It would “Not be too Difficult” to Build a Secret Plant to Produce Highly Enriched Uranium, AEC warned. U.S. Officials Worried that Unless U.S. and Allies Imposed Classification and Export Controls “Unfriendly” Countries Such as China Could Acquire Gas Centrifuges – Published on The National Security Archive, Electronic Briefing Book No. 385, by William Burr, July 23, 2012.
Washington, D.C., July 23, 2012 – The possibility that highly motivated countries, such as Iran in today’s environment, could secretly build gas centrifuge plants to produce highly enriched uranium was foreshadowed over fifty years ago by senior officials at the Atomic Energy Commission (AEC) and its contractors.
They perceived that countries determined to acquire a nuclear weapons capability could secretly build gas centrifuge facilities to enrich uranium, although it required solving complex technical problems. A recently declassified Union Carbide Nuclear Company report, published for the first time today by the National Security Archive and the Nuclear Proliferation International History Project, declared that “in general, it would not be too difficult to build a relatively small clandestine gas centrifuge plant capable of producing sufficient enriched uranium for a small number of nuclear weapons.”
AEC contractor Union Carbide found that even a relatively underdeveloped country could covertly develop a centrifuge plant for a nuclear weapons program, although to do so in a shorter time frame it would need assistance from other countries with more experience in the technology. This is what later happened with Pakistan, which used Dutch-German-British technology stolen by A.Q. Khan, and with Iran, whose Pakistan-assisted centrifuge program remained largely secret until 2002.
Some of the highlights of today’s publication:An early CIA report [document 1] on the Soviet gas centrifuge project based on an interview with a returned German prisoner-of-war.
- An AEC study [document 6] which found that the gas centrifuge method posed a somewhat greater proliferation risk compared to the “plutonium reactor route” because it was a “slightly more attractive” method of producing fissile materials. According to the study, while reactors had a “proven” track record as a source of fissionable material, they required more specialized equipment, more labor power, were difficult to hide, and required more uranium, among other considerations.
- According to the Union Carbide study [document 4] “Class X” highly industrial countries with up-to-date educational systems, such as Germany or Sweden, would need about 5 years to get to the point where they could produce HEU with a gas centrifuge. Class “Y” intermediate countries with “limited internal industrial activity,” such as Israel or Brazil, would require about 6.5 years to reach the point where they could produce nuclear weapons with the help of gas centrifuges. “Class Z” non-industrial countries with low technological levels, such as Cuba or Egypt, would take about 8 years. They would, however, need the assistance of a “Class X” country and would have difficulty building a completely clandestine plant.”
- AEC experts found that West Germany had the “most extensive and most complete gas centrifuge program in the world at this time” and as long as their work proceeded on an unclassified basis it could aggravate the “Nth power” problem. For example, the AEC’s director of classification worried that an “unfriendly” country like China might someday acquire the gas centrifuge on the open market [see documents 2 and 6].
- To prevent the diversion of gas centrifuge technology into weapons programs, in 1960 the AEC staff recommended safeguards and classification of technology. Because classification could only limit dissemination of the latest centrifuge advances, safeguards on the export of centrifuges and controls over uranium trade would be important elements of an international system [see document 6].
- AEC and Union Carbide studies recognized that an important technical problem to be solved was how to operate a “cascade” of gas centrifuges so that they could produce HEU in large quantities. The 1960 Union Carbide study argued that an important element of the time required to develop a gas centrifuge plant was to “solve the problems encountered when one attempts to connect large numbers of centrifuges together and run them in the series-parallel arrangement which constitutes the separation cascade.”
- Union Carbide revised its estimate of the time frame for building a centrifuge plant in 1964, finding that class “X” countries would require 8 years, but 5 years if they had some “technical knowledge” of U.S. developments. Class “Y’ countries would need about 9 years, but about 7 years if they had knowledge of U.S. developments. They would have to import some hardware and equipment. Class “Z” countries could not develop centrifuges on their own, but with technical advisers, knowledge of U.S. developments, and imported equipment, they could do it in about 9 years [see document 9].
The possibility that gas centrifuges could be used to produce highly enriched uranium became understood early in the 20th century. If uranium was converted into uranium hexafluoride, whichcan become a gas at the right temperature, it could flow through high-speed centrifuges which would separate the lighter and fissionable uranium isotope, U-235, from the heavier element, U-238, not unlike a cream separator separating cream from milk. During World War II scientists and technicians working for the Manhattan Project looked closely at the centrifuge option as a way to produce uranium-235 which in turn could be turned into uranium metal for a “gun-type” nuclear weapon. Yet, project director General Leslie Groves and his advisers shut down the project because the centrifuges could not operate for long periods of time without breaking down. The Manhattan Project turned to the highly expensive, but more certain, gaseous diffusion method for producing enriched uranium  … //
… Note on Secondary Sources:
Much declassified information has become available on the Pakistani case, but more needs to be learned about the role of the gas centrifuge technology in U.S. policy and international relations. In recent years historians, political scientists, and scientists have expanded knowledge of the history of the gas centrifuge through archivally-based work. Besides R. Scott Kemp’s contributions, historians Stephen Twigge and Susana Schraffstetter have produced important work on the British centrifuge program in Anglo-American relations and the emergence of the British-Dutch-West German cooperative project that led to URENCO. Recently, historian of science John Krige has shed further light on the role of the gas centrifuge in Anglo-American nuclear relations during the 1960s and on the centrifuge in the negotiating record of the Nuclear Nonproliferation Treaty. The latter, an article recently published inNonproliferation Review, was one of the winners of the Doreen and Jim McElvany Nonproliferation Challenge Essay Competition. 
(full text, Docs 1 to 9 and Notes 1 to 8).