In April 1986 reactor number 4 of the Chernobyl nuclear power plant suffered a catastrophic failure. This cause of the failure can be linked to many different problems, however the primary cause was inadequate training of the operators. On 25th of April the operators began a series of operations designed to test the spin-down time of the steam turbines. Conducting this test involved running the reactor at very low power with various safety features disabled. This was done in spite of the fact that it was known that the reactor was unstable when operated at minimum power settings. Once it was realized that the reactor output was increasing, the operators attempted to shutdown the reactor, unfortunately this resulted in a large steam explosion that lifted the top off the reactor and, combined with the following fire, vented approximately 25 % of the core into the atmosphere. After the fire was put out and the remaining core sealed in concrete it was time to assess the damage.
The immediate loss of human life was 30 people, 28 of whom died from radiation poisoning. Large parts of Europe were within the fallout region of Chernobyl, however the main area's effected were Belarus, Russia and the Ukraine. 600,000 workers were involved in the clean up operation and received radiation doses many times in excess of recommended limit. Initially the radiation was direct external radiation (i.e., gamma and beta decay), however in later months the routes of exposure became quite varied. In the months following the accident 116,000 people were evacuated from the surrounding countryside, however during their time in the exposed area they received doses in excess of the recommended limit, from inhaling and consuming short lived radioactive products (mainly cesium and iodine). A further 220,000 people were evacuated in the following year, they also received excessive doses of radiation through inhalation, food and drink. A further 5 million people continue to live in areas known to be contaminated by fallout from Chernobyl. The question that has been asked (ever since 1986) is what can we learn about the health effects of radiation from this.
