IPFM International Panel on Fissile Materials

Nuclear-Weapon and Fissile-Materials Stocks

Almost the entire global stockpile of HEU was produced for nuclear-weapons and naval propulsion reactors – mostly during the Cold War by the Soviet Union and the United States. About half of the global stockpile of separated plutonium was similarly produced for weapons during the Cold War. The other half was produced by reprocessing civilian spent power reactor fuel.

Nuclear Weapon Arsenals

Nine states are thought to have nuclear weapons. These are, in historical order, the United States, Russia, the United Kingdom, France, China, Israel, India, Pakistan and North Korea. The first five are parties to the Nonproliferation Treaty (NPT). All but North Korea, and possibly Israel, have tested nuclear weapons. Israel has maintained public ambiguity about its nuclear-weapon status. North Korea has stated that it has nuclear weapons.

Figure 1, based on estimates by the Natural Resources Defense Council (NRDC), shows the huge scale of U.S. and Soviet nuclear-weapons-production during the Cold War.

FIGURE 1. Rise and fall of the U.S. and Russian nuclear weapon stockpiles. The Natural Resources Defense Council (NRDC) estimates suggest the number of U.S. warheads peaked at about 30,000 in the mid-1960s, and the Soviet/Russian warheads at 40,000 in the 1980s. Since then, the nuclear arsenals of both countries have dropped sharply. The United States and Russia are each committed to reducing their number of deployed strategic warheads to 1700-2200 by 2012. The NRDC estimates that the number of total operational warheads in the U.S. arsenal by that date will be about 6000, with the Russian operational arsenal likely to be no more than this same number. However, both countries may still at that time have many thousands of additional warheads and components in the dismantlement queue.

In June 2003, the U.S.-Russia Strategic Offensive Reduction Treaty (SORT) entered into force. Under SORT, the United States and Russia are committed to reduce their deployed strategic arsenals to 1700-2200 warheads each by the end of 2012. Although the treaty does not require the elimination of warheads removed from deployment, it appears likely that the United States and Russia will reduce their total stockpiles of nuclear warheads substantially. In mid-2004, the United States announced that by 2012 it would shift almost half of the current U.S. nuclear-warhead stockpile into the queue for dismantlement.

Non-governmental analysts have estimated that, after the reductions, about 6,000 warheads will remain in the U.S. stockpile, including non-strategic and reserve warheads. The number of operational nuclear warheads in the Russian arsenal could also fall by 2012 to 6000 or lower.

By comparison, the remaining nuclear weapon states are estimated to possess a combined total on the order of 1000 warheads (see Table).


Country	Nuclear Warheads
U.S.	10,000
Russia	10,000
U.K.	200
France	350
China	200
India	40-50
Pakistan	<50
Israel	75-200
North Korea	<15

Table 1. U.S. and Russian nuclear warhead totals dwarf those of other countries. They could be reduced ten-fold and still be equal to the sum of the stocks of the other nuclear weapon states. The totals for U.S. and Russia do not include warheads awaiting dismantlement. These numbers are approximate.

Non-weapon Uses of Fissile Materials

Most of the global fissile materials stockpile has been produced for nuclear-weapon purposes. HEU and plutonium are also used to fuel some reactors however. This has resulted in the production of additional fissile materials and, in some cases, has prevented disposition of excess weapons-materials.

HEU use in naval and other reactor fuels. In addition to using HEU for weapons, Russia, the United Kingdom and the United States each use HEU to fuel their submarine and (in the case of the United States) aircraft carrier propulsion reactors. France is shifting from HEU to LEU fuel for its nuclear submarines. During the Cold War, the Soviet Union and United States each used more than two metric tons of HEU per year. Today, the United States uses about two tons per year of weapon-grade uranium and Russia about one ton of weapon-grade equivalent.

HEU is also used to fuel military and civilian research reactors and Russia's fleet of seven nuclear-powered ice-breakers. The United States and the Soviet Union/Russia also supplied HEU to many countries for civilian research reactors and medical-isotope production as part of their Atoms for Peace programs. Most of this material is in the weapons states but more than 10 metric tons are in non-nuclear weapon states. Very roughly 50 tons of the HEU shown in Figure 2 is in the fuel cycles of research reactors worldwide and in Russia's nuclear-powered icebreakers. Even though this material currently represents only a few percent of the global total, it would be sufficient for about 1000 gun-type weapons and is located at more than 100 sites – many inherently difficult to secure. This HEU is currently the object of a global "clean-out" campaign.

The United States and Russia have also used HEU to fuel plutonium and tritium production reactors.

Civilian separated plutonium. In a few countries, large quantities of plutonium have been separated in reprocessing plants from civilian spent fuel. Some of this plutonium has been mixed with uranium and fabricated into "mixed-oxide" fuel and recycled, but most remains stockpiled at the reprocessing plants where it was separated in France, the United Kingdom, and Russia. The total amount of separated civilian plutonium is about 250 metric tons and growing. At 8 kg per warhead, this would be enough for more than 30,000 warheads.

Global Stocks and National Holdings of Fissile Materials

All five NPT nuclear-weapon states have declared (China informally) that they have ended or suspended their production of fissile materials for weapons. Both the United Kingdom and the United States have published the totals for their stocks of plutonium and HEU. The countries holding most of the world’s civilian plutonium annually submit information on the sizes of their stockpiles to the IAEA for publication on its website. A few of these countries also submit numbers for their civilian stocks of HEU. The IAEA has exact information on the fissile holdings of the non-weapon states but publishes only global totals. Published estimates of the remaining stocks of weapons materials are estimates by independent non-governmental analysts. Such estimates have substantial uncertainties.

The most complete compilation of publicly available data and estimates of global production and consumption of fissile materials -- unfortunately, now a decade old -- can be found in the book, Plutonium and Highly Enriched Uranium 1996, by Albright, Berkhout and Walker. Albright and collaborators have updated this information on the website of the Institute for Science and International Security. Where countries have not published their stocks, the numbers below are largely based on this work.

Highly enriched uranium. As shown in Figure 2, as of mid-2006, the global stockpiles of HEU totaled very roughly 1400 tons plus about 325 tons of excess weapons uranium that is to be blended down to low enriched uranium. More than 99 percent of this material is in the possession of the nuclear-weapon states.

FIGURE 2. National Stocks of Highly-Enriched Uranium as of mid-2006. The quantity of weapon-grade uranium in the world is overwhelmingly a consequence of the U.S-Soviet nuclear arms race, with the two countries accounting for over 95 percent of the total world stockpile. However, with the Cold War ended, Russia declared 500 tons of its HEU excess, and the United States similarly 198 tons (about 145 tons 93% equivalent); and both countries have begun to eliminate this HEU. As of mid-2006, Russia had blended down about 275 tons and the United States about 60 tons to non-weapons-usable low enriched uranium for reactor fuel. Aside from the use of HEU in weapons, the United States has reserved 180 tons of HEU for naval and other reactor fuel. Russia is assumed here to have reserved 100 tons for such purposes. Numbers of military stocks are estimates.

The only states believed currently to be producing HEU are Pakistan (for weapons) and India (for naval-reactor fuel). Their estimated production rates are each on the order of a hundred kilograms per year. While significant in terms of weapon-equivalents, this production has an insignificant impact on the total global stock.

In fact, the total amount of HEU in the world is shrinking. In 1993, Russia contracted 500 tons of 90-percent enriched uranium in redundant Cold War warheads to be blended down to 4-5 percent U-235 to be sold to the United States for use as power-reactor fuel. As of mid-2006, 275 tons had been blended down -- the equivalent to about 11,000 nuclear bombs. In 1994, the United States similarly declared 174 tons of its weapons HEU excess (this was revised to 178 tons in 2001) and began to blend down most of it to low-enrichment for use in U.S. power reactor fuel. By the end of 2005, about 60 tons had been blended down.

In late 2005, the United States declared an additional 200 tons of HEU excess for weapons purposes. However, only 20 tons of this material will be blended down to low-enriched uranium. Of the remainder, 160 tons of weapon-grade uranium will be reserved for U.S. and U.K. naval-reactor fuel and 20 tons for space reactors and research reactors. We assume that Russia has similarly reserved the equivalent of 100 tons of weapon-grade uranium for future naval-reactor use. This would leave 400-1000 tons of HEU in Russia’s weapons stockpile and 310 tons in the U.S. weapons stockpile.

The recent U.S. designation of 160 tons of weapon-grade uranium for future use in naval reactors highlights naval reactor use as a second military challenge to reducing global stocks of HEU. At 25 kg per warhead, the U.S. stockpile of weapon-grade uranium reserved for naval reactor fuel would be comparable to the amount of HEU in the U.S. stockpile of 6000 operational warheads projected for 2012.

FIGURE 3. Global HEU Stockpiles and Potential for Reductions (metric tons). Global stockpiles of HEU could shrink dramatically in the future if the United States and Russia continue to reduce their nuclear-weapons arsenals and continue to blend-down HEU recovered from dismantled warheads. If future naval and other reactors were to use LEU fuel, the stockpiles of HEU could be still further reduced. The weapons stockpile numbers assume 25 kg of HEU per warhead. They also assume that total HEU holdings of all countries other than the United States and Russia stay constant at approximately 90 tons.

If Russia and the United States reduced to 1000 nuclear warheads each -- as many analysts believe they could before expecting that other countries join them in similar disarmament measures -- they would only require about 25 tons of HEU each for weapons.

On this scale, the 300 or so tons of HEU which the United States and Russia have so far kept in reserve for naval and other reactors would appear huge (see Figure 3). This suggests that the question of HEU-fueled reactors will have to be dealt with before such deep cuts in the stockpiles of weapons HEU will be politically feasible.

Separated plutonium. The global stockpile of separated plutonium is about 500 tons, approximately equally divided between weapon and civilian stocks, but all weapons-usable. It is mostly in the nuclear-weapon states, but Japan and a few non-weapon states in Europe also have significant stockpiles of civilian plutonium.

FIGURE 4. National Stocks of Weapons and Separated Civilian Plutonium. By the end of 2004, the global stockpile of separated plutonium was about 500 tons. This was divided approximately equally between weapons and civilian stocks. Numbers for military stocks are estimates.

The United States, Russia, the United Kingdom, France and reportedly China have stopped producing plutonium for weapons.

There is no indication that Israel, India, Pakistan or North Korea have halted their production of plutonium for weapons. Once again, however, the quantities that they may be producing, while significant in weapons equivalents, do not significantly increase the total global stock.

In 2000, the United States and Russia agreed to each dispose of, in parallel and irreversibly, 34 metric tons of their excess weapons plutonium. But there has been little progress so far.

By the end of 2004, about as much plutonium had been separated from civilian spent fuel as had been produced for weapons. Most of this material is now stockpiled at the reprocessing plants at La Hague, France; Sellafield, United Kingdom; and Ozersk (Mayak), Russia. The global stockpile of civilian separated plutonium is still growing.

Assuming 4 kilograms of plutonium in the average Russian or U.S. warhead, each country would require only about 24 tons of weapon-grade plutonium to support the roughly 6,000 warheads that they are each expected to retain through 2012. The United States and Russia therefore could declare excess about half and more than three quarters of their respective remaining stockpiles. If they reduced the number of their nuclear weapons to 1000 each, Russia and the United States would require only 4 tons of weapon-grade plutonium each.

FIGURE 5. Global Plutonium Stockpiles. Potential for Reductions (metric tons). Global stockpiles of plutonium could shrink substantially if the United States and Russia reduced further their nuclear weapons arsenals and disposed of weapons plutonium made excess by the reductions. If reprocessing of civilian spent fuel continues at its present rate and the recycling of the separated plutonium in light water reactors remains limited, however, civilian plutonium stocks will continue to rise.

Alternative fissile materials. Among the exotic fissile materials, U-233 has been produced in the largest quantities: "The U.S. has investigated using U-233 in nuclear weapons, in reactors, and for other purposes. The United States and several other countries have significant quantities of separated 233U. Somewhat [less than] 2 metric tons of separated U-233-containing uranium are in the U.S. inventory. Half of this material is considered high-quality ... with few isotopic impurities." The global U-233 stockpile may grow substantially in the future if thorium-based fuels start to play a more prominent role in the nuclear fuel cycle as envisioned especially in India.

Spent nuclear fuel contains weapons-usable neptunium-237 and americium-241 as well as plutonium. The global stock of neptunium-237 in spent fuel is variously estimated from 54 tons to 80 tons. Some has been separated for targets that when irradiated in reactors produce Pu-238. The radioactive decay heat from this 88-year half-life isotope is used to power long-lived thermoelectric generators for spacecraft sent to explore the outer planets, where solar cells are considered impractical. Estimates of americium isotope stocks in spent fuel range from 87 to 150 tons. Small amounts (on the order of several kg/year) have been separated. One use of americium-241 is in smoke detectors.

The IAEA does not consider either neptunium-237 or americium as "direct use material," and does not safeguard them. However, in 1999, the IAEA Board of Governors called on "all States to protect and control these materials" and has monitored their production in and transferred to non-nuclear weapon states under a voluntary arrangement. In its 2004 Safeguards Statement, the IAEA reported that it "continues to experience difficulties in obtaining information from States… regarding neptunium and americium."