The U.S. Nuclear Stockpile,Today and Tomorrow

Congress is weighing several significant questions related to nuclear weapons that could emerge during the 2008 presidential campaign. These questions include the current and future size of the U.S. nuclear arsenal; the status of the Stockpile Stewardship Program; and whether there is a need for new warheads and a production complex to manufacture them. Although secrecy shrouds details on these issues, some pertinent facts and estimates can contribute to an informed discussion.

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Snapshot
The United States has nearly 10,000 nuclear warheads.
The United States plans to dismantle nearly 4,500 warheads.
The U.S. stockpile in 2012 is likely to include about 5,470 warheads.
Congress is considering the future of the aging stockpile.

A brief history of the stockpile. The United States built few atomic bombs immediately after World War II; by the time the Soviet Union conducted its first atomic test in August 1949, the U.S. stockpile numbered about 170. But the Soviet test sparked an enormous expansion of the U.S. nuclear research and production complex, and the stockpile grew exponentially. Remarkably, in 1959 and 1960, the average number of builds was more than 7,000 a year. By 1961, the stockpile contained more than 22,000 warheads. An intense interservice rivalry among the air force, navy, and army drove U.S. nuclear growth, in time becoming inextricably linked with the actual and imagined capabilities of the Soviet Union, producing a mighty action-reaction engine that propelled the arms race. Adding to the intensity was a fierce competition between the laboratories at Los Alamos and Lawrence Livermore to design new warheads. The constant invocation of the “Soviet threat,” and the emergence of new enemies and competitors such as China, added to the irrational accumulation of megatons. The stockpile reached its historic high in 1967, with more than 32,000 warheads of 30 different types. As the stockpile gradually declined in the 1970s, its composition changed, with strategic warheads eventually outnumbering tactical ones.

The stockpile's total firepower peaked in 1960 at just over 20,491 megatons, according to the Energy Department, equivalent to 20 billion tons of TNT, or enough for 1.36 million detonations the size of the one exploded over Hiroshima. From the late 1940s to the mid-1960s, the predominant strategic weapon delivery system was the heavy bomber, with more than 1,600 B-47, B-58, and B-52 aircraft allocated some 3,000 bombs, most of them with multimegaton yields. But as intercontinental ballistic missiles (ICBMs) and submarine-launched ballistic missiles (SLBMs) were deployed, the number of bombers and bombs declined, with a corresponding drop in megatonnage. As missile accuracy increased, lower-yield warheads replaced higher-yield versions, contributing to the downward trend.

We estimate that from 1945 to 1990 the United States produced approximately 70,000 nuclear weapons of some 75 types for more than 120 weapon systems. Today's stockpile contains about 2,400 megatons, a little more than one-tenth the 1960 level, but still equivalent to 159,000 Hiroshimas.

Past, present, and future stockpiles. At the end of the Cold War, the U.S. arsenal held about 22,000 nuclear warheads. Several unilateral actions and arms control treaties in the early 1990s led to the retirement of approximately 9,500 warheads; subsequent actions have reduced the stockpile to today's level of just under 10,000. In June 2004, the Bush administration declared that the U.S. nuclear stockpile would be cut “nearly in half” by 2012. We believe the number of warheads will decline from approximately 9,938 today to about 5,470 by the end of 2012 (see “The U.S. Nuclear Arsenal, 2007 and 2012,” p. 61).

There are three categories of stockpiled warheads: active deployed, responsive, and inactive. Active deployed warheads are those on or associated with fielded systems such as ICBMs, SLBMs, bombers, and fighter-bombers. The responsive category includes spares and what have been referred to as “active non-deployed” warheads, which can be deployed quickly. All active and responsive warheads contain limited-life components such as tritium and are maintained through regular surveillance schedules. Inactive warheads are intact but have had limited-life components removed, thus making it harder to return them to service.

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THE U.S. NUCLEAR ARSENAL, 2007 AND 2012

WARHEAD TYPE	ACTIVE DEPLOYED∗	RESPONSIVE/INACTIVE	TOTAL	ACTIVE DEPLOYED∗	RESPONSIVE/INACTIVE	TOTAL	WARHEADS TO BE DISMANTLED
B61-3	200	186	386	200	50	250	136
B61-4	200	204	404	200	50	250	154
B61-7	215	224	439	120	300	420	19
B61-10	0	206	206	0	0	0	206
B61-11	20	21	41	20	15	35	6
W62	325	255	580	0	0	0	580
W76	1,344	1,686	3,030	122	1,252	1,374	1,010
W76-1	0	0	0	646	0	646	0
W78	550	244	794	200	200	400	394
W80-0	100	189	289	0	0	0	289
W80-1	1,452	354	1,806	300	228	528	1,278
B83-0	0	298	298	0	293	293	5
B83-1	323	3	326	100	220	320	6
W84	0	383	383	0	0	0	383
W87	50	502	552	300	247	547	5
W88	384	20	404	384	20	404	0
TOTAL	5,163	4,775	9,938	2,592	2,875	5,467	4,471 ∗∗

NOTES AND ASSUMPTIONS

∗

“Active deployed” means warheads on fi elded systems such as intercontinental ballistic missiles (ICBMs), submarine-launched ballistic missiles, and bomber and fi ghter-bomber weapons. Responsive means warheads fully maintained in storage but not operationally deployed. Inactive means the warhead has had its tritium removed.

∗∗

Warheads withdrawn for dismantlement during 20072012 could be dismantled by 2023, according the National Nuclear Security Administration.

The table estimates that U.S. “operationally deployed” strategic forces under the 2002 Moscow Treaty will number 2,192 warheads by the end of 2012, and that another 3,275 warheads will not be counted under the treaty. This is based on the following assumptions: There are 450 Minuteman III ICBMs with 500 warheads, including 150 W87 warheads deployed at both Warren Air Force Base (AFB) and at Malmstrom AFB, and 200 W78 warheads at Minot AFB; there are 12 nuclear-powered ballistic missile submarines (SSBNs), multiple independently targetable reentry vehicles 4 with 1,152 warheads (2 SSBNs in overhaul not counted), 646 W76-1s from the life extension program (full program consists of 2,000 W76-1s), and no W88 depletion due to new pit production; there are 32 B-52 and 16 B-2 Combat Coded bombers with 540 warheads at Barksdale, Minot, and Whiteman AFBs; all 528 air-launched cruise missiles will be consolidated at Minot AFB, and all advanced cruise missiles retired; all B61-10 bombs will be retired; all W62 warheads will be retired; all W80-0 submarine-launched cruise missile warheads will be retired; all W84 ground-launched cruise missile warheads will be retired; some W78, W76, W80-1, B61-3/4 warheads will be retired.

The warheads removed from the stockpile are retired and eventually dismantled. Retired warheads stored in weapons bunkers at military bases are under Defense Department custody until they are handed over to Energy and sent to the Pantex Plant outside of Amarillo, Texas, for dismantlement. (Thermonuclear secondaries are sent from Pantex to the Y-12 plant in Oak Ridge, Tennessee, for storage or dismantlement.) Approximately 4,500 warheads are scheduled to be retired by 2012.

Warhead dismantlement. The last major turnover of the stockpile occurred in the 1980s. Eight of the nine basic warhead types in today's stockpile were produced mainly from 1980 to 1990. When new production was halted in 1990 and 1991 because of egregious, ongoing safety and environmental concerns, the dismantlement of retired warheads became the major activity at Pantex, and 11,198 warheads were dismantled from 1990 through 1999, according to Energy (see “Dismantling U.S. Nuclear Warheads,” January/February 2004 Bulletin). Energy released annual dismantlement figures on request, as well as future projections, until 1999, when the information suddenly became classified.

In March 2006, Energy's National Nuclear Security Administration (NNSA) sent Congress its plan for accelerating the dismantlement rate. From a baseline figure, the goal was to increase the rate by 25 percent per year. While we do not know the baseline figure, it is probably in the 100-200 per year range, given the last known projections. In June 2007, the NNSA announced that it was speeding up warhead dismantlements by more than 50 percent for fiscal 2007, that it had met that goal four months early, and that by the end of the year it might be double. 1 By our calculations, this could mean that as many as 200-400 warheads will be dismantled by September 30, 2007, the end of the fiscal year.

These are encouraging figures especially if they can be sustained in tackling the 4,500 warheads scheduled for retirement. To better gauge whether this acceleration serves Energy's avowed purpose of “ensuring that the weapons can no longer be used,” and to show that “this country is serious about nonproliferation,” as Energy has proclaimed, the department should return to its policy of transparency, announcing annual dismantlement figures as it did in the past. 2

Dismantlement has not been Pan-tex's top priority. As Energy has acknowledged, it considered extending the lives of active warheads and the ongoing surveillance of the stockpile more important. The resources at Pantex are limited, and it will be interesting to see if the accelerated dismantlement rates can be sustained once W76 and B61 life extension programs (LEPs) get fully under way. The House Armed Services Committee has demanded a report with current plans and schedules as well as an assessment of the capacity of the Pantex and Y-12 plants to accommodate accelerated dismantlement. 3

The aging stockpile. A concern often voiced by Energy officials is that the stockpile is aging. This is no doubt true, but its significance is debatable. The average stockpile warhead age is approximately 24 years old; no new warheads have entered the stockpile in 17 years. From 1991 to 1993 some 9,500 warheads were retired, causing the average age to decrease, but since then the trend has been steadily upward. Once the commitment to cut the stockpile “nearly in half” is implemented, the average age will decrease again.

Determining the age of each warhead type is tricky. Manufacturing hundreds or thousands of a new warhead type normally took place over a span of years. It took almost 10 years, 1978-1987, to produce 3,250 W76 warheads for the Trident missile system. Current plans call for retaining about 2,000 W76s, modifying them, extending their service lives, and improving their military capabilities. Sometimes older weapons are modified by adding new components, as when about 48 B61-7 bombs were converted into B61-11 earth-penetrating bombs by adding, among other elements, 450 pounds of steel to the front end. The thermonuclear secondaries, manufactured from 1969 to 1971, were retained. The B61-7 itself is a modified B61-1 that was converted between 1985 and 1990. How old thenistheB61-ll?

These extensive and expensive LEPs address the problems of warhead aging by replacing certain components, often enhancing the weapons' military capabilities; LEPs have been implemented or are scheduled for every warhead type that will be retained in the stockpile. As to the issue of plutonium and pit aging, the independent Jason group recently concluded that “primaries of most weapons system types in the stockpile have credible minimum lifetimes in excess of 100 years and that the intrinsic lifetime of [plutonium] in the pits is greater than a century.” 4 In other words, existing long-lived nuclear components can be recycled and “new” weapons built around them.

Stewardship and beyond. The pre-1990 stockpile was dynamic, with new warheads introduced after being tested at the Nevada Test Site. The United States conducted its last nuclear test on September 23, 1992, and a testing moratorium began on October 2, 1992. On September 24, 1996, President Bill Clinton was the first world leader to sign the Comprehensive Test Ban Treaty (which was never ratified by the Senate). The Stockpile Stewardship Program was begun in 1993 to ensure that warheads continue to meet stringent safety and reliability requirements without full-scale testing. Since then, the program's non-nuclear testing, computer simulations, and other diagnostic techniques have been used to monitor the stockpile, and each year the secretaries of Defense and Energy have certified to the president that the stockpile is safe and reliable. By general consensus, the program has been highly successful. 5

Throughout the fiscal 2008 budget process, Congress was skeptical of the Reliable Replacement Warhead (RRW) Program, which the Bush administration has promoted as a more reliable, proliferation-proof option, and some committees cut funding for RRW dramatically. 6 They felt that it is premature to rush forward with a new warhead design and a production complex before basic questions are answered. Such questions include how many bombs will be built, and more fundamentally, what the role of nuclear weapons in U.S. security policy is to be. In part to address these issues, the Senate Armed Services Committee directed Defense and Energy to submit a new Nuclear Posture Review (NPR) to Congress in December 2009. The committee advised: “The new NPR would include a review of policy objectives with respect to nuclear forces and weapons and include the relationship among United States nuclear deterrence policy, targeting strategy, and arms control objectives.” 7

The House Armed Services Committee also took action after declaring that “clear policy objectives should be established before Congress commits to ambitious new programs.” 8 The committee demanded a report from a Commission on the Strategic Posture of the United States, which will be created to deal with basic policy questions. The congressionally appointed bipartisan commission will examine the role of deterrence in the twenty-first century, assess the role of nuclear weapons in U.S. national security policy, and make recommendations on the most appropriate U.S. strategic posture.

Supplementary Material

Pit Lifetime