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Stockpile Stewardship and Management

The President and the Congress have directed DOE to maintain the safety and reliability of the nation's nuclear deterrent without underground nuclear testing. In order to do that, DOE has established a program of science-based stockpile stewardship. Stockpile stewardship refers to the activities associated with research, design, development and testing of nuclear weapons and the assessment and certification of their safety and reliability. Stockpile management refers to the activities associated with production, maintenance, surveillance, refurbishment and dismantlement of the nuclear weapons stockpile.

Optical isolation of weapons firing sets is an integral component of modern surety themes. Sandia researchers are investigating laser triggering of the small vacuum switches called Sprytrons in the firing sets. By optimizing the laser focus and the Sprytron design, in 1999 researchers reduced the laser energy required by a factor of 1,000 to 10 micro-joules. This allowed the research team to demonstrate triggering of a Sprytron through an optical fiber using a microlaser

The NPR stated a goal to reduce the operationally-deployed strategic stockpile to 3800 nuclear warheads by 2007 and 1700-2200 nuclear warheads by 2012. The force would be based on 14 Trident SSBNs (with 2 SSBNs in overhaul at any time), 500 Minuteman III ICBMs, 76 B-52H bombers, and 21 B-2 bombers. There would also be a non-strategic stockpile whose exact quantities and readiness requirements are still to be determined.

Although the NPR did not determine specific stockpile quantities or readiness requirements, it did introduce to the stockpile lexicon the categories operationally-deployed and responsive. Operationally-deployed warheads are warheads fully ready for use and either mated on, or allocated to, operational delivery systems; these warheads are part of the active stockpile. Responsive warheads are warheads available to be uploaded to delivery systems in the event that world events require a more robust deterrence posture; most or all of these warheads would also be part of the active stockpile. 3 Active weapons are fully maintained with all Limited Life Components (LLCs, e.g., tritium bottles) installed. Inactive weapons have the LLCs removed upon expiration.

Remaining warheads not slated for retirement or dismantlement would be retained in the inactive stockpile, available for use in stockpile evaluation support or as one- for-one reliability replacements for warheads in the operationally deployed or responsive forces. Several factors would determine the nature, size and scope of warheads in this "other" category including: (1) progress in reestablishing lost production capabilities and infrastructure, (2) response times to fix problems in the stockpile, carry out other required refurbishme nts to sustain the stockpile, and develop and produce new or modified warheads, and (3) desire to retain a sub-population of non-refurbished warheads to hedge potential common mode failures. Some warheads in this category would, based on future decisions, be retired and eliminated. NNSA and DoD will work together to clarify the NPR "drawdown" in terms of the numbers and types of warheads, by year, to be maintained in the active and inactive stockpiles at various states of readiness.

Stockpile stewardship includes nuclear weapons testing and science-based weapons experimentation and ensures the safety, reliability, and performance of the nation's nuclear stockpile. The research and development of the technologies required for stockpile management are included under stockpile stewardship.

The Science-Based Stockpile Stewardship (SBSS) program will build on existing means and develop new means to assess the performance of nuclear stockpile systems, predict their safety and reliability, and certify their functionality. The SBSS program not only must respond to the loss of nuclear testing, but also must deal with constraints on nonnuclear testing, the downsizing of production capability, and the cessation of new weapon designs to replace existing weapons. Further complicating matters, weapon components will exceed their design lifetimes, and manufacturing issues and environmental concerns will force changes in fabrication processes and materials of weapon components.

With the termination of underground nuclear weapons testing, the Department of Defense and the Department of Energy must maintain the nation's enduring stockpile on the basis of data about the weapons as they have actually been built, as opposed to how they were designed. For the foreseeable future, computer simulations will replace underground testing, and this calls for accumulating and analyzing even more as-built data as simulation input. The primary repositories of as-built data are the DOE manufacturing facilities such as the Oak Ridge Y-12 Plant. The simulations, however, will be run by the research and design laboratories, such as those at Los Alamos, Lawrence Livermore, and Sandia.

In many ways, nuclear weapons are typical high-technology manufactured products. Their design and production involves metallurgy and materials science, and the process includes typical industrial processes like casting, forming, and precision machining. Fabrication processes are followed by quality-assurance processes like inspection and radiography. Except for the particular materials used and the requirement for high levels of security, a weapons factory differs little from other precision manufacturing facilities. Weapons manufacturing does differ from other manufacturing, of course, in that it has never been possible to pull a sample off the production line and crash test it like an automobile. Even in the days when undergournd testing was permitted, test devices were uniquely designed and specially instrumented.

In such a manufacturing environment, quality assurance and collection of data from the manufacturing process becomes especially important. Every batch of raw material is analyzed for its composition and material properties. Machining and assembly are guided by exacting procedures. Each component coming from machining must be measured and certified on computerized coordinate-measuring machines before it can proceed to the next assembly step. As subassemblies come together, they are tested further, and radiographs (X-rays) are made after almost every major step. All of the procedures and design drawings for each step are kept under configuration control, and certification data is coordinated with the versions of the process documents. Assembly histories for regular production units, for this reason, run to several hundred pages, and those for special test devices can be even longer.

Nuclear weapons that reside in the stockpile have various configurations. But they generally incorporate plutonium, uranium, high explosives, plastics, adhesives, foams, and other materials that together make the weapon generate its designed yield.

To date, many changes related to aging and to incompatibilities between weapon materials have been observed. In the six high explosives used in various weapons, changes include swelling, plasticizer migration, binder degradation, mechanical property degradation, adhesive bond rupture, and incompatibilities. In addition, changes related to load retention and compression were found in the polymer foam cushions that provide padding between various weapon components.

Surveillance data on HE from the B83, W84, and W87 programs show no evidence of aging effects. Because the W87 system must be requalified for an additional 25 to 30 years, additional data are being gathered and analyzed to improve Livermore's long-term predictive capability. Aged LX-17 is being subjected to far more comprehensive testing than usual for stockpile laboratory test units. In essence, properties of control material from various sources are compared to the chemical, physical, mechanical, and performance properties of aged LX-17 for signs of age-induced changes.

Uranium, plutonium, lithium, and even gold exhibit surface corrosion. Several materials are affected by radiation from uranium and plutonium. Researchers also found incomplete curing, depolymerization, and hydrogen outgassing in some silicone compounds. In plastic parts, some polycarbonate material was degraded by ammonia gas emitted from a nearby component. An undesirably strong adhesion has developed between some plastic components. Some adhesives have incompletely cured, some are outgassing, and some bonds have weakened.

Organic materials are a particular concern. By their very nature, they can be less stable than many other materials. They have weaker bonds and tend to be reactive. They also are more readily damaged by the radiation that emanates from uranium and plutonium. Nevertheless, organics are an essential part of a weapon. Some serve chemical functions such as hydrogen "getters," which absorb damaging hydrogen in a weapon's hermetically sealed environment.

Other organics (such as silicone stress cushions, adhesives, and coatings) fill gaps, transmit loads, and mitigate vibration and shock, allowing a weapon to survive what is known as the stockpile-to-target sequence (STS). A weapon sitting in the stockpile encounters few traumas, but during the STS, it must endure transport on a truck, temperature changes during storage, and perhaps ultimately a launch and flight from under the wing of a plane, from a submarine, or from a land-based missile silo.

Insensitive high explosives are used in nuclear weapons for greater safety. An insensitive high-explosive component dropped during assembly or disassembly should not harm personnel, and a weapon that accidentally falls from a truck or even from an airplane should not detonate. Because the insensitive high explosive LX-17 is used in three of the four Livermore-designed weapons in the enduring stockpile, its reliability is paramount. Voids in high explosives are necessary to drive the detonation wave. But if voids increase in size as the explosive ages, the explosive may become somewhat less safe. High explosives are therefore a primary focus of work on aging weapons

Cellular silicone stress cushions fill gaps between components, compensate for manufacturing tolerances of adjacent components, allow for thermal expansion of components and age-induced swelling of high explosives, and provide thermal insulation. For the cushions to perform these jobs successfully, they must exert a specific range of compressive forces at predetermined maximum and minimum gaps. Because the cushions fill gaps for the life of the weapon, the long-term stress behavior of the cushion under load in the chemical and radiation environment of a weapon is an ongoing concern.