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Updated on August 2, 2011

This is about the accident at the nuclear plant in Chernobyl, Ukraine. The aim of this hub is to give you a better understanding of what took place before, during, and after the accident at Chernobyl.

The Aftermath
The Aftermath

On April 26,1986 at 1:23 am an unsupervised test was being done on reactor number four. When all of a sudden there was an explosion that rocked the whole building, threw the one thousand-pound lid off the reactor, and ripped open the side of the reactor casing. This resulted in the worst nuclear accident, even worse then the Atomic bomb. Also, there were certain radioactive materials being let out into the air.

There were fifty megacuries* of Caesiun-137 and Iodine-131, two different kinds of radionuclides, along with another fifty megacuries* of chemically inert gasses. This radiation spread throughout Europe, Asia, Northern Africa, along with small traces in California.

The world first learned about the accident on April 28, when someone monitoring a radiation detector in Sweden inquired about the high levels of Caesiun-137 and Iodine-131. Then the people at Chernobyl had to admit that there had been an explosion that had sent off more radiation then the atomic bomb.

*A megacurie is 1,000,000 curies. A curie is the rate of decay of an atom. The activity of 3.7x1010 s-1 is equal to one curie.

This is a chronology of the accident. April 26th, 11:00pm the load dispatcher from Kiev gave the station permission to begin the shutdown of reactor number four.

At 11:10, the shift supervisor for unit number four gave the order to drop the control rods, which would slow the reactor. This went on until about 1:00 am when the fourth main cooling pump was connected to the heat-transport system.

At 1:22 am the person in charge of dropping the control rods saw that the reactor was running at half power, this would have led to an immediate shutdown, so he told his superior. His superior then told him to keep lowering the control rods anyway.

1:23 am the emergency regulating valves to the generator were turned off incase it was necessary to repeat the experiment. Then there was the sound of multiple thuds that were coming from the reactor, these were the explosions that blew the lid off the reactor and ripped open the side of the reactor casing. The experiment that they were doing was to see if the turbines would have enough energy, as they were powering down, to keep power in the station until the diesel generators started to work. The diesel generators were only necessary in the event of an emergency shutdown.

Spread of the Fallout
Spread of the Fallout

This is what happened after the explosions. They had to lower the control rods and fill the reactor with water, which would cool it down. Two people went out side to survey the damage done by the explosions.

The next step was to call the firefighters to come and put the fire out. When it was apparent that the firefighters were not able to control the fire, the people at the power plant called in a Russian General who was in charge of a helicopter squadron.

It was the middle of the night when the General, so he brought two Mi-6s (helicopters) that had night scanning equipment just to asses the damage. Then he was instructed to being larger helicopters (Mi-8s) which were used to dump sand and other materials such as lead. These materials were able to put the fire without sending off radioactive steam, as water would have done. They ended up having to put more than five hundred tons of sand on the reactor.

Soon the decision was made to evacuate Pripyat (the city that was made to house all of the workers of Chernobyl). Chernobyl is located approximately 130 km (80 mi.) north of Kiev.

More Destruction
More Destruction

High whole-body doses of radiation produce a characteristic pattern of injury. Doses are measured in grays, 1 gray (Gy) being equal to an amount of radiation that releases 1 joule of energy per kilogram of matter. Doses of more than 40 Gy severely damage the human vascular system, which leads to profound shock and neurological disturbances; death occurs within 48 hours.

Whole-body doses of 10 to 40 Gy cause less severe vascular damage, but they lead to a loss of fluids and electrolytes into the intercellular spaces and the gastrointestinal tract; death occurs within ten days as a result of fluid and electrolyte imbalance, severe bone-marrow damage, and terminal infection.

Absorbed doses of 1.5 to 10 Gy cause destruction of human bone marrow, leading to infection and hemorrhage; death, if it occurs, can be expected about four to five weeks after exposure.

Currently only the effects of these lower doses can be treated effectively; but if untreated, half the people receiving as little as 3 to 3.25 Gy to the bone marrow will die.

Some of the radiation spread across northern Europe and into Britain and Sweden. The biological effects of a large dose of radiation delivered rapidly differ greatly from those of the same dose delivered slowly. The effects of rapid delivery are due to cell death, and they become apparent within hours, days, or weeks.

Prolonged exposure is better tolerated because some of the damage is repaired while the exposure continues, even if the total dose is relatively high. If the dose is sufficient to cause acute clinical effects, however, repair is less likely and may be slow even if it does occur. Exposure to doses of radiation too low to destroy cells can induce cellular changes that may be detectable clinically only after some years. Both types of radiation were given off after the accident, but most people only suffered from large doses that came rapidly.

Statements from the Soviet Union, of which Ukraine was then part, indicate that 31 people died as a result of the accident, but the number of radiation-caused deaths is yet unknown although expected to be much greater. In tests taken after the accident, many types of animal and plants were seen to have defects and abnormalities that could have come only after great exposure to radiation. More than 100,000 people were evacuated from areas around the reactor site, and Chernobyl and some other settled regions remained unoccupied one year later.

 Officials who were responsible for the reactor were tried in 1987, and six of them were sent to labor camps.

The other three Chernobyl reactors were returned to operation that same year, and the immediate evacuation zone of the disaster was later declared a national park.

In 1991,the government pledged to close down the entire Chernobyl plant, but energy demands delayed the move.


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