AS the 18-wheeler slowly eased up to the loading dock under a heavily armed escort, massive steel doors opened from the inside of a partially buried structure. An announcement was broadcast over the public address system alerting specially trained personnel of the arrival of a safe and secure transport vehicle. This special big rig is part of a fleet used by the U.S. government to transport nuclear weapons or weapon components from one secure site to another. Technical specialists stood ready to unload the shipment. The scene of this activity at the Nevada Test Site is the Department of Energy's newest facility, located 90 miles northwest of the famous Las Vegas strip in a remote part of the Nevada desert. The recently opened Device Assembly Facility, or DAF, offers one of the safest, most secure locations anywhere in the U.S. weapons complex to conduct nuclear explosive operations. Other than the Pantex Plant in Amarillo, Texas, the Nevada Test Site is the only location in the country where special nuclear material such as plutonium can be mated with high explosives. Under a unique arrangement with the Department of Energy, Lawrence Livermore and Los Alamos national laboratories are designated joint operators and users of the facility. Since the facility's inception, the laboratories have collaborated on every aspect of the facility-including its design, construction, certification, management, and use. Management responsibility is rotated between the laboratories, nominally every two years. "This is truly a joint-lab facility," explains James Page, DAF startup team leader for Livermore. "We share common procedures and integrated hazards analyses and operate with a management team composed of personnel from both laboratories." In contrast, nuclear explosive operations at the Nevada Test Site in the past were conducted in two separate facilities according to Laboratory affiliation. Adapting to Challenges DAF dates from the mid-1980s, when the weapons laboratories were engaged in active nuclear testing. As with many aspects of the Department of Energy's weapons program, DAF has been adapted to a changing environment brought about by changes in national nuclear testing policy. Designed and built for the purpose of assembling the two laboratories' nuclear test devices prior to placing them underground for testing, the new facility retains its original name. Its mission, however, has evolved since the nuclear testing moratorium began in October 1992. Instead of the underground test assembly work for which the facility was originally intended, DAF will accommodate other hands-on activities involving high explosives, special nuclear material, nuclear weapon components, and nuclear devices. These projects, an integral part of DOE's Stockpile Stewardship Program, will include assembly work to support new subcritical (no-nuclear-yield) experiments being conducted nearby as well as stockpile maintenance activities, such as enhanced surveillance technology development and personnel training. These activities will provide necessary data to help maintain the nation's nuclear deterrent. Future use could also include DOE activities to maintain a nuclear emergency response capability. Anatomy of the Facility In a bunker-style arrangement, DAF is a collection of 30 individual steel-reinforced concrete buildings connected by a rectangular racetrack corridor. The entire complex, covered by compacted earth, spans an area the size of eleven football fields (see schematic drawing below). Because the buildings were designed to accommodate potentially hazardous operations, they meet the most stringent set of safety regulations. Explains Page, "This facility was intended to provide the safest possible environment for conducting hands-on operations involving special nuclear material and high explosives. The DAF design incorporates the most modern safety and security features in the weapons complex." The DAF multistructure occupies about 10,000 square meters of usable floor space and consists of operational buildings for work involving high explosives and special nuclear material and support buildings for laboratories and offices. Most isolated of the operational buildings are five assembly "cells" for activities involving uncased conventional high explosives and special nuclear material. Four high bays and three assembly bays provide facilities for less hazardous operations, such as those involving uncased insensitive high explosives. When radiography is required to verify the integrity and spatial relationships of objects, a 9-megaelectron-volt, movable-beam, linear accelerator is available in one of two radiography bays. Five staging bunkers provide ample space for interim storage of nuclear components or high explosives. Finally, all materials packages arrive or depart DAF through either of two shipping and receiving bays. The support buildings include three small vaults for storing small quantities of high explosives or special nuclear material; two decontamination areas; and an administration area containing office space, a conference area, personnel changing and shower rooms, and a machine shop. In addition, two buildings provide laboratory space: one for conducting component, instrumentation, and environmental testing and the other for controlling remote operations of an adjacent assembly cell.

Blast Protection and Containment To provide the utmost protection for personnel working within the facility and for the environment, DAF employs several state-of-the-art safety features. Chief among them are blast doors on all operational buildings to mitigate the propagation of an accidental explosion, blast-actuated valves on the ventilation system to prevent the spread of contamination, special ventilation features such as zoned air-supply systems and high-efficiency particulate air filters, and the unique design of the assembly cells. Indeed, the assembly cells are whimsically called "gravel gerties," after a 1950s Dick Tracy comic-strip character because the roof is overlaid with nearly 7 meters of gravel, said to resemble the original Gravel Gertie's thick curly gray hair. Modeled after the structures at Pantex, where hands-on assembly and disassembly of U.S. nuclear weapons take place, they provide the maximum environmental and personnel protection in the event of an inadvertent high-explosive detonation. The cells are designed to absorb the blast pressure from a detonation of up to 192 kilograms of plastic-based explosives (equivalent to 250 kilograms of TNT, or approximately one-fifth of the explosive energy released in the World Trade Center bombing). Should a detonation occur, the gravel gertie would minimize environmental release of nuclear material and propagation of the event to other areas in the facility. "Although it is extremely unlikely that the cells would ever be required to perform to their full potential," says Page, "their design provides the extra assurance necessary for moderately hazardous activities, such as weapon assembly and dismantlement and some processes for monitoring changes due to aging. In addition, the assembly cells could be used to disable nonstandard explosives, such as a clandestine nuclear device."

A National Resource The design of the facility, its remote location, and its safety features make DAF well suited to address new national challenges-both predicted and as yet unforeseen-in maintaining the nuclear stockpile. Like Livermore's Laser Programs, started in the 1960s to research electrical power but now studying fundamental physics issues as well, DAF is a valuable national resource whose future applications will likely extend far beyond its original mission. "DAF is the first facility of this complexity," sums up Livermore physicist Willy Cooper, Nevada Experiments and Operations Program Leader, "for handling unique and potentially hazardous nuclear weapons components and operations that DOE has brought online in several decades. With its 21st-century focus on environmental, safety, and health considerations, DAF is a functional testimony to the vision of the former generation of weapons scientists, valid today even with a shift in strategic national policy." -- Lori McElroy

Key Words: Device Assembly Facility (DAF), DOE, high explosives, Nevada Test Site, nuclear-explosive operations, nuclear weapon assembly and disassembly, stockpile stewardship, subcritical experiments.

For further information contact James Page (925) 423-1195 (jpage@llnl.gov).