Plutonium Production

Production of weapons grade plutonium at the early Hanford reactors involved several steps:

  • converting Uranium-238 first to Uranium-239 by stripping away a single neutron
  • allowing radioactive decay to occur and yield a small amount of Plutonium-239
  • cooling the mix with large amounts of Columbia River water
  • processing the result in a chemical bath to separate out the plutonium

Water for cooling was eventually returned to the Columbia, but contained radioactive materials including phosphorus, neptunium, zinc, arsenic and chromium. Gases produced in the chemical baths used to separate out the plutonium, primarily Iodine-131, were released directly into the atmosphere until filters were added in 1948 to remove some, but not all, of the radioactive material.

Safety was obviously an important concern in the development and use of the Hanford reactors. However, in 1941 there was little beyond theoretical knowledge of the dangers of working with the radioactive byproducts of plutonium production and about the safe storage of the material itself. Plutonium had only been produced in minute amounts in a laboratory to that point and not at the scale needed to produce enough fissionable material to build multiple bombs. The location of the reactors, though, in a relatively isolated location away from concentrations of population is testimony not only to the need for secrecy, but safety concerns as well.

In the early years at Hanford, however, time was a greater consideration. The rush to beat the Germans and the Japanese to produce the first atomic bomb during World War II and then the arms race with the Soviet Union during the Cold War meant that the highest premium was not placed on control of radioactive materials released into the environment - either the gases released into the air, the radioactive effluent released into the Columbia River, or the seepage into the Hanford soils.1

The table below details the most common radioactive materials released into the environment at Hanford from 1944 to 1971 indicating the amount of each and its radioactive half life.

To Start You Thinking

1) What is a curie? a half-life?

2) Which of the airborne materials seems to present the greatest threat? the waterborne materials? Explain.

3) Do some research and discover why Krypton-85 released from Hanford presents less of a threat to humans than Iodine-131.

4) The largest release of Iodine-131 came as a result of the "Green Run," an experiment conducted in December 1949 to cool uranium fuel for only 16 days as opposed to the normal 90 - 100 days. The process was being used by the Soviet Union and allowed for the production of greater amounts of plutonium. Study the table above and explain what it is about Iodine-131 that would make this a more dangerous proposition.


1Michele Stenehjem Gerber, On the Home Front: The Cold War Legacy of the Hanford Nuclear Site, Lincoln: University of Nebraska Press,

data from Hanford Environmental Dose Reconstruction (HEDR) Project as found at the Hanford Health Information Network, Wahington Department of Health

Last modified in August, 2019 by Rick Thomas