Chernobyl Accident is the destruction on 26 April 1986 of the fourth reactor of the Chernobyl Nuclear Power Plant located on the territory of Ukrainian SSR (Ukraine). Chernobyl accident is regarded as the largest of its kind in the history of nuclear power in the number of victims affected by its impact.

Chernobyl Helicopter Tour by Robinson R44, EC120, Bell 407

The destruction was of an explosive nature and the reactor was completely destroyed. In the environment were released large quantities of radioactive substances.

The main long-lived radionuclides that caused the pollution of Chernobyl Disaster Zone are:
- Strontium-90 (half-life of around 29 years)
- Cesium-137 (half-life of around 30 years)
- Americium-241 (half-life of around 432 years)
- Plutonium-239 (half-life of around 24 110 years)

Other radioactive elements (including isotopes Iodine-131, Cobalt-60, Cesium-134) to the present time because of the relatively short half-life is almost completely disintegrated and not contribute to the contamination of the area.

Chernobyl Disaster Zone also know as "30-km Zone" is forbidden for access area affected by the intense pollution of long-lived radionuclides due to the accident at the Chernobyl Nuclear Power Plant. Chernobyl Disaster Zone has three controlled territories:
- Special zone (Chernobyl Nuclear Power Plant)
- 10-kilometer zone.
- 30-kilometer zone.

The citizens of Pripyat (47 000 citizens) in which lived workers of Chernobyl Power Plant was evacuated on 27th of April 1986 due to the Chernobyl accident. It was used by more than 1 200 buses (including 100 buses in reserve), about 200 lorries and two diesel trains with 1500 seats. In Pripyat at 13:10 local radio was sent the message about evacuation of Pripyat's citizens and already at 16:30 the evacuation has been completed.

Pripyat is now in the Chernobyl Disaster Zone. After the accident there were the works on cleaning up the city which has led to a significant reduction of background radiation. Pripyat is also called "Ghost Town" ("Ghost City").

The main reason of fourth reactor explosion of Chernobyl Nuclear Power Plant is constructive disadvantages of RBMK-1000 reactor. Reactor designers are Academicians Nikolai Dollezhal and Anatoly Alexandrov.

In 1983 at Chernobyl Nuclear Power Plant were found a very dangerous phenomenon - the emergency protection rods as they move down for five seconds were added into the reactor not negative but positive reactivity. However official commission found it possible to allow the reactor to operate.

Academician Nikolai Dollezhal claimed that reactor RBMK-1000 needed additional absorbers in the core. Only after the accident at the Chernobyl Nuclear Power Plant in some channels for the fuel were installed additional absorbers.

Another drawback of the construction of RBMK-1000 reactor was operating time of protective system (speed of rods absorbers in the core to shut down the reactor). It was around 18 seconds while the development of the instability in the RBMK-1000 reactor is for 3-4 seconds.

After the Chernobyl accident all RBMK-1000 reactors were changed and it was made a new high-speed protection so the rods of absorbers go down in the core during only 2,5 seconds and completely shut down the reactor.

Because of economic reasons in order to reduce the cost of building nuclear power plants RBMK-1000 reactors were not equipped with the device contain the concrete cap over the reactor. It under unforeseen contingencies or case of explosion simply would not let the radiation escape.

After 23 years and one day of operation on 15th of December 2000 Chernobyl Nuclear Power Plant stopped generating electricity. This was preceded by the following events.

On 11 of October 1991 in the engine room of the second reactor of Chernobyl Nuclear Power Plant occurred loud explosion and fire. The engine room was almost completely destroyed. The reactor was not possible to use any more and was done the decision to stop it. Also have been stopped first and third reactors.

In 1993 it was decided to resume the work of the first and third reactors. But on 30th of November 1996 reactor number one had to be stopped for serious technical problems. More it did not work and in December 1997 it was decided to prematurely withdraw it from work. In 2000 it was in work only the third power reactor of Chernobyl Nuclear Power Plant. On 1st of December 2000 accident occurred in the electrical systems and reactor number three had to be stopped. After repairs it was started but on 6th of December the reactor had a serious accident and again stoped. For technical reasons the administration of Chernobyl Nuclear Power Plant categorically refused to give permission to run the reactor. But under the pressure of higher officials the reactor number three was started to work at 5% power without connection to the power grid and again stoped forever during official ceremony of Chernobyl Nuclear Power Plant closing.

After formation of "30 km Zone" around the Chernobyl Nuclear Power Plant some people began to come on its territory illegally. They call themselves - "stalkers". Widely known one of the most famous professional guide to Chernobyl Disaster Zone. He is Alexander Naumov - a former Chernobyl worker and police colonel who worked for many years for protection the Chernobyl Zone and knows it the best.

In addition to professional experts in the study of the Chernobyl Zone there are illegal Chernobyl stalkers which can be divided into two conventional categories:
- young people who get the knowledge of Chernobyl Disaster Zone of the computer game "STALKER" and Internet. The average age of the categories of stalkers around 20 years and they visiting the territory of Chernobyl Zone 1-2 times.
- Ideological stalkers come to Chernobyl Disaster Zone for several days and in some cases up to a week. They use dosimeters and respiratory protection.

Chornobyl Zone is also home for Starosel - now around 200-300 people in old age who returned to their homes after the Chernobyl disaster. Starting from autumn 1986 to spring 1987 in Chernobyl Disaster Zone has returned more than 1 200 people. They back to their homes and treated their gardens and plants.

Chernobyl Disaster Zone is famous throughout the World and is a great tourist potential for Ukraine.