Publications
O9705
Australian Safeguards Office, Canberra ACT, Australia
IAEA-SM-351/64
Abstract
Current developments - including the increasing stocks of excess
fissile material from weapons dismantlement, plans to utilise
this material in power reactors or dedicated plutonium burning
reactors, and the prospect of separation of weapons-grade plutonium
from fast breeder reactor blankets - draw attention to the position
of low burn-up plutonium in the nuclear fuel cycle. This is not
just an issue for the future - there are already at least 100
SQs of very low burn-up plutonium under safeguards. Hence it is
timely to examine safeguards and non-proliferation issues related
to this material.
The situation which arose with the DPRK highlights the fact
that production of separated weapons-grade material by a non-nuclear-weapon
State should not be accepted as a normal activity. Even for nuclear-weapon
States, the proposal for a convention on the cut-off of production
of fissile material for weapons purposes has implications in this
regard. A proscription on the production - or separation - of
plutonium at or near weapons-grade would be an important confidence-building
measure in support of the disarmament and non-proliferation regime.
Although low burn-up plutonium, if available, would be of greatest
interest to a diverter, current safeguards practice does not provide
for the application of more rigorous safeguards measures to such
plutonium. There would seem a good case to take account of the
greater attractiveness of low burn-up plutonium and to apply safeguards
measures accordingly. Although the quantity of plutonium currently
under safeguards in this category is not insignificant, it is
a relatively small proportion of total safeguarded plutonium,
and a more intensive regime for such plutonium does not appear
to have major resource implications for the IAEA or facility operators.
The paper also touches on more general issues, such as implications
of the use of remote monitoring and the relevance of timeliness
goals.
1. INTRODUCTION
In response to the various demands and expectations placed
upon it, the IAEA is giving attention to the re-orientation of
safeguards resources to areas recognised as having highest priority,
and to a greater use of technology in order to enable the most
efficient use of available inspection resources. In this context
it is timely to examine safeguards issues related to plutonium.
To date the isotopic composition of plutonium has not been
a major issue for safeguards, because most plutonium under safeguards
is of a similar composition, ie "reactor-grade". The
IAEA applies similar safeguards measures to all plutonium, regardless
of isotopic composition, apart from an exemption for plutonium
containing 80% or more of the isotope Pu-238 [1]. This is a policy
position intended to reflect that all isotopes of plutonium are
fissionable by fast neutrons, and that theoretically a nuclear
explosive device, albeit perhaps of unpredictable yield, could
be constructed using any grade of plutonium. For IAEA safeguards
purposes all plutonium, even including that still in spent fuel,
is defined as "direct-use" material, ie material that
can be used for the manufacture of nuclear explosives.
This policy position is underscored by reference to the announcement
by the US in 1977, that in 1962 it had successfully conducted
an underground test of an explosive device made from "reactor-grade"
plutonium [2]. Additional information concerning the test, including
the fact that the yield was less than 20 kilotons, was provided
by the US Department of Energy (DOE) in June 1994 [3]. In accordance
with DOE policy not to reveal the actual isotopic composition
of plutonium used in specific weapons or tests, the US has never
revealed the isotopic quality of the plutonium used in the 1962
test. At the time of this test the definition of "reactor-grade"
plutonium was substantially different to the contemporary definition,
which encompasses an intermediate category, "fuel-grade",
recognised since the 1970s - ie the definition of "reactor-grade"
used in the 1960s had an isotopic content of just over 7% Pu-240
as its lower boundary, compared with the current definition which
has an isotopic content of 19% Pu-240 as its lower boundary. There
are suggestions that the material used in the 1962 test was what
would now be termed "fuel-grade," probably closer to
the weapons-grade end of the fuel-grade range [4].
The point of this discussion is, not to contend that a nuclear
explosive device could not be made from reactor-grade plutonium,
or that reactor-grade plutonium is unattractive for potential
proliferants, but rather to note that the argument about the efficacy
of reactor-grade plutonium has obscured the case for a more rigorous
approach to plutonium having an isotopic composition much closer
to that actually used in nuclear weapons.
2. ISSUES DISCUSSED IN THIS PAPER
This paper argues that from the non-proliferation perspective,
clearly it is preferable to avoid the production of significant
quantities of plutonium at or near weapons-grade, even if under
safeguards. This is not to imply that safeguards are inadequate,
but rather to recognise that such a development could engender
fears about what might happen to the material in the future, eg
if the State concerned were to renounce the NPT. Thus the production
of plutonium at or near weapons-grade could undermine the confidence
which safeguards are intended to provide. The point can be illustrated
by reference to the DPRK - had that State been in full compliance
with its safeguards agreement, it might now be accumulating weapons-grade
material with legal impunity.
Fuel cycle technologies have inherently differing levels of
proliferation risk, which affect the assurance required from international
safeguards measures [5]. From the safeguards perspective, this
paper argues it should be recognised that if diversion of plutonium
were attempted, low burn-up material would be the most attractive
target. Hence it is prudent to apply more rigorous safeguards
measures to such material. This could be done in the context of
a general re-orientation of safeguards resources to areas recognised
as having greater priority. Practical aspects of doing this are
discussed below.
Although not specifically covered in this paper, similar considerations
arise in the case of uranium-233, which is a product of the thorium
fuel cycle. U-233 is a fissile material which theoretically could
be used for nuclear weapons, and as such is subject to the same
safeguards requirements as U-235. The authors suggest that the
non-proliferation and safeguards aspects of the thorium fuel cycle,
particularly the separation of U-233, should be examined in line
with the discussion in this paper of plutonium issues.
The paper does not attempt to canvass the non-proliferation
issues related to storage, conversion, stabilisation and disposition
of weapons-grade plutonium released from dismantled weapons and
declared excess to national security needs [6].
3. DEFINITIONS OF PLUTONIUM GRADES
Before proceeding any further, it will be useful to take up
some questions of definition. Without wishing to prejudge the
definitions of "high burn-up" and "low burn-up"
plutonium which might be adopted for future safeguards/non-proliferation
purposes, attention is drawn to the following DOE definitions
which are in general use [7]. Prior to the 1970's, there were
only two terms in use (by DOE) to define plutonium grades: weapons-grade
(£7% Pu-240) and reactor-grade (>7% Pu-240). In the early
1970's, the term fuel-grade (>7 - <19% Pu-240) came into
use, which shifted the starting point of the reactor-grade definition
(³19% Pu-240).
"Weapons-grade" plutonium (WGPu) contains no more
than 7% of the isotope Pu-240. WGPu is produced in heavy water-
or graphite-moderated production reactors fuelled with natural
or slightly enriched uranium. All production reactors are on-load
refuelled to allow for short fuel irradiation times. Within weapons-grade
there is the sub-category of "super-grade" plutonium
(SGPu), containing no more than 3% Pu-240.
Another way to produce WGPu is through irradiation of U-238
by fast neutrons. Such are the conditions in the (natural or depleted
uranium) blanket of a Liquid Metal Fast Breeder Reactor (LMFBR).
The composition of plutonium produced in the blanket of a LMFBR
(about 4% Pu-240) places it in the WGPu category.
WGPu can inadvertently be produced in power reactors. In the
early 1970s, this happened, for example, in the US when leaking
fuel rods caused the utility operating the Dresden-2 reactor to
discharge the entire initial core containing a few hundred kg
of plutonium with 89-95% Pu-239 [8].
"Fuel-grade" plutonium (FGPu) contains more than
7%, but less than 19%, of the isotope Pu-240. FGPu is produced
in some nuclear reactors that have a spent fuel burn-up lower
than that resulting in reactor-grade plutonium, but higher than
that resulting in WGPu. For example, FGPu is often produced in
tritium production reactors. FGPu can also be produced in power
reactors, in initial core loads and in damaged fuel discharged
after one year's irradiation.
"Reactor-grade" plutonium (RGPu) is produced in power
reactors and contains 19% or more of the isotope Pu-240. In general,
plutonium derived from current commercial light- and heavy-water
reactors contains around 50-65% Pu-239, the remainder being largely
Pu-240 and heavier isotopes of plutonium. As there are many types
of power reactors, and differences in fuel composition, coolant
and moderator system and burn-up level, plutonium commonly called
RGPu can have various isotopic compositions, as illustrated in
Table I. For the current generation of fuel, 60,000 MWd/t is seen
as the limit, but eg DOE budget documents for FY 1998 show that
the Department hopes to develop an advanced LWR fuel capable of
reaching burn-ups of 100,000 MWd/t with enrichment levels of 5%
U-235 [9].
Discharge from Power Reactors [10]
GWd/t
GCR
3.6
77.9
18.1
3.5
0.5
PHWR
7.5
66.4
26.9
5.1
1.5
AGR
18.0
53.7
30.8
9.9
5.0
RBMK
20.0
50.2
33.7
10.2
5.4
BWR
27.5
59.8
23.7
10.6
3.3
PWR
33.0
56.0
24.1
12.8
5.4
It should be noted that the plutonium isotope composition in
the reactor core is not evenly distributed. Hence the figures
discussed here for plutonium composition are average figures for
discharged fuel. Even though fuel assemblies are moved around
during refuelling, some parts of fuel rods will have a plutonium
isotope composition closer to that of WGPu.
There is an additional sub-category: "MOX-grade"
plutonium (MGPu), containing about 30% or more Pu-240 (MOX = mixed-oxide,
ie a uranium and plutonium mix). MGPu is recycled plutonium, the
plutonium in irradiated MOX--fuel made of RGPu.
4. ATTRACTIVENESS OF LOW BURN-UP PLUTONIUM
Irrespective of the arguments on what is theoretically possible
with RGPu, there is no doubt that plutonium at a suitably low
burn-up level is extremely attractive for nuclear weapons purposes,
and that RGPu is less so.
The higher plutonium isotopes (especially Pu-240 and Pu-242)
have substantially higher spontaneous fission rates than Pu-239,
hence are prone to cause "pre-initiation" during a nuclear
explosion (adversely affecting reliability and yield). Decay of
the higher isotopes is also a cause of radiation and heat problems.
A further problem, from the weapons perspective, is the Pu-238
content of higher burn-up plutonium. A number of commentators
have noted that the isotopic composition of plutonium has a marked
influence on its effectiveness for first generation weapon designs
[11].
The particular attractiveness of WGPu is illustrated by former
US practices and programs (no doubt similar examples can be found
in the military programs of other weapon States):
- plutonium blending - at one time it was US practice to extend
its stocks of WGPu through the dilution of FGPu with SGPu - a
clear indication that fuel-grade plutonium was not considered
desirable for weapons produced at that time; - Fuel Segregation Program - this involved extraction of WGPu
which was present in some fuel-grade assemblies; - Special Isotope Separation Program - several countries have
undertaken research on technology for plutonium isotope separation.
The US had a program in this area in the 1980s. Amongst the objectives
were the enrichment of RGPu recovered from commercial power reactor
spent fuel, or FGPu from the military program.
The point can be made, that if the foremost nuclear-weapon
State was unwilling to produce weapons from FGPu, neither reactor-grade
nor even fuel-grade would be the material of first choice for
a would-be diverter. Certainly there would be a premium on obtaining
plutonium of the lowest possible Pu-240 content, if possible of
weapons-grade or at least at the lower end of fuel-grade.
Reduced Shielding Requirements
Apart from questions of weapon performance, there is another
reason for lower burn-up plutonium to be more attractive for diversion.
Current safeguards approaches take into account the fact that
spent fuel elements in reactor storage ponds are highly radioactive.
This consideration led to the assumption that the conversion time
(ie the time which would be required to convert the material concerned
into the metallic components of an explosive device) for irradiated
fuel in clandestine reprocessing activities would be increased
considerably by the need for shielding. In addition to such activities
being slower than for unirradiated material, the facilities would
be more expensive and require sophisticated remote handling equipment.
Plutonium from low burn-up spent fuel, however, particularly
if it has also had a long cooling time, would have substantially
reduced shielding requirements [12], needing a much less massive
facility than current reprocessing plants. For such material,
after one cycle of solvent extraction (or ion exchange) downstream
processing requirements could possibly be reduced to glove-box
systems. Clandestine facilities of this kind could be extremely
difficult to detect.
5. PLUTONIUM CURRENTLY UNDER SAFEGUARDS
At the end of 1996, there were some 586.4 tonnes of plutonium
under IAEA safeguards. 528.2 tonnes were contained in irradiated
fuel, 53.7 tonnes comprised separated plutonium outside reactor
cores, and 4.5 tonnes were in the form of recycled plutonium in
reactor cores [13]. These figures include plutonium in reactor
cores. A significant fraction of the plutonium undergoing irradiation
in reactor cores is of low burn-up, though this situation will
have changed by the time the fuel is discharged.
Currently almost all the plutonium arising in the civil fuel
cycle is from the normal operation of "thermal" reactors.
Such plutonium is of high burn-up, well outside the range defined
as weapons-grade. There are some exceptions, however, where the
production of irradiated fuel containing low burn-up plutonium
will be unavoidable - for LWRs, the examples of initial core loads
and damaged fuel have been mentioned already. The content of higher
plutonium isotopes in such fuel, while normally above that of
weapons-grade material, is sufficiently low to warrant special
safeguards attention.
The normal operation of on-load refuelling reactors (eg certain
gas-graphite and heavy water reactors) can also result in some
low burn-up fuel. Defective fuel is removed from PHWRs using the
same normal refuelling procedures that are in place for removing
intact fuel, and is generally treated no differently from normally
discharged fuel [14]. However, defective fuel at some stations
is stored in a special location. Reinsertion of failed fuel is
not practised at PHWRs, for economic reasons. Apart from damaged
fuel, fuel assemblies from the outer fuel channels would have
lower burn-up levels.
Burn-up levels from the operation of various reactor-types
are illustrated in Table II.
|
Reactor type |
Burn-up level corresponding to WGPu (7% Pu-240) |
Burn-up level in typical initial cores |
Burn-up level from normal operation |
|---|---|---|---|
|
PWR |
4.8 |
14 |
33.0 |
|
PHWR |
1.6 |
n/a |
7.5 |
|
RBMK |
2.0 |
n/a |
20.0 |
|
GCR |
1.0 |
n/a |
3.6 |
The IAEA does not publish figures showing how the plutonium
is distributed by category, or at least by reactor type. But recently
the information indicated in Table III was made available to the
authors.
Table III. Distribution of plutonium in spent fuel of LWRs
under safeguards by category [15] (as of 31.10.96)
under safeguards by category [15] (as of 31.10.96)
Burn-up range, GWd/t
1.0-5.0
5.0 - 10.0
10.0 - 15.0
>15.0
(corresponding to WGPu)
(corresponding to FGPu)
(corresponding to RGPu)
0.06
0.74
4.20
152.4
0.04
0.47
2.67
96.82
It can be seen from Table III that, of the civil plutonium
currently under IAEA safeguards, there are at least 800 kg in
the very low burn-up category (<10.0 GWd/t - corresponding
to weapons-grade and the lower end of fuel-grade), and a further
4.2 tonnes in the upper range of fuel-grade. It should be noted
these figures relate only to LWR fuel, and do not take into account
low burn-up plutonium which may exist elsewhere.
At present there are limited quantities of separated weapons-grade
plutonium under safeguards. There are small quantities in laboratory
use, and there are critical assemblies which use such material
in the form of coupons. The major source of weapons-grade plutonium
under safeguards is excess plutonium from dismantled weapons.
Currently this material is confined to the nuclear-weapon States,
though there have been some suggestions that ex-weapons plutonium
might be transferred to non-nuclear-weapon States for use in MOX
fuel.
In the future, another major source of low burn-up plutonium
will be the blanket material from fast breeder reactors (FBRs).
FBR blankets will contain plutonium well within the weapons-grade
range, even of "super-grade" (around 3% Pu-240). While
it is commonly assumed this is not an immediate issue, because
there has been a slow-down of FBR development, there are currently
a number of FBRs and FBR demonstration projects. The Japanese
reactor Monju is one example - depending on when Monju is restarted,
blanket material could be being reprocessed within the next 3-4
years. It is reported that France has obtained WGPu from reprocessing
blankets from the Rapsodie and Phénix prototype FBRs at
Marcoule [16].
6. NON-PROLIFERATION ISSUES
The Canberra Commission on the Elimination of Nuclear Weapons
was an international group of experts on security and disarmament
issues convened by the Australian Government to develop ideas
and proposals for a concrete and realistic program to achieve
a world totally free of nuclear weapons. One of the conclusions
in the Commission's Report, presented in August 1996, was that:
"A prohibition on production of all nuclear material at
or near weapons grade may prove a practical step of considerable
value in support of the eventual elimination of nuclear weapons
and could be included in the proposed cut-off convention or a
complementary international agreement" [17].
A proscription on the production of plutonium at or near weapons-grade
would be an important confidence-building measure in support of
the non-proliferation regime. As noted earlier, in the case of
production of significant quantities of weapons-grade material
the application of safeguards measures, though technically sound,
might not provide the requisite degree of assurance about the
future intent of the State concerned.
Weapons-grade plutonium has very limited use in civil nuclear
activities, and there is no legitimate civil (or military) requirement
for such materials which could not be met from existing stocks.
Therefore a proscription on the production of low burn-up plutonium
should not cause practical difficulties. There is a clear case
for an international norm to this effect.
In addition to current operating situations where production
of low burn-up plutonium cannot be avoided, potentially there
will be large-scale arisings of low burn-up plutonium in the blanket
material from fast breeder reactors. Since in the future production
of blanket material will be the major reason for operating FBRs
(ie to obtain plutonium for recycle), obviously it is not practicable
to proscribe the production of such plutonium in irradiated blanket
material. The real sensitivity over very low burn-up plutonium
arises where it exists as a separated product, in other words
if it is reprocessed so as to recover unirradiated low burn-up
plutonium.
The concerns relating to the unavoidable production of low
burn-up plutonium can be alleviated if there were an undertaking
not to reprocess so as to separate such plutonium in unirradiated
form. Where reprocessing of low burn-up material is proposed,
arrangements could be put in place to ensure that it is reprocessed
in stream with high burn-up material, such as FBR core fuel or
LWR fuel, so that the resultant product will have a sufficiently
high proportion of the higher plutonium isotopes. Obviously there
is a need to adopt a definition which will avoid undue practical
problems for industry while meeting non-proliferation objectives.
Definitional issues are discussed further in Section 8 of this
paper.
It is recognised there may be some economic penalty in the
reprocessing arrangements outlined here, but the States concerned
should be prepared to accept such costs in the broader interest
of the international security environment.
Japan, which is proceeding with an FBR development and demonstration
program, has indicated in-principle commitment to the approach
outlined above, through a policy of blending, with reactor-grade
plutonium, low-burn-up plutonium recovered during experimental
reprocessing of FBR blanket material [18]. While commitments by
individual States are important, clearly multilateral commitments
will have greater effect. Consideration should be given to mechanisms
for achieving this. As the Canberra Commission has suggested,
one avenue is to address a general proscription on the separation
of low burn-up plutonium as part of, or in parallel to, the development
of proposals for a cut-off convention.
7. SAFEGUARDS ISSUES
Since it is a primary objective of safeguards to address the
possibility of diversion, and it is difficult to escape the conclusion
that low burn-up material would be most attractive to a would-be
diverter, the assurance provided by safeguards would be enhanced
if they were to place particular emphasis on such material.
If low burn-up plutonium is to receive special safeguards attention,
what kind of measures might be taken? In terms of current safeguards
practice, two parameters are particularly relevant in determining
the inspection regime: timeliness and detection probability. If
the current safeguards system were to continue unchanged, the
authors would propose changes to both these parameters in order
to recognise the sensitivity of low burn-up plutonium.
Timeliness
The current concept of timeliness is intended to reflect possible
conversion time, ie the time which would be required to process
plutonium into weapon components. For unirradiated plutonium,
the timeliness goal is one month. The adequacy of this goal is
debatable, especially where material more attractive for diversion
is involved. For example, it is noted that the Agency has considered,
though not introduced, a shorter timeliness goal, two weeks, for
unirradiated plutonium in metallic form. Under the current concept
of timeliness, isotopic composition is not taken into account,
as it is not considered directly relevant.
However, isotopic composition can be relevant to timeliness.
As discussed in Section 4, low burn-up fuel has significantly
lower radiation levels, resulting in reduced shielding requirements.
A shorter conversion time may well be possible compared with the
diversion assumptions on which the current three months timeliness
goal for irradiated material is based. Accordingly, in principle
it can be argued that the timeliness goal for low burn-up material
should be less than three months. Rather than propose a new timeliness
goal, say six weeks, which would be necessarily arbitrary, the
authors suggest this might be the same as for unirradiated plutonium,
ie one month (assimilating low-irradiated fuel to fresh MOX fuel).
Another question is whether the timeliness goal could be extended
for very high burn-up fuel, say above 30% Pu-240 (essentially,
plutonium recycled in MOX fuel), for example six months instead
of three. This is difficult to justify under the current concept
of timeliness, which is based on conversion time. The radiation
levels of high burn-up fuel are not sufficiently different to
those of normal burn-up fuel to have a significant effect on shielding
requirements, hence conversion time. Further, since high burn-up
fuel is likely to be stored with fuel of normal burn-up, the practical
benefit of a longer timeliness goal is not clear. On the other
hand, this issue might be examined further when we reach the point
where MOX fuel is being reprocessed. Plutonium which has undergone
two or more cycles will have a very high Pu-240 content, and it
is questionable whether the current timeliness requirement of
monthly inspections for unirradiated plutonium would be warranted
for plutonium of this quality.
Detection probability
This refers to the probability, if diversion of a given amount
of nuclear material has occurred, that verification activities
will lead to detection. The Agency's current detection probability
goals for plutonium depend on the form of the plutonium and on
the particular circumstances - for separated plutonium it is "high",
90%; for spent fuel under INFCIRC/153 safeguards, without containment
and surveillance (C/S), it is "medium", 50%; where there
is satisfactory C/S then in some situations the detection goal
will be "low", 20%, or verification might consist only
of an item count.
Detection probability is based largely on sampling and measurement
plans. If low burn-up plutonium were to receive special attention,
for a start it would be necessary to specifically identify it
as such, so that it could be subjected to a specific sampling
and measurement plan. Because at present there are limited holdings
of unirradiated low burn-up plutonium, identification should be
straightforward. In the case of irradiated low burn-up plutonium,
it would be necessary to identify the particular fuel elements
concerned. The verification task would be simplified if these
fuel elements were grouped at a particular place in the spent
fuel pond.
Low burn-up plutonium having been specifically identified,
the authors suggest that its attractiveness be recognised by increasing
the relevant detection probability goal by one level, ie where
"low" would otherwise apply the goal should become "medium",
and so on.
The Strengthened Safeguards System (SSS)
Under current safeguards procedures, prima facie the adoption
of a reduced timeliness goal would require more frequent inspections.
Likewise, achievement of a higher probability goal would require
more inspection effort. The SSS however will provide the opportunity
to obtain the additional assurance appropriate to low burn-up
plutonium and at the same time to make substantial efficiency
gains.
In particular, remote monitoring has the capability to allow
the monitoring of events in or close to real-time, thereby achieving
much shorter timeliness targets than can be attained through regular
inspections. Thus remote monitoring can reduce inspection costs
while at the same time increasing safeguards effectiveness. For
these reasons the IAEA is working towards the widespread application
of remote monitoring technologies.
Remote monitoring has major implications for current concepts
of timeliness. It can be argued that if a remote monitoring system
is well-designed and reliable, the current concept of timeliness
would cease to have any practical application. If it is considered
that some additional assurance is needed as to the ongoing integrity
of the remote monitoring system (eg that it has not been defeated
in some way), this could be provided through unannounced inspections.
Unannounced inspections will form an important part of new safeguards
approaches, serving a number of purposes, one of which could be
to complement remote monitoring in this way. Whether the concept
of timeliness should be a factor in determining the incidence
of unannounced inspections would seem to merit further study.
Practical implications for safeguards
As indicated at Table III, the proportion of plutonium currently
under safeguards derived from burn-up of 15,000 MWd/t or less
is around 3% (note this figure applies only to LWR fuel). Information
available to the authors indicates there are currently some 120
LWRs (ie ¾ of those under safeguards) with start-up fuel
or spent fuel which has been unloaded after 1 year, which would
fall into this category.
Key features of a safeguards approach suggested for low burn-up
spent fuel might include the following:
- low burn-up fuel would be specifically identified and if
possible grouped together in a separate location in the storage
pond (if this is not already the case); - taking into the account the characteristics of each facility,
an integrated remote surveillance system would be installed,
to monitor flask loading and above-water movements. Underwater
cameras might be included to provide additional coverage of activity
in the pond, particularly if fuel element disassembly and pin
exchange were practiced at the facility. Consideration might
be given to the desirability of dual C/S systems covering the
low burn-up portion of the spent fuel inventory; - one sense in which timeliness issues are relevant to remote
monitoring concerns the frequency both of data transmission and
data evaluation. If an event is detected which requires investigation,
by enquiry or possibly by unannounced inspection, the time-frame
within which this can occur must bear an appropriate relationship
to the nature of the material involved. For low burn-up material
data would be transmitted close to real-time (at least daily),
and reviewed as soon as practicable (for less sensitive material,
the interval both for transmission and for evaluation might be
lower, for example weekly); - in the event of inconclusive surveillance, the low burn-up
portion of the inventory would be subject to a higher detection
probability goal, as discussed above; - where there is a significant inventory of low burn-up fuel
at an LWR, it is a matter for consideration whether that facility
would receive on average only one unannounced inspection per
year, or should receive more than this. A pragmatic approach
may be to allocate an additional unannounced inspection (ie a
total of two during the year) to some such LWRs selected on a
random basis.
A strengthened safeguards approach for unirradiated low burn-up
plutonium might include dual C/S remote monitoring with real-time
or near real-time data transmission and review, and a higher incidence
of unannounced inspections.
Conclusions
Two points which emerge from the foregoing discussion are:
that there is not necessarily a direct correlation between the
current concepts of timeliness, detection probability and the
strategic value of different nuclear material; and that in any
event timeliness will have much less relevance where remote monitoring
is deployed.
Assuming that low burn-up plutonium will not normally be produced
or separated (in accordance with the proposals in this paper),
but that more rigorous safeguards arrangements would apply where
this does occur, then it does not appear that the increased inspection
load on the IAEA will be substantial. It is recommended that the
Agency make a detailed study of the disposition of low burn-up
material and practical measures to provide adequate assurance
with respect to this material.
8. DEFINITION OF "LOW BURN-UP" FOR NON-PROLIFERATION/SAFEGUARDS
PURPOSES
As mentioned earlier, it will be important to determine a criterion
for "low burn-up" which does not cause undue practical
difficulties for facility operators and the IAEA, while at the
same time meeting non-proliferation concerns. Is the appropriate
dividing point fuel-grade, ie just under 19% Pu-240, or might
some lower figure be considered?
It is understood one figure which has been looked at informally
within the IAEA is 17% Pu-240. This would still be well outside
the weapons-grade range, and may be a satisfactory figure for
the purposes discussed here. Application of the 17% figure would
have some practical benefit, in reducing the total quantity of
plutonium which would require more rigorous safeguards procedures
under the "low burn-up" category. From the limited information
available, it would appear the total number of fuel elements falling
within the "low burn-up" category might be halved. On
the other hand, the additional safeguards effort involved does
not appear to be onerous, and any saving might be considered marginal
compared with additional assurance derived from applying the higher
(19%) figure.
9. CONCLUSIONS
As a consequence of most plutonium under safeguards to date
being "reactor-grade", the isotopic composition of plutonium
has received only limited attention. Events in the DPRK serve
to highlight an issue which, in the absence of appropriate action,
can be expected to assume increasing importance - that the production
and possession of significant quantities of plutonium at or near
weapons-grade has the potential to undermine the confidence on
which the non-proliferation regime is built. Accordingly, the
authors argue that such material should be subject to the most
rigorous control - the most effective measure being to limit its
production and separation to the greatest possible extent.
There is a view that safeguards and non-proliferation measures
should not differentiate between plutonium grades, because this
might be seen as minimising the proliferation risks of reactor-grade
plutonium and could lead to pressure to reduce controls on such
plutonium. A reduction in controls on reactor-grade plutonium
is by no means a natural consequence of differentiating between
plutonium grades, however, and such a reduction is not advocated
in this paper. Rather, the concern is that ignoring the different
degrees of attractiveness resulting from isotopic composition
could be counter-productive to non-proliferation objectives.
The authors suggest that an outline of a non-proliferation
approach satisfactorily addressing the issue of low burn-up plutonium
might contain the following elements:
(a) States would refrain from any avoidable production of
low burn-up plutonium, eg through abnormal operation of reactors;(b) reprocessing would not be undertaken so as to obtain low
burn-up plutonium as a separated product (low burn-up plutonium
would be reprocessed in stream with high burn-up material);(c) where possible, accumulation of low burn-up fuel would
be avoided - where a State uses reprocessing (by itself or by
another State) as part of its spent fuel management strategy,
low burn-up fuel would be given priority (with reprocessing carried
out in accordance with (b) above);(d) where significant quantities of unirradiated weapons-grade
plutonium are held, eg for critical assemblies, consideration
would be given to the possibility of replacing that plutonium
by non-weapons-grade plutonium (similar to the international
program to convert research reactors from HEU fuel);(e) existing stocks of unirradiated low-burn-up plutonium
would be diluted, or given priority for fuel fabrication, or
permanently disposed of.
While non-proliferation arrangements along these lines can
limit the production of low burn-up plutonium, where such plutonium
does exist there is the question whether current safeguards measures
are appropriate. If diversion of plutonium from safeguards were
contemplated, it seems reasonable to assume that low burn-up plutonium
would be of greatest interest to the diverter. The assurance derived
from safeguards would be enhanced if safeguards approaches took
this into account.
Where there are significant holdings of unirradiated plutonium,
it is debatable whether the current timeliness goal of one month
is appropriate as far as low burn-up plutonium is concerned, and
remote surveillance with real-time, or near real-time, reporting
to the IAEA would represent a considerable improvement. It can
also be argued that the current timeliness goal of three months
for irradiated plutonium is not appropriate in the case of low
burn-up plutonium - while this conclusion might suggest the need
for more frequent timeliness inspections, these could be obviated
through the introduction of remote monitoring. In the case of
both unirradiated and irradiated plutonium, unannounced inspections
would be an important part of the safeguards approach. In addition,
an increased concentration of verification activities is suggested
for low burn-up plutonium.
Having regard to the relatively small proportion of plutonium
currently under safeguards which is in the low burn-up category,
a more intensive regime for such plutonium would not appear to
have significant resource implications for the IAEA, nor to create
any particular difficulty for facility operators.
REFERENCES
[1] INFCIRC/153, paragraph 36 (c).
[2] See eg GILLETTE, R., "US Test Shows Nuclear Bombs
Can Be Made From Low--Grade Plutonium", Washington Post,
September 13, 1977.
[3] "Additional Information Concerning Underground Nuclear
Weapon Test of Reactor-Grade Plutonium", DOE Facts (1994)
186-7.
[4] See for example, the French Government publication "L'énergie
nucléaire en 113 questions" (1996) 113.
[5] PERSIANI, P.J., "Comments on Fuel Cycle Concepts and
Impacts on Non-Proliferation and Safeguards Concerns", Proceedings
of 19th ESARDA Annual Symposium (1997).
[6] See eg JAEGER, C., et al., "Joint US/Russian Plutonium
Disposition Study. Nonproliferation Issues", 37th Annual
Meeting Proceedings of the Institute of Nuclear Material Management,
Naples, Florida (1996) 884-889.
[7] See eg "Plutonium: The First 50 Years. United States
Plutonium Production, Acquisition, and Utilisation from 1944 to
1994," DOE (1996).
[8] WOHLSTETTER, A., "Spreading the Bomb Without Quite
Breaking the Rules", Foreign Policy, vol. 25 (Winter 1976/1977)
88-96, 145-179.
[9] HURIO, E., "DOE Program Aimed at Stretching Fuel Burnup
to 100,000 MWd/MT," Nuclear Fuel, February 24, 1997, 3.
[10] Compiled from a number of sources.
[11] MEYER, W., et al., "The Homemade Nuclear Bomb Syndrome",
Nuclear Safety, vol. 18, no 4 (1977) 427-418; VON SEIFRITZ, W.,
"Remarks on the Plutonium-240 Induced Pre-Ignition Problem
in a Nuclear Device", Nuclear Technology, vol. 54, no. 3
(1981) 431; CARSON MARK, J., "Nuclear Weapons Technology",
in FELD, B.T., et al. eds., "Impact of New Technologies on
the Arms Race: A Pugwash Monograph", MIT Press (1971) 133-138;
"Can Terrorists Build Nuclear Weapons", in LEVENTHAL,
P., YONAH, A., eds., "Preventing Nuclear Terrorism: The Report
and Papers of the International Task Force on Prevention of Nuclear
Terrorism," Lexington Books (1987) 91-103; "Reactor-Grade
Plutonium's Explosive Properties," Nuclear Control Institute,
Washington DC (1990); GARWIN, R.L., "Explosive Properties
of Various Types of Plutonium", paper presented at NATO Advanced
Research Workshop "Managing the Plutonium Surplus: Applications
and Options," Chatham House, London (1994).
[12] BRAGIN, V., ONG, L., "Radiation Levels Associated
with Nuclear Reactor Spent Fuel", IAEA, STR-287 (1992).
[13] IAEA Annual Report for 1996, 74.
[14] MACDONALD et al., "Detecting, Locating and Identifying
Failed Fuel in Canadian Power Reactors," Report AECL 9714.
[15] Information received from the IAEA.
[16] ALBRIGHT, D., BERKHOUT, F., and WALKER, W., "World
Inventory of Plutonium and Highly Enriched Uranium 1992,"
SIPRI, Oxford University Press (1993) 44.
[17] "Report of the Canberra Commission on the Elimination
of Nuclear Weapons", Department of Foreign Affairs and Trade,
Australia (1996) 93.
[18] "Outline of 1993 White Paper on Nuclear Energy, Atomic
Energy Commission General Remarks", Japan (1993) 11.