Nuclear Weapon Development without Nuclear Testing?
NUCLEAR WEAPON DEVELOPMENT WITHOUT NUCLEAR TESTING?
by
Richard L. Garwin
IBM Fellow Emeritus
IBM Research Division
Thomas J. Watson Research Center
P.O. Box 218
Yorktown Heights, NY 10598
(914) 945-2555
FAX: (914) 945-4419
Email: RLG2 AT WATSON.IBM.COM
and
Vadim A. Simonenko
Deputy Scientific Director
Russian Federal Nuclear Center
Institute of Technical Physics (VNIITV)
Snezhinsk, Chelyabinsk Region
RUSSIA
(7-351) 722-4327
FAX: (7-351) 723-2077
Email: sva at nine.ch70.chel.su
Prepared for the Pugwash Workshop on
PROBLEMS IN ACHIEVING A NUCLEAR-WEAPON-FREE WORLD
October 25-27, 1996
London, ENGLAND
V299NWDT 102596NWDT 11/19/97
CONTENTS
Introduction. . . . . . . . . . . . . . . . . . . . . 1
A caution: . . . . . . . . . . . . . . . . . . . . 1
Activities in nuclear weapon states under the CTBT. 1
Activities in non-nuclear weapon states under a CTBT. 1
The technology of nuclear weapons. . . . . . . . . . 1
Inside a nuclear weapon. . . . . . . . . . . . . . 1
The acquisition of a nuclear weapon. . . . . . . . 1
The boosted fission weapon. . . . . . . . . . . . . 1
Two-stage thermonuclear weapons. . . . . . . . . . 1
Nuclear explosions and nuclear weapon tests. . . . . 1
More about non-nuclear-explosion testing. . . . . . 1
If the U.S. needs science-based stockpile
stewardship, how will the other NWS manage? . . . . 1
What fission experiments are banned under a zero-
yield CTBT? . . . . . . . . . . . . . . . . . . . 1
A working definition of zero-yield fission exper-
iments. . . . . . . . . . . . . . . . . . . . . . 1
Does a CTBT impede nuclear proliferation? . . . . . 1
Peaceful nuclear explosions. . . . . . . . . . . . . 1
Defense of Earth against an asteroid or comet. . . 1
A few comments on electrical energy from PNEs
(R.L. Garwin). . . . . . . . . . . . . . . . . . . 1
Conclusions. . . . . . . . . . . . . . . . . . . . . 1
INTRODUCTION.
With the signing of the Comprehensive Test Ban Treaty
(CTBT),(1) much of the uncertainty regarding future nuclear
explosion testing has been removed. Even though the Treaty
will not enter into force for the foreseeable future, the
signatories are bound by the Vienna Convention on the Law of
Treaties not to conduct nuclear tests. The relevant pro-
scriptions are contained in the CTBT Article I: BASIC OBLI-
GATIONS, here reproduced:
1.Each State Party undertakes not to carry out any nu-
clear weapon test explosion or any other nuclear explo-
sion, and to prohibit and prevent any such nuclear
explosion at any place under its jurisdiction or con-
trol.
2.Each State Party undertakes, furthermore, to refrain
from causing, encouraging, or in any way participating
in the carrying out of any nuclear weapon test explo-
sion or any other nuclear explosion.
The negotiating record makes clear that the CTBT permits no
yield at all from fission explosions-- not one kiloton; not
one ton; not one kilogram; not one milligram of fission
yield. "Peaceful nuclear explosions" (PNEs) are also
banned, although they may be considered in a Review Confer-
ence(2) normally to be held 10 years after entry into force.
PNEs then could take place only if a majority of states
voted in favor, with no state casting a negative vote; so it
may be expected that no PNEs will occur unless they are
judged to provide a compelling benefit for all humankind;
any nation (or group of nations) wishing to conduct a PNE
will need to convince the international community of the ne-
cessity to carry out the particular PNE.
All five nuclear weapons states (NWS) signed the Treaty 24
September 1996 at the United Nations, as did many other
states. India, however, has stated that it will not sign a
CTBT, even if the "entry into force" (EIF) clause is changed
so that the CTBT can take effect without India's partic-
ipation.(3)
Among the reasons for the enormous popularity of the CTBT
(158 of 161 States voted in the General Assembly 9 September
1996 to open the CTBT for signature, with only India,
Bhutan, and North Korea voting against) is that every State
favoring the CTBT seems to value the impediment it places
against the spread of nuclear weapons to states beyond the 5
NWS, and the barrier to the development of advanced types of
nuclear weapons among the 5 NWS. As might be expected, the
nuclear weapons establishments in each of the NWS advanced
arguments supporting the value of nuclear explosion tests of
some type or schedule, but the leadership of each State
found the State's security to be improved by a CTBT that
would keep others from nuclear explosion tests, and hence
they have decided to deny themselves the freedom to test.
In this paper we discuss first the nature of activity com-
patible with the CTBT that is to be expected in the NWS in
maintaining a safe and reliable stockpile of nuclear weap-
ons, and then speculate on the types of advances in nuclear
weaponry that might possibly be achieved while respecting
fully the text of the CTBT. We then discuss the means the
NWS may use to retain their nuclear weapon expertise both
for activities to be conducted under a CTBT and as a precau-
tion against the possibility of collapse of a CTBT regime.
Finally, we discuss the degree to which a CTBT would limit
the nature of nuclear weaponry that might be achieved by a
non-NWS state-- either a State outside the Non-Proliferation
Treaty (NPT) but still Party to a CTBT, or one in violation
of its NPT obligations.
Perhaps slightly off the main subject of this paper, we
treat briefly the utility of PNEs of various types, in order
to provide some insight into the discussions that may occur
10 years after the Treaty enters into force, in regard to
PNEs.
A CAUTION: From the point of view of the great majority of
non-NWS that have signed the CTBT or will do so, the purpose
of the CTBT is to place further impediments to the spread of
nuclear weapons to additional states, supplementing the bar-
riers created by the NPT. For the most part they support
also the barriers inherent in the CTBT to the advancement of
nuclear weapon technology in the NWS, where the NPT provides
no impediment at all. It would be a tragedy if actions un-
der a CTBT, including irresponsible distribution of informa-
tion, undermined the barriers to the spread of nuclear
weapons so painfully erected by the NPT and the CTBT.
It is natural for those involved in nuclear weapon develop-
ment in the NWS to consider the designs of 30 to 50 years
ago as obsolete, as indeed they are for their own purposes;
but "obsolete" does not mean that these designs should be
freely discussed or allowed to leak to non-NWS. Even if the
CTBT persists forever, we shall see that it does not consti-
tute such an effective barrier to proliferation that weapon
designs can be freely communicated; no test is needed for a
weapon built according to a certified blueprint. Worse,
there is some possibility that the CTBT era will come to an
end, and it would be most unfortunate if negligence during
its duration would facilitate the spread of nuclear weapons.
ACTIVITIES IN NUCLEAR WEAPON STATES UNDER THE CTBT.
A CTBT is only that-- a ban on nuclear explosion tests of
any yield exceeding zero; it is not a Treaty by which na-
tions agree to give up their nuclear weapons or even to re-
duce their numbers. Therefore it is of interest for
citizens of the NWS as well as of non-NWS to understand what
activities may lawfully be conducted in the NWS under a CTBT
and how these activities may be monitored as fully compliant
with a CTBT. It may be expected that the weapons establish-
ments in NWS will desire to proceed with the following ac-
tivities (to the extent perceived possible) unless limited
by unilateral decisions or by further treaty agreements:
o Stockpile maintenance and refabrication.
The primary tools are inspection, disassembly, refabri-
cation, with guidance from experts in the engineering
and science of nuclear weaponry.
o Product improvement.
The weapon establishments may wish to reduce the mass of
a warhead, have the option of increasing the yield, im-
prove safety and reliability, and reduce the cost of
maintenance and remanufacture.
o New product development.
Among "new products" might be such audacious develop-
ments as the nuclear-explosion pumped x-ray laser or
other nuclear-weapon powered directed energy weapons
which were under development in the SDI program of the
1980s.(4) More ordinary development might lead to nu-
clear explosives with various kinds or amounts of nu-
clear materials (for instance, without need for
tritium), enhanced radiation characteristics or reduced
production of radioactive materials in the PNE environ-
ment.(5)
But even though a NWS may desire to continue its programs of
nuclear weapon development, we shall see that the ability to
do so will be strongly limited by the CTBT constraints, and
the accomplishments of the NWS will probably be limited to
the maintenance of their weapon stockpiles.
ACTIVITIES IN NON-NUCLEAR WEAPON STATES UNDER A CTBT.
States party to the NPT are committed not to build or other-
wise obtain nuclear weapons or other nuclear explosives, and
for them a CTBT adds no new obligation. When it enters into
force, the International Monitoring System of the CTBT will
provide augmented capability to verify that no nuclear ex-
plosion has occurred anywhere under the control of that
State or by its citizens or other entities.
Some states not Party to the NPT have signed and are ex-
pected to abide by the CTBT-- for instance, Israel. Such
states have no legal commitment to restrain from building
nuclear weapons but they have not in general conducted nu-
clear explosive tests despite the absence thus far of any
Treaty banning them; the one exception is India, which
tested a nuclear explosive underground in 1974.
Almost all of the world's states oppose the spread of nu-
clear weapons to additional states or to non-state entities,
and some states believed to have nuclear weapons either in-
tact or ready to be assembled (Israel and Pakistan) have not
seen it in their interest to conduct an explosive test, de-
spite their legal right to do so. Will they find it easier
to test now when the nations of the world have demonstrated
their overwhelming support for a CTBT?
In discussing the acquisition of nuclear weapons by addi-
tional states we must avoid placing too much reliance on
history. For example, if we were trying to understand the
status of a State toward the acquisition of advanced tele-
communications capability, it would be ludicrous to expend
much effort in monitoring its production of "vacuum tubes"--
i.e., hot-cathode radioelectronic valves. For ordinary com-
munications it is now both more effective and simpler tech-
nology to use solid-state (transistor- based) electronic
devices, and it would be a great mistake to imagine that
such capability could emerge only after a State passed
through a phase of competence in and widespread use of vac-
uum tubes.
In the 51 years since the detonation of the first nuclear
weapons great progress has been achieved: in various fields
of basic physics important for implementation of advanced
nuclear weapons; sequential revolutions in the ability to
model physical systems on computers and an enormous expan-
sion in the population that has access to such tools; en-
hanced experimental technique and high technology were
developed for reliable experimental implementation of vari-
ous sophisticated nuclear weapon principles. Many other as-
pects of technology which can be important for nuclear
weapon proliferation have evolved over the half century,
among them the widespread deployment of nuclear reactors for
the production of electrical power, that each produce some
hundreds of kg of plutonium per year (for a reactor powering
the nominal million kilowatt generating plant). Further-
more, hundreds of tons of "weapon-grade" Pu have been incor-
porated (between them) into nuclear weapons in the Russian
and U.S. inventories, and tens of tons of weapon-Pu have
been declared excess by the U.S.. On each side, at least
50 tons of Pu from weapons is expected to be declared excess
by the year 2003, as a result of the START-I and START-II
reductions, but there is already more than 100 tons of sepa-
rated "reactor-grade Pu"(6) from commercial reprocessing of
spent fuel from power reactors, and more than 1000 tons of
reactor Pu is present in spent fuel worldwide.(7)
Some 2000 tons of highly enriched uranium "HEU"-- much of it
85-95% U-235-- has been built into the Russian and U.S.
weapon stockpiles or produced for use in reactors for pro-
pulsion of ships or submarines, and some of this naval HEU
would be suitable for use in nuclear weapons.
With the evolution and spread of technology and the enormous
amount of weapon material in the world (in comparison with
the 6 kg of Pu or 60 kg of HEU used in the first two nuclear
explosives in 1945), constraints on the spread of nuclear
weapons are more legal and political than technical-- al-
though the NPT's barriers to transfer of weapon-usable mate-
rial (especially plutonium and high-enriched uranium)-- are
extremely important.
The world's first two nuclear weapons typify two approaches:
o "Gun assembly," in which two sub-critical masses are
brought together in some milliseconds by ordinary
propellant such as is used to propel artillery shells.
o Implosion assembly, in which high explosive with similar
energy content to propellant but much higher speed of
reaction (detonation) is used to propel and to compress
fissile materials to exceed a critical mass in a time
measured in microseconds rather than milliseconds. Less
material is required, as well, because the critical mass
is inversely as the density squared; thus if the
plutonium can be compressed by the implosion to twice
normal metallic density, only 1/4 of a normal-density
critical mass suffices to become critical at the in-
creased density.
The world-class team assembled at Los Alamos in 1943 actu-
ally to design and build the nuclear weapons from the high
enriched uranium and the plutonium that were to become
available from the production facilities, solved the design
problems for the gun-type explosive, and then faced the un-
expected need for a faster assembly system because of the
large spontaneous neutron production from the Pu-240 isotope
present as a small percentage in the weapon plutonium. In
addition to solving design problems and working with materi-
als that are highly radioactive and chemically reactive, the
Los Alamos group avoided such pitfalls as apparently trapped
Heisenberg (head of the World War-II German nuclear energy
program) into an estimate that the critical mass would be
tons of U-235.
Just about one bare-sphere critical mass of HEU was used in
the Hiroshima gun-type weapon, and only about 0.6 bare-
sphere critical mass of plutonium in the first implosion
weapon.(8) In both cases neutron sources were devised that
would begin emitting neutrons at the appropriate time, and
rapidly enough so that the chain reaction would with high
probability be initiated before the material disassembled
mechanically at speeds similar to that with which it was as-
sembled.
While it is possible to produce weapons of implosion type
without a nuclear explosion test, real organizations of real
people would not have much confidence in a stockpile of such
untested weapons. The tests to validate an exact copy are
different from those that might be required in a native de-
velopment. But anyone seeing the unclassified pictures of
mangled steel tubes that were supposed to be uniformly
imploded by early attempts at implosion driven by high ex-
plosive begins to get a feeling for the problems inherent in
an indigenous nuclear weapon program. The implosion test
work soon graduated to "pin" shots, in which multiple small
wires make contact with an advancing metal surface, or to
other schemes for diagnosing the motion of material that
microseconds earlier was a rigid solid.
Only in the last few years has it been generally accepted,
as was briefed by U.S. weapons scientists 20 years ago(9) in
support of the NPT, that nuclear weapons can quite readily
be made from reactor-grade plutonium. This was published at
length by Kankeleit(10) et al, and by Carson Mark,(11) and
the CISAC (Committee on International Security and Arms Con-
trol of the National Academy of Sciences) study(12) mentions
the additional problems of reactor-grade plutonium for
weapon use-- high neutron background, more highly penetrat-
ing gamma rays, and increased heat evolution-- and concludes
"In short, it would be quite possible for a potential
proliferator to make a nuclear explosive from reactor-
grade plutonium using a simple design that would be as-
sured of having a yield in the range of one to a few
kilotons, and more using an advanced design."
This is not to say that making an implosion weapon of
reactor-grade plutonium is easy, but that it is not much
more difficult than making an implosion weapon from "weapon-
grade" Pu-239, and the difficulties involved are not of a
different type,
The fact that there are no national nuclear weapon stock-
piles built of reactor-grade plutonium does not in any way
reduce the possibility that separated reactor-grade
plutonium could be used to make one, a few, or even hundreds
of nuclear weapons. So there is a real threat that a poten-
tial proliferator will try to use the reactor-grade
plutonium for NW production.
THE TECHNOLOGY OF NUCLEAR WEAPONS.
INSIDE A NUCLEAR WEAPON. The first design of nuclear weapon
in the United States was a "gun assembled" system, by which
some 60 kg of high-enriched uranium(13) was moved by normal
artillery propellant in a short gun barrel from a "subcrit-
ical" configuration into a more compact over-critical con-
figuration so that only a relatively small fraction of the
neutrons from each fission escaped.(14) A nuclear explosion
can take place only when an exponentially growing ("diver-
gent") fission chain reaction can occur, in which a neutron
causes fission, liberating two or three neutrons, more than
one of which goes on to cause another fission, and so on.
This chain breeding of neutrons and, consequently, fission
of fissionable materials is terminated by hydrodynamic dis-
assembly (expansion) of the system caused by the rapid en-
ergy release or partial burning of fissionable materials.
The assembly of a supercritical mass of fissionable materi-
als, the initiation of a chain reaction in it, and the re-
sulting rapid disassembly is the essential sequence in
explosive nuclear systems, and the process is called a nu-
clear explosion.(15)
In the fissionable materials used in nuclear weapons--
U-235, plutonium-239, and U-233-- the fission is caused
mainly by fast neutrons, which go only a distance of 7-10 cm
before colliding with a nucleus, so that each doubling of
the neutron population occurs in about 0.01 microseconds.
The power of compound interest is such that if one begins
with a single fission, the time required at this doubling
interval to cause fission of 1 kg of fissionable material
(approximately 2.5 x 10**24 nuclei) is the time required for
80 such doublings or less than one microsecond. This corre-
sponds to an energy release equivalent to about 17 thousand
tons(16) 17 kilotons (17 Kt) of trinitrotoluene (TNT)-- a
typical high explosive (HE). The explosive termination of
the chain reaction produced slightly less than this energy
release-- about 15 Kt (in about 60 kg of fission material)
for the case of Hiroshima bomb.(17)
The result of such rapid energy release (17 Kt of HE equiv-
alent per kilogram of material fissioned) is not only the
blast effect that is similar to the actual detonation of ap-
proximately equal but slightly less amount of HE, but also
the radiation of a substantial fraction of that total as
thermal radiation, giving rise to combustion of wood, etc.,
out to a radius ranging from kilometers to tens of kilome-
ters depending on the yield. In addition, the neutrons left
over that escape from the nuclear explosive, together with
the gamma radiation from the fission process itself and the
fission products contribute an enormous source of "prompt"
radiation which is additional major damaging weapon effect.
Sometimes, special provisions were made to enhance some of
these additional effects, e.g., in so-called neutron weap-
ons.(18) For large-yield weapons, the prompt radiation is
confined to a region well within that destroyed by blast,
and so is less important. However, the fallout from a
multi-megaton ground-burst nuclear explosion may deliver a
lethal dose of radiation within hours to a region covering
ten thousand square kilometers.
THE ACQUISITION OF A NUCLEAR WEAPON. The separation of U-235
from the 140-times as abundant U-238 is a costly and diffi-
cult process, which was not sure to provide fissile material
as rapidly as was thought to be needed in the U.S. weapon
program during the 2nd World War. Accordingly, with the
discovery of the artificial element plutonium, in partic-
ular, its 239 isotope, manufacturable in natural-uranium nu-
clear reactors by the parasitic capture of neutrons on
U-238, production reactors were built at Hanford(19) to
produce such plutonium. A reactor with a thermal power of
250 megawatts (MW) produces about 250 g of Pu per day, of
which about 6 kg was used in the bomb first tested at
Trinity (New Mexico) July 16, 1945. An identical weapon was
detonated over Nagasaki, three days after the gun-type bomb
was used at Hiroshima. However, Pu cannot be used in a gun-
assembled weapon, since the metallic components are moved
too slowly(20) by the propellant used in artillery or naval
guns.
Thus the implosion method of assembly was mandatory for the
plutonium weapon, in which the assembly occurs on a time
scale of microseconds or tens of microseconds-- so to speak,
between the individual stray neutrons. Nevertheless, there
was a significant probability for the Nagasaki bomb that a
spontaneous neutron would occur at the worst possible time,
and even that would have led to a yield no less than
1 Kt.(21)
In the years following 1945, innovations were made to reduce
the amount of costly fissionable material needed for nuclear
weapons and to improve the safety. The initial configura-
tion was thus much farther from "criticality" or unbridled
neutron multiplication, and was hence safer against unde-
sired nuclear explosion. Nevertheless, one could conceive
of accidents in which the high explosive would detonate at
one point, for instance by the impact of a rifle bullet on
the explosive, or accidental dropping of the nuclear bomb,
as happened several times. Thus almost from the beginning
it was required that nuclear weapons be safe against such
undesired nuclear explosions. For some years this was ac-
complished by systems in which the fissile core of the
weapon would be kept separate from the explosive and in-
serted only during the flight of the aircraft. This impeded
military readiness and flexibility, so later weapons were
designed with internal mechanical safing devices(22) or
eventually so that they were "inherently" one-point
safe.(23),(24)
THE BOOSTED FISSION WEAPON. In 1951, the United States first
tested the "boosting concept" under which a small amount of
thermonuclear fuel was added to the ordinary fission bomb.
This is currently accomplished by the use of a gas mixture
of deuterium and tritium within the hollow "pit" of an
implosion weapon. At the temperatures reached in the incip-
ient nuclear explosion, a fraction of the T nuclei react
with the D nuclei to form ordinary helium nuclei, plus neu-
trons of 14 million volt energy, which are extremely effec-
tive at causing fission in the now compressed fissionable
material in the neighborhood. Thus the relatively small
amount of energy from the thermonuclear reaction produces a
substantial number of neutrons and steps up or "boosts" the
fission reaction to a higher level. This further increases
the safety of such an explosive, since otherwise to reach
the yield that can readily be achieved by boosting, a larger
amount of fissionable material would need to be used.(25)
However, boosting adds its own problems to nuclear weapon
design and maintenance, because hydrogen reacts chemically
with plutonium or uranium. Furthermore, the artificial
isotope of hydrogen, tritium, has a 12.3 year half-life, so
that the tritium supply must be renewed on a scale of some
years. This imposes the requirement for production of
tritium if nuclear weapon numbers do not fall with time
faster than the decay rate of tritium.(26)
TWO-STAGE THERMONUCLEAR WEAPONS. In 1952, the U.S. MIKE test
demonstrated with its ten megaton yield the concept intro-
duced in early 1951 by Edward Teller and Stanislaw Ulam, by
which the energy from a "primary" nuclear explosion is used
to assemble a "secondary" charge containing thermonuclear
fuel. Initially the secondary contained liquid deuterium,
and the U.S. built as well several Emergency Capability
Weapons (named "Jughead") deliverable by the B-36
aircraft.(27) These were soon replaced by "solid-fuel"
thermonuclear weapons, using deuterium that was solidified
by chemical binding to lithium, in particular to the na-
turally occurring lighter isotope of lithium--
Li-6.(28),(29)
It has long been a rule of thumb that many thermonuclear
weapons typically produce about half of their total energy
from the thermonuclear fuel and half from the fission of
uranium in the proximity of that thermonuclear fuel.(30)
The nuclear weapon stockpiles of the NWS are probably mostly
boosted single-stage weapons or two-stage weapons as de-
scribed here.(31)
NUCLEAR EXPLOSIONS AND NUCLEAR WEAPON TESTS.
In an unconstrained environment, nuclear explosions were
carried out with the following functions:
o Development of new models of nuclear weapons.
o Production verification of a developed design.
o Proof of concept of some new weapon idea.
o Development of peaceful nuclear explosives (PNEs).
o Study and demonstration of PNE effects.
o Study of weapon effects.
o Obtaining physics results related to weapon design.
o Non-weapon basic physics.
o Conduct of PNEs for non-military benefit.
o The use of two nuclear explosives in war.
It is obvious that not every nuclear explosion is a test of
a nuclear weapon. A substantial number of the explosions
were carried out for peaceful purposes or for basic re-
search.(32) However most of the announced explosions were
carried out in relation to military programs.(33)
The United States typically has used some six nuclear explo-
sion tests in the development of each new model of nuclear
weapon, while France is said to have used some 22 per
model.(34) The study of a new concept might include all the
aspects of traditional nuclear weapon functions, or essen-
tially new design physics research and validation as in the
case of exploratory work directed toward the x-ray laser.
As for weapon physics, such nuclear explosion tests might be
used to measure the properties of materials ("equation of
state" or opacity) in the relevant range of pressure and
temperature that can not be reached by high explosives, al-
though these ranges are now accessible in part (at very
small physical scale) by laser-driven x-ray sources.(35) As
for non-weapon physics, this might include such interesting
questions as the existence of metallic hydrogen, the proper-
ties of metals like iron when squeezed to ten times their
normal density (high-pressure, high matter- and energy-
density physics), inertial confinement fusion physics, nu-
clear physics under high neutron flux (high atomic number
nuclei study), and the like.
To the extent that all knowledge is valuable and has benefi-
cial applications, such experiments have been pursued in the
past. Some, such as the U.S. "Halite-Centurion" series of
experiments in inertial confinement fusion (ICF)(36) have
provided advanced information at affordable cost. And
electron-shell occupation effects on thermodynamic proper-
ties of matter were studied in Soviet nuclear explosion ex-
periments,(37) while the laser facilities are still
approaching such physics with much more expensive invest-
ments.
An additional set of experiments and applications of nuclear
explosions is to be found in the "Peaceful Nuclear Explo-
sions", toward which the United States dedicated more than
20 nuclear explosions, and the former Soviet Union more than
100. We shall return to these later, stating now that the
United States found no application that was economically
competitive with accomplishing these missions by conven-
tional means. And in 1995, the current Minister of Atomic
Energy in Russia (Viktor Mikhailov) in an published inter-
view commented on the US and Soviet PNE programs, "So far,
they have not proven to be economical." However, the 39
deep seismic sounding explosions throughout the Soviet ter-
ritory provided valuable information that Russian scientists
believe well worth the expenditure. Still operating are two
underground "fractured collectors" produced by two under-
ground PNEs, to receive and safely store toxic waste.(38)
Still, Mikhailov accedes only reluctantly to the limitation
of any tool of scientific progress.
MORE ABOUT NON-NUCLEAR-EXPLOSION TESTING. Of course, much of
the maintenance of stockpile weapons is done without nuclear
explosion testing, and indeed very few tests thus far have
been for the purpose of verifying that weapons are still all
right. In the non-explosion testing realm, a whole panoply
of techniques has been created both for weapon development
and for monitoring of weapon health.(39)
First, there are the various quality control methods used
largely in production to verify that the materials of fabri-
cation (or refabrication) are up to standard. To the extent
that the individual component can then be fully tested (as
is the case of the detonators for the high explosive), addi-
tional confidence is available.
The high explosive itself is tested before fabrication and
after. A bar can be cut from the fabricated material and
its detonation velocity and other characteristics compared
with the standard. Similarly for the fabrication of metal
parts, pressure vessels, and the like.
Even the flight of a nuclear weapon can be mimicked by drop-
ping a bomb with an inert weapon or launching a missile, so
that the "weapon" itself goes through the entire stockpile-
to-target sequence (STS) as would a real weapon, right up to
the point of firing the high explosive. High-fidelity
telemetry can be used, or some of the warheads or bombs
could be recovered rather than allowed to impact, in order
to verify that unexpected problems have not intervened.
In the development of nuclear weapons, a lot of effort is
placed on "pin shots" or other means of determining the per-
formance of the pit-- that is, the fissile material sur-
rounded by a metal shell to constitute the "sealed pit" and
driven by high explosive.(40)
The designer wants to prescribe the position vs. time of the
inner surface of the plutonium shell, and this is measured
in multiple experiments by the use of numerous fine "pins"
or metal contacts. Laser imaging of the imploding pit is
also used, and all of these techniques can be useful to en-
sure that high explosive in the actual weapons in storage as
well as HE for remanufacture is within original production
specification.
If actual plutonium needs to be used in experiments, the ex-
periments can be done at reduced scale, so that of the ap-
proximately three neutrons from fission, less than one
remains within the assembly to cause further fission, and
the system will be subcritical with no energy release. Be-
cause of the toxicity of Pu arising from its natural radio-
activity, such experiments must either be done
underground(41) or, alternatively, experiments involving
tens or even hundreds of pounds of HE could well be done in
rugged steel containment, above ground, at Los Alamos, for
instance.(42)
Many modern nuclear weapons may have a boosted primary; for
it to work properly, the design conditions must be achieved
for the boost gas and the fissile material. Uncontrolled
mixing under high-explosive impact between them must be
avoided, and that mixing may depend upon the surface condi-
tion of the plutonium. To detect deterioration not visible
on static radiographs, some of the pits taken at random from
the stockpile can be cut open and their condition inspected
by microscope.(43)
A lot of information can be obtained in an actual nuclear
test, and that same information is not available without nu-
clear explosion testing. Nevertheless, so called
"hydrotesting" in which inert material is used, or material
at "subscale"(44) so that one does not reach criticality,
can allow the gas and the metal to be brought to the stage
that in a larger assembly or with the correct material would
result in the initiation of a nuclear chain reaction. So
much use is made of flash radiography by pulsed x-ray sys-
tems in order to observe the interior of such
hydrotests.(45)
Such measurements provide information in addition to that
from static high-resolution radiography and other measure-
ments of the pits in storage, either without disassembly of
the weapon or among the eleven of each type disassembled
each year.
Since flash radiography plays such an important role, it is
natural to want to upgrade it in two ways-- by providing a
smaller source for the x-rays (and thus better resolution in
the photographs) and by allowing multiple temporal and/or
spatial views of the imploding assembly. Both DARHT at Los
Alamos (Dual Axis Radiographic Hydro Test facility) and the
AHTF (Advanced Hydro Test Facility) at Livermore would move
in this direction, with DARHT providing two spatial and two
temporal views, while AHTF might provide four to six.(46)
These facilities and their relationship to the SBSS are de-
scribed in a report publicly available,(47) and by a more
recent review devoted largely to the National Ignition Fa-
cility.(48) These supplement official material available
from the Department of Energy-- e.g., at www.doe.gov. Only
a portion of the NIF capability is coupled to the stockpile
stewardship task, and much of that portion may have more to
do to maintaining expertise and developing capability that
would be useful in case of a collapse of the CTBT regime
rather than for maintaining the enduring stockpile of six
existing weapon designs safe and reliable indefinitely.
The major facilities are to be very substantially improved,
at a budget that for the next five years in DOE is expected
to average almost $4 B per year. Thus, a primary emphasis
for stockpile maintenance has been placed and will be placed
on the disassembly and inspection program, according to
which 11 representatives of each type of weapon in the
stockpile are brought back for detailed inspection and dis-
assembly. The entire system is radiographed and inspected
in fine detail. It is disassembled and each part tested for
function. In some cases the high explosive is removed and
the detonators and explosive tested. We emphasize that all
of the elements of the nuclear weapon can be tested to de-
tect any degradation except the physics package (the primary
explosive and the secondary nuclear explosive), although not
every element can be tested in the assembled system.
In routine stockpile maintenance, there is a replacement in
the field of "limited life components" or LLC, such as bat-
teries, tritium reservoirs, and the like. In the future,
every element of the nuclear weapon will need to be regarded
as an LLC, to be replaced either on some schedule or on some
signal.
So far as the primary and secondary are concerned, even
these elements are not inert, and over the years there have
been problems with chemical reaction due to volatile compo-
nents in the high explosive, and the like.
In some cases, these problems have been solved by replace-
ment of components that would certainly not effect the oper-
ation of the nuclear weapon (according to analysis and
certification by the nuclear weapon laboratories), but in
some cases remanufacture of critical elements has been re-
quired.
Evidently, a key component of the maintenance of a safe and
reliable stockpile is the ability to remanufacture every el-
ement of the nuclear weapon, or to certifiably substitute
some other component for an existing one.
In addition to the elements in the direct line of operation
from detonation of the high explosive to implosion of the
primary, to criticality, to heating of the contained boost
gas, to fission chain explosion, to full boosting, and to
full primary yield, to emission of large amounts of energy
as radiation from the primary, to convey the necessary part
of the energy to the secondary, to implosion of the second-
ary, and to thermonuclear reaction and explosion of the sec-
ondary,(49),(50),(51) there are many other required
functions of the nuclear weapon, with its 4000 parts in a
typical unit.
Some of these are the Arming, Firing, and Fuzing (AFF)
chain, while others simply have to do with the safe trans-
port and carriage of the weapon itself. Most of these can
be tested either nondestructively or destructively, and in-
deed they can be substituted by modern, state-of-the-art el-
ements that can be thoroughly tested for function and that
can be proven without suspicion to have no impact on the nu-
clear explosion itself. However, a high degree of conserva-
tism is necessary in the maintenance of this stockpile, and
ultimately there is required the expertise to certify that a
substitution in one of these noncritical elements will in-
deed have no effect on the nuclear explosion.
IF THE U.S. NEEDS SCIENCE-BASED STOCKPILE STEWARDSHIP, HOW
WILL THE OTHER NW As we have discussed at some length, the
United States has adopted a very aggressive program for the
maintenance of its nuclear arsenal and of its nuclear exper-
tise, known as the Science-Based Stockpile Stewardship Pro-
gram-- SBSS. This involves several aspects ranging from an
Advanced Scientific Computing Initiative, to a greater in-
volvement of weapon designers with the detailed results of
the Stockpile Surveillance Program, to the building and op-
eration of major new facilities for improved experimental
observation of aspects of nuclear weaponry without nuclear
explosion testing. A large part of the SBSS program has the
goal of maintaining nuclear weapon expertise, and also the
ability to design, test, manufacture, and certify new nu-
clear weapons if the CTBT era should come to an end. And of
course the nuclear weapons that are now in the inventory
were designed with computers far less powerful than the
multi-teraflop systems that will be available in the SBSS
era.(52)
The great demand for computation ("modeling") and for much
of the experimental "simulation" (e.g., hydrodynamic test
with flash radiography) systems comes from the desire to be
able to investigate the effects of flaws that may be found
in a stockpile weapon. Examples of such flaws are corro-
sion, warping of metallic and non-metallic elements, opening
of assembly joints,-- all problems that may occur within the
primary or secondary and that can not be tested by weapon
detonation under a CTBT.(53)
In the earliest days of nuclear weaponry, computational ca-
pability was so minimal that only systems of one-dimensional
(1-D) spherical or cylindrical symmetry could be considered
and diagnostic systems were also extremely limited. With
the evolution of computers and of electronics, it became
possible to consider systems of axial symmetry (like an or-
ange or an American football) which have some advantages in
packaging and also in safety. But a fine-scale computation
might have 1000 points along the radius of a spherical sys-
tem; to do the same job in a system of axial symmetry might
require a thousand points in each coordinate, or a million
points altogether. Simply cycling through all those points
means that the computation is at least a thousand times
longer for this 2-dimensional (2-D) than for the 1-D case.
There seems no great benefit in designing weapons without
axial symmetry, but if one has a flaw in a 2-D weapon, then
the computation becomes 3-dimensional. A full 3-D computa-
tion, as is evident, could then require a further factor
1000 in mass points, and a factor 1000 or more growth in
computing capability to handle it.
On the experimental side, it can be seen that for a spheri-
cal system any orientation of an x-ray picture (or the
equivalent) would do to confirm that the assembly in reality
moves as predicted, while for a 2-D system one would need
specific views. For a 3-D system much more information
would have to be gathered, as in the case of the CAT
(Computer-Assisted Tomography) scan(54) for medical diagnos-
tic purposes.
But computation does not make a weapon work that would not
otherwise have functioned, nor does simulation or static di-
agnostics. If the weapon would have worked when it was put
into the stockpile, then it will assuredly not work after
10,000 years (when a good fraction of the plutonium will
have decayed). Nor is it likely to work after 100 years,
even if the tritium (of 12.3 year half-life) is replenished
on schedule. Clearly, if nuclear weapons are to be main-
tained reliable and safe for a long time, it will be neces-
sary to remanufacture them or their components, in view of
the aging of plastics, the build up of helium in the solid
plutonium, and the accumulated effects of radiation on vari-
ous elements of the weapon. A guide to the reliable life is
provided by the age of nuclear weapons already in the stock-
pile.
Although other nations have not indicated how they maintain
their nuclear weapons, the U.S. in recent years has been
quite open(55) about its procedures, which involve the dis-
mantling of 11 weapons of each type, taken at random from
the stockpile, every year(56) with close inspection for po-
tential flaws. High resolution radiography is used as well.
The non-nuclear components such as batteries, valves, fuzes,
detonators for the high explosive are all tested, and if a
flaw is found, a wider inspection for that fault in the in-
spection may be conducted.
Age-related problems will not affect all weapons of the same
type at the same instant, and so there is ordinarily time to
remedy the problem by refitting a component of the same or
of an improved type. In some cases, such as a battery or
capacitor, the system can be tested initially and frequently
after installation, in order to ensure that one has not in-
troduced a new problem.
The fissile materials are an exception, because to subject
them to high-explosive or more severe shock, is to destroy
them. This would be no different from that of testing a
valve or power device driven by high explosive, in which one
obtains information about the device no longer in existence,
but also about the population from which that was drawn.
Worse, to test them in the operational configuration means
that one will obtain a nuclear yield of a kiloton, plus or
minus a factor 10. But this means that one must greatly
change the environment of the tested fissile "pit", for in-
stance, in order not to violate a CTBT.(57)
One could in this way trephine a sector of the pit and fire
it with close observation of its internal surface, but with-
out approaching criticality.(58) Alternatively, when the
surface or the dimensions of the pit are no longer well
within the variation accepted thus far in the stockpile, one
would remanufacture the pit to the original specifications.
One way for a nation to take steps that actually imperil the
safety and reliability of their nuclear weapon stockpile
would be to make changes in the design or processes by which
the untestable items are fabricated. We judge that the most
reliable stockpile can be maintained by periodic remanufac-
ture (in addition to remanufacture in case of discovered
problems), using processes that from the point of view of
the material are within the range defined in initial pro-
duction. Changing materials or processes and relying on ex-
tensive computation in order to show the equivalence (or
improvement!) seems a lot riskier, and with potential bene-
fits that are not worth the risk.(59)
However, a nation might instead try to maintain a safe and
reliable stockpile by what has been termed(60)
"custodianship" (CS) analogous to the preservation and re-
newing of precious works of art. If the U.S. maintains the
capability of remanufacture, the difference between SBSS and
CS may involve the decision in SBSS to permit somewhat dete-
riorated weapons to remain in the stockpile, in view of the
SBSS-based confidence that performance would be degraded by
no more than 5% on average-- just to take an arbitrary num-
ber. Under CS, weapons would need to be remanufactured at
an earlier stage.
That remanufacture is not an inferior option is inherent in
the Congressional testimony of the President of the Sandia
National Laboratories(61) "Ideally, we would like to train
our junior weapon design engineers alongside experienced en-
gineers, but this will not be possible during a decades-long
hiatus of no weapon development. The Russian laboratories,
by contrast, will be able to pass along their critical
weapon design skills to a new generation under their an-
nounced plans to rebuild thousands of weapons each year."
Of course, the combination of manufacture within initial
specifications, with understanding and computation would
provide still more assurance of reliability and safety, and
that is a reasonable approach if it can be afforded and if
strong management prevents changing the design or process of
the untestable parts.
We believe that each of the five nuclear states will be able
to maintain its stock of nuclear weapons reliable and safe
by measures appropriate to those particular weapons.
At this point we note the hazard of focusing on new facili-
ties to the detriment of the task of stockpile maintenance.
Expenditures on new facilities and the "less exciting" work
of actually surveying and analyzing and fixing the enduring
stockpile compete for funds and people. Nuclear weapon
states would do well to ensure that the tools and conditions
afforded to those engaged in this task are upgraded mod-
estly, and that resources are not diverted excessively to
new tools that may not be so directly relevant.
Additional material is to be found in two recent Pugwash pa-
pers(62),(63) from which we draw heavily in the following
section.
WHAT FISSION EXPERIMENTS ARE BANNED UNDER A ZERO-YIELD CTBT?
Compared with fusion, the definition of a "zero yield" fis-
sion explosion is considerably more difficult. First, a
nominal nuclear power reactor fissions one ton of heavy
nuclei per year, corresponding to an energy release of some
17 megatons of high explosive equivalent. But that is no
explosion. In one millisecond (which might be deemed to
separate an explosive regime from a steady regime), the fis-
sion energy produced corresponds to that of 500 g of HE. It
is of interest to note that even for a one microsecond in-
terval, the fission energy produced in a normal reactor is
about 0.5 g HE.
The fission energy release from the power reactor is not an
explosion, because it operates in a steady state.
Other reactors, however, like the TRIGA, have a very sub-
stantial and short-duration energy release, sufficient to
raise the temperature of the material by 100 deg or more
within a time determined by the moderation time of the neu-
trons.
Like water-moderated reactors, normal "fast reactors" are
dependent upon the delayed neutrons for their
controllability. Only under very special circumstances, such
as the "dragon" experiments, is a system made critical with
prompt and fast neutrons. This is achieved by a projectile
accelerated by gravity or in some other way, briefly passing
through a near-critical assembly, so that the overall re-
production factor exceeds 1.0 on prompt neutrons alone.
Even though there is a substantial release of fission en-
ergy, there is no disruption, and there is no significant
increase in information gained beyond that achieved with
sub-critical experiments in which there is steady neutron
multiplication 1/(1-k).
The CTBT should not be interpreted as to impose any re-
strictions on experiments conducted to understand and im-
prove the safety of fast reactors, for instance, where it
would be perfectly in order to mock up the core of an
energy-producing reactor, and then to suddenly drive out
control rods in order to confirm some analysis that the en-
ergy release in fission in this simulated accident does not
exceed 1 kg of high-explosive or 100 kg of high-explosive or
whatever level the containment is designed safely to with-
stand. Such experiments contribute nothing to the under-
standing or advancement of nuclear weapon design, and in our
opinion are in no way limited by the CTBT. Of course, they
should be done with full transparency.
More relevant to weapon design in the NWS are so-called
"hydronuclear" experiments and (finally) sub-critical exper-
iments.
The United States during the 1958-1961 moratorium conducted
more than 40 hydronuclear experiments, some in shallow
wells(64) in the facilities of the Los Alamos Laboratory,
and some at the Nevada Test Site. "Hydronuclear" refers to
a system in which the material flow is described by
hydrodynamic equations, as in the assembly and compression
of fissile material by the use of high explosive; together
with a nuclear chain reaction. It is clearly intended to
distinguish from a nuclear explosion, and various criteria
might be invoked for this purpose:
o Fission yield less than the energy of the high explosive
used for the assembly.(65)
o Fission yield so small that it does not perturb signif-
icantly the hydrodynamic disassembly of the metal "pit".
During the 1958-1961 era, an upper limit was established for
the yield of a hydronuclear experiment-- 2 kg of HE equiv-
alent. This is related to the standards(66) that the U.S.
set in 1968 for the safety of its nuclear weapons-- given a
detonation initiated at any one point in the high explosive
system, less than 10**-6 likelihood of fission energy re-
lease exceeding 2 kg; and less than 10**-9 probability over
the stockpile life of a weapon under normal non-accident
circumstances.
Many of the accident scenarios involve the detonation of the
high explosive at one point-- by a rifle bullet or a frag-
ment from an explosion, so the relevant aspect of the U.S.
standard is that the fission yield from the worst-case "one-
point" detonation of the primary must be less than 2 kg HE.
To determine which U.S. designs were one-point safe and to
take corrective measures for those that were not was the
primary purpose of the hydronuclear experiments. For a de-
sign that proves to be one-point safe, the proof is the ac-
tual firing of a primary by one-point detonation at the
point determined by theory or experiment to be that giving
greatest criticality. Because such one-point detonation
could in principal give a considerable yield in the range of
tons or hundreds of tons of HE, a series of experiments is
conducted with gradually increasing amounts of fissile mate-
rial (or of high explosive) A design found not to be inher-
ently one-point safe might be rendered one-point safe, but
still usable, by a mechanism such as inserting removable ma-
terial in the hollow of the fissile pit.
The important point is that once a design has been demon-
strated to be one-point safe, such experiments need never
again be done on that weapon design.(67) Banning
hydronuclear tests is compatible with the U.S. commitment to
retaining a nuclear weapon stockpile that is reliable and
safe, based on weapons of types already in the stockpile.
It has been suggested that hydronuclear tests can add sig-
nificantly to confidence that re-manufactured weapons (for
example, pits that needed to be refabricated because of dis-
tortion of the metal) will perform within the same yield
range as the original weapon. Clearly, a full-yield test of
a re-manufactured weapons would give such evidence, but to
remain within the "hydronuclear" range for a symmetrical
firing of the explosive would require a very big change in
the configuration; either the amount of explosive would need
to be significantly reduced, or a hollow pit would need to
be filled with a dense gas.(68)
In either case, as demonstrated by a close examination by
the JASON group of consultants for the U.S. Department of
Energy, the necessary modifications are so great that
hydronuclear tests would add little to stockpile confidence.
The Summary and Conclusions(69) of the JASON study were re-
leased by the U.S. Government August 4, 1996. The study was
led by Prof. Sidney Drell, and one of us (Garwin) was a mem-
ber of the group, together with several other JASONs with
nuclear weapons experience, supplemented by 4 authors who
have spent their lives in the nuclear weapon design program
at the U.S. DOE laboratories.
Hydronuclear tests will not be conducted under a CTBT re-
gime. They have no great significance to the military capa-
bility in any case, but it would be desirable to be able to
verify that they are not being performed. In this regard it
would be helpful for all permitted activities to be con-
ducted above ground. Hydrodynamic tests of weapon config-
urations are be permitted under a CTBT, although they are
forbidden to non-nuclear weapon states by the NPT. Because
such hydrodynamic tests may involve kilograms of Pu, they
cannot be done in the atmosphere under current standards; as
proposed(70) they should be done in a containment vessel,
above ground.
A configuration that, assembled, provides two critical
masses at the maximum density achieved, will be subcritical
if the mass of every element involved is multiplied by 0.4,
and radiography of the system is correspondingly easier, be-
cause it is less "thick" at every stage of the assembly.
Such model tests are not prohibited and likely will be used,
and even smaller scale models can be useful.
Other sub-critical experiments may involve masses of fissile
material and configurations that have no chance at all of
criticality, such as explosively driven equation of state
(EOS) experiments.(71) To provide greatest assurance of com-
pliance with a CTBT, such experiments (which are not prohib-
ited by the CTBT) also should be done above ground, in steel
containments, like the hydrodynamic tests described above.
If experiments involving plutonium or other fissionable ma-
terial are nevertheless to take place underground, the plan-
ning should include through-pipes into which States could
agree to put their measuring equipment to ensure that there
is no neutron or gamma ray output from the test. The stem-
ming must be adequate at least to contain the high explosive
and the plutonium dust-- a different problem from containing
kilotons of nuclear yield.
A WORKING DEFINITION OF ZERO-YIELD FISSION EXPERIMENTS. We
would interpret "zero-yield" as satisfied if the prompt re-
production factor for a fissile system k <. 1 in any exper-
iment-- that is, if the static neutron multiplication
M = 1/(1-k) was bounded. This is in contrast with
hydronuclear tests, which are not permitted under a CTBT. M
is the more readily measured and more fundamental quantity;
k is the fraction of neutrons present after one 'generation'
or neutron lifetime within the material. Thus k may be two
or three in the compressed material of a fission bomb, but
k <. 1 in not perme weapon before it is assembled or com-
pressed.
A practical upper limit on k in systems involving high ex-
plosives, might be k = 0.8 or less.
In contrast, a hydronuclear test that might have involved a
yield up to 2 kg of HE or 8.4 MJ must be compared with the
energy yield of a single fission, which would contribute
promptly about 150 MeV or some 24 picojoules (24 pJ). So
the yield of 2 kg HE corresponds to some 3 x 10**17 fis-
sions, equivalent to 10**17.5 or e**40, or 58 doublings.
A typical nuclear yield of 20 Kt is evidently larger by a
factor 10**7 than is a yield of 2 kg of HE, corresponding to
another 16 factors of "e", or 23 more doublings.
DOES A CTBT IMPEDE NUCLEAR PROLIFERATION? A CTBT greatly im-
pedes vertical proliferation-- that is, the development of
thermonuclear weapons or weapons using substantially modi-
fied design.
It also has a significant effect on horizontal prolifer-
ation, in limiting the choice of configuration to those that
might be imagined reasonably sure of performance-- the
U-235 gun weapon that was used at Hiroshima and that was
built in six copies by South Africa before that nation de-
stroyed them and became a non-nuclear weapon state. Or a
state might choose a primitive implosion device, with vari-
ous forms of fissile material.
For the use of plutonium, even the use of some supposedly
sure-fire configuration would not provide a lot of confi-
dence without a nuclear explosion test, and to reach for
weapons with substantially smaller fissile content (allowing
therefore more weapons for a given stock of fissile mate-
rial) would raise the question as to whether any one of the
weapons would work. What about Israel, supposed to have a
stock of plutonium weapons from the Dimona reactor of some
60 MW power (and thus 60 g of Pu created per day)? This
would be some 18 kg per year and this three to four nuclear
weapons per year would correspond to a stock of some 100 nu-
clear warheads. This is to be contrasted with the NRDC es-
timate of 150 plus or minus 30% as referenced in this book.
The revelations of Vanunu have been interpreted by
T.B. Taylor as indicating that the plutonium fission yield
may be augmented with fusion fuel containing deuterium, much
like the first Soviet experiment with thermonuclear fuel,
dubbed by the Americans "Joe-4."(72) This was a single-stage
fission system augmented with fusion fuel, rather than hav-
ing a separate second-stage fusion assembly. Without know-
ledge of the facts, we imagine that the Israelis have chosen
a design that would provide a significant yield without
fusion boosting, but that their first detonation in war
would confirm whether or not they could count on the higher
yield that they have presumably designed into the weapon.
Without a test, the designers and the military could not be
sure of the performance of such a design-- but this would
not be the first instance of overconfidence on the part of
the Israelis, or of overconfidence on the part of their
critics! Presumably they have validated their calculations
against known information, such as that regarding gun-type
nuclear weapon used by the United States in 1945 or the
first plutonium implosion weapon used in 1945, about which
much information has been released. Or they may have re-
ceived information one way or another from countries with
large nuclear stockpiles.
The largest non-proliferation influence of a CTBT, however,
is political. As the nuclear weapon states see it in their
national security interest to reduce the number of nuclear
weapons held by others in the world (and perforce their
own), they need the support of the other members of the NPT
in order to preserve and universalize the non-proliferation
regime. They will not retain that support if they continue
nuclear test explosions.
Even without testing, they could squander the good will and
political support that might otherwise be theirs (for in-
stance, by not reducing severely the number of nuclear weap-
ons), but there seems no way in which one of the nuclear
weapon states could continue to test without provoking the
others to do the same, and thereby imperil the NPT regime.
A universal CTBT would put the might and will of the nuclear
weapon states on the side of the other NPT adherents, and
this could lead to a strong reaction against a state outside
the NPT building nuclear weapons or, in particular, having a
nuclear test explosion.
PEACEFUL NUCLEAR EXPLOSIONS.
In its PNE program from 1957 to 1973, the U.S. carried out
12 explosions for applications (6 cratering and 6 contained
explosions) and some 15 for development of specialized PNE
devices. Of these 15 tests, ten were to develop ultra-low
fission explosives for excavation purposes, one was to de-
velop an ultra-low tritium explosive for oil or gas applica-
tions, and 5 were to create heavy elements beyond fermium
(which has 100 protons in the nucleus as compared with the
92 in chemical element uranium or 94 in plutonium).
The Soviet program began in 1965 and ended in 1988. Some
112 explosions were used in applications and many in PNE de-
velopment work.
In addition to excavation (a proposal to link the Kama and
Pechora Rivers in order to feed Siberian water into the
Caspian Sea rather than into the Arctic Ocean) work was con-
ducted on oil stimulation, closure of runaway gas wells, and
the production of storage cavities. Notably, some 39 PNEs
were used in deep seismic sounding across the vast expanse
of the Soviet Union. In fact, the primary utility of Soviet
PNEs was deep seismic sounding and the excavation of storage
cavities (or fragmented reservoirs underground). Some of
the cavities were to be used for storing natural gas
condensate, and the fragmented reservoirs typically to re-
ceive toxic materials instead of liberating them to the en-
vironment.
Much technical progress was made in this work. For in-
stance, a 140 Kt nuclear explosive in 1965 had some 7 Kt of
fission yield, while one developed in 1970 had less than
0.3 Kt fission yield at 100 Kt.(73)
Concepts were developed to reduce the contamination due to
the explosive by designs that would "self bury" the radioac-
tive debris,(74) and such devices were tested in 1971 and
1974 and apparently used in mining experiments.(75)
Economic and cost-benefit evaluations of the Soviet program
are not widely available, but for the U.S. program a sub-
stantial study was conducted.(76) One of the authors
(Garwin) was a participant in that study and author of an
Appendix(77) dealing specifically with a concept for the
production of electrical power by use of thermonuclear ex-
plosives-- Project PACER.(78) The other PNE applications in
the U.S. were for production of gas from "tight gas forma-
tions", rubblizing of oil shale, production of underground
storage cavities, rubblizing copper ore, and general exca-
vation.
A striking result of that study was to recognize the great
effectiveness and controlability of non-nuclear means for
accomplishing most of the tasks. For instance, for the con-
trol of runaway gas or oil wells, precision drilling and the
application of sensible technology handles the problem, as
was the case with the more than 500 Kuwaiti oil wells set
afire in 1991. Even more striking is the substantial scale
at which most of the applications would need to be con-
ducted, if nuclear explosives were to be used. This will be
seen in the later comment on Project PACER.
More recently, Soviet nuclear weapon scientists have pro-
posed(79) the use of underground nuclear explosions to de-
stroy toxic chemical agents and chemical weapons, and to
render excess nuclear weapons harmless and unavailable; the
authors see many obstacles in implementing these proposals.
Regarding the proposal to use underground PNEs to destroy
and detoxify chemical agents and munitions, a great deal of
the problem of such materials is in the transport to the de-
struction site, and that would not be eased by the require-
ment to transport them on the surface and then underground
for destruction. Furthermore, there are satisfactory proc-
esses for the transformation and destruction of bulk agent,
differing according to the nature of the agent and espe-
cially as to whether it contains inorganic material such as
arsenic.
Chemists and chemical engineers are perfectly capable of de-
signing and conducting such transformations, and no very
large amount of material need be present in the plant at any
time. Ultimately, the effluent gas can go through a super-
heater and cooler (regenerator) in order to ensure that no
organic toxic materials remain. The U.S. is using
incineration to destroy its stock of nerve agent, but it is
also possible to use hydrolysis, and such operations would
provide employment in Russia in the chemical and related in-
dustries.
As for the underground destruction of nuclear warheads, one
has to decide whether this means the destruction of intact
warheads or of portions of the nuclear warheads. Surely it
is not proposed to destroy high enriched uranium, which has
a substantial value and can be blended down at low cost with
natural uranium or depleted uranium to provide valuable fuel
for light water reactors or even fast reactors. If the pro-
posal is to destroy the much smaller amount of fissile mate-
rial in the primaries of two-stage weapons (and it has been
discussed to use a single 50 Kt explosive to vaporize 5000
such primaries and to mix them with the surrounding melted
rock) one has a number of questions about the safety of such
an activity-- accidents while emplacing 5000 primaries, and
the like.(80) But it is interesting to note that this is not
really a "disposal" means, and does not even make the mate-
rial highly inaccessible. According to the rule of thumb of
one ton of melted rock per ton of nuclear yield, each pri-
mary would at best be mixed with ten tons of rock. So at
some later time, anyone who drilled down into the mass
underground would need to bring up only ten tons of rock in
order to be able to extract one primary's worth of
plutonium. It is also interesting to note that the radio-
activity associated with this plutonium is less by a factor
60,000 or so than that associated with weapon plutonium in
spent fuel in a production reactor.
But the primary argument against using underground nuclear
explosions to destroy either chemical agents or excess nu-
clear weapon components is that it is efficient to do this
in other ways, without perpetuating the use of nuclear ex-
plosives-- any one of which could destroy a city and hundred
of thousands of human beings.
DEFENSE OF EARTH AGAINST AN ASTEROID OR COMET. In recent
years it is accepted that an asteroid or comet of some 5 km
diameter struck the Earth some 65 million years ago and the
global disruption(81) led to the distinction of the
dinosaurs and 70% of the species on Earth at that time. In
the last decade a lot of work has been done to catalog ob-
jects that might strike the Earth, and to consider what
might be done about the threat. With very high probability,
we have thousands of years before significant damage will be
done to a portion of the Earth, and millions of years to an
event that could cause extinction.(82) Russian scientists
warn that even a modest size asteroid striking the ocean
could cause a tsunami along many hundreds of km of shore,
and could kill many millions of people with higher probabil-
ity than if that same asteroid needed to land on a city in
order to kill by blast. Since an asteroid weighing two
million tons has a kinetic energy of 100 megatons at
20 km/s, an asteroid of only a little more than 100 m diam-
eter would provide this energy. One of the options for
dealing with such bodies is to meet them at a considerable
distance (the greater distance the better), and either to
burst them or to gradually deflect them so that they safely
miss the Earth. Taking an asteroid of 1 km diameter and
10**9 tons mass, moving toward Earth at 20 km/s, one could
enforce a miss distance of 20,000 km by giving the asteroid
a transverse velocity of some 0.7 m/s one year before im-
pact.(83) The kinetic energy would be a mere 0.05 kilotons.
But the efficiency of transferring energy from a nuclear ex-
plosion to a massive asteroid is not great.
One of the ways that comes to mind is to use penetrating
gamma rays that would deliver their energy over a depth of
some ten grams per square centimeter and to deliver enough
energy that the material to that depth would be heated and
vaporized, perhaps to emerge with a kinetic energy corre-
sponding to some 3000 K or a velocity (for a molecular
weight of 20) of some 1 km/s. Since the asteroid needs to
be given a momentum of 7 x 10**16 gram-cm/s, and the momen-
tum imparted by the departure of a ton of this overburden is
assumed to be 10**11 g-cm/s per ton, some 7 x 10**5 tons of
materials must be ablated in this way. This really means
ablating the entire face of the asteroid to a depth of 70 cm
or so, which would require repeated explosions. Since the
material at 1 km/s has an energy content of 10**-4 Kt per
ton, only a total of some 70 Kt of energy needs to be depos-
ited in such layers to accomplish the job.
Should the task be to similarly divert an asteroid of a mere
100 m diameter, the required momentum transfer is 1000 times
less and if repeated explosions are permissible, the job
could be done with a deposition of a mere 70 tons of radi-
ation energy. On the other hand, with a single blast
ablating only 10 cm, the required energy deposition is ten
times as large.
Since such considerations have only begun in the last few
years, other approaches have been considered as well, such
as the focusing of sunlight by mirrors tethered to or near
the asteroid, so as to ablate the material in the focused
spot and provide a more gentle rocket propulsion for months
or years.
Comet-like objects of relatively modest size might be de-
tected only months away from impact, and if they are small
enough, the best solution might be to fragment them with a
single explosion or with a chain of smaller nuclear explo-
sions laid out in the path of the comet.
On the nuclear side, one could imagine a soft landing on the
asteroid, and drilling into its core so that a much smaller
nuclear yield would do the job, depending on the strength of
the asteroid.
We believe that we ought to take seriously such threats to
humanity, and we should work on them together. It would be
a tragedy, however, if nuclear explosives kept alive for the
purpose were to be used in war, and the mechanism set up in
the CTBT to review periodically the prospective benefits of
PNEs seems adequate for the purpose of responding to these
threats.
A FEW COMMENTS ON ELECTRICAL ENERGY FROM PNES (R.L. GARWIN).
Having been involved in the study of peaceful nuclear explo-
sions (PNEs) for 35 years or more, I want to emphasize the
fact that such proposals for U.S. PNEs, when thoroughly ana-
lyzed, have not proved to be of economic merit. Certainly
some explosions that might be counted as PNEs have had sci-
entific merit, such as the Halite/Centurion series of exper-
iments in which the radiation from a nuclear explosion was
used instead of the (thus far unavailable) radiation from
lasers in a gold cavity to implode rather large pellets to
study inertial confinement fusion. And a Soviet PNE in 1962
quenched a high-pressure gas well that had leaked to a lower
pressure reservoir-- a task that the conventional technology
in the Soviet Union was apparently incapable of performing
at that time.
Indeed, one can achieve a useful goal with a PNE, but the
cost of doing so turns usually out to be greater than the
cost of non-PNE approaches.
I excerpt from a report which I prepared in 1975 for the
U.S. Arms Control and Disarmament Agency. This proposed
Project Pacer was to build plants equivalent to a nominal
nuclear power plant generating 1000 MW(e), by replacing the
nuclear-heated steam supply by a steam supply heated by re-
peated thermonuclear explosions in an underground cavity.
Since one ton of HE contributes 4.2 GJ, and at 30% effi-
ciency a 1000 MWe reactor requires 3.3 GJ/s, about 60 kilo-
tons of nuclear explosive per day is required to provide the
necessary heat.
First, one should note that the United States has about 100
nominal reactors, so to replace them (without any further
growth) by Pacer-like systems would require some 365 nuclear
explosions per year at each plant of some 60 Kt energy re-
lease-- or about 36,000 such nuclear explosions per year in
the United States alone.
And this would provide only 17% of the electricity used at
present in the United States.
My calculation in 1975 showed that if one assumed that there
were no technical problems, the normal nuclear reactor would
still be preferred until the cost of natural uranium rose to
some $160-220/kg, compared with the present price of around
$20/kg. And at higher prices, Pacer (still on the assump-
tion that it is feasible) would need to compete with breeder
reactors or with uranium from seawater.
CONCLUSIONS.
We are confident that compliance with a CTBT will prevent
any nation from developing third-generation nuclear weapons
such as the nuclear-explosion-pumped x-ray laser.
We believe that the CTBT will prevent states from
confidently acquiring new-design two-stage thermonuclear
weapons, although a state might design and build weapons
within the existing range of experience, in which it would
not have full confidence.
Available experience shows that nuclear weapon states will
be able to maintain their nuclear weapons stockpiles safe
and reliable for some decades at least, by means of appro-
priate programs of inspection, analysis, and remanufacture,
under a CTBT. Different states may put different emphasis
on periodic remanufacture vs. science-based stockpile
stewardship, vs. full funding of the mechanisms that they
have used in the past.
Non-nuclear states or sub-state entities building nuclear
weapons under a CTBT could with reasonable confidence make
gun-type weapons using U-235, and with somewhat lesser con-
fidence could reproduce the first implosion-type weapons us-
ing weapon-grade fissile materials. Somewhat greater
uncertainty and difficulty would be associated with the use
of plutonium metal produced from separated plutonium from
reprocessing of commercial reactor-grade spent fuel. In-
creasing uncertainty would be associated with more advanced
implosion system chosen to use less fissile material than
the original solid-sphere design.
Still greater uncertainly would be incurred if an organiza-
tion designed and produced a stockpile of boosted fission
weapons without test, and very little confidence would be
associated with a stockpile of two-stage thermonuclear weap-
ons that had never been tested.
As for the ban of peaceful nuclear explosions, the world
community has chosen the nonproliferation goal over possible
benefits to the economy or to basic research. There is even
wide spread doubt that such net benefits exist. If an acute
need occurred the decision to use PNEs should be made on the
base of consensus. One potential application of nuclear ex-
plosions might be approved unanimously in time, but still
requires much study-- the use of nuclear explosions to pre-
vent impact on the Earth by space bodies, asteroids and
comets. Although the effectiveness of nuclear explosions in
this role is far from assured, there is as yet no alterna-
tive technology as promising for prevention of large impacts
on the Earth. The threat of such impacts must be studied
widely before any decision should be made on the technology
that might be used. However, the loss caused by such im-
pacts could be so great (even up to global extinction) that
it may be desirable to institute a program (without nuclear
explosion testing) to develop the technology or lay the ba-
sis for a system of intercept; this should be done at a mod-
est level of effort commensurate with the expected annual
loss to be prevented. Using arbitrary numbers, if the loss
is $100 billion, and the interval between such events is an-
ticipated to be 10,000 years, then the expectation of annual
loss would be $10 million.
----------------
1 "Chairman's Draft Text of the Comprehensive Test Ban
Treaty" Arms Control Today August 1996. Also at
http://www.acda.gov/
2 ARTICLE VIII: REVIEW OF THE TREATY, "...On the basis of
a request by any State Party, the Review Conference
shall consider the possibility of permitting the conduct
of underground nuclear explosions for peaceful pur-
poses...
3 As of October 18, 127 States have signed the CTBT, as
have 40 0f the 44 whose signature is required for entry
into force. Of these latter, only Bangladesh, India,
North Korea and Pakistan have not yet signed.
4 W.J. Broad, "Star Warriors", Simon & Schuster, 1985.
5 M.D.Nordyke, The Soviet Program for Peaceful Uses of Nu-
clear Explosions, UCRL-ID-124410 October 1996.
6 Pure Pu-239 is the plutonium isotope of choice for mak-
ing nuclear weapons, in view of its high fission cross
section, long halflife and hence modest heat evolution,
negligibly small spontaneous neutron emission, and lack
of pentrating gamma radiation. The Pu weapons in the US
stockpile are made of 94% Pu-239 and about 6% Pu-240--
so-called weapon-grade Pu. The Pu that could be ex-
tracted from fully irradiated spent uranium fuel in the
normal fuel cycle of the world's 400-some light-water or
heavy water reactors contains some 60-65% Pu-239, with
most of the remainder being Pu-240. While reactor-grade
Pu is often called "civil plutonium" we use the term
"reactor-grade" to avoid possible confusion with Pu-238
used in some electrical generators powered by radio-
activity, including some pacemakers. Because of its
very short halflife of 87 years and the consequent heat
evolution of 560 watt per kg, Pu-238 is the only Pu
isotope from which one could not make an effective nu-
clear weapon.
7 J.P. Holdren (Chair), C.M. Kelleher, W.K.H. Panofsky,
J.D. Baldeschwieler, P.M. Doty, A.H. Flax, R.L. Garwin,
D.C. Jones, S.M. Keeny, J. Lederberg, M.M. May,
C.K.N. Patel, J.D. Pollack, J.D. Steinbruner,
R.H. Wertheim, and J.B. Wiesner, "Management and Dispo-
sition of Excess Weapons Plutonium," Report of the Na-
tional Academy of Sciences, Committee on International
Security and Arms Control, January 1994.
8 R. Serber, "The Los Alamos Primer", University of
California Press, Berkeley, California, 1992.
9 R.W. Selden, "Reactor Plutonium and Nuclear Explosives,"
December 1976.
10 E. Kankeleit, C. Kuppers, and U. Imkelle, "Bericht zur
Waffentauglichkeit von Reaktorplutonium", Institut fur
Kernphysik Technische Hochschule Darmstadt, December
1989.
11 J.C. Mark, "Explosive Properties of Reactor-Grade
Plutonium," Science and Global Security, vol. 4, no. 1,
1993, pp. 11-128.
12 J.P. Holdren (Chair), C.M. Kelleher, W.K.H. Panofsky,
J.D. Baldeschwieler, P.M. Doty, A.H. Flax, R.L. Garwin,
D.C. Jones, S.M. Keeny, J. Lederberg, M.M. May,
C.K.N. Patel, J.D. Pollack, J.D. Steinbruner,
R.H. Wertheim, and J.B. Wiesner, "Management and Dispo-
sition of Excess Weapons Plutonium," Report of the Na-
tional Academy of Sciences, Committee on International
Security and Arms Control, January 1994, pp. 32-33.
13 More than 90% U-235, although HEU is a term used to re-
fer to anything more than 20% U-235.
14 R. Serber, op. cit.
15 R. Serber, op. cit.
16 Rather loosely we use "tons" for "tonnes" or 1000 kilo-
grams.
17 Frank H. Shelton, "Recollection of a Nuclear Weaponeer"
1988, p. 1-35.
18 R. Rhodes, "Dark Sun: The Making of the Hydrogen Bomb",
Simon & Schuster, 1995. "The Making of the Atomic
Bomb", Simon & Schuster, 1987.
19 In the state of Washington, the extreme northwest of the
United States.
20 U-235 is hardly radioactive at all, half of it surviving
700 million years. On the other hand, the most common
plutonium isotope in nuclear weapons (Pu-239) has a
half-life of 24,000 years-- almost 30,000 times shorter
than that of U-235. Furthermore, Pu-239 is accompanied
to some extent by Pu-240, which has a "spontaneous fis-
sion" decay that injects neutrons continuously into any
mass of Pu. Thus, the relatively slow (milliseconds)
assembly of metallic blocks in a plutonium gun would al-
low time for such neutrons to start the chain reaction
when the assembly is barely supercritical, leading to
much reduced yield (See R. Serber, op. cit.)
21 Mark, J.C., "Explosive Properties of Reactor-Grade
Plutonium," by J.C. Mark in Science & Global Security,
1993, Vol. 4, pp. 111-128.
Garwin, R.L., "Technical Interpretation" and "Explosive
Properties of Various Types of Plutonium," by
R.L. Garwin, published in "Managing the Plutonium Sur-
plus: Applications and Technical Options" edited by
R.L. Garwin, M. Grubb, and E. Matanle, pp. 1-22, NATO
ASI Series, 1. Disarmament Technologies - Vol. 1, Novem-
ber 1994.
22 S.D. Drell and Bob Peurifoy, "Technical Issues of a Nu-
clear Test Ban" in Annu. Rev. Nucl. Part. Sci, 1994,
44:285-327.
23 R.E.Kidder, "Report to Congress "Assessment of the
Safety of U.S. Nuclear Weapons and Related Nuclear Test
Requirements" UCRL-LR-107454 (July 1991).
24 R.L. Garwin, "The Maintenance of Nuclear Weapon Stock-
piles Without Nuclear Explosion Testing," presented at
24th Pugwash Workshop on Nuclear Forces "Nuclear Forces
in Europe", London, ENGLAND, September 22-24, 1995.
25 H.F. York, "The Advisors: Oppenheimer, Teller, and the
Superbomb" Stanford University Press, Stanford,
California, 1989.
26 Indeed, the United States is committed a rate of re-
duction faster than that, even if by the year 2003 one
only has the START-I level of some 8000 nuclear war-
heads. And if one is optimistic about reducing nuclear
weapon holdings, it may be that U.S. and Russian war-
heads could be reduced to 2000 or fewer total warheads
on each side by that time. This has significant conse-
quences for the required tritium production or acquisi-
tion capability, which we will discuss later.
27 T.B.Cochran, W.M.Arkin, R.S.Norris, and M.M.Hoenig, "Nu-
clear Weapons Databook: Vol. II U.S. Nuclear Warhead
Production" Natural Resources Defense Council, page 16
(1987).
28 R.H. Rhodes, "Dark Sun".
29 G.A.Goncarov, Physics Today, November 1996.
This is an informative review of the U.S. and Soviet
thermonuclear weapon development programs.
30 R.L. Garwin, Testimony to the Senate Foreign Relations
Committee on Effects of Thermonuclear War (RLG find full
reference). Also, United Nations Scientific Committee
on Effects of Atomic Radiation (UNSCEAR 1993) page 94
gives full yield of atmospheric tests as 545 megatons,
of which 217 are stated to be fission.
31 R.L. Garwin, "The Maintenance of Nuclear Weapon Stock-
piles..." op. cit.
32 M.D.Nordyke, op.cit.
33 "Towards a Comprehensive Test Ban Treaty" Expert Study
on Questions Related to a Comprehensive Test Ban Treaty,
by the Royal Norwegian Ministry of Foreign Affairs, May
1992.
34 R.S. Norris, "French and Chinese Nuclear Weapon Test-
ing", Security Dialogue, vol. 27(1), pp. 39-54 (1996).
35 National Ignition Facility documentation from Livermore
and DOE.
36 In which pellets of ICF fuel such as deuterium-tritium
mixture were driven by nuclear explosions rather than
the eventual laser-driven x-ray source.
37 E.N. Avrorin, B.V. Litvinov, V.A. Simonenko, "Nuclear
Explosive Experiments for Matter Property Study: Re-
sults and Opportunities" Zababhakin Scientific Talks,
Phyiscs of Explosion, Shock and Detonation Waves,
Russian Federal Nuclear Center-- All-Russian Scientific
Research Institute of Technical Physics, Snezhinsk,
Russia, (1995).
38 M.D. Nordyke, "The Soviet Program for Peaceful Uses of
Nuclear Explosions," (The 'Kama' waste-disposal exper-
iments of 1973 and 1974).
39 S.D. Drell and Bob Peurifoy, op. cit.
40 R.L. Garwin, "The Maintenance of Nuclear Weapon Stock-
piles..." op. cit.
41 As planned by DOE for two subcritical experiments ini-
tially scheduled for June 18, 1996 and September 12,
1996, and for more during the following fiscal year. In
a DOE fact sheet of 10/30/95 available on the Internet,
it is announced that the 1996 experiments will be con-
ducted in the "Lyner facility", 980 feet below ground at
the National Test Site.
See
http://www.doe.gov/html/doe/whatsnew/factsheet/f103095.html/
42 R.L. Garwin, "The Maintenance of Nuclear Weapon Stock-
piles..." op. cit.
43 S.D. Drell and Bob Peurifoy, op. cit.
44 Drell, S.D., Chairman, Callan, C. Cornwall, M.,
Eardley, D., Goodman, J., Hammer, D., Happer, W.,
Kimble, J., Koonin, S., LeLevier, R., Max, C.,
Panofsky, W., Rosenbluth, M., Sullivan, J.,
Weinberger, P., York, H., and Zachariasen, F. "Science
Based Stockpile Stewardship," JASON Report JSR-94-345,
November 1994.
45 "Science Based Stockpile Stewardship" (1994).
46 "Science Based Stockpile Stewardship" (1994).
47 "Science Based Stockpile Stewardship" (1994).
48 Hammer, D., Chairman, F. Dyson, N. Fortson, R. Novick,
W. Panofsky, M. Rosenbluth, S. Treiman, H. York,
"Inertial Confinement Fusion (ICF) Review," JASON Report
JSR-96-300, March 1996.
49 R.H. Rhodes, "Dark Sun".
50 Drell and Peurifoy, op. cit.
51 G.A.Goncharov, op. cit.
52 "Science Based Stockpile Stewardship" op. cit.
53 ibid
54 Computed Axial Tomography.
55 S.D. Drell and B. Peurifoy, op. cit.
56 Formerly every two years. The magic number, 11, is cho-
sen to provide 70% probability of detecting a flaw that
affects 10% of the weapons in the stockpile.
57 S.D. Drell, Chairman, J. Cornwall, F. Dyson, D. Eardley,
R.L. Garwin, D. Hammer, J. Kammerdiener, R. LeLevier,
R. Peurifoy, J. Richter, M. Rosenbluth, S. Sack,
J. Sullivan, and F. Zachariasen. "Nuclear Testing -
Summary and Conclusions," JASON Report JSR-95-320, Au-
gust 3, 1995.
58 Because of the smaller mass and reduced symmetry.
59 R.L.Garwin, "Nuclear Tests Are No Longer Required (to
keep a stockpile of weapons in good shape)" (in French),
La Recherche pp. 70-76, December 1995.
60 Jonathan I. Katz, Bulletin of the Atomic Scientists.
61 C.P. Robinson, Statement to the United States Senate
Committee on Armed Services, Hearing of the Subcommittee
on Strategic Forces, March 12, 1996.
62 R.L. Garwin, "Monitoring and Verification of a CTBT,"
presented at 3rd Pugwash Workshop on the Future of the
Nuclear-Weapon Complexes of Russia and the USA. Moscow,
RUSSIA, 03/24-26/96.
63 R.L. Garwin, "The Comprehensive Test Ban Treaty in Sep-
tember 1996," presented at the 46th Pugwash Conference
on Science and World Affairs, SECURITY, COOPERATION AND
DISARMAMENT: THE UNFINISHED AGENDA FOR THE 1990s, Sep-
tember 2-7, 1996, Lahti, FINLAND.
64 R.L.Garwin, "Monitoring and Verification..." 1996.
65 ibid.
66 Drell and Peurifoy, op. cit.
67 S.D. Drell, Chairman, J. Cornwall, F. Dyson, D. Eardley,
R.L. Garwin, D. Hammer, J. Kammerdiener, R. LeLevier,
R. Peurifoy, J. Richter, M. Rosenbluth, S. Sack,
J. Sullivan, and F. Zachariasen. "Nuclear Testing -
Summary and Conclusions," JASON Report JSR-95-320, Au-
gust 3, 1995.
68 R.L.Garwin, "Monitoring and Verification..." 1996.
69 S.D. Drell, Chairman, J. Cornwall, F. Dyson, D. Eardley,
R.L. Garwin, D. Hammer, J. Kammerdiener, R. LeLevier,
R. Peurifoy, J. Richter, M. Rosenbluth, S. Sack,
J. Sullivan, and F. Zachariasen, "Nuclear Testing - Sum-
mary and Conclusions," JASON Report JSR-95-320, August
3, 1995.
70 R.L.Garwin, "Monitoring and Verification..." 1996.
71 E.N.Avrorin, et al, op. cit.
72 G.A.Goncharov, op. cit.
73 M.D.Nordyke, op. cit.
74 A concept apparently first introduced in the U.S. PNE
program.
75 M.D.Nordyke, op. cit.
76 F.A. Long, Chairman, L.E. Elkins, R.L. Garwin,
T. Greenwood, C. Hocott, H. Jacoby, G.W. Johnson, and
R. Morse, "An Analysis of the Economic Feasibility,
Technical Significance, and Time Scale for Application
of Peaceful Nuclear Explosions in the U.S., with Special
Reference to the GURC Report Thereon," April 1975.
77 F.A. Long, Chairman, L.E. Elkins, R.L. Garwin,
T. Greenwood, C. Hocott, H. Jacoby, G.W. Johnson, and
R. Morse, Appendix C: "Comparative Cost Analyses for
Electric Power from Project Pacer," from "An Analysis of
the Economic Feasibility, Technical Significance, and
Time Scale for Application of Peaceful Nuclear Explo-
sions in the U.S., with Special Reference to the GURC
Report Thereon," April 1975,
78 Such concepts have also been explored in Russia, but
they are not currently being developed because of the
economic situation, among other circumstances.
79 e.g., Y.A.Trutnev and A.K.Chernyschev, presented at the
Fourth International Workshop on Nuclear Warhead
Eliminatin and Nonproliferation, Washington DC, Febru-
ary 1992.
80 J.P.Holdren, op. cit. (Appendix C, pp. 272-275).
81 Dust, smoke, nitric oxide in the atmosphere, etc.
82 Of course, there is a tiny probability that the
cataclysmic event will happen next year or in ten years,
but with the improvement in observation systems, we
should be able to increase the lead time for errant
asteroids. Wayward comets, on the other hand, are more
difficult to predict.
83 Although in free space the required velocity is in-
versely proportional to the travel time, this is not
true for orbital dynamics. For short-period asteroids,
the maximum deviation for a given velocity is obtained
by applying it about one-half of the asteroid "year" be-
fore impact. However, spaced multiple impulses can be
of use.
