A curie is a unit used to describe the rate of decay of a radioactive material. One curie is equal to 37 billion particle emissions, or disintegrations, a second. The greater number of curies, the more energy is being released. How hazardous a curie of radiation is to a person depends on the type of radiation emitted, what tissue was exposed, intensity of the exposure, and age of the person.

Forty percent of the 1 billion curies of radionuclides remaining at all U.S. nuclear material and weapons sites rests at Hanford. Of these 400 million curies of radioactivity, more than 99 percent consist of two radionuclides. These are cesium-137 and strontium-90. Each has a half life of around thirty years. When they decay to nonradioactive elements, Hanford will be left with the longer-lived radionuclides of plutonium, iodine, technetium, and americium.

During the years that Hanford was in operation, 140 million curies of radionuclides were released into the Columbia River and the atmosphere. Even though most of these were short-lived radionuclides, workers and members of the public were exposed. Of the thirty-two million curies that were released into the air, 12 million came from reactors and 20 million were from the reprocessing plants. Some of these radionuclides accumulated in the bodies on people living down wind. Their half lives were long enough and were released in high enough quantities to increase the radiation exposures of these down winders.

References

Gephart, R. E. Hanford: a Conversation about Nuclear Waste and Cleanup. Columbus, OH: Battelle, 2003.