3.5 Gaseous (Barrier) Diffusion
143
235 U content from 0.72 to 0.86%. This product would be fed to first-stage calutrons,
known as “Alpha” calutrons, which could raise the enrichment level to about 20%.
Second-stage “Beta” calutrons, which were smaller, took the enrichment to 90%.
When enough K-25 stages were on-line to produce 20% enriched material directly,
the original Alpha units were shut down, and K-25’s product was directed to “secondgeneration” Alpha units and thereafter to Beta units. K-25’s enrichment level peaked
at 36%, although postwar extensions to the plant brought the level up to bomb-grade
enrichment. Enriched uranium tetrachloride from the calutrons was converted to
uranium hexafluoride for shipment to Los Alamos, with chemical processing carried
out in gold trays to minimize contamination.
By the end of the war, the continuous-feed K-25 gaseous diffusion process
had proven itself more efficient at enriching uranium than the electromagnetic
method; shutdown of Alpha calutrons began on September 4, 1945. Some Beta
calutrons remained in operation until 1998 to separate various isotopes, which, after
neutron bombardment in a reactor, could be used as radioactive tracers for medicalimaging and cancer-treatment applications. The K-25 plant (plus other similar plants)
continued to operate to produce both highly-enriched and low-enriched uranium at
Oak Ridge until it was shut down in 1985; by this time, centrifugation had become a
more economical means of enrichment. The last remnants of K-25 were demolished
in early 2013.
According to a 2011 report by the International Panel on Fissile Materials, the
United States produced a total of some 610 metric t (610,000 kg) of highly-enriched
uranium between 1945 and 1995 (Global Fissile Material Report 2011).
References
Compere, A.L., Griffith, W.L.: The U.S. calutron program for uranium enrichment: history,
technology, operations, and production. Oak Ridge National Laboratory report ORNL-5928
(1991)
Fermi, E.: Experimental production of a divergent chain reaction. Am. J. Phys. 20, 536–558 (1952)
Garwin, R.L., Charpak, G.: Megawatts and megatons: a turning point in the nuclear age? Alfred A.
Knopf, New York (2001)
Global Fissile Material Report. International Panel on Fissile Materials (2011). http://fissilemater
ials.org/library/gfmr11.pdf
Hewlett, R.G., Anderson, O.E.: The New World 1939/1946: Volume I Of A History of the United
States Atomic Energy Commission. The Pennsylvania State University Press, University Park,
PA (1962)
Historic American Engineering Record: B Reactor (105-B) Building, HAER No. WA-164.
DOE/RL-2001-16. United States Department of Energy, Richland, WA (2001). http://wcpeace.
org/history/Hanford/HAER_WA-164_B-Reactor.pdf
Jones, R.C., Furry, W.H.: The separation of isotopes by thermal diffusion. Rev. Mod. Phys. 18,
151–224 (1946)
Parkins, W.E.: The uranium bomb, the calutron, and the space-charge problem. Phys. Today 58(5),
45–51 (2005)
Reed, B.C.: Understanding plutonium production in nuclear reactors. Phys. Teach. 43, 222–224
(2005)
143
235 U content from 0.72 to 0.86%. This product would be fed to first-stage calutrons,
known as “Alpha” calutrons, which could raise the enrichment level to about 20%.
Second-stage “Beta” calutrons, which were smaller, took the enrichment to 90%.
When enough K-25 stages were on-line to produce 20% enriched material directly,
the original Alpha units were shut down, and K-25’s product was directed to “secondgeneration” Alpha units and thereafter to Beta units. K-25’s enrichment level peaked
at 36%, although postwar extensions to the plant brought the level up to bomb-grade
enrichment. Enriched uranium tetrachloride from the calutrons was converted to
uranium hexafluoride for shipment to Los Alamos, with chemical processing carried
out in gold trays to minimize contamination.
By the end of the war, the continuous-feed K-25 gaseous diffusion process
had proven itself more efficient at enriching uranium than the electromagnetic
method; shutdown of Alpha calutrons began on September 4, 1945. Some Beta
calutrons remained in operation until 1998 to separate various isotopes, which, after
neutron bombardment in a reactor, could be used as radioactive tracers for medicalimaging and cancer-treatment applications. The K-25 plant (plus other similar plants)
continued to operate to produce both highly-enriched and low-enriched uranium at
Oak Ridge until it was shut down in 1985; by this time, centrifugation had become a
more economical means of enrichment. The last remnants of K-25 were demolished
in early 2013.
According to a 2011 report by the International Panel on Fissile Materials, the
United States produced a total of some 610 metric t (610,000 kg) of highly-enriched
uranium between 1945 and 1995 (Global Fissile Material Report 2011).
References
Compere, A.L., Griffith, W.L.: The U.S. calutron program for uranium enrichment: history,
technology, operations, and production. Oak Ridge National Laboratory report ORNL-5928
(1991)
Fermi, E.: Experimental production of a divergent chain reaction. Am. J. Phys. 20, 536–558 (1952)
Garwin, R.L., Charpak, G.: Megawatts and megatons: a turning point in the nuclear age? Alfred A.
Knopf, New York (2001)
Global Fissile Material Report. International Panel on Fissile Materials (2011). http://fissilemater
ials.org/library/gfmr11.pdf
Hewlett, R.G., Anderson, O.E.: The New World 1939/1946: Volume I Of A History of the United
States Atomic Energy Commission. The Pennsylvania State University Press, University Park,
PA (1962)
Historic American Engineering Record: B Reactor (105-B) Building, HAER No. WA-164.
DOE/RL-2001-16. United States Department of Energy, Richland, WA (2001). http://wcpeace.
org/history/Hanford/HAER_WA-164_B-Reactor.pdf
Jones, R.C., Furry, W.H.: The separation of isotopes by thermal diffusion. Rev. Mod. Phys. 18,
151–224 (1946)
Parkins, W.E.: The uranium bomb, the calutron, and the space-charge problem. Phys. Today 58(5),
45–51 (2005)
Reed, B.C.: Understanding plutonium production in nuclear reactors. Phys. Teach. 43, 222–224
(2005)