There have been a number of nuclear reactor accidents occurred around the world, such as the 
    Three Mile Island Incident and the  Chernobyl Incident. The Chernobyl incident was regarded as
    the worst nuclear reactor accident ever happened. Now let us focus on what happened at 
    Chernobyl and how this accident affected the people.

 The Chernobyl Incident


  The Chernobyl nuclear power station was situated 
  beside the Pripcat River in the former Soviet Union. 
  The reactors involved belong to the RMBK reactor 
  class, which could be unstable at low power and 
  might experience a rapid, uncontrollable power
  increase. The fuel used was natural uranium, with 
  water as the coolant and graphite as the moderator. 
  Though these RMBK reactors were shielded with 
  heavy concrete covers, containment structures, 
  which were required for U.S. reactors, were 
  absent.

   Nuclear power stations produce electricity as well 
   as consuming it, such as to power the turbines 
   which circulate the coolant. 
   
  When a reactor is operating but not producing power, like in the process of shutting down, an 
  external source of electricity is needed to keep the coolant circulating the reactor, so as to give 
   the reactor a sufficient safety margin. Generators are usually used to provide the extra power.

   The accident at Chernobyl on the 26th April 1986 happened during a test to determine whether 
   a coasting turbine could generate enough power to keep the emergency cooling machinery 
   working until the standby diesel generators could be initiated, in case of a planned or accidental
   shutdown of reactors. However, due to the failures of managerial control and errors made by 
   operators, the system went out of control. Two explosions, including the blowing off of the roof of 
   the nuclear plant by the violent expansion of steam and explosion caused by reaction between 
   hydrogen and atmospheric oxygen. 
   
   For a detailed sequence of event, click here.

   the course of radioactive dust cloud from Chernobyl

    The explosion released about 50 tonnes of radioactive fuels into the atmosphere, sparks and 
    debris caused fires in neighbouring buildings. 50 million curies of radioactive fission products
    were released and contaminated parts of Western Europe as they were carried away by wind 
    and rain.160,000 people living within 30km of Chernobyl were evacuated right after the accident. 
    31 radiation workers were killed and over 500 people were injured. The major radiological 
    impact expected to date (i.e. within the first ten years after the accident) is leukaemia.  Many 
    people were seriously affected by the effects of radiation, many women who were pregnant 
    during the accident gave birth to abnormal babies and many of the people exposed to radiation
    developed thyroid cancer.

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