Abstract
Since the end of the Cold War, the main activity at the Pantex Plant in Texas has been dismantling warheads removed from the U.S. nuclear stockpile. Over the next decade, the plant's primary workload will shift toward modifying warheads to extend their service life.
Pantex is located 17 miles northeast of Amarillo, in the Texas panhandle near Highway 60. The plant employs nearly 3,200 people. Its Web site indicates a five-day work week with three shifts. Pantex has more than 323 buildings containing 1,900,000 square feet. The plant's replacement value was estimated at more than $3 billion in the early 1990s.
Today Pantex is the only U.S. assembly and disassembly site for stockpiled nuclear weapons, but many sites since World War II have at different times shared those responsibilities. The major components of the Fat Man and Little Boy bombs (the plutonium pit and uranium target insert and projectile, respectively) were cast at Los Alamos in New Mexico in July 1945 and shipped to Tinian in the Marianas Islands. There they were assembled into the bombs that were dropped on Hiroshima and Nagasaki in August. Immediately after World War II, bomb parts were fashioned and nuclear weapons were assembled at facilities at Los Alamos, Sandia Army Base in Albuquerque, and the Naval Ordnance Test Station at Inyokern, California.
In 1949, the army's Iowa Ordnance Plant in Burlington, Iowa, began producing chemical high explosive components for nuclear warheads. The first warhead, a Mark IV (Fat Man-type) bomb, was assembled there in 1949–minus its fissile core. The core was kept separate from the bomb assembly mainly for reasons of civilian-military custody, but also because of the bomb's design.
The U.S. Atomic Energy Commission (AEC) selected Pantex as a second assembly facility in 1951. Originally built under the supervision of the Army Corps of Engineers in 1942, Pantex was used during World War II to load conventional munitions (bombs and artillery shells) with TNT. The plant was rehabilitated and began full operation assembling Mark VI bombs in May 1952. Procter & Gamble, makers of Ivory soap and Crisco, operated Pantex for the AEC. Mason & Hanger took over on October 1, 1956, and ran Pantex until 2001, when the contract was awarded to BWXT Pantex, an independent company comprised of BWX Technologies, Honeywell, and Bechtel that was formed solely to manage Pantex.
The Burlington plant closed in 1975, and its functions were transferred to Pantex. Until then, with some exceptions, warheads designed at Lawrence Livermore National Laboratory were assembled at Pantex, and Los Alamos-designed warheads at Burlington.
Storage bunkers at Pantex.
In November 1951, with the Cold War heating up, the AEC estimated it might need as many as five plants to build the number of warheads scheduled. A third facility was planned at Spoon River, Illinois, but by 1953 it was deemed unnecessary and was cancelled.
The first bombs, with sandbags packed tightly around them, were shipped by rail from Burlington in normal boxcars. Later, special rail-cars were built to transport nuclear weapons. Today, land transport is the responsibility of the Albuquerque-based Office of Secure Transportation (OST).
OST operates a fleet of special 18-wheel tractor-trailers to transport nuclear weapons, non-nuclear weapon components, special nuclear materials, and limited life components (which contain tritium). The main routes–between Albuquerque, Amarillo, and Oak Ridge, Tennessee–follow the interstate highway system. The trucks have traveled more than 100 million miles since 1975. They are ruggedly designed to survive severe accidents and to withstand extreme temperatures in case of fire. Armed federal agents accompany each convoy of one or more trucks and their escort vehicles. The convoys keep in constant communication with Albuquerque.
We estimate that from 1945 to 1990, the United States produced at several sites approximately 70,000 nuclear weapons of approximately 70 types for more than 120 weapon systems. Annual production rates rose dramatically throughout the 1950s. In 1959 and 1960, there were 7,088 and 7,178 new builds, respectively, or about 28 warheads each workday. By 1967 the stockpile reached a historic high with approximately 32,000 warheads of 30 different types, from sub-kiloton landmines (atomic demolition munitions) to multi-megaton strategic bombs. The historic high for megatonnage was reached in 1960 with nearly 20,500 megatons (that's 20 billion tons, or 40 trillion pounds, of TNT)–the equivalent of about 1,400,000 Hiroshimas. Today the total is about one-tenth the 1960 level, or about 2,000 megatons, or 140,000 Hiroshimas.
The United States has dismantled approximately 60,000 warheads. For four decades, there was a steady rhythm to the size of the stockpile; old warheads were retired, their plutonium and uranium components recycled, and new warheads were fabricated and fielded. This ended in 1989, when the Rocky Flats plant in Colorado, where the pits were made, was shut down for safety and environmental reasons. Since then, no new warheads have been produced.
When the Cold War ended, there were approximately 21,500 nuclear warheads in the U.S. stockpile. More than 11,000 nuclear warheads were disassembled and disposed of during the 1990s, leaving about 10,400 in the current stockpile. Only a few hundred more are slated for dismantlement. Work at Pantex also includes modifying certain warheads and randomly removing small numbers of different types from the stockpile for testing and evaluation. Some are converted into “joint test assemblies”–the nuclear material (“physics package”) is removed and an instrumentation package substituted. The instruments record and transmit data when the Pentagon tests the warhead on an actual delivery system.
Part of the Pantex site outside Amarillo, Texas.
We estimate that it takes one to two weeks to dismantle an average warhead. Disassembly is essentially a reversal of the assembly process. The chemical high explosive is separated from the nuclear components and burned at Pantex. The separation is done in one of 13 assembly cells known as “Gravel Gerties,” specially reinforced rooms able to withstand an explosion equivalent to 250 kilograms of TNT. From 1981 to 1986, the amount of high explosives burned annually averaged about 227,000 pounds.
Subassemblies and components are further broken down in assembly bays for salvage or disposal. A wide variety of non-nuclear components are returned to the facilities where they were originally manufactured. Among the items returned to the Kansas City Plant (operated for the Energy Department by Honeywell) are radars, contact fuses, arming and firing sets, permissive action links, safing components, thermal batteries, capacitors, and crystal resonators. Neutron generators once made at the Pinellas Plant in Clearwater, Florida, are now the responsibility of Sandia National Laboratories. The explosive actuators and other pyrotechnic components that were fabricated at the Mound Plant near Dayton, Ohio, are now also returned to Kansas City.
Thermonuclear secondaries (canned subassemblies) contain uranium and lithium-6 deuteride (the fusion material of a hydrogen bomb) and are returned to the Y-12 Plant at Oak Ridge for storage or processing. Tritium, a hydrogen isotope with a half-life of 12.3 years used for boosting the yield of the primary, is shipped to Savannah River Site in South Carolina. For the past 15 years, that tritium has been recycled into active warheads. From the mid-1950s until 1988, Savannah River reactors were used to produce tritium. In October 2003, the civilian Watts Bar Nuclear Power Plant, located 50 miles south of Knoxville, Tennessee, began producing tritium for nuclear weapons. [See “Nuclear Weapons: The Death of No-Dual-Use,” page 15.]
Pantex workload, 1990–1999
Source: Energy Department. Figures after 1999 are classified.
Includes warheads intentionally dismantled and disposed of, and warheads dismantled for evaluation purposes and disposed of. Excludes warheads dismantled for evaluation and reassembled and returned to the stockpile.
Includes 553 warheads disassembled at the Y-12 plant in Oak Ridge.
A modern pit is a hollow, spherical or aspherical shell of plutonium encased in stainless steel or other metal or alloy, that is, with its other components, a fission (atomic) bomb. In a thermonuclear weapon, the fission bomb acts as the first (primary) stage in triggering the fusion (secondary) stage. After removal, the plutonium pits are placed in drums or containers and stored in the Pantex igloos. A few pits are sent to Los Alamos and Livermore laboratories for research and analysis.
More than 12,000 pits are stored at Pantex. In 1995, President Bill Clinton declared that 38.2 tons of weapon-grade plutonium were in excess of military needs. To account for plutonium waste and scrap, this amount was later reduced to 34 tons. Russia agreed to dispose of a similar amount of its plutonium. The schedule for the final disposition of the excess plutonium has not been set. Most of the U.S. share exists in the form of about 7,000 pits at Pantex. The United States plans to convert the metallic pits into a plutonium oxide that, when added to uranium oxide, forms a mixed-oxide fuel (MOX) that can be used to fuel nuclear reactors.
The remaining 5,000 pits in storage at Pantex are currently considered a strategic reserve. The U.S. government claims it is essential to keep this many pits to be used as possible replacements should warheads in the active stockpile become unreliable. Theoretically, these pits could also be used in new nuclear weapons, if it were decided to produce new types. For now, the “excess” pits sit next to the “strategic reserve” pits in dozens of igloos.
In Pantex's Zone 4, about two kilometers from the disassembly area, are 60 igloos that routinely housed (for temporary periods of a few months) new warheads that were awaiting shipment to Military First Destination points for transfer to the air force, army, or navy. Because there is no new production, the igloos now store the pits that were once returned to Rocky Flats. A small number of igloos are used to store warheads awaiting immediate dismantlement.
There are two types of igloo: 18 Richmond, and 42 Steel Arch Construction. Both kinds are 39 feet deep, 25 feet wide, and a maximum of 15 feet high. Each igloo can store 240 pits if they are single-stacked (two rows in the igloo divided by a center aisle for forklift operations; containers stacked four to six high). If the pits are double-stacked (four rows), each igloo could hold 400 pits. Theoretically, the 60 igloos can hold as many as 14,400 pits (single-stacked) or 24,000 pits (double-stacked). Analyses and environmental assessments were prepared to examine safety concerns associated with double-stacking.
In 1999, Pantex began repackaging pits into AL-R8 2030 sealed-insert containers to improve storage conditions. At an average rate of more than 200 pits per month, the 8,000th pit was repackaged on October 10, 2003. Presumably all the pits will be repackaged, which could be accomplished by the summer of 2005.
Preparations are underway to produce new pits at Los Alamos National Laboratory. The goal is to be able to manufacture as many as 80 pits per year. The W88 warhead for the Trident II submarine-launched ballistic missile was chosen as the initial type. Prototypes have been produced. A certifiable pit that meets all manufacturing requirements and specifications will soon begin extensive computer simulations and non-nuclear testing. Under the current schedule, it will enter the war reserve stockpile in 2007. The Bush administration has more ambitious plans and wants to build the Modern Pit Facility capable of producing 250-900 pits annually by 2018.