# K-25

(Redirected from SAM Laboratories)
The K-25 building of the Oak Ridge Gaseous Diffusion Plant aerial view, looking southeast. The mile-long building, in the shape of a "U" was completely demolished in 2013.

K-25 was the codename given by the Manhattan Project to the program to produce enriched uranium for atomic bombs using the gaseous diffusion method. Originally the codename for the product, over time it came to refer to the project, the production facility located at the Clinton Engineer Works in Oak Ridge, Tennessee, the main gaseous diffusion building, and ultimately the site. When it was built in 1944, the four-story K-25 gaseous diffusion plant was the world's largest building, comprising over 1,640,000 square feet (152,000 m2) of floor space and a volume of 97,500,000 cubic feet (2,760,000 m3).

Gaseous diffusion is based on Graham's law, which states that the rate of effusion of a gas is inversely proportional to the square root of its molecular mass. The highly corrosive uranium hexafluoride (UF
6
) was the only known compound of uranium sufficiently volatile to be used in this process. Before this could be done, the Special Alloyed Materials (SAM) Laboratories at Columbia University and the Kellex Corporation had to overcome formidable difficulties to develop a suitable barrier.

Construction of the K-25 facility was undertaken by J. A. Jones Construction. At the height of construction, over 25,000 workers were employed on the site. Gaseous diffusion was but one of three enrichment technologies used by the Manhattan Project. Slightly enriched product from the S-50 thermal diffusion plant was fed into the K-25 gaseous diffusion plant. Its product in turn was fed into the Y-12 electromagnetic plant. The enriched uranium was used in the Little Boy atomic bomb used in the atomic bombing of Hiroshima. In 1946, the K-25 gaseous diffusion plant became capable of producing highly enriched product.

After the war, four more gaseous diffusion plants named K-27, K-29, K-31 and K-33 were added to the site. The K-25 site was renamed the Oak Ridge Gaseous Diffusion Plant in 1955. Production of enriched uranium ended in 1964, and gaseous diffusion finally ceased on the site on 27 August 1985. The Oak Ridge Gaseous Diffusion Plant was renamed the Oak Ridge K-25 Site in 1989, and the East Tennessee Technology Park in 1996. Demolition of all five gaseous diffusion plants was completed in February 2017.

## BackgroundEdit

The discovery of the neutron by James Chadwick in 1932,[1] followed by that of nuclear fission in uranium by the German chemists Otto Hahn and Fritz Strassmann in 1938,[2] and its theoretical explanation (and naming) by Lise Meitner and Otto Frisch soon after,[3] opened up the possibility of a controlled nuclear chain reaction with uranium. At the Pupin Laboratories at Columbia University, Enrico Fermi and Leo Szilard began exploring how this might be achieved.[1] Fears that a German atomic bomb project would develop atomic weapons first, especially among scientists who were refugees from Nazi Germany and other fascist countries, were expressed in the Einstein-Szilard letter to the President of the United States, Franklin D. Roosevelt. This prompted Roosevelt to initiate preliminary research in late 1939.[4]

Niels Bohr and John Archibald Wheeler applied the liquid drop model of the atomic nucleus to explain the mechanism of nuclear fission.[5] As the experimental physicists studied fission, they uncovered puzzling results. George Placzek asked Bohr why uranium seemed to fission with both fast and slow neutrons. Walking to a meeting with Wheeler, Bohr had an insight that the fission at low energies was due to the uranium-235 isotope, while at high energies it was mainly due to the far more abundant uranium-238 isotope.[6] The former makes up just 0.714 percent of the uranium atoms in natural uranium, about one in every 140;[7] natural uranium is 99.28 percent uranium-238. There is also a tiny amount of uranium-234, which accounts for just 0.006 percent.[8]

At Columbia, John R. Dunning believed that this was the case, but Fermi was not so sure. The only way to settle this was to obtain a sample of uranium 235 and test it.[1] He got Alfred O. C. Nier from the University of Minnesota to prepare samples of uranium enriched in uranium-234, 235 and 238 using a mass spectrometer. These were ready in February 1940, and Dunning, Eugene T. Booth and Aristid von Grosse then carried out a series of experiments. They demonstrated that uranium-235 was indeed primarily responsible for fission with slow neutrons,[9] but were unable to determine precise neutron capture cross sections because their samples were not sufficiently enriched.[10][11][12]

At the University of Birmingham in Britain, the Australian physicist Mark Oliphant assigned two refugee physicists—Otto Frisch and Rudolf Peierls—the task of investigating the feasibility of an atomic bomb, ironically because their status as enemy aliens precluded their working on secret projects like radar.[13] Their March 1940 Frisch–Peierls memorandum indicated that the critical mass of uranium-235 was within an order of magnitude of 10 kilograms (22 lb), which was small enough to be carried by a bomber of the day.[14]

## Gaseous diffusionEdit

Gaseous diffusion process. Stages are connected together to form a cascade. A, B and C are pumps. In traveling through successive barriers, the feed becomes slightly enriched as it moves from stage 1 to stage 2 to stage 3. Depleted uranium is drawn off in the reverse direction, slowly becoming completely depleted at the bottom. Completely enriching the uranium would require thousands of these stages.

In April 1940, Jesse Beams, Ross Gunn, Fermi, Nier, Merle Tuve and Harold Urey had a meeting at the American Physical Society in Washington, D.C. At the time, the prospect of building an atomic bomb seemed dim, and even creating a chain reaction would likely require enriched uranium. They therefore recommended that research be conducted with the aim of developing the means to separate kilogram amounts of uranium-235.[15] At a lunch on 21 May 1940, George B. Kistiakowsky suggested the possibility of using gaseous diffusion.[16]

Gaseous diffusion is based on Graham's law, which states that the rate of effusion of a gas through a porous barrier is inversely proportional to the square root of the gas's molecular mass. In a container with a porous barrier containing a mixture of two gases, the lighter molecules will pass out of the container more rapidly than the heavier molecules. The gas leaving the container is slightly enriched in the lighter molecules, while the residual gas is slightly depleted.[17] A container wherein the enrichment process takes place through gaseous diffusion is called a diffuser.[18]

Gaseous diffusion had been used to separate isotopes before. Francis William Aston had used it to partially separate isotopes of neon in 1931, and Gustav Ludwig Hertz had improved on the method to almost completely separate neon by running it through a series of stages. In the United States, William D. Harkins had used it to separate chlorine. Kistiakowsky was familiar with the work of Charles G. Maier at the Bureau of Mines, who had also used the process to separate gases.[16]

Uranium hexafluoride (UF
6
) was the only known compound of uranium sufficiently volatile to be used in the gaseous diffusion process.[17] Fortunately, fluorine consists of only a single isotope 19
F
, so that the 1 percent difference in molecular weights between 235
UF
6
and 238
UF
6
is due solely to the difference in weights of the uranium isotopes. For these reasons, UF
6
was the only choice as a feedstock for the gaseous diffusion process.[19] Uranium hexafluoride, a solid at room temperature, sublimes at 56.5 °C (133.7 °F) at 1 standard atmosphere (100 kPa).[20][21] Applying Graham's Law to uranium hexafluoride:

${\displaystyle {{\mbox{Rate}}_{1} \over {\mbox{Rate}}_{2}}={\sqrt {M_{2} \over M_{1}}}={\sqrt {352 \over 349}}\approx 1.0043}$

where:

Rate1 is the rate of effusion of 235UF6.
Rate2 is the rate of effusion of 238UF6.
M1 is the molar mass of 235UF6 ≈ 235 + 6 × 19 = 349 g·mol−1
M2 is the molar mass of 238UF6 ≈ 238 + 6 × 19 = 352 g·mol−1

Uranium hexafluoride is a highly corrosive substance. It is an oxidant[22] and a Lewis acid which is able to bind to fluoride.[23] It reacts with water to form a solid compound, and is very difficult to handle on an industrial scale.[19]

## OrganizationEdit

Booth, Dunning and von Grosse investigated the gaseous diffusion process. In 1941, they were joined by Francis G. Slack from Vanderbilt University and Willard F. Libby from the University of California. In July 1941, an Office of Scientific Research and Development (OSRD) contract was awarded to Columbia University to study gaseous diffusion.[9][24] With the help of the mathematician Karl P. Cohen, they built a twelve-stage pilot gaseous diffusion plant at the Pupin Laboratories.[25] Initial tests showed that the stages were not as efficient as the theory would suggest,[26] and that they would need about 4,600 stages to enrich to 90 percent uranium-235.[17]

The Woolworth Building in Manhattan housed the offices of the Kellex Corporation and the Manhattan District's New York Area

## OperationsEdit

The K-25 control room

The preliminary specification for the K-25 plant in March 1943 called for it to produce 1 kilogram (2.2 lb) a day of product that was 90 percent uranium-235.[77] As the practical difficulties were realized, this target was reduced to 36 percent. On the other hand, the cascade design meant that construction did not need to be complete before the plant started operating.[78] In August 1943, Kellex submitted a schedule that called for a capability to produce material enriched to 5 percent uranium-235 by 1 June 1945, 15 percent by 1 July 1945, and 36 percent by 23 August 1945.[79] This schedule was revised in August 1944 to 0.9 percent by 1 January 1945, 5 percent by 10 June 1945, 15 percent by 1 August 1945, 23 percent by 13 September 1945, and 36 percent as soon as possible after that.[80]

## NotesEdit

1. ^ a b c Hewlett & Anderson 1962, pp. 10–14.
2. ^ Rhodes 1986, pp. 251–254.
3. ^ Rhodes 1986, pp. 256–263.
4. ^ Jones 1985, p. 12.
5. ^ Bohr, Niels; Wheeler, John Archibald (September 1939). "The Mechanism of Nuclear Fission". Phys. Rev. American Physical Society. 56 (5): 426–450. Bibcode:1939PhRv...56..426B. doi:10.1103/PhysRev.56.426.
6. ^ Wheeler & Ford 1998, pp. 27–28.
7. ^ Manhattan District 1947a, p. S1.
8. ^ Manhattan District 1947a, p. 2.1.
9. ^ a b c Smyth 1945, p. 172.
10. ^ Hewlett & Anderson 1962, p. 22.
11. ^ Nier, Alfred O.; Booth, E. T.; Dunning, J. R.; von Grosse, A. (March 3, 1940). "Nuclear Fission of Separated Uranium Isotopes". Physical Review. 57 (6): 546. Bibcode:1940PhRv...57..546N. doi:10.1103/PhysRev.57.546.
12. ^ Nier, Alfred O.; Booth, E. T.; Dunning, J. R.; von Grosse, A. (April 13, 1940). "Further Experiments on Fission of Separated Uranium Isotopes". Physical Review. 57 (8): 748. doi:10.1103/PhysRev.57.748.
13. ^ Rhodes 1986, pp. 322–325.
14. ^ Hewlett & Anderson 1962, p. 42.
15. ^ Hewlett & Anderson 1962, pp. 22–23.
16. ^ a b Hewlett & Anderson 1962, pp. 30–31.
17. ^ a b c Jones 1985, p. 152.
18. ^ Manhattan District 1947a, p. S2.
19. ^ a b Beaton L (1962). "The slow-down in nuclear explosive production". New Scientist. 16 (309): 141–143. Retrieved 20 November 2010.
20. ^ "Glossary of High Energy Weapons Terms". Nuclear Weapons Archive. Retrieved 8 June 2016.
21. ^
22. ^ Olah GH, Welch J (1978). "Synthetic methods and reactions. 46. Oxidation of organic compounds with uranium hexafluoride in haloalkane solutions". Journal of the American Chemical Society. 100 (17): 5396–402. doi:10.1021/ja00485a024.
23. ^ Berry JA, Poole RT, Prescott A, Sharp DW, Winfield JM (1976). "The oxidising and fluoride ion acceptor properties of uranium hexafluoride in acetonitrile". Journal of the Chemical Society, Dalton Transactions (3): 272–274. doi:10.1039/DT9760000272.
24. ^ a b Manhattan District 1947a, pp. S2–S3.
25. Jones 1985, pp. 150–151.
26. ^ Smyth 1945, p. 175.
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34. ^ a b "Manhattan Project Spotlight: The Chrysler Corporation". Retrieved 13 June 2016.
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36. ^ a b Hewlett & Anderson 1962, p. 101.
37. ^ a b c Hewlett & Anderson 1962, p. 125.
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40. ^ a b Hewlett & Anderson 1962, pp. 126–129.
41. ^ Hewlett & Anderson 1962, pp. 132–134.
42. ^ Hewlett & Anderson 1962, pp. 136–138.
43. ^ Hewlett & Anderson 1962, p. 138.
44. ^ Hewlett & Anderson 1962, pp. 139–140.
45. ^ Manhattan District 1947c, pp. 6.1–6.2.
46. ^ a b Groves 1962, pp. 112–113.
47. ^ "History of J.A. Jones, Inc." FundingUniverse. Retrieved 10 June 2016.
48. ^ a b c Jones 1985, pp. 160–161.
49. ^ a b Manhattan District 1947d, p. H1.
50. ^ a b Manhattan District 1947d, p. S17.
51. ^ Jones 1985, pp. 383–384.
52. ^ a b Manhattan District 1947c, pp. 6.3–6.4.
53. ^ Manhattan District 1947d, p. S4.
54. ^ a b c d "Powerhouse area / S-50". K-25 Virtual Museum. Retrieved 10 June 2016.
55. ^ a b Manhattan District 1947d, p. 3.21.
56. ^ Jones 1985, pp. 384–385.
57. ^ Manhattan District 1947d, pp. 3.10–3.12.
58. ^ Jones 1985, pp. 440–442.
59. ^ a b c Manhattan District 1947d, p. S14.
60. ^ Manhattan District 1947d, p. 3.15.
61. ^ Manhattan District 1947d, p. 3.64.
62. ^ Manhattan District 1947d, pp. 3.8–3.9.
63. ^ a b c Jones 1985, p. 161.
64. ^ a b c Manhattan District 1947d, pp. 3.28–3.29.
65. ^ Jones 1985, p. 158.
66. ^ Manhattan District 1947e, p. S3.
67. "K-25 Virtual Museum – Site Tour". Department of Energy. Retrieved 12 June 2016.
68. ^ Manhattan District 1947d, pp. 3.67–3.68.
69. ^ Manhattan District 1947d, pp. 3.72–3.75.
70. ^ Manhattan District 1947d, p. 5.3.
71. ^ a b c d Manhattan District 1947d, pp. 3.31–3.41.
72. ^ a b Manhattan District 1947e, p. S5.
73. ^ a b Manhattan District 1947e, pp. 2.6–2.7, 12.6.
74. ^ Manhattan District 1947d, p. 3.40.
75. ^ Manhattan District 1947f, p. 5.
76. ^ a b Jones 1985, p. 165.
77. ^ Manhattan District 1947c, p. 7.1.
78. ^ Jones 1985, p. 157.
79. ^ Manhattan District 1947d, p. 3.2.
80. ^ Jones 1985, p. 162.
81. ^ a b Manhattan District 1947e, pp. S1–S3.
82. ^ Manhattan District 1947e, pp. 2.4–2.6, 12.5.
83. ^ a b Jones 1985, pp. 166–168.
84. ^ Jones 1985, p. 148.
85. ^ a b Jones 1985, p. 169.
86. ^ Manhattan District 1947g, pp. 1–2.
87. ^ Jones 1985, p. 183.
88. ^ Jones 1985, pp. 522, 535–538.
89. ^ Manhattan District 1947f, pp. 1–7.
90. ^ Manhattan District 1947f, pp. 16–20.
91. ^ Manhattan District 1947f, pp. 8–10.
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