Why was Chernobyl such a horrendous disaster? What were some long-term effects of the Chernobyl disaster?

Chernobyl was one of the worst nuclear disasters the world has ever seen, and is even blamed for bringing about the beginning of the end of The USSR

Explanation:

Chernobyl  is a nuclear disaster that released radioactive contamination into the environment. Trees, animals and people were all irridated and many never told. The official death toll  around 40 people, however but it is believed to have caused Thyroid cancer in thousands of people who were exposed to the radiation for 48 hours before being evacuated for "3 days" buy in actuality never were able to return.  The liquidators and minors who went to put out the fire at the exposed radioactive core also died or got radiation sickness even though their official causes of death were recorded as occupational hazard.  An exclusion zone of 30 miles in all directions were established affecting what is now Blearus, Ukraine and Russia.  Many people had to move back over the years in order to receive a small monthly stipend after the fall of the USSR.  The world had to join together to raise over 1 billion U.S.D. to construct a new containment chamber over the  old one which was disintegrating due to radiation exposure.  This new containment chamber should contain the radiation for at least 100 years while workers try to dismantle the rusting reactor building surrounding reactor #3. Hundreds of villages were buried and destroyed due to radiation, people today who grew up around the exclusion zone are sterile, develop cancers young have damaged babies all due to the long lasting invisible poison that is radiation.  The half life of some of the strontium, cesium and iodine is around 30 years, so that pollution has decreased by half.  The Uranium 238 will not go away in our lifetimes as it has a half-life of 4.5billion years.