radiation into the atmosphere. Safety measures were ignored, the uranium fuel in the reactor overheated and melted through the protective barriers. RBMK reactors do not have what is known as a containment structure, a concrete and steel dome over the reactor itself designed to keep radiation inside the plant in the event of such an accident. Consequently, radioactive elements including plutonium, iodine, strontium and caesium were scattered over a wide area. In addition, the graphite blocks used as a moderating material in the RBMK caught fire at high temperature as air entered the reactor core, which contributed to emission of radioactive materials into the environment.
2. How many people died as an immediate result of the accident?
The initial explosion resulted in the death of two workers. Twenty-eight of the firemen and emergency clean-up workers died in the first three months after the explosion from Acute Radiation Sickness and one of cardiac arrest.
3. How many people were evacuated?
The entire town of Pripyat (population 49360), which lay only three kilometres from the plant was completely evacuated 36 hours after the accident. During the subsequent weeks and months an additional 67000 people were evacuated from their homes in contaminated areas and relocated on government order. In total some 200000 people are believed to have been relocated as a result of the accident.
4. What are the major health effects for exposed populations?
There have been at least 1800 documented cases of thyroid cancer children who were between 0 and 14 years of age when the accident occurred., which is far higher than normal. The thyroid gland of young children is particularly susceptible to the uptake of radioactive iodine, which can trigger cancers, treatable both by surgery and medication. Health studies of the registered cleanup workers called in (so-called “liquidators”) have failed to show any direct correlation between their radiation exposure and an increase in other forms of cancer or disease. The psychological affects of Chernobyl were and remain widespread and profound, and have resulted for instance in suicides, drinking problems and apathy.
5. What radioactive elements were emitted into the environment?
There were over 100 radioactive elements released into the atmosphere when Chernobyl’s fourth reactor exploded. Most of these were short lived and decayed (reduced in radioactivity) very quickly. Iodine, strontium and caesium were the most dangerous of the elements released, and have half-lives of 8 days, 29 years, and 30 years respectively. The isotopes Strontium-90 and Caesium-137 are therefore still present in the area to this day. While iodine is linked to thyroid cancer, Strontium can lead to leukaemia. Caesium is the element that travelled the farthest and lasts the longest. This element affects the entire body and especially can harm the liver and spleen.
6. How large an area was affected by the radioactive fallout?
Some 150,000 square kilometres in Belarus, Russia and Ukraine are contaminated and stretch northward of the plant site as far as 500 kilometres. An area spanning 30 kilometres around the plant is considered the “exclusion zone” and is essentially uninhabited. Radioactive fallout scattered over much of the northern hemisphere via wind and storm patterns, but the amounts dispersed were in many instances insignificant.
7. How was this area cleaned up after the accident?
Emergency workers (liquidators) were drafted into the area and helped to clean up the plant premises and the surrounding area. These workers were mostly plant employees, Ukrainian fire-fighters plus many soldiers and miners from Russia, Belarus, Ukraine and other parts of the former Soviet Union. The exact number of liquidators is unknown because there are no completely accurate records of the people involved in the clean-up. The Russian registries list approximately 400,000 liquidators as of 1991 and approximately 600,000 people were granted the status of “liquidator”. These 600,000 individuals received special benefits because of their involvement, on- and off-site, in tackling the accident’s aftermath.
The duties of the liquidators varied. They worked on decontamination and major construction projects, including the establishment of settlements and towns for plant workers and evacuees. They also built waste repositories, dams, water filtration systems and the “sarcophagus”, which entombs the entire fourth reactor to contain the remaining radioactive material.
8. Was the rest of Europe/the world affected?
Scandinavian countries and other parts of the world were affected by the radioactive releases from Chernobyl. Caesium and other radioactive isotopes were blown by wind northward into Sweden and Finland and over other parts of the northern hemisphere to some extent. During the first three weeks after the accident, the level of radiation in the atmosphere in several places around the globe was above normal; but these levels quickly receded. No studies have been able to point to a direct link between Chernobyl and increased cancer risks or other health problems outside the immediately affected republics of Ukraine, Belarus and the Russian Federation.
9. What happened to the environment and animals after the accident?
Mutations did occur in plants and animals after the plant explosion. Leaves changed shape and some animals were born with physical deformities. Despite the increased radiation levels, rare species are now returning in large numbers to the area. These animals include beavers, moose, wolves and wild boar, plus species of birds.
10. Is it safe to visit the area now?
One may certainly visit the Chernobyl area, including even the exclusion zone, which is a 30 kilometre radius surrounding the plant, all of whose reactors are now closed. Although some of the radioactive isotopes released into the atmosphere still linger (such as Strontium-90 and Caesium-137), they are at tolerable exposure levels for limited periods of time. Some residents of the exclusion zone have returned to their homes at their own free will, and they live in areas with higher than normal environmental radiation levels. However, these levels are not fatal. Exposure to low but unusual levels of radiation over a period of time is less dangerous than exposure to a huge amount at once, and studies have been unable to link any direct increase in cancer risks to chronic low-level exposure.
11. What was done to ensure the safety of other RBMK reactors, so that this scenario will not present itself again?
Lessons learned from the accident were a significant driving force behind a decade of IAEA assistance to the countries of Central and Eastern Europe and the former Soviet Union. Much of this work focused on identifying the weaknesses in and improving the design safety of VVR and RBMK reactors. Upgrading was performed on all RBMK units to eliminate the design deficiencies which contributed to the Chernobyl accident, to improve shutdown mechanisms and heighten general safety awareness among staff. Just as important as the design safety work has been the focus on operational safety and on systems of regulatory oversight.
12. How do the inhabitants live now?
There are 187 small communities in the exclusion zone that remain virtually abandoned to this day. A few inhabitants chose to return to their homes in the exclusion zone, but children are not allowed to live in this area. The evacuated population lives mainly in newly constructed towns such as Slavutich in areas with very little or no contamination.
13. What will happen to the plant now that it is closed?
On December 15, 2000, the last reactor in operation at the Chernobyl site was shut down and the phase of decommissioning began. This involves the removal and disposal of fuel and wastes, decontamination of the plant and the area surrounding it, including any soil and water that may be radioactive. There are three retired reactors to be decommissioned on site, a project expected to take several decades. The project will be conducted under the supervision of the Ukrainian government. The IAEA will assist by providing planning, engineering and administrative advice. The fate of the fourth reactor where the tragic accident occurred in 1986 is as yet undetermined.
14. What is the state of the protective shelter built around the fourth reactor?
Under extremely hazardous conditions, thousands of "Liquidators" worked to contain the remains of the fourth reactor. The shelter surrounding the reactor was completed less than six months after the explosion during peak radioactivity levels. The massive concrete and steel "Sarcophagus", quickly constructed using "arms length" methods, has deteriorated over the years, creating a potentially hazardous situation. Several repairs were made to the current shelter, including the stabilisation of the ventilation stack and reinforcement of the roof. In addition, a plan for the construction of a more secure and permanent structure to be built around the existing Sarcophagus was drafted; work has already begun on the infrastructure of this new shelter. The plan, called the Shelter Implementation Plan, is a project of the Chernobyl Shelter Fund. Both efforts, whose combined expected expenditures over the next eight or nine years exceed $765 million, are administered by the European Bank for Reconstruction and Development.
- In Focus: Chernobyl
- The Chernobyl Forum: 2003-2005
