Kilowatts to Kilotons: Wartime Electricity Use at Oak Ridge

By Cameron Reed

Kilowatts to kilotons graph

Late-1943 through late-1945 electricity generation and consumption in millions of kilowatt-hours. The red horizontal line (top) shows 1% of average 1943-1945 national monthly generation (227 MkWh), the blue curve (middle) 10% of TVA monthly generation, and the green curve (bottom) Y-12 consumption.

The vastness of the Clinton Engineer Works (CEW) uraniumenrichment complex located at Oak Ridge, Tennessee, has been the subject of numerous book and articles. By any measure – construction and operations costs, number of workers and operators involved, or square footage of plant constructed – the Clinton complex was an unprecedented testimony to the scientific, organizational, and engineering skills which made the Manhattan Project so successful.

In his 1987 autobiography, Manhattan District Engineer Colonel Kenneth Nichols (1907-2000) gives a statistic that is impressive even by Manhattan Project standards: that by the time the CEW was fully operational, it was consuming one-seventh of the electric power being generated in the United States at that time [1]. The same figure also appears in various editions of a Department of Energy booklet on the Project, attributed to Nichols [2]. When I first encountered this claim, it struck me as improbable: the Clinton complex was enormous, but could one facility have really been consuming some 14% of the electricity being generated in the entire country at a time when industries were working flat-out in support of the war effort? A bit of sleuthing through available records on national electricity generation and Oak Ridge power consumption shows that Nichols’ figure is grossly in error. In this brief article, I examine the relevant data, and offer a speculation as to the origin of his number.

In his meticulously researched book on the Army’s role in the Manhattan Project, Vincent Jones states that by mid-1945, transmission facilities at CEW could provide electrical power up to 310 megawatts (MW), of which 200 MW were for the Y-12 electromagnetic separation plant [3]. Jones states that peak consumption for any extended period during the war occurred in August, 1945, when the electricity used by all facilities for the month totaled about 200 million kilowatt-hours (MkWh). Jones’ figures are internally consistent: 200 MkWh over a 31-day month (744 hours) gives an average power of (200 MkWh/744 h) = 0.269 MkW = 269 MW.

Statistics on national generating capacity can be obtained from online back issues of the Statistical Abstracts of the United States [4]. Figures published in the 1949 edition of the Abstracts indicate that generating capacity grew rapidly during the early years of the war, but from 1943 to 1945 remained fairly steady at an average of about 272.8 billion kWh per year. One month’s worth would be about 22.7 billion kWh, or 22,700 MkWh. The August, 1945, CEW fraction would then have been (200 MkWh/22,700 MkW) = 0.0088, or about 0.9%. One percent of national capacity is still impressive, but a far cry from the one-seventh claimed by Nichols.

How might Nichols have arrived at his figure? Clinton drew its power from the Tennessee Valley Authority (TVA). TVA Historian Patricia Ezzell very kindly provided me with some data on the growth of TVA generating capacity. In November, 1942, when planning for Clinton was beginning, TVA capacity stood at 1,493 MW, and by the time of the Japanese surrender in August, 1945, had grown to 2,507 MW. The full CEW capacity of 310 MW would represent just over 12% of the latter figure, or about one-eighth. I suspect that Nichols was referring to CEW consumption as a fraction of TVA capacity.

The bulk of Clinton’s electricity consumption went to operating Y-12’s uranium-enriching “calutrons.” A month-by-month record of Y-12 electricity consumption can be found in Manhattan Engineer District records available online from the Department of Energy [5]. The accompanying graph shows Y-12 consumption, 10% of TVA capacity (assuming 30-day months), and 1% of average monthly national electricity generation from 1943 to 1945. The total amount of electrical energy consumed by Y-12 between November, 1943, through the end of July, 1945, totaled just over 1.6 billion kWh, about 100 times the energy released by the U-235 Little Boy bomb. To put these numbers in some perspective, this author’s monthly household electricity consumption typically averages about 600 kWh; a million kWh would supply my family for over 135 years! As evidenced by the graph, Y-12 was promptly shut down at the end of the war.

Nichols’ error may well have been a simple oversight motivated by his justifiable pride in being associated with Oak Ridge. For my students, I use this little piece of historical detective-work as an example of the old adage that “If it sounds too good to be true, it probably is.”

I am grateful to TVA Tribal Liaison and Corporate Historian Patricia Ezzell, Y-12 Historian D. Ray Smith, former Oak Ridge chemist Bill Wilcox and DoE Historian Skip Gosling for helpful comments.

  1. K. D. Nichols. The Road to Trinity (New York: William Morrow and Company, 1987), p. 146.
  2. F. G. Gosling. The Manhattan Project: Making the Atomic Bomb (Washington: Department of Energy). An online version is available at The one-seventh figure appears on p. 21.
  3. V. C. Jones. Manhattan: The Army and the Atomic Bomb (Washington: Center of Military History, United States Army, 1985), p. 391. Available at
  4. Statistical Abstract of the United States. 1949 edition, p. 512.
  5. The Manhattan District History is available at See specifically Book V (Electromagnetic Project), Volume 6 (Operations), Appendix B (Documents: Y-12 Power Consumption).

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