Large doses of radiation are released at Japan's Tokaimura nuclear plant on this day in 1999. It was Japan's worst nuclear accident, caused by a serious error made by workers at the plant. One person was killed, 49 were injured and thousands of others were forcibly confined to their homes for several days.
The Tokaimura nuclear plant is located 87 miles northwest of Tokyo and supplies power to much of the surrounding region. On September 30, workers were mixing liquid uranium when they made a serious, and inexplicable, mistake. Instead of pouring five pounds of powdered uranium into nitric acid, the workers poured 35 pounds, seven times too much. The resulting chain reaction caused gamma rays and stray neutrons to flood the purification chamber, where the radioactive water was treated. One employee immediately collapsed and the others fled the scene.
The emergency team at the plant were forced to seek outside assistance, as they could not contain the reaction themselves. As a precaution, trains and roads leading to and from the area were blocked. However, the plant workers forgot to turn off the plant's ventilation system and radiation was inadvertently sent into the air, reaching nearby towns. The Tokyo Electric Power Company brought in 900 pounds of sodium borate to absorb the radiation, but they could not safely get close enough to the source to deploy it properly. Eventually, many hours later, they figured out how to get the sodium borate into hoses so that it could be sprayed onto the source of the radiation. By that time, it was too late to save everyone.
Hisashi Ouchi, a plant worker, died after spending two weeks in a coma. Forty-nine others were exposed to enough radiation to make them seriously ill. Further, 33,000 people living near the plant had to be quarantined for several days. Tomi Oshiro, an area resident, said "I am furious. It took place right next to people's houses, and it still took a long time before people were warned or any emergency measures were taken." Radioactive iodine-131 lingered in the air for a week.