Preventing Nuclear-explosive Terrorism by Eliminating Fissile Material:
A Progress Report
Frank von Hippel, co-chair, International Panel on Fissile Materials
Program on Science and Global Security, Princeton University
The mission of the International Panel on Fissile Materials is to develop the basis of initiatives to
secure, to consolidate, and to reduce global stocks of nuclear weapon usable fissile materials.
Fissile materials (primarily highly enriched uranium (HEU, uranium enriched to more than 20%
U-235) and separated plutonium) are essential in all nuclear weapons, and controlling and
reducing their stocks is critical to all efforts to reduce nuclear-weapon stockpiles, increase
barriers to proliferation and prevent nuclear terrorism. This paper is a progress report on this
effort.
Global stocks of fissile material
The fission of 1 kg of plutonium or HEU releases energy equivalent to the explosion of about
17,000 tons of chemical explosive – approximately the yield of the explosions that destroyed
Hiroshima and Nagasaki. Figures 1 show national declarations and non-governmental estimates
(indicated by asterisks) of stocks of HEU and plutonium of the weapon states, some key nonweapon states and the other non-weapon states collectively for 2011. The total is about 2,000 tons
of fissile material, enough for over 100,000 nuclear explosives. In fact, in 1967, the U.S. had
about 31,000 nuclear warheads and, in the mid 1980s, the Soviet Union is believed to had about
40,000 warheads.1
Figure 1a. Global stocks of HEU currently total about 1500 tons– sufficient (at 25 kg per warhead) for
60,000 nuclear warheads (Ref. Global Fissile Material Report 2011, GFMR2011).
Figure 1b. Global stocks of separated plutonium currently total about 500 tons – sufficient (at 8 or 4 kg
per warhead for 60,000 or 120,000 warheads. (Ref. GFMR2011).
Securing, consolidating and eliminating nuclear material
Securing. Russia accounts for about half of the global HEU and one third of the separated
plutonium stock. After the collapse of the Soviet Union, the U.S. was greatly concerned about the
security of fissile materials and nuclear warheads in Russia and has spent about $10 billion
dollars in upgrading security there. This effort continues today.
Processing
High Security
Area Boundary
Storage
1.6 km
Figure 2. Consolidation at the Y12 HEU site in Oak Ridge, Tennessee. Historically, all U.S. HEU weapon
component fabrication, dismantlement and HEU central storage has taken place in the complex of
buildings within the heavy line. Two fortified buildings, will replace this complex: one for HEU storage
(complete) and one for processing (under construction).
Consolidating. The U.S. Department of Energy (DoE) spends more than $1 billion per year on
nuclear-material security at its own facilities. This has motivated a considerable amount of
consolidation. The DoE is cleaning plutonium and HEU out of two of the three U.S. nuclear
weapons labs (Livermore, California and Sandia, New Mexico) as well as other DoE sites. On
sites where significant quantities will remain, the material is being consolidated the into highsecurity buildings (Figure 2).
Eliminating. Russia and the U.S. have eliminated a great deal of HEU and are planning on
eliminating a considerable amount of excess weapons plutonium as well.
2
The white areas in Figure 1a show that Russia and the U.S. together have blended down about
600 tons of excess HEU to 4 to 5 percent low-enriched uranium (LEU). They are committed to
blend down about 100 tons more. The LEU is being used mostly to fuel U.S. nuclear power
plants (more than half of U.S. nuclear capacity). The blend-down of the 500 tons of HEU that
Russia has committed to dispose has been at a level of 30 tons per year for about 15 years and
will be completed in 2013. The blend-down rate of excess U.S. HEU has dropped from about 10
tons per year to about 3 to 4 tons a year, due to bottlenecks in the warhead and HEU-component
dismantlement process and currently is expected to take a decades or more to complete.
Much more HEU could be blended down. A global nuclear arsenal of about 10,000 nuclear
warheads – roughly the situation today, not counting warheads in the dismantlement queue –
would require only about 250 tons of weapon-grade (90+% U-235) HEU, vs. the approximately
1000 tons that are in the weapon-state military stockpiles.
Russia and the U.S. also each are committed to converting into fuel 34 tons of weapon-grade
plutonium. Both are building “mixed-oxide” (MOX, uranium-plutonium) fuel-fabrication
facilities. The U.S. plans to produce MOX for once-through use in light-water reactors while
Russia plans to produce MOX for fast-neutron breeder reactors, which require plutonium recycle.
Russia therefore will not be permanently disposing of its separated weapons plutonium but rather
simply will be passing this plutonium through breeder reactors into its stockpile of separated
civilian plutonium.
Much more weapons plutonium could be declared surplus. A global stockpile of about 10,000
warheads would require only about 40 tons of weapon-grade plutonium, vs. approximately 140
tons in the weapon stockpiles today.
Reducing the use of HEU and separated plutonium for reactor fuel
The principal non-weapon use of HEU and plutonium is in nuclear fuel.2 HEU is used in
research reactor fuel in about 30 countries, and in naval reactor fuel in the US, UK, Russia and
India. Plutonium is recycled in MOX fuel in light-water reactors in France, and soon, in
prototype breeder reactors in India and Russia. Japan has been planning to recycle plutonium in
light water reactors. China has breeder reactor plans.
In all of these uses, there is a risk of diversion to weapons. After India’s use of civilian plutonium
for a “peaceful nuclear explosion” in 1974, the U.S. abandoned civilian reprocessing at home and
actively tried to prevent the spread of plutonium separation to new countries and to minimize
HEU fuel use in research reactors. Only in the case of HEU-fueled civilian research reactors,
however, is there a real international consensus on minimization of the use of weapon-usable
fissile materials in reactor fuel. Plutonium separation continues in Europe, Japan, Russia, India
and China.
Research reactors. Since 9/11, the U.S. has led an intensified campaign to convert the world’s
HEU-fueled research reactors and medical fission isotope production targets to LEU (in practice
uranium enriched to 19.75% U-235). This is an appropriate priority, since research reactor
facilities are often not as secure as are facilities where nuclear weapons are assembled and
disassembled and where naval reactor fuel is manufactured.
The technical approach that is being used is to develop fuels with roughly five times higher
uranium density than the current fuels containing weapon-grade (> 90% U-235) uranium. This
density increase makes it possible to add U-238 to reduce the enrichment of the uranium without
reducing the concentration of the U-235. The HEU densities mostly are below 1.5 gms/cc. Thus
far, fuels with densities up to 4.8 gms/cc have been developed and fuels with LEU densities up to
15 gm/cc are under development.
3
-Mexico, Ukraine
-Taiwan; Libya, Romania
-Greece
- South Korea
-Denmark, Portugal, Sweden;
-Bulgaria, Latvia
-Chile, Serbia Turkey
+Nigeria
-Spain
-Georgia
+Ghana
+Syria - Columbia
+Jamaica
+Romania
+Thailand
-Brazil, Philippines, Slovenia, Thailand
10
+Belarus, Georgia, Kazakhstan, Latvia,
Ukraine, Uzbekistan, Slovenia - Iraq
20
+Turkey; Libya
30
+Chile; Poland
40
Soviet Union and Yugoslavia
break up, Iraq denuclearized
+Iran; Iraq
+Argentina, Mexico
50
Eisenhower Atoms for Peace Speech
Non-weapon states with HEU fuel
60
+Brazil, Canada, Columbia, Japan; Czechoslovakia
+Germany, Spain
+Hungary, Yugoslavia
+Austria, Denmark, Italy, Sweden, Switzerland
+Belgium, Greece, Taiwan; Bulgaria
+Australia, South Korea, Portugal, S. Africa
+Netherlands, Philippines; Vietnam
HEU has been “cleaned out” (reduced to less than 1 kg) in more than 20 non-weapon states
(Figure 3). Most of the remaining HEU-fueled research reactors are in the weapon states –
Russia, in particular. Also, as steady-power research reactors are converted to LEU (61 so far,
with about 50 left to convert or retire), reactors with lifetime cores – especially HEU-fueled
critical-facilities and pulsed reactors are becoming an increasingly large fraction of the HEUfueled research reactor population (see Table 1).
0
! " #$%
! " &$%
! " ' $%
! " ( $%
! " " $%
) $$$%
) $! $%
Figure 3. Number of non-weapon states with plutonium (updated from GFMR2011).
There are at least three challenges to completing the task of phasing out HEU use in a research
reactor fuel:
1. Make it a priority for the Russian government. Russia’s Government has been happy to
support the U.S. financed effort to convert Soviet-designed HEU-fueled reactors and retrieve
Soviet and Russian-origin HEU fuel outside Russia – but has not given any priority to
converting its own HEU-fueled reactors. In 2010, however, after repeated requests from the
U.S. Government at the highest levels, Russia’s Government agreed to allow the U.S. Global
Threat Reduction Initiative (GTRI) to fund conversion feasibility studies for six of its civilian
reactors. Also, since the March 2012 Nuclear Security Summit in Seoul, Rosatom has been
showing more committed to the agenda of phasing out civilian HEU use.
2. Higher-density uranium fuels. To convert high-power reactors that require the highest
uranium-fuel densities, the GTRI program is focusing on developing the most dense fuel
possible: metallic uranium, alloyed with up to 10 weight-percent molybdenum to improve its
mechanical properties. Such fuel would have a uranium density of about 15 gm/cc.
Russia
&NIS
China
Europe
USA
Others
Total
Critical
Assemblies
Pulsed
≈29
≈17
1
4
≈5
3
≈42
?
≈3
2
0
≈22
Research
≤0.25 0.25-250
MWt (+targets)
1
16
2
5
1
11
20
0
6 (+1)
6
2 (+1)
30 (+2)
IsotopeProd.
Breeders
Total
1
Naval
(including
icebreakers)
≈63
2
0
0
0
0
2
1
0
0
0
3
0
10 (UK)
100
1 (India)
≈174
≈4
≈22
≈113
≈17
≈285
≈129
Table 1. The global population of HEU-fueled reactors includes much more than the steady-power
research reactors that thus far have been the focus of the cleanout effort.3
4
3. Critical assemblies and pulsed reactors. Military research reactors include critical assemblies
that mock up naval reactors and pulsed reactors to generate neutron bursts that can be used to
test the effect on electronics of nearby nuclear explosions. Fortunately, computer simulations
have made critical assemblies almost obsolete except for experiments need to benchmark the
codes. Computer simulations probably also have taken over in Russia but RosAtom is retiring
obsolete critical assemblies only slowly and still has them at about ten sites.
In the US, four of the five remaining HEU critical assemblies have been moved to the highsecurity Device Assembly Facility (DAF) on the Nevada Test Site from a location in Los
Alamos that was not considered adequately secure (Figure 4).4 Sandia National Laboratory
also has shipped to the DAF the HEU fuel of its last pulsed reactor and is developing
computer simulations of the effects of neutron bursts on the transistors in chips.
Most of Russia’s dozen pulsed reactors are at its two weapons design laboratories. The U.S.
had a similar number5 but today, due to security concerns, reduced relevance of nuclear warfighting scenarios and improved computational capabilities,6 only has one pulsed reactor, the
Army’s Fast Burst Reactor at the White Sands Proving Ground in New Mexico. Recently, the
Army put out a request for proposals for alternative ways to produce neutron pulses so that it
can retire this last pulsed reactor.7 Most military pulsed reactors have annular cores made up
of massive pieces of solid uranium alloy.8
Figure 4. The U.S. has consolidated all of its weapon-design-related critical assemblies in the highsecurity Device Assembly Facility at the Nevada Test Site.
More information is available about the designs of fast critical facilities than about military
critical facilities. These designs are therefore useful for illustrating the security problem with
critical facilities fueled with HEU and plutonium. The two BSF facilities at the Institute of
Physics and Power Engineering, which are designed for modeling the cores of large fast breeder
reactors, for example, are built up of about 100,000 different disks, including tens of thousands
containing plutonium and HEU. These disks contain a total of 700 kg of HEU(90%), 500 kg of
plutonium and 2800 kg of 36% HEU(36%) (Figure 5).
5
Figure 6. In the BSF-2 fast critical assembly at the Institute of Physics and Power Engineering in Obninsk
Russia, disks of plutonium, HEU and depleted uranium can be stacked in tubes to test the criticality of
breeder-reactor cores. The diagram inset shows the arrangement of tubes in the core into which the disks
are stacked.9
Naval reactors. The U.S. and U.K. fuel their naval propulsion reactors with weapon-grade
uranium. Russia and India are believed to use HEU that is less highly enriched. France and China
are believed to use low-enriched uranium. Russia’s Artic fleet of civilian nuclear-powered
icebreakers and transports also uses HEU fuel.
The U.S. fabricates an average of about 2 tons of weapon-grade uranium into naval fuel per year
and has established a reserve of 130 tons of weapon-grade uranium for future naval-reactor use.
Although naval fuel cycle facilities are more secure than research reactors, thefts of HEU have
occurred. It would be desirable to shift to LEU-fueled reactors. Also, if much lower levels of
nuclear weaponry can be achieved, large stocks of HEU justified by the future needs of naval
reactors would raise concerns about breakout.
In 1994, the U.S. Congress required the U.S. Navy to study the possibility of moving to LEUfuel. The report from the Director of Naval Nuclear Propulsion argued that the costs would be
high and the benefits insignificant.10 In 2008, the Senate Armed Services Committee, in its
report on the Defense Authorization Act for Fiscal 2009, stated that:11
“The committee directs the Office of Naval Reactors to review carefully options for using low
enriched uranium fuel in new or modified reactor plants for surface ships and submarines.”
The Office has ignored this language. As of 2012, the design of a new aircraft propulsion reactor
was about 96 percent complete and the design of the reactor for a new ballistic-missile submarine
was launched in fiscal year 2012. 12 Both designs are HEU fueled. The HEU-fueled Virginia-class
attack submarine will be in production for at least another decade.
Nevertheless, it would be desirable to continue the effort to establish the use of low-enriched
uranium as a norm for naval as well as other reactors. If, in the future, the production of HEU for
weapons is banned but production for naval fuel is not by a Fissile Material Cutoff Treaty, one of
the most difficult verification challenges will be difficult to detect governmental diversion of
HEU from naval fuel cycles.
What are the objections of the U.S. nuclear navy to shifting to LEU? The objections in the 1995
related primarily to cost. It was assumed that conversion to LEU would require either:
6
1. Retreat from lifetime cores to refueling (3 times in a submarine lifetime and two times in an
aircraft carrier lifetime). The cost of purchasing the extra cores was estimated at about $100
million each for submarines and $600 million for twin aircraft carrier cores. It also was
estimated that refueling would extend the duration of major overhauls in port by 10 months
for submarines and 22 months for the aircraft carriers and the cost of each overhaul by about
$60 million for the submarines and $300 million for aircraft carriers. Because of the extra
time in port, it was assumed that the Navy would have to buy an additional four attack
submarines, one ballistic-missile submarine and one aircraft carrier to maintain the same atsea strength.
2. Build reactors with bigger cores. It was estimated that this would cost about $300 million
extra for the submarine reactors and $1.2 billion extra per aircraft carrier. In addition, it was
estimated that the size of attack submarines would have to be increased to accommodate the
larger cores and reactors at a cost of $150 million each. (The estimated cost increases for the
larger ballistic missile submarines and aircraft carriers were relatively minor.)
Thus the lifetime core option was found to be less costly at about an extra $1 billion/year vs.
about $2.5 billion/year for the return to refueling (1995 $). The report concluded, however, that,
“[n]either option for using LEU in place of HEU offers the Navy a technical, military or
economic advantage. Either option would be extremely costly.”
The UK, which obtains HEU and its fuel design from the U.S., would change to LEU only if the
U.S. did. France and China, however, have made different decisions.
In the case of France, there appear to be three differences in the cost-benefit calculation:
1. France, unlike the U.S. does not have a huge stockpile of excess Cold War HEU and did not
want to replace its costly HEU-production plant, which was based on gas-diffusion
technology and was expected to expire around 2000. 13 In its newest nuclear submarine, it will
move to fuel using the same enriched used in power reactors, about 5% enriched uranium;14
2. French submarines have large hatches that allow refueling without an extension of refit time,
15
whereas refueling U.S. submarines requires cutting a hole in the hull; and
3. The fabrication cost for U.S. naval-reactor fuel is very high.16
China too may not have a large stockpile of HEU in excess to its weapons needs. Also, its first
submarine reactor design was based on published descriptions of the propulsion reactors of
Russia’s first nuclear-powered icebreaker, whose fuel was 5 percent enriched.17
Plutonium use in power reactors. Separation of civilian plutonium was launched by the major
industrialized countries in the 1960s and 1970s because of twin beliefs: i) Global nuclear power
capacity would quickly grow to thousands of gigawatts, and ii) The world does not have enough
low-cost uranium to support on that scale nuclear power based primarily on a once-through fuel
cycle not involving plutonium recycling (Figure 6).
7
Global Nuclear Capacity (GWe)
%#! ! "
NEA-IAEA, 2009
Projected nuclear
capacity (1975, IAEA)
%! ! ! "
$#! ! "
Estimated Low-cost Uranium
(40-year supply for LWRs)
High
$! ! ! "
#! ! "
!"
$&' ! "
IAEA, 1975
Low
Projected band for nuclear
capacity (2011, IAEA)
$&( ! "
$&&! "
%! ! ! "
%! $! "
%! %! "
%! ) ! "
%! *! "
%! #! "
Figure 6. IAEA projections in 1975 and in 2011 of global nuclear power growth and of global resources of
low-cost (< $130/kgU) uranium.
On that basis, several countries decided to launch major efforts to develop plutonium breeder
reactors whose ultimate fuel would be the U-238 that constitutes 99.3% of natural uranium.
Despite the expenditure of about $100 billion on attempts to commercialize fast-neutron sodiumcooled breeder reactors, however, the effort failed. And, because of slow growth of global
nuclear generating capacity and growing estimates of global uranium resources, most countries
concluded that breeder reactors would not in any case be required for more than a century.
One legacy of this effort is about 250 tons of separated civilian plutonium from reprocessing
programs that were originally launched to obtain plutonium for initial breeder reactor cores. In
India and Russia plutonium separation continues on a small scale (1 to 2 tons per year) with this
rationale and China has built a pilot reprocessing plant (1 ton/year if it is operated at full
capacity) and is considering building a larger reprocessing plant. All three countries are still
concerned that available uranium supplies may not be able to keep up with their ambitious plans
for nuclear power expansion.
The large reprocessing plants are in France, Japan and the UK, however– although the two U.K.
reprocessing plants are only operating at partial capacity and Japan’s reprocessing plant is not
operating at all. France recycles its separated plutonium in “mixed-oxide” (MOX, uraniumplutonium) fuel into the light water reactors from whose spent uranium fuel the plutonium was
separated. Spent MOX fuel is stored pending decisions on whether to dispose of it in an
underground repository or to reprocess it and use the recovered plutonium for either startup fuel
for future breeder reactors or perhaps repeated recycle in light-water reactor fuel. In the wake of
the Fukushima accident, Japan is currently debating whether or not to continue with its
reprocessing plans. The UK has decided to end reprocessing when its foreign and domestic
contracts have been completed – currently estimated in 2018.
Japan is starting to build a MOX plant, despite the fact that its efforts to recycle MOX fuel
coming back from France had been delayed by a decade by public opposition even before the
Fukushima accident. The U.S. is mid-way in building a MOX plant for its excess plutonium but
has encountered huge cost overruns and schedule delays. The UK has accumulated approximately
100 tons of separated civilian plutonium that it now has to dispose of. It built one MOX fuel
fabrication plant that only operated at about one percent of its design capacity for ten years before
being abandoned in 2011. It is currently planning to build a second MOX plant to produce fuel
that would be used in light-water reactors that it hopes will be built in the UK (the UK currently
as only one LWR). Some of us have suggested direct disposal of plutonium as an alternative to
MOX.18
8
Conclusions
1. Reduction of the Cold War stockpiles of HEU has begun on a substantial scale and reductions
of the weapons stockpiles of plutonium are planned.
2. There is an emerging consensus to phase out the civilian use of HEU.
3. There has been an intense debate over plutonium separation and recycle for almost 40 years.
Most countries have abandoned reprocessing because of its large costs and few benefits, but a
few major countries remain committed to reprocessing.
4. A policy debate over whether to move away from the use of HEU fuel in naval propulsion
reactors has not really begun.
United States, US Department of Defense, “Increasing Transparency in the U.S. Nuclear Weapons Stockpile,” Fact
Sheet, 3 May 2010; Soviet Union/Russia, Natural Resources Defense Council estimate,
http://www.nrdc.org/nuclear/nudb/datab19.asp.
2
About 50 kg of weapon-grade uranium annually has been used in neutron “targets” to produce fission radioisotopes
for medical purposes. This use is being phased out.
3
Update of table in Ole Reistad and Styrkaar Hustveit, “HEU Fuel Cycle Inventories and Progress on Global
Minimization,” Nonproliferation Review, Vol. 15, # 2, 2008, p. 265.
4
The fifth U.S. critical assembly is associated with the Advanced Test Reactor at the Idaho National Laboratory. It is
also possible that the U.S. has a naval critical facility.
5
C. Paxton, A History of Critical Experiments at Pajarito Site (Los Alamos National Laboratory, LA-9685-H, 1983
H.), p. 13.
6
In 2004, U.S. Secretary of Energy Spencer Abraham announced that “the Sandia Pulsed Reactor [at the Department
of Energy’s Sandia National Laboratory, where nuclear-weapons work is done] will no longer be needed because
computer simulations will be able to assume its mission…When its mission is complete, this reactor’s fuel will be
removed…allowing us to reduce security costs at Sandia and further consolidate our nuclear materials”, “Remarks
prepared for Energy Secretary Spencer Abraham for the Security Police Officer Training Competition,” May 7,
2004, reprinted in U.S. Nuclear Weapons Complex: Homeland Security Opportunities, Project on Government
Oversight, May 2005, Appendix B. Sandia has a program on Qualification Alternatives to the Sandia Pulsed Reactor
(QASPR), which focuses on computer modeling of neutron effects on transistors. Predictions are compared to
experimental results obtained by the Ion Beam Laboratory.
7
US Army, “Alternative Source for Neutron Generation,” 2012),
http://www.dodsbir.net/sitis/display_topic.asp?Bookmark=42661
8
The Idaho National Laboratory has not used the last U.S. civilian pulsed reactor, the Transient Reactor Test
(TREAT) reactor, for 20 years. This reactor is a lesser security concern, however, because its HEU is in solutionimpregnated graphite – one atom per ten thousand carbon atoms.
9
BFS-2 image captured from the website of the Institute of Physics and Power Engineering, Obninsk, Russia. Inset
diagram from Alessandro Marinoni et al, “Analysis of the BN-600 fast-spectrum core mock-up at BFS-2 zero-power
facility using MCNPX,” Annals of Nuclear Energy, Vol. 44 (2012) p. 26
10
Report on Use of Low Enriched Uranium in Naval Nuclear Propulsion, Director, Naval Nuclear Propulsion, 1995.
11
U.S. Senate Armed Services Committee fiscal year 2009 Authorization Report (p. 515)
12
National Nuclear Security Administration, FY 2013 Congressional Budget Request, p. 484.
13
Y. Girard, Techmcatome of France, presentation, Conference on The Implication of the Aquisition of NuclearPowered Submarines (SSN) by Non-Nuclear Weapons States, MIT, 27-28 March 1989;
14
“France’s Future SSNs: The Barracuda Class,” Defense Industry Daily, 21 Dec. 2011.
15
Y. Girard, op. cit.
16
A U.S. Trident submarine contains about 1 ton of HEU and a Virginia-class submarine about 0.7 tons, IPFM,
Global Fissile Material Report 2010, endnote 131. On this basis, the figures quoted above from the 1995 report by
the Director, Naval Nuclear Propulsion suggest that the fabrication costs for these cores were about $100 million or
about $100,000/kgU.
17
John Lewis and Zue Litai, China’s Strategic Seapower (Stanford University Press, 1994), p. 31; Global Fissile
Material Report 2010, op. cit., endnote 282.
18
Frank von Hippel, Rodney Ewing, Richard Garwin and Allison Macfarlane, “Time to Bury Plutonium,” Nature,
10 May 2012, p. 167
1
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