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OCR for page 11
Clarifying the Spent-Fuel Standard
We begin with a review of the definition and application of the spent-
fuel standard in the initial CISAC study, before turning to issues raised
subsequently and the challenge of making the standard easier to apply.
THE STANDARD AS ORIGINALLY CONCEIVED
CISAC's original formulation (CISAC, 1994, p. 34) held that "Options
for the long-term disposition of weapons plutonium should seek to meet
a 'spent-fuel standard' that is, to make this plutonium roughly as inac-
cessible for weapons use as the much larger and growing stock of pluto-
nium in civilian spent fuel." What was meant by the "inaccessibility" of
plutonium in spent fuel was elaborated In a two-page box later in the
same volume (CISAC, 1994, pp. 150-151) and further clarified ~ a passage
In the successor volume (CISAC, 1995, p. 73) staking that the spent-fuel
standard
does not imply a specific combination of radiation barrier, isotopic mix-
ture, and degree of dilution of plutonium. Rather, it describes a condi-
tion in which weapons plutonium has become roughly as difficult to
acquire, process, and use in nuclear weapons as it would be to use plu-
tonium in commercial spent fuel for this purpose. The rationale for the
spent-fuel standard is, first, that the bulk, composition, and ionizing-
radiation field of spent fuel pose very appreciable barriers to the theft or
diversion of this material and extraction of contained plutonium for use
in nuclear weapons and, second, that the existence in the world of many
hundreds of tons of civilian plutonium in spent fuel means that there
11
OCR for page 12
12 SPENT-FUEL STANDARD FOR DISPOSITION OF EXCESS WEAPON PLUTONIUM
would be little security gain from special efforts to eliminate the weapons
plutonium, or to render it much less accessible even than the plutonium
in spent fuel, unless society were prepared to take the same approach
with the global stock of civilian plutonium.
The terms "accessible" and "inaccessible" in short formulations of the
spent-fuel standard, then, referred to the ease or difficulty of acquiring,
processing, and using in weapons the plutonium that is embedded in
typical spent fuel. A footnote to the above passage added this further
important point about the time dimension of the standard
Concerning the spent-fuel standard, we are aware that the accessibility
of plutonium in commercial spent fuel is quite variable and increases
with time as the fission-product radioactivity that provides the principal
barrier to processing of the material for weapons use decays. An appro-
priate interpretation of what sort of spent fuel constitutes the standard
follows from consideration of the situation that will exist at the time in
the future when most of the surplus weapons plutonium at issue here is
being processed for final disposition, say, between 2000 and 2030. There
is likely to exist, in that period, upwards of 1,000 tons of civilian plutonium
in spent fuel, ranging in age from freshly discharged to several decades
old. If the inaccessibility of weapons plutonium is made comparable to
that of civilian plutonium In the middle of this age distribution—that is,
civilian plutonium In spent fuel 20-30 years old the existence of the
weapons plutonium In this form would not markedly increase the secu-
rity risks already associated with the civilian spent fuel.
Dependence on intrinsic properties only
The CISAC reports also stressed that meeting the spent-fuel standard
depends only on the intrinsic properties of the final plutonium form asso-
ciated with a disposition option. "Intrinsic" means, in this context, the
properties of the smallest plutonium-containing item that could be
removed from an interim or final repository for the dispositioned form, or
from a vehicle transporting plutonium in this form to such a repository,
without a degree of physical processing likely to be impractical for any-
body but the host state itself. (By "physical processing" we mean cutting,
blasting, melting, dissolution, and the like. The determination of what
would be "impractical" must take into account the amount of time likely
to be available before the authorities discover the attempt and intervene.)
In the case of ordinary spent fuel itself, we would consider the rel-
evant item to be the fuel assembly—an item removable intact from the
reactor, or spent-fuel storage pool, or shipping task, but not further sub-
dividable without a substantial amount of cutting (made more difficult, of
course, by the radiation field associated with the item.) We do not include
OCR for page 13
CLARIFYING THE SPENT-FUEL STANDARD
13
the casks in which ordinary spent fuel would be shipped or stored as part
of the 'intrinsic' barriers associated with such fuel, because the lid of such
a cask can be removed by cutting or blasting In a matter of a few m~nutes.9
Nor do we count as part of the 'intrinsic' barriers the other types of engi-
neered and institutional barriers that may surround spent-fuel assemblies
or other plutonium forms, including vaults, buildings, fences, alarms,
guard forces, and so on.
It is) of course, the combination of intrinsic properties with additional
engineered and institutional barriers that governs the overall prolifera-
tion resistance of a dispositioned plutonium form. The spent-fuel stan-
dard was not developed to describe overall proliferation resistance, but
only to describe the contribution to overall proliferation resistance that
should appropriately be sought from the intrinsic properties of the final
plutonium form. The original CISAC formulations about this standard
were intended to make clear that it should be regarded as (a) a necessary
but not a sufficient criterion for adequate overall proliferation resistance
of the final plutonium form and (b) a ceiling as well as a floor on what is
worth achieving In this intr~nsic-property contribution to proliferation
resistance. Because these important points seem not to have been made
entirely clear (or not to have been entirely accepted!),~° we revisit them
here.
· We believe the spent-fuel standard is a necessary condition for
meeting convincingly the criterion that the existence of
dispositioned plutonium should not constitute a sigruficant addi-
tion to the security risks posed by plutonium in ordinary spent
fuel (a form In which much more plutonium resides than In the
military stockpiles). This is so in part, we think, because addi-
tional engineered and institutional barriers may not have as high a
degree of reliability (or demonstrability of reliability) as Me intrinsic
9Approaches in which ordinary storage and shipping casts and/or their contents have
been modified to make the contents substantially more difficult to extract as might be
done to try to compensate for barriers to plutonium recovery from the items inside that
were lower than those for ordinary spent-fuel assemblies would need to be analyzed on
a case-by-case basis. This would entail initially considering the entire object to be the
"item" whose intrinsic resistance to attack must be assessed, and ultimately reaching a
conclusion, based on analysis and comparison, as to whether this item's degree of resis-
tance to attack, together with the properties of its contents, constitute compliance with the
spent-fuel standard. That is just what has been done in this report for the can-in-canister
immobilization option and the CANFLEX variant of the CANDU MOX option.
10See, e.g., Leonard W. Gray and Thomas H. Gould, Jr., Immobilization Team Comments on
Interim Report of NAS Panel Review of Spent-Fuel Standard for Disposition of Excess Weapons
Plutonium, Lawrence Livermore National Laboratory Report PIP-99-152, 28 October 1999.
c
OCR for page 14
14 SPENT-FUEL STANDARD FOR DISPOSITION OF EXCESS WEAPON PLUTONIUM
barriers do (and indeed are certainly less reliable in Russia than in
the United States), and in part because the imposition of intrinsic
barriers sends a much stronger signal about the intention of the
possessor state with respect to irreversibility of arms reductions
than does the imposition of engineered and institutional barriers
that, in many circumstances, would hardly impede the possessor
state's recovery of the plutonium at all.
· At the same time, the spent-fuel standard is not sufficient because,
as the original CISAC reports stressed, the intrinsic barriers to
acquiring, processing, and using in weapons the plutonium embed-
ded in typical spent fuel are not high enough for this material to be
considered adequately "self protecting." Thus additional engi-
neered and institutional barriers are appropriate for this material
and for other plutonium forms with intrinsic barriers comparable
to those of typical spent fuel. Indeed, society should plan to increase
these engineered and institutional barriers against the weapons
use of spent fuel and comparable material over time (including,
eventually, by emplacement of the material in a monitored geologic
repository), as the technological capacity to handle and reprocess
this material becomes more commonplace and the radiation bar-
rier to handling it becomes less daunting.
The spent-fuel standard is a ceiling as well as a floor on what is
worth achieving in the degree of proliferation resistance conferred
by the intrinsic properties of dispositioned weapons plutonium.
Achieving this much would eliminate the excess proliferation haz-
ard represented by the weapons plutonium in comparison with
the "background" hazard represented by the much larger stocks
of civilian plutonium embedded in spent fuel. Spending addi-
tional time and money to bring the intrinsic-property proliferation
resistance of dispositioned weapons plutonium to a higher level
than that of plutonium in typical spent fuel would not signifi-
cantly reduce proliferation risks overall. Indeed, incurring delays
in disposition in order to reach a higher standard would add to
those risks.
Intrinsic characteristics, we repeat, are only a part of adequate secu-
rity. But they are an important part. That is why CISAC defined a spent-
fuel standard, and why CISAC and we have emphasized that material
that does not meet this standard, based on its intrinsic properties, cannot
be made to meet the standard by increasing the engineered and institu-
tional safeguards that are applied. If the spent-fuel standard is deemed to
be satisfiable based on such engineered and institutional barriers as vaults
and alarms and guards alone no matter what the characteristics of the
.
OCR for page 15
CLARIFYING THE SPENT-FUEL STANDARD
15
plutonium form inside then one could assert that pure plutonium ingots
or even intact plutonium "pits" (nuclear-weapon cores) meet the spent-
fuel standard, as long as the vault is strong enough, the alarm sensitive
enough, the guards competent enough. By reductio ad adsurdum, this dem-
onstrates the need for a criterion based on intrinsic properties alone. After
all, no matter what engineered and institutional safeguards were applied,
storing plutonium ingots or pits indefinitely in Russia would not be
regarded by the United States as an adequate approach to the risks of
reincorporation of the material into new Russian nuclear weapons or its
theft for incorporation into someone else's weapons—nor would this
approach in either Russia or the United States be deemed, by others, an
adequate indication of good intentions.
Further qualifications on the application of the standard
The 1994 and 1995 CISAC reports defining and elaborating the spent-
fuel standard emphasized several further disclaimers about its applica-
tion. We reiterate them here and associate ourselves with them.
.
.
First, not only is a judgment on intrinsic properties of the final
plutonium form insufficient (even though necessary) for conclud-
ing that the risks associated with the final form are sufficiently
small, but consideration of the final form and the protection af-
forded it is not sufficient for reaching a judgment about the overall
resistance of a disposition method to re-use of the plutonium in
weapons. Resistance to acquisition and weapons re-use of the plu-
tonium at earlier stages of the disposition process must also be
taken into account. Typically, pursuit of increased resistance to
proliferation in the final plutonium form entails additional han-
dling and processing steps that add to proliferation risk. A judg-
ment must be made that the gain at the end warrants the loss
along the way.
Second, actual resistance to acquisition and weapons re-use of the
plutonium is not the only criterion for judging a disposition
method satisfactory. Demonstrability of and perceptions about
resistance are also important, as are timing, safety characteristics,
environmental hazards, economics, tractability of institutional and
regulatory requirements, domestic and international political accept-
ability, and influences on the proliferation resistance of nuclear-
energy systems not directly involved in the disposition effort
(which influences may be positive or negatively ).
|lSee, e.g., CISAC, 1995, p. 256.
OCR for page 16
16 SPENT-FUEL STANDARD FOR DISPOSITION OF EXCESS WEAPON PLUTONIUM
.
Finally, getting to final disposition of excess weapons plutonium
is not the only important part of managing the hazards of excess
nuclear weapons and nuclear materials in the post-Cold-War
world. The initial CISAC study and many others on this topic have
emphasized the importance of de-activating, consolidating, ~nvento-
rying, and dismantling excess weapons; consolidating and invento-
rying weapons-usable nuclear materials; storing and protecting all
nuclear-weapon components and directly weapons-usable nuclear
materials with the degree of diligence appropriate to intact nuclear
weapons; blending down highly enriched uranium to levels not
directly usable in weapons; subjecting all of these activities to a
high degree of bilateral (U.S.-Russian) and eventually international
monitoring and transparency; and increasing the attention given
to improving the resistance of civilian nuclear-energy systems to
the diversion of weapons-usable materials. Defining and imple-
menUng standards for disposition of excess weapons plutonium is
important, but it is not a substitute for and should not distract
attention from these other steps.
Application of the standard to final plutonium forms in the initial
CISAC study
The first volume of the CISAC plutonium study (1994) concluded that
the two most promising plutonium-disposition options for meeting the
spent-fuel standard and other disposition desiderata In a timely way were
(1) fabrication of weapons plutonium into MOX fuel for once-through use
in selected civilian power reactors of currently operating types and
(2) immobilization of weapons plutonium by vitrification together with
12Besides the CISAC reports cited in Note 1, see, e.g., Frank van Hippel, "Fissile material
security in the post-Cold-War world," Physics Today, June 1995, pp. 26-30; Graham Allison,
Owen Cole, Richard Falkenrath, and Steven Miller, Avoiding Nuclear Anarchy: Containing the
Threat of Loose Russian Nuclear Weapons and Fissile Material, Cambridge, MA: MIT Press,
1995; Matthew Bunn and John P. Holdren, "Managing military uranium and plutonium in
the United States and the former Soviet Union," Annual Review of Energy and the Environ-
ment, vol. 22, 1997, pp. 403~86; U.S.-Russian Independent Scientific Commission on Pluto-
nium Disposition, Final Report, Washington, DC: Office of Science and Technology Policy,
Executive Office of the President of the United States, September 1997; Committee on Dual-
Use Technologies Export Controls and Materials Protection, Control, and Accounting,
National Research Council, Proliferation Concerns: U.S. Efforts to Help Contain Nuclear and
Other Dangerous Materials and Technologies in the Former Soviet Union, Washington, DC:
National Academy Press, 1997; and Committee on International Security and Arms Con-
trol, National Academy of Sciences, The Future of U.S. Nuclear Weapons Policy, Washington,
DC: National Academy Press, 1997.
OCR for page 17
CLARIFYING THE SPENT-FUEL STANDARD
17
high-level radioactive wastes In glass logs of the approximate size and
composition already selected for use in immobilizing high-level defense
wastes at the Savannah River site of the U.S. nuclear-weapons-production
complex. The second CISAC volume (1995) went beyond the "most prom-
ising" characterization to state flatly that current-reactor options using
light-water or CANDU reactors and the then-envisioned heavy-log/
vitrification-with-wastes option would both be able, if implemented, to
meet the spent-fuel standard (CISAC, 1995, p. 10~3
With respect to security of the final plutonium forms, the current-reactor
options obviously meet the spent-fuel standard, and the Panel judges
that the vitrification option meets this standard also. The plutonium In
the spent fuel assembly would be of lower isotopic quality for weapon
purposes than the still weapons-grade plutonium In the glass log, but
since nuclear weapons could be made even with the spent fuel plutonium
this difference is not decisive. Under typical assumptions, Me radiological
barrier presented by glass logs would be about three times smaller than
that presented by a fuel assembly (but still very high), and the mass of a
glass log~ontaining, coincidentally, about the same amount of pluto-
nium as a fuel assembly- would be about three times greater. The diffi-
culty of separating the accompanying materials would be roughly com-
parable In the two cases.
This conclusion, In which a MOX spent-fuel form containing about
twice as much plutonium as typical spent fuel and a vitrified waste form
with weapon-pluton~um isotopics were both deemed to meet the spent-
fuel standard, underlined CISAC's view that the standard should be
understood to mean "roughly" as resistant to acquisition and use In
weapons as is plutonium In typical spent fuel, not necessarily identical to
typical spent fuel (which would then itself require more precise deft
tion) In each characteristic that matters.
Questions about the Spent-Fuel Standard
The ambiguity inherent in judging whether a weapons-plutonium-
disposition form meets a standard of "roughly" equivalent to typical spent
13The indicated comparison was between a 660-kg pressurized-water-reactor fuel assem-
bly, irradiated to 40,000 megawatt-days per metric ton of heavy metal, and a 2,200-kg glass
log of the type foreseen for production at Savannah River, containing 20 weight percent
defense high-level wastes and 1.3 weight percent weapons plutonium mixed with the glass.
Radiation doses from both were computed at the surface of the objects, 30 years after fuel-
discharge and log production, respectively.
OCR for page 18
18 SPENT-FUEL STANDARD FOR DISPOSITION OF EXCESS WEAPON PLUTONIUM
fuel in resistance to acquisition and use of the plutonium for weapons has
naturally given rise to questions about whether particular forms meet the
standard or not, as well as to calls for greater precision in the specification
of the standard for use In making these determinations. Some have ques-
tioned whether any plutonium form in which the isotopic composition of
the plutonium is that of weapons plutonium should be judged to meet the
spent-fuel standard. Others have wondered by how much the plutonium
concentration in MOX should be allowed to exceed the value typical for
spent fuel arising from once-through use of low-enriched uranium before
such MOX is deemed out of compliance with the standard. Still others
have questioned at what point the combination of smaller fuel-assembly
size and lower radiation barrier associated with CANDU fuel at the
burnups typical for this reactor type would disqualify such fuel under the
standard. And some have expressed worries that an overly strict interpre-
tation of the spent-fuel standard in any or all of these cases could lead to
degrees of delay in moving ahead with plutonium disposition, in the
United States or Russia, that would increase proliferation dangers overalls
Of particular concern to DOE and others interested in current U.S.
plutonium-disposition plans is whether DOE's current design for the final
plutonium form in the immobilization track in the dual-track option can
reasonably be deemed to meet the spent-fuel standard. This design was
developed subsequent to the 1995 CISAC report's determination that the
then-current vitrification-with-wastes immobilization option and the
once-through MOX option both meet the spent-fuel standard. In the new
variant—called the "can-in-canister" approach plutonium oxide is incor-
porated in ceramic pucks that themselves contain no fission products; the
pucks are stacked in an array of cans suspended on a frame in a large steel
canister; and molten borosilicate glass, bearing fission products, is poured
into the canister to solidify around the cans and thus contain them in a
massive, highly radioactive glass log. In the immobilization approach
previously considered by CISAC, by contrast, the plutonium oxide would
have been added directly to the fission-product-bearing molten glass with
the aim of creating a more-or-less homogenous mixture of plutonium and
fission products in the resulting highly radioactive glass log.
14Publications raising the questions mentioned in this paragraph are cited, and prelimi-
nary responses to the questions are provided, in John P. Holdren, John F. Ahearne, Richard
L. Garwin, Wolfgang K. H. Panofsky, John J. Taylor, and Matthew Bunn, "Excess weapons
plutonium: how to reduce a clear and present danger," Arms Control Today, November/
December 1996, pp. 3-9. Virtually all of these questions were posed also in the briefings and
public comment sessions arranged in connection with the meetings of this Panel (see Appen-
dix B).
OCR for page 19
CLARIFYING THE SPENT-FUEL STANDARD
19
The can-in-canister approach was chosen by DOE in preference to the
homogeneous plutonium-in-glass approach for several reasons.~5 It had
become apparent that designing, testing, and implementing modifica-
tions to the Savannah River melter and the composition of its glass-
required in order to enable addition of adequate quantities of plutonium
directly to the melt while observing criticality constraints would be
technically difficult, costly, and likely to substantially set back the time-
table for the already scheduled high-level-waste immobilization program
at the Savannah River site. In particular, a change in glass composition
from the original borosilicate glass to a lanthan~de borosilicate glass would
have been necessary to achieve the desired plutonium loading, but the
processing temperature needed for the new composition (around 1475°C)
was too high to allow incorporation of the cesium needed to provide the
radiation barrier. (Cesium volatilizes above 1200°C.) It might also have
been necessary to reduce the log size In order to maintain criticality mar-
gins, which not only would have entailed a new melter design but also
would have reduced the resistance of individual logs to theft. Switching
from glass to a homogeneous ceramic incorporating plutonium and
cesium would entail producing all of this ceramic by hot isostatic pressing
in hot cells, a considerable complication compared to the cold-press-and-
s~nter method, In glove boxes, which can be used if the ceramic contains
plutonium but no fission products.
DOE's choice of the heterogeneous can-~n-can~ster approach allowed
staying with the original glass composition to contain the fission prod-
ucts, while gaining the improved performance of ceramic as the pluto-
n~um-conta~n~ng material (including greater durability under repository
conditions and greater ease of nondestructive assay for verification pur-
poses) and avoiding criticality concerns attendant on adding multiple
critical masses of plutonium to 1,700 kilograms of molten glass and fission
products at a time. And leaving fission products out of the plutonium-
bear~ng ceramic pucks In the can-~n-can~ster approach allowed for lower
manufacturing costs than would be entailed if the pucks themselves con-
ta~ned strong gamma-ray emitters
The most difficult question about the can-in-canister approach's meet-
~ng the spent-fuel standard is whether extraction of the plutonium from
i5See, e.g., Office of Fissile Materials, Department of Energy, Technical Summary Reportfor
Surplus Weapons-Usable Plutonium Disposition, Rev. 0, Washington, DC: Department of En-
ergy, 1996; M. J. Plodinec et al., "Survey of glass plutonium contents and poison selection,"
in Plutonium Stabilization and Immobilization Workshop, Washington, DC: Department of
Energy, 1995, pp. 229-239; and Leonard Gray and Malvyn McKibben, An Analysis of Pluto-
nium Immobilization Versus the "Spent Fuel Standard," Lawrence Livermore National Labora-
tory Report POP-98-073, August 1998.
OCR for page 20
20 SPENT-FUEL STANDARD FOR DISPOSITION OF EXCESS WEAPON PLUTONIUM
the fission products in the heterogeneous pucks-in-glass arrangement is
significantly easier than extracting plutonium from spent fuel. The corre-
sponding questions about the MOX option's meeting the spent-fuel stan-
dard relate to whether the high residual plutonium concentration in spent
light-water reactor (LWR) MOX or the relatively low mass and radiation
field associated with spent CANDU MOX fuel assemblies would make
these plutonium forms significantly more proliferation prone than typical
spent fuel from lightly enriched uranium (LEU)-fueled LWRs. As prepa-
ration for addressing these questions, we proceed first to elaborate some
ingredients of a systematic approach to applying the spent-fuel standard.
A SYSTEMATIC APPROACH TO CONSIDERING COMPLIANCE
WITH THE STANDARD
Until now there has been no simple formula that can be mechanisti-
cally applied to determine whether the final plutonium form resulting
from a disposition process is sufficiently close to typical spent fuel in the
array of characteristics governing resistance to acquisition, processing,
and use in weapons of the contained plutonium that it can be deemed to
meet the spent-fuel standard. In the current study, we considered whether
such a formula could usefully be constructed. We concluded that doing
so is very difficult; neither are we convinced that it would even be
desirable.
Many characteristics are germane; the importance of these character-
istics relative to one another may vary with the type of threat that is
deemed most important at a given time and place; the range of variation
with respect to the relevant characteristics is substantial within the array
of fuel types, degrees of irradiation, and ages since discharge in the global
spent-fuel inventory; a final disposition form's departures from typical
spent-fuel characteristics in the direction of lower resistance to prolifera-
tion in some respects may be offset by departures in the direction of
higher resistance in other respects; and the benefit of trying to narrow a
given "gap" between a characteristic of a final disposition form and the
corresponding characteristic of typical spent fuel must be weighed against
the delays and other increases of in-process proliferation risks that may
result from this effort. In so complex a space of possibilities, it seems to us,
the considered judgment of experienced people in answering the ques-
tion, "How close to spent fuel is close enough?" will continue to be diffi-
cult to replace with a mechanistic formula.
We do think, however, that the needed judgments can usefully be
informed by systematic comparison of the relevant quantitative and quali-
tative characteristics of candidate final plutonium forms, against those of
typical spent fuel, in a matrix format that groups the characteristics by the
OCR for page 21
CLARIFYING THE SPENT-FUEL STANDARD
21
kinds of barrier against proliferation they confer and that indicates the
relative importance of these different barriers against the main categories
of proliferation threat. We employ such an approach here.
Interactions of threats and barriers
The three main classes of proliferation threats to which intrinsic bar-
riers provided by final plutonium forms are germane are as follows:
(1) "Host-nation breakout" means that the country legitimately hold-
ing the dispositioned plutonium elects to recover it for re-use in its
nuclear arsenal. This is likely to entail large amounts of plutonium
(from several hundred to thousands of kilograms), no physical
limitations on access to the dispositioned plutonium forms and
the ability to transport them, high technical capabilities for sepa-
rating the plutonium and employing it to make sophisticated
nuclear weapons, high performance requirements for the weapons,
and concerns with detection of the effort while it is underway
ranging from negligible in the case of overt breakout to very sub-
stantial in the case that breakout is intended to be clandestine.
(2) "Theft for proliferant state" means that members of a subnational
group and/or agents of a proliferant state including, potentially,
facility insiders steal the material by stealth or force and transfer
it to the state for use in nuclear weapons. Much smaller amounts
of material are germane here (tens to perhaps one or two hundred
kilograms); physical barriers to access and transport are impor-
tant, in the context of limits on the time and technological capaci-
ties available to the thieves for dealing with these barriers; the
technical capacities of the state receiving the material for process-
ing it and employing it in nuclear weapons are likely to be moder-
ately high albeit lower than in the "host-nation breakout" case; the
performance requirements for the resulting weapons are likely to
be moderate; and concerns with detection would be high in the
theft and transport stages before the material is on the territory of
the proliferant state and moderate to high thereafter.
(3) "Theft for subnational group" means that a subnational group
steals the material by stealth or force and either tries to use it to
make nuclear weapons itself or transfers it to another subnational
group for this purpose. In this case the quantity of material of
interest can be as small as one bomb's worth; the situation with
respect to physical barriers to access and transport in relation to
limits on the time and technological capacities available to the
thieves are the same as in the "theft for proliferant state" category;
OCR for page 22
22 SPENT-FUEL STANDARD FOR DISPOSITION OF EXCESS WEAPON PLUTONIUM
the technical capacities available for processing and employing
the stolen material in nuclear weapons are likely to be less than in
the "proliferant state" case; the performance requirements for the
resulting weapons are likely to be low; and concerns with detec-
tion would be high at all stages of the effort.
The indicated differences in the characteristics of these three types of
threat give rise to differences in the relative importance of the various
intrinsic characteristics of final plutonium forms as barriers against the
threats.
We summarize our judgments on the interaction of threats and intrin-
sic barriers in Table 1, which arranges the characteristics of final pluto-
nium forms according to the barriers these characteristics provide at dif-
ferent steps in the proliferation chain and indicates the relative importance
of these barriers against the three classes of proliferation threats. The
relative-importance ratings reflect a combination of the needs/capabili-
ties of the threat groups with the nature of the barriers. We choose a scale
of only four ratings- zero, low, moderate, and high to reflect distinc-
tions in relative importance without implying more precision than the
complexity and judgmental character of these considerations permit.
The term "item" as used in Table 1, refers to the smallest embodiment
of the final plutonium form that could be removed from a storage facility
or transport operation without a degree of on-site physical processing
(cutting, blasting, melting, dissolution, and so on) likely to be impractical
for anybody but the host state itself. The term "technical difficulty" in-
cludes requirements for manpower and specialized knowledge, skills,
and equipment, as well as an allowance for the amount of time likely to be
required to complete a task with a given level of resources.
The detectability of an activity, which is an important barrier in cases
where concealment is important to the proliferators, depends on resource
and time requirements for the activity and on other signatures (e.g., ther-
mal, chemical, nuclear) arising from the interaction of the intrinsic prop-
erties of the dispositioned plutonium form with the operations being car-
ried out on it. Detectability also depends on the capabilities deployed to
achieve detection. This underlines that, although Table 1 is intended to
address the intrinsic properties of final plutonium forms and not the char-
acteristics of the engineered and institutional protections supplementing
these, there are interactions between intrinsic properties and the engi-
neered and institutional protections (as, for example, in the relation be-
tween intrinsic properties related to detectability and the monitoring sys-
tems in place to achieve detection).
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CLARIFYING THE SPENT-FUEL STANDARD
TABLE 1
Intr~nsic-barrier and threat characterization for final plutonium forms
23
Importance of barrier against the threat
Barrier
Host-nation Theft for a
breakout proliferant state
Theft for a
subnational group
Barriers to acquisition of
the Pu from its storage
site
Mass and bulk of itema Zero to lowb
(low) concentration of Zero to lowb
Pu in item
Radiation hazard to Low
acquirers
Technical difficulty of
partly separating Pu
from bulk components
of item on sitea
Thermal, chemical,
and nuclear signatures
aiding detection
Barriers to separation of
the Pu from diluents and
fission products
Technical difficulty
of disassembly
Technical difficulty
of dissolution and
separation
Quantity of material
to be processed
Hazards to separators
Signatures aiding
detection
Moderate
High
Moderate
Zero to lowb
High
Moderate
High
Moderate
High
Zero to Moderate to Moderate to
moderateb'C highc highc
Low
Low
Low to
moderates
Low
Zero to
moderates
Barriers to use of the
separated Pu in nuclear
weapons
Deviation of isotopic
composition from
"weapons grade"
Low to
moderate
Moderate to
high
Moderate to
high
Moderate
Moderate to
highC'd
Moderate
High
High
Moderate
Highc
Moderate Moderate Low
a Barrier relates both to technical difficulty and detectability, which are themselves related
(see text).
b Importance depends on whether breakout is open or clandestine.
c Importance depends on sensor capabilities.
d Importance depends on degree of proliferant state concern with detection.
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24 SPENT-FUEL STANDARD FOR DISPOSITION OF EXCESS WEAPON PLUTONIUM
Explanations of judgments in Table 1
The first set of intrinsic barriers comprises those that impede the
acquisition of the plutonium i.e., removal of the plutonium-bearing item
from its place of storage or transport- including barriers to processing
the item before it is removed in order to extract the plutonium from it or
otherwise simplify its removal. In this category:
.
~ ,
The mass and bulk of an individual item would be barriers against the
threat of host-nation breakout only in the case where the breakout
was intended to be clandestine, in which case the item size might
be expected to have some effect on the detectability of operations
to remove the items from storage or divert them in transport. (We
judge this to be of low overall importance in light of the relative
ease with which a host country could probably overcome it.) If
breakout was open, item size would be of no consequence to a host
state (which would be well equipped to handle items of any mass
and bulk). In the cases of theft for a proliferant state or a sub-
national group, the barriers posed by mass and bulb to ready removal
of an item are more important we rate them "moderate"
because of their effect on the character of the equipment needed to
accomplish the theft (which affects, to some degree, the resources
the thieves would need and the chance of their operation's being
detected).
· The concentration of plutonium in the item is a barrier the lower the
concentration the higher the barrier insofar as it affects the total
mass of material (and thus the number of items) that must be
acquired in order to obtain a given quantity of plutonium. As
with item size, and for the same reasons, this factor would be of no
consequence at the material-acquisition stage (although of some
consequence at the processing stage, about which more below) to
a state engaged in open breakout, and of only low consequence to
a state engaged in clandestine breakout. But we believe it is of
high importance in relation to theft for a proliferant state or a
subnational group, because concentration even more than indi-
vidual item size determines the scale of the entire theft operation
(personnel and equipment), directly affecting both the resources
the thieves would need to mobilize, the time required for the acqui-
sition operation, and the chances of their being detected and
thwarted in the course of it.
· The radiation hazard to the acquirers of the plutonium (as opposed to
the radiation hazard to the processors, which is treated below)
would be of low but not zero importance as a barrier to host-
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CLARIFYING THE SPENT-FUEL STANDARD
.
25
nation breakout; such a state would be well equipped to minimize
this hazard with shielding and remote-handling equipment. This
barrier would be greater against theft for a proliferant state or a
subnational group, but we rate it as "moderate" in importance
rather than "high" for two reasons: first, even the highest radiation
fields associated with spent fuel and other plutonium-disposition
forms would not produce immediately incapacitating doses if the
thieves took modest precautions; and, second, many potential
thieves (and their bosses) might not give high priority to the avoid-
ance of the kinds of doses that would be involved (either out of
ignorance or out of willingness to bear the risk or impose it on
someone else—in exchange for expected high reward).
The technical difficulty of partly separating the plutoniumfrom the bulk
components of the item on site would be of no importance in the case
of open breakout by a host nation, which would face no difficulty
in transporting the intact items to a processing site of its choice.
The barrier would be a bit higher if the host-nation breakout was
intended to be clandestine, since transporting the intact items to a
processing site might be at least somewhat easier for other coun-
tries to detect than transporting more concentrated forms of pluto-
nium would be. In the case of theft for a proliferant state or for a
subnational group, however, it would be a great advantage for the
thieves if the quantity and/or radioactivity of the material that
needed to be removed from the site of the theft could be signifi-
cantly reduced by operations that could be effected at the site
without greatly prolonging the thieves' stay there or otherwise
increasing the chance of their being detected in the act. This would
ease substantially the thieves' subsequent problems of transport
and concealment of storage and processing. Thus we rate the
barriers against this as being of "high" importance.
· Thermal, chemical, and nuclear signatures that would aid detection dur-
ing the course of a they and subsequent transport and storage would be
of no importance to a host nation engaged in open breakout. In
the event the breakout was intended to be clandestine, however,
such signatures could significantly affect the chance that other
countries would detect the activity; thus we consider this barrier
of "moderate" importance in this case (the highest of any of the
barriers to host-nation breakout at the plutonium-acquisition
stage). Sensitivity to detection during theft and subsequent trans-
port and storage would be even greater in the cases of theft for a
proliferant state or a subnational group, so we rate the barrier as
"moderate to high" in these cases.
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26 SPENT-FUEL STANDARD FOR DISPOSITION OF EXCESS WEAPON PLUTONIUM
The second set of intrinsic barriers listed in Table 1 relate to the
work of separating weapons-usable plutonium from the structure,
diluents, and fission products accompanying the plutonium in the form
in which it was acquired (that is, either its final dispositioned form or
something derived from that by processing undertaken at the site of acqui-
sition, as discussed above). In the case of host-state breakout, this activity
could take place either clandestinely or openly, using old facilities or new
ones constructed openly or clandestinely for the breakout purpose. In the
case of theft for a proliferant state, this processing could be accomplished
by the thieves before transfer of the material to the state, in which case it
would likely be done on the territory of the state from which the material
was stolen or, after smuggling it across one or more borders, on the terri-
tory of a third state. Or the thieves might manage to transfer the stolen
items themselves to the proliferant state, whereupon the latter would do
the subsequent processing in facilities on its own territory (in which case
these could, again, be either open or clandestine, but more likely the
latter). In the case of theft for a subnational group, this processing would
most likely be in clandestine facilities, on whatever territory. The intrinsic
barriers against these activities and the bases for our judgments about
their relative importance are as follows:
.
The technical difficulty of mechanical disassembly of the plutonium-
containing items would be a barrier of only low importance in the
context of host-nation breakout, inasmuch as such nations would
have facilities adequate to handle this rather easily for any imagin-
able disposition form. It would also be of low importance to a
proliferant state that is conducting this processing itself, since the
technology for this mechanical disassembly step is not very
demanding. If the processing were being done by the thieves
before transferring the plutonium to the proliferant state, how-
ever, this barrier would be of moderate importance, as it would be
in the case where a subnational group was the final recipient,
because the relevant technologies/facilities would be harder for a
subnational group to acquire anal use (and hide) than for a state to
do so.
· The technical difficulty of dissolution of the plutonium-containing com-
pounds and chemical separation of the plutoniumfrom the other elements
present is, like the technical difficulty of mechanical disassembly, a
barrier of low importance to a host nation (although not zero,
insofar as the differences could be great enough to motivate the
choice of one plutonium source over another if they were equally
attractive—or equally difficult in other respects). We judge the
importance of this barrier to be "moderate to high" in the case of
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CLARIFYING THE SPENT-FUEL STANDARD
.
.
27
theft for a proliferant state (depending on whether the processing
is being done by the state or by the thieves themselves) and "high"
in the case of theft for a subnational group. Although the relevant
technologies for at least some disposition forms are well described
in open literature, they are fundamentally more demanding for
small states and subnational groups than are the mechanical-
disassembly technologies.
The quantity of material to be processed (which of course is related to
the plutonium concentration, discussed separately above as a bar-
rier to initial acquisition as opposed to a barrier to separation) is a
barrier of low importance in the case of open host-nation breakout
(although not of zero importance, because it increases time and
cost in some combination). It is of moderate importance in the
case of clandestine host-nation breakout, because its effect on the
scale of the operation increases the chance of detection. We judge
the importance of this barrier to be "moderate to high" in the case
of theft for a proliferant state, depending on who is doing the
processing and, in the event it is being done by the proliferant
state, depending on the importance attached to concealment and
on the sophistication of the facilities available to the particular
state.
The radiation, criticality, and toxic hazards during the separation pro-
cess are barriers of only low importance in the case of host-nation
breakout, because these nations have ample facilities and experi-
ence for minimizing these risks. Radiation and criticality are more
important barriers in the cases of theft for a proliferant state or for
a subnational group, because protection against these hazards
during processing requires the development (and in some cases
the concealment) of facilities and capabilities that the processing
entities did not possess before. (Still, we do not rate these barriers
"high" for proliferant-state processors because the needed capa-
bilities are well within the means of most states, and we do not
rate them "high" for subnational-group processors, even though
their capabilities would generally be less than those of states,
because such groups are likely to be willing to assume higher risks
in these categories than states are.) Toxic hazards are not likely to
be great enough to constitute more than a low barrier in any of the
cases.
· Detectability of processing operations may be based on the scale of the
required operations (including floor space, electrical power, spe-
cialized supplies, and the duration of the activities) and on chemi-
cal, nuclear, and thermal signatures from the specific operations
involved. (Dissolution and separation of plutonium, for example,
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28 SPENT-FUEL STANDARD FOR DISPOSITION OF EXCESS WEAPON PLUTONIUM
can release effluents derived from the solvents involved, which
are detectable remotely through technologies such as LIDAR
(LIght Detection And Ranging), as well as releasing radionuclides
that are detectable by various means. Chemical and radioactive
"taggants" chosen for detectability may be deliberately added to
disposition forms to raise this barrier. Infrared interrogation and
observation of infrared emissions moreover, can determine
whether or not known processing facilities are operating.) Of
course, the importance of the detectability barriers depends on
whether the activities are clandestine or open; it depends on
whether discovery would necessarily be fatal to the enterprise (as
it almost certainly would In the case of processing by a subnational
group, might be In the case of processing by a proliferant state,
and probably would not be In the case of clandestine host-state
breakout); and it depends as well on the state of the sensor capa-
bilities In relation to the strength of the signatures. These consider-
ations In combination lead us to rate the detectability barriers as
"zero to moderate" for the case of host-nation breakout, "moder-
ate to high" In the case of theft for a proliferant state, and "high"
for the case of the theft for a subnational group.
The last set of intrinsic barriers addressed In Table 1 are those against
the utilization of the plutonium that the proliferators are able to separate
for the fabrication of functional nuclear weapons. If it is assumed that
proliferators In all categories will ultimately be capable of obtaining rea-
sonably pure plutonium metal starting from the dispositioned forms as
we believe to be the cas~then the main intrinsic barriers In this category
are those associated with deviation of the plutonium's isotopic composi-
tion from "weapons grade."
The isotopic composition of the plutonium in the spent fuel is com-
pared with that of weapons-grade plutonium in Table 2. The indicated
differences lead to a neutron background nearly 7 times higher in the
spent-fuel plutonium than In weapons-grade plutonium, a heat genera-
tion rate about 6 times larger, and a surface gamma-ray dose about 16
times higher. These differences would produce additional difficulties
for those who might choose to design, manufacture, and deploy nuclear
weapons made from typical spent-fuel plutonium rather than from
16The unshielded surface gamma ray dose from reactor-grade plutonium is in the range
of 20 rem/hour (see, e.g., CISAC, 1995, p. 270~. This may be compared with the short-term
dose that would be associated with a 50 percent chance of death within 30 days from acute
radiation syndrome, which is in the range of 500 rem.
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CLARIFYING THE SPENT-FUEL STANDARD
TABLE 2
Isotopic composition of plutonium in typical LWR spent fuel versus
that in weapons-grade plutonium
29
Isotope
Type of plutonium
Pu-238 Pu-239 Pu-240 Pu-241 Pu-242 Am-241
Typical spent-fuel
plutonium from
light-water reactors
Weapons-grade
plutonium
1.3% 60.3% 24.3%
0.01% 93.8% 5.8%
5.6% 5.0% 3.5%
0.13% 0.02% 0.22%
Source: CISAC, 1995, p. 45.
weapons-grade plutonium difficulties that account for the historical
preference of nuclear-weapon states for using weapons-grade material.
But, as emphasized In the previous CISAC plutonium reports and In other
unclassified but authoritative studies, the differences do not preclude the
design and construction of effective nuclear weapons from typical spent-
fuel plutonium, at all levels of sophistications
We rate the barrier posed by isotopic deviations from weapons grade
as "moderate" In importance for host-nation breakout In Table 1 mainly
because recovery of weapons-grade plutonium from dispositioned forms
would permit production of weapons from existing designs without new
nuclear-explosive tests, whereas use of plutonium of different isotopic
compositions would be likely to entail design modifications and, even if
not, would probably require new nuclear-explosive tests to confirm that
the change in isotopic composition had not unacceptably degraded per-
formance. In the case of theft for a proliferant state we rate the barrier
likewise as "moderate" In importance: such a state would probably prefer
to avoid if possible the burdens posed by isotopic deviations for design,
fabrication, and maintenance of nuclear weapons, but it would also prob-
ably have the capabilities to cope with these burdens In ways that achieved
a level of weapon performance adequate for a proliferant state's initial
purposes. We rate importance of the isotopic barrier as "low" in the case
17See CISAC (1994, pp 29-33), CISAC (1995, pp. 43-46), and Department of Energy, Non-
proliferation and Arms Control Assessment of Weapons-Usable Fissile Material Storage and Excess
Plutonium Disposition Alternatives, Washington, DC: Department of Energy, January 1997,
pp. 37-39.
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30 SPENT-FUEL STANDARD FOR DISPOSITION OF EXCESS WEAPON PLUTONIUM
of theft for a subnational group because, although the weapon-related
capabilities of such a group would probably be lower than those of a
proliferant state, the subnational group would be likely to be much less
concerned about deviations from ideal performance inasmuch as a
lower-than-expected yield would still mean an explosive force more than
adequate for the likely purposes of such a group and probably less
concerned about radiation exposures to those making and handling the
weapons.
Relative importance of threat categories
For purposes of deciding which characteristics of dispositioned plu-
tonium forms are most germane to a determination of compliance with
the spent-fuel standard, it might be thought useful to ask which of the
three categories of threat is deemed to be of greatest concern. It is our
view, however, that the answer to this question is likely to vary with time
and with other circumstances. For present purposes, therefore, we give
equal weight to the three threat categories.
It is to be emphasized that none of these three classes of threat to
dispositioned plutonium will pose much danger of actually being carried
out until a time In the future when sources of plutonium in much more
convenient forms for proliferators have been considerably diminished
compared to their abundance today. The countries of greatest potential
concern in terms of host-nation breakout, for example, are Russia and the
United States, which will have the largest quantities of dispositioned plu-
tonium; but both countries are likely to retain, for some time to come,
such large quantities of deployed and reserve nuclear weapons and
reserve nuclear material, compared to any imaginable need, that it is
difficult to envision any incentive for them to want to recover plutonium
from the amounts they have declared excess and eligible for disposition.
With respect to the ''theft for proliferant state" and "theft for subnational
group" threats, various military and civilian stocks of already separated
plutonium and highly enriched uranium are likely to remain more attrac-
tive targets for proliferators than spent fuel or dispositioned plutonium
forms would be for some years to come.
It is, nonetheless, important to move forward now with plutonium
disposition- and, in that connection, important to determine the compli-
ance of candidate approaches with the spent-fuel standard both because
disposition of excess plutonium is a process that will require decades
under the best of circumstances (during which time it may be hoped that
the stocks of warheads, separated plutonium, and highly enriched ura-
nium will have been greatly reduced) and because, as the 1994 and 1995
CISAC plutonium reports emphasized, the barriers provided by pluto-
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CLARIFYING THE SPENT-FUEL STANDARD
31
nium disposition against host-state breakout have arms-control and non-
proliferation value through the signals they send (between the host states
and to the rest of the world) about the intended irreversibility of nuclear
arms reductions.
With these disclaimers, we conclude from the ratings in Table 1 that
the characteristics that should receive the most weight in the determina-
tion of a disposition form's compliance with the spent-fuel standard are
as follows.
(1) With respect to barriers to acquisition of the plutonium from its
storage site: (a) the concentration of plutonium in the items that
could be stolen, (b) the technical difficulty of partly separating the
plutonium from the bulkier components of the item on site, and
(c) the strength of the aids to detection of the items provided by
their thermal, chemical, and nuclear signatures.
(2) With respect to barriers to subsequent separation of the plutonium
from diluents and fission products: (a) the quantity of material
that needs to be processed to obtain a weapon's worth of pluto-
nium, (b) the technical difficulty of dissolution of the plutonium,
(c) the technical difficulty of chemical separation of the plutonium
from solution, and (d) the size of the aids to detection of these
activities provided by their thermal, chemical, and nuclear signa-
tures and the scale of the needed facilities.
Characteristics deserving somewhat smaller but still significant
weight in the determination of compliance with the spent-fuel standard
are the mass and bulk of the items that would need to be removed from
the storage site, the radiation and criticality hazards associated with acqui-
sition and processing of the material, and the deviation of the plutonium's
isotopic composition from "weapons grade."
3:
s
Representative terms from entire chapter:
final plutonium
