Hanford is one of three atomic cities that were built as part of the Manhattan Project. In 1943, work was begun on three reactors there that produced plutonium for the first atomic test explosion and for the atomic bomb that was dropped on Nagasaki.
The following decade saw five additional reactors built at Hanford. This total of eight reactors continued to operate up until the years 1964 and 1971. By then they had produced 50 tons of weapons-grade plutonium - enough to build 1,000 Nagasaki bombs.
This huge production of plutonium was not without health risks. Aside from the obvious one, huge clouds of radioactive iodine, ruthenium, caesium, and other elements were released into the atmosphere, contaminating people, animals, crops, and water for hundreds of miles around. Between 1944 and 1956, 530,000 curies of radioactive iodine poured from the plant. 340,000 curies were emitted in 1945 alone. This would be considered a major nuclear accident today.
On December 2, 1949 an experiment went horribly wrong. Documents released under FOIA in 1989 show that the government was trying to locate Soviet plutonium plants by simulating the conditions they expected the Soviets to create in their rush to build bombs. On this particular day, an experiment involving one ton of irradiated uranium which had been processed after only 16 days of cooling rather than the normal 83 to 101 days couldn't be contained.
The experiment began on the night of the second and continued until 5AM the following morning. The radiation that was released contained 20,000 curies of xenon-133 and 7,780 curies of iodine-131 and formed a radioactive plume measuring 200 by 40 miles. This deposited high concentrations of radiation all over Hanford and in communities as far as 70 miles away. There were no public health warning and no follow up studies. By comparison, the accident at Three Mile Island released only 15-24 curies.
The US Federal CDC began a five year study two years after these documents were released. They believe that 20,000 children in the area could have been exposed to dangerous levels of iodine in milk produced by cows grazing in contaminated pastures. It is believed that the doses may rival those received by children in the Marshall Islands due to US nuclear testing.
During Hanford's first two decades, an average of 8,000 curies of radioactive materials were dumped into the Columbia river each day. By 1957, with eight reactors churning out plutonium at high levels, the emissions to the river averaged 50,000 curies per day.