ARMS-D-Request@XX.LCS.MIT.EDU (Moderator) (02/24/86)
Arms-Discussion Digest Sunday, February 23, 1986 4:37PM
Volume 6, Issue 52
Today's Topics:
Cooperative Verification of Nuclear Weapons
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Date: Sun, 23 Feb 1986 16:36 EST
From: LIN@XX.LCS.MIT.EDU
Subject: Cooperative Verification of Nuclear Weapons (draft for comments)
Below is a DRAFT paper on which I would like comments. I need them by
Wed (2/26) at 9 AM for maximum utility. Hostile comments especially
invited. This file is about 12 K characters.
Cooperative Verification of Nuclear Weapons
Copyright 1986 Herbert Lin
The political viability of arms control agreements today
depends on the ability of one side to count the number of
nuclear weapons that the other side has. For the most part,
this ability depends upon the ability of national technical
means (NTM) such as satellites to identify launch platforms
(e.g., missile silos, submarines). Assumptions about the
number of nuclear weapons carried on each platform derived from
observations of missile tests are then used to convert a
platform count into a weapon count. This verification process
is mostly unilateral, though agreements to refrain from
impeding NTM do add a cooperative spirit to the endeavor.
With greater cooperation between the U.S. and the Soviet
Union, it should be possible to verify deployments of nuclear
weapons in greater detail than is currently feasible with a
primary reliance on unilateral means. This note is intended as
a conceptual exploration of how one generic method of
cooperative verification might proceed. An important warning
to the reader is that many technical and procedural details
remain to be worked out.
A cooperative verification scheme could involve an agreement
between the U.S. and the Soviet Union to allow the placement of
nuclear weapons detectors on each other's weapons-carrying
platforms. (Of course, such an agreement would be entirely
symmetric between the U.S. and the Soviet Union, and the
discussion of U.S. verification procedures below applies
equally to the Soviet Union.) These sensors would relay their
report to American authorities using Soviet communication
systems; the authenticity of these reports would be guaranteed
through the use of a public-key encryption scheme. Each
element of the scheme is described below.
Nuclear weapon detectors depend on the ability to sense
nearby the presence of fissionable material, either U-235 or
Pu-239. Detectors would be placed at every opening through
which a nuclear weapon might be loaded into the platform; thus,
detectors would have to operate at ranges of only a few feet.
The technology base for these detectors has been developed
in the context of monitoring nuclear materials used in nuclear
power plants. These monitoring technologies are capable of
measuring with reasonable precision small amounts of nuclear
material within the reactor fuel cycle so that illegal
diversions can be detected with confidence. By contrast, a
weapon detector requires only the ability to distinguish
between one weapon or two -- a much less technically demanding
task.
Generically, two monitoring methods are available. Passive
sensing and measurement of fissile materials depends on the
natural radiation that these materials emitted. Active sensing
and measurement depends on the ability to probe the immediate
vicinity of the detector with an interrogator of some sort,
such as a pulse of neutrons. The interrogator probe would
interact with any fissile material in the vicinity, producing a
characteristic radiation spectrum. Sensors located nearby
would detect this spectrum thus signaling the presence of a
nuclear weapon.
The Soviets could be concerned that the detector could
compromise the security of the platform. This concern could be
allayed by the construction of twice as many detectors as are
to be installed. The Soviets would choose half the detectors
for their own technicians to disassemble, who would verify that
these boxes posed no threat. The other detectors would be
installed on the appropriate platforms.
Public-key encryption was originally designed as a method by
which the key to encoding a message and the key to decode the
message are not identical. Thus, an encryption key could be
made public, enabling anyone to encode a message, though
knowledge of the encryption key alone would not allow the
decoding of an encrypted message. However, public-key
encryption schemes also provide the tools necessary to verify
that a received message has indeed been sent legitimately,
i.e., by a party in possession of the decryption key.
American authorities would interrogate their detectors by
asking Soviet authorities to use their own (Soviet)
communication channels to transmit orders and receive
information from American detectors mounted on Soviet
platforms. Since the authenticity of a message sent by a
detector can be guaranteed, the U.S. could be confident that
the data it received from the Soviet authorities had not been
compromised or altered. On the other hand, the use of Soviet
communication channels would allow Soviet platforms to maintain
their operational flexibility with minimal loss of security.
The U.S. would be allowed to interrogate its detectors
periodically. The interval between interrogations should be
long enough to intrude only minimally on Soviet operational
practices, but short enough that an upper limit on the total
number of nuclear weapons could be verified with reasonable
confidence. A protocol to handle a small number of
communications failures should also be included.
If the data provided by a platform-by-platform interrogation
were determined to compromise operational security to a large
extent, it would be possible to feed the data to a secure
computer in Soviet possession but programmed by the U.S. to
report total deployments but not the total numbers of weapons
aboard individual platforms.
The feasibility of this cooperative verification scheme
depends on the resistance of the detector to tampering of
various sorts. The detector itself can be designed to detect
changes in its magnetic environment, so that it could record
the fact that it had been moved. More serious is the
possibility that somehow nuclear weapons could pass the
detector undetected. If the detector is based on passive
sensing, a nuclear weapon shielded by lead (to reduce gamma ray
emissions) and by hydrogenated material such as paraffin (to
reduce neutron emissions) might pass undetected. Therefore, it
is likely that active detection means would be necessary.
An active detector might require the placement of sensors
opposite a pulsed neutron source; weapons enter the platform
passing between the sensors and the neutron source. At random
intervals determined by electronics in the detector, a pulse of
neutrons would be emitted. The sensors opposite would detect
both the probe's neutrons and the radiation induced by fission
in a nuclear weapon that happened to be present. If the weapon
were shielded, the shielding on the weapon would block the
induced emissions, but would also block the probe's neutrons;
thus, the presence of shielding would be indicated. One
determining issue then becomes the extent to which it is
possible to mimic the signature of the probe; careful placement
of multiple sensors and accurate time of flight measurements on
the probe neutrons could increase the confidence that a signal
received by the sensors was in fact transmitted by the probe.
The second determining issue is the extent to which the use of
active probes would realistically degrade confidence in the
reliability of a nuclear weapon so probed.
Even if technically feasible, the method of cooperative
verification described above does not settle a number of
important issues.
- All cooperative verification schemes are useful only in
peacetime, and are thus essentially confidence-building
measures. They provide no protection in the event of
war.
- Sudden strategic break-out of an agreement based on a
cooperative verification scheme is possible, since nothing
in such agreements necessarily prohibits unlimited
production (as opposed to deployment) of the nuclear
weapons to be limited.
- Sudden tactical break-out is possible if many more nuclear
weapons than allowed can be loaded into many platforms on
a time scale smaller than the interval between
interrogations. A good agreement regarding times between
interrogating and also provisions for re-interrogating an
already-interrogated platform would help to keep but not
to guarantee) possible violations to militarily
insignificant levels.
- An initial on-site inspection of all platforms capable of
carrying the nuclear weapon to be limited is necessary to
"initialize the count" of nuclear weapons aboard. This
inspection is of necessity highly intrusive, but it is
consistent with Secretary John Lehman's offer to allow
in-port inspection of Navy ships as part of any
arms-control agreement.
- All platforms capable of carrying the nuclear weapon to be
limited must be equipped with detectors.
- Tactical and strategic warheads cannot be distinguished.
Therefore, this cooperative verification scheme forces
possibly difficult trade-offs between tactical and
strategic applications.
All of these issues must be addressed before cooperative
verification schemes would be viable. However, it should not
be surprising that cooperative schemes to verify deployments of
nuclear weapons are more intrusive and less secure than
unilateral methods; indeed, cooperative verification schemes
are necessary only when the specific types of weapons to be
limited are not verifiable by unilateral means.
Finally, the method described above for communicating with
detectors can be used to verify compliance with mutually agreed
keep-out zones. A platform (e.g., a submarine) designated as
one that must refrain from entering a given deployment area
would be equipped with an inertial navigation unit that could
keep track of platform movements. To avoid giving away its
precise deployment track, the unit would be programmed with the
geographical boundaries of the agreed-upon keep-out zones. The
read-out from the navigation unit would be limited to one bit
-- a determination of whether or not the keep-out zone had been
violated.
Herb Lin
Center for International Studies
E38-668
Massachusetts Institute of Technology
Cambridge, Massachusetts 02139
(617) 253-8076
February 1986
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End of Arms-Discussion Digest
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