Office of the Historian

67. Aide-Mémoire From the Department of State to the Soviet Embassy1

Washington, undated.

The aide-mémoire from the Soviet Government, dated January 22,2 requests that the Government of the United States provide clarification [Page 185] regarding the Kiwi reactor safety experiment as to whether it constituted a nuclear explosion falling under the prohibition stipulated by the “Treaty Banning Nuclear Weapons Tests in the Atmosphere, in Outer Space and Under Water.” Reactors are designed as stable power sources and are intrinsically unsuitable for use as weapons. Neither reactor safety experiments nor reactor accidents which they are designed to stimulate or reproduce constitute nuclear explosions. Therefore, they do not fall under the prohibition stipulated in the Treaty. Nevertheless, in view of the interest of the Soviet Government, the Government of the United States provides the following information concerning this experiment.

The Kiwi experiment of January 12, 1965, at the Nuclear Rocket Development Station in Nevada, was the latest of the series of reactor safety experiments to obtain information to ensure the safe operation of nuclear reactors and to assess the potential consequences in the unlikely event that a reactor accident occurred. Reactor safety experiments have been freely discussed at the Third International Conference on the Peaceful Uses of Atomic Energy3 and elsewhere. All of the previous U.S. reactor safety experiments including those involving reactor destruction, such as the Spert test conducted during November 1963, and the Snaptran test in April 1964, have been reported in the open literature. The same procedure is being followed for this experiment. The experiment was announced publicly in advance and the press was present.

The Kiwi reactor safety experiment involved a deliberate burn-up of a nuclear rocket reactor designed for space exploration. This experiment was necessary to obtain data on the behavior of reactors of this type under rapid changes in power levels. Extensive safety studies have been performed to determine the effects of various postulated accident conditions which might theoretically cause such rapid changes in power levels. This experiment was conducted to confirm or correct the predictions of those safety studies.

The Kiwi reactor is a uranium carbide fueled, graphite moderated reactor of approximately 1,000 megawatts thermal power. The experiment was conducted as planned and produced a relatively small amount of energy over a time period thousands of times longer than the period involved in nuclear explosions. Specifically, according to preliminary data, a total energy of about 15,000 megawatt-seconds was produced over several milliseconds. This release of energy caused portions of the reactor to vaporize and the reactor to destroy itself.

[Page 186]

Results were in good agreement with pre-test predictions. The experiment therefore lends confidence to the reactor safety studies which are so important in the use of nuclear energy for peaceful purposes.

  1. Source: Johnson Library, National Security File, Subject File, Nuclear Testing—USSR, Vol. I, Box 31. Confidential; Limit Distribution. A copy of the aide-mémoire is reproduced in Seaborg, Journal, Vol. 10, pp. 98-100. The source text is undated, but is attached to a January 26 memorandum from G. William Moser to the Committee of Principals indicating that a copy of the aide-mémoire was given to Ambassador Dobrynin on the same day. Llewellyn Thompson, who handed it to Dobrynin, wrote of their meeting:

    “I handed the Ambassador our reply to their aide-mémoire on the Kiwi reactor. After reading it, the Ambassador quoted from the language of the Treaty, stating that in addition to weapons tests, ‘any other nuclear explosion anywhere which would take place in any of the environments described’ was prohibited. He stated that this experiment had been described by the American press as a nuclear explosion. I said that although the matter was a technical one, my understanding was that the operation of any nuclear reactor could, in one sense of the word, be described as a nuclear explosion. My understanding was that in this case in order to develop reactor safety, a reactor was speeded up to the point where it burned itself up, but that this was not comparable to what we would consider a nuclear explosion by a very wide margin.

    “Dobrynin said he would of course transmit our aide-mémoire and that it would be studied in Moscow, but he clearly indicated that he did not consider we had made a convincing case.”

    (Memorandum of conversation, January 26; Johnson Library, National Security File, Subject File, Nuclear Testing—USSR, Vol. I, Box 31)
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  2. Document 65.↩
  3. Regarding this conference, held in Geneva, August 31-September 9, 1964, see Seaborg, Journal, Vol. 9, pp. 145-156 and 178-180.↩