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145. Memorandum From the Acting Director of the Arms Control and Disarmament Agency (Sloss) to the President’s Assistant for National Security Affairs (Brzezinski)1


  • Nuclear Test Cessation and PNEs

This Agency believes there are serious risks in attempting to accommodate “peaceful nuclear explosions” under a comprehensive test ban treaty. The purpose of this early warning is simply to prevent further steps that could be construed as prejudging the issue before it has been thoroughly examined and Soviet positions tested in negotiations.

Such an accommodation—which may well not prove necessary to achieving Soviet agreement on a CTB—would introduce a major shortcoming in the treaty, provide the USSR with an important military asset, weaken the Limited Test Ban Treaty, and do incalculable harm to our non-proliferation efforts. Early encouragement of a Soviet impression that the US may already be persuaded that a PNE allowance in a CTB is necessary and tolerable could quickly grow into a serious impediment to negotiation with the USSR of an advantageous agreement.

We offer the following points for your consideration:


(1) Both the US and the USSR have acknowledged that the technology of nuclear explosive devices for peaceful purposes is indistinguishable from that of nuclear explosive devices for weapon purposes.

(2) Point (1) is the central difficulty of the “PNE verification problem.” No techniques have been devised to verify that a nuclear explosion in a PNE project is not also a weapon test simply because there are no meaningful criteria on which to base the distinction. This intrinsic difficulty cannot be eased by international arrangements for “inspection” or other procedures.

(3) Criteria to govern PNEs in ways that do not substantially compromise the objectives of an agreement limiting a weapon test can be devised if, and only if: (a) the constraints to be imposed on weapon activities are less than complete, and (b) the weapon benefits available under the permissive PNE regime do not extend substantially beyond those permitted in the weapon test regime.

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(4) Much of the international discussion of CTB benefits has dwelled on interrupting the process of developing new improved nuclear weapons; and recent Soviet statements at the UN have also taken this line. This way of thinking about the matter is deficient on two counts:

(a) basic advancement of nuclear weapon technology is not the only substantial reason for nuclear weapon testing—it may no longer even be the main reason. Primary reasons for such testing now and in the foreseeable future are to prove out weapon designs that have been tailored in detail to best match new delivery systems; to test the effects of nuclear explosions on other military equipment, and to verify experimentally the functional soundness of weapons in the stockpile. All of these can be done through PNE operations;

(b) any meaningful PNE program will, itself, include development efforts to advance and test nuclear explosive technology and specific designs. The civil engineering reasons for such continued development and testing (e.g., to reduce the diameter of a device, to establish designs that are more economical of fissionable materials, to establish the ability of the device to deliver reliably its design yield with acceptable precision) could not be challenged as unnecessary or inappropriate; however, they generally parallel corresponding desiderata in the military field. Some of the kinds of device advancements to be sought for PNE applications are on the frontier of current nuclear weapon R&D.2


(5) The US does not have a significant PNE program; and, based on current estimates of economic value in the US plus environmental and regulatory factors, there is no evident justification for a significant US program.


(6) Because of the inactive current and projected status of the US PNE program, allowing an active Soviet program under a complete ban on acknowledged weapon tests would extend to the USSR a substantial unilateral military asset (i.e., a clear basis for indirect continuance of weapon testing).

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(7) The actual PNE plans of the USSR are not reliably known to the US Government. More importantly, the depth of political support for PNE plans is very unclear. We certainly do not know how far the USSR would go in order to retain a PNE allowance against US negotiating opposition. While we surely should display a complete willingness to consider any proposals of the Soviet side, it would be very disadvantageous to provide them at an early stage with any reason to believe that a PNE allowance has been accepted by the US as necessary or tolerable in a CTB.


(8) Discussions in the open literature of Soviet PNE interest include canal building and river diversion projects (primarily the Kama-Pechora river project3 which, if undertaken, might be an effort of 5 to 10 years). The kinds of nuclear explosions necessarily involved in river-diversion or canal building would, with virtual certainty, violate the LTBT. The USSR has played fairly loose with LTBT compliance in their nuclear weapon test program but has always retained the “out” of claiming accident or technical deficiencies if need be. A planned, announced and described PNE excavation project (perhaps with US observers present) would stand naked of any supportable defense in violating the LTBT. The Soviets have labored under this burden for many years, and have not gone forward with any river-diversion or canal-building project. What they have tried to do is co-opt the US into sharing this problem with them—e.g., by advocating international agreement on “acceptable” levels of radioactivity, which could then be “interpreted” as an adequate index of compliance with the LTBT. Such a relaxation of the radioactivity prohibition would both loosen the present inhibitions on underground weapons testing and weaken the protection which the treaty affords to the environments of neighboring states and international waters.

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(9) The USSR has not expressed any interest in seeking an amendment to the LTBT to accommodate excavation-type PNEs. Amendment would not be possible without the assent of the US and the UK. Moreover, an amendment that relaxed the radioactivity limitation of PNEs for all parties would reduce the value of the LTBT as an inhibition on nuclear explosive development by non-nuclear-weapon states, while an amendment which relaxed that limitation only for nuclear-weapon states might well fail to be adopted by the requisite majority of parties to the treaty.

(10) The Soviet Union did agree to inclusion in the PNE Treaty of an operative reaffirmation of the obligation to comply with the LTBT—albeit with a display of real or feigned reluctance.

(11) The draft text of a CTB Treaty proposed by the USSR in the UNGA would prohibit all nuclear weapon tests but would allow PNEs to continue under the terms of a separate agreement.4 The language of their proposed preamble and operative provisions point rather clearly to a process in which the new treaty would replace the LTBT and the LTBT would cease to be operative. This scheme, if allowed to proceed, would leave PNEs to be governed by new provisions which would presumably not include the “no radioactive debris” element that is the substance of LTBT limitation on underground nuclear explosions.


(12) If any technological criteria—valid or contrived—ever are set forth to distinguish between weapon and non-weapon explosions or explosives, then a principle argued by many potential proliferators will have been explicitly affirmed. There were some discussions of this matter during the PNET negotiations, and the point was clearly taken as a very serious one by the Soviet side.

(13) A major objective of establishing a CTB would be to help prevent the further spread of nuclear explosive capabilities. A test ban which made an exception for PNEs would:

(a) legitimize PNEs as distinct from weapon tests and thus do major damage to our efforts to establish that PNEs must not be conducted by any non-nuclear-weapon state, since the technology of a nuclear explosive device for a peaceful application is indistinguishable from that of a weapon and its development is the development of nuclear weapons.

(b) if limited to nuclear-weapon states, create an excuse for not joining the CTB on the grounds that the treaty was “discriminatory” for a number of those non-nuclear-weapon states that we are most inter[Page 322]ested in having join the treaty (e.g., India, Israel, Pakistan, Argentina, Brazil). Joining in a CTB that banned PNEs for all parties is probably the most promising way to head off a second Indian explosion.5

(c) if not limited to nuclear-weapon states, undermine the non-proliferation benefits of the CTB, create an intractable problem of devising criteria and verification schemes and negotiating them with all parties involved, and discriminate against parties to the NPT (who have foresworn such explosions) in favor of non-parties.

Leon Sloss
  1. Source: Washington National Records Center, OSD Files: FRC 330–80–0017, Box 63, A–400.112 Test Ban (Jan–July) 1977. Secret. Copies were sent to Vance, Harold Brown, Fri, and Turner.
  2. Carter wrote Brezhnev on February 14 and said that he welcomed “your willingness to intensify efforts to reach agreement on a comprehensive test ban. I recognize that there are remaining issues with respect to other countries who continue to have test programs and the possible use of peaceful nuclear explosions for mining or construction, but I believe there are satisfactory ways of dealing with these issues. I intend to ratify the existing agreements which have been negotiated between our two governments but I consider these only steps toward a common objective of a complete cessation of nuclear tests. In the meantime these unratified agreements will be honored by our government.” The letter is printed in full in Foreign Relations, 1977–1980, vol. VI, Soviet Union, Document 7.
  3. In a February 8 news conference, Carter said that he had “called upon the Soviet Union to join us in a comprehensive test ban to stop all nuclear testing for at least an extended period of time, 2 years, 3 years, 4 years. The Soviets are interested in using nuclear explosives to divert the course of a river in Northern Russia. I don’t think they need to test any more. If they want to put that as a proviso in the agreement that they would like to go ahead and divert that river, I think that would be something that we could negotiate and let us have observers there to learn from them and vice versa. But I think that the initiation of proposals that might be mutually acceptable of the kind is very, very important.” (Public Papers: Carter, 1977, pp. 92–100)
  4. “Soviet Draft Treaty Introduced in the First Committee of the General Assembly on the Complete and General Prohibition of Nuclear-Weapon Tests,” November 22, 1976. (Documents on Disarmament, 1976, pp. 820–824)
  5. India conducted its first nuclear explosion on May 18, 1974.