LANL Meets Plutonium Pit Production Goal

On August 17, Los Alamos National Laboratory's Plutonium Sustainment Program presented the National Nuclear Security Administration (NNSA) with the 29th—and final—plutonium pit for replacement in existing W88 warheads. The W88 is a thermonuclear weapon designed by LANL in the late 1980s for the U.S. Navy and deployed on Trident II submarine-launched ballistic missiles. Undeployed W88s are stored in the U.S. nuclear stockpile. The plutonium pit is the core of the W88. It initiates the weapon's nuclear chain reaction when imploded (explosively compressed) into a supercritical mass.

US Navy Photo

The Ohio-class ballistic submarine USS Alabama returns to Naval Base Kitsap from a deterrent patrol. The USS Alabama is one of 14 Ohio-class submarines, which are currently armed with the W88 nuclear warhead. –U.S. Navy photo by Ray Narimatsu/Released

The Laboratory's achievement demonstrates the United States' re-established capability to produce plutonium pits for weapons, and it completes a requirement for NNSA and the Department of Defense.

"For 19 years, the United States was the only nuclear superpower unable to build a pit and put it in a stockpile. That ended in 2007," notes Robert Putnam, director for the Plutonium Sustainment Program, which is responsible for pit manufacturing.

Since 2007, the Laboratory has manufactured new pits to replace pits destroyed as part of the U.S. Stockpile Stewardship Program (SSP).

"For 19 years, the United States was the only nuclear superpower unable to build a pit and put it in a stockpile. That ended in 2007."
–Robert Putnam, director for the Plutonium Sustainment Program

The goal of the SSP is to provide, without underground testing, high confidence in the safety, security, effectiveness, and reliability of the U.S. nuclear deterrent. After production and acceptance by the Department of Energy (DOE) and NNSA, the NNSA's Office of Secure Transportation ships these pits to the Pantex Plant outside of Amarillo, Texas. At Pantex the new pits are installed in disassembled W88 weapons, making the weapons once again fully assembled ("full up") and ready for deployment.

Better, Faster, and Cheaper

Putnam attributes the program's success to a solid and definitive production model that helps the program define costs and process improvements to increase efficiency and efficacy. "We've gotten significantly better at what we do. The program has achieved a significant reduction in overall cost for capability, demonstrating the program's commitment to manufacturing better, faster, and cheaper pits."

In 1993, NNSA gave LANL the mission to re-establish the nation's capability to manufacture pits for the stockpile. This mission followed the closure of the Rocky Flats Plant (near Denver, Colorado), the plant where pits were manufactured from 1952 to 1989. Under this mission, Putnam states, the Laboratory would "capture the technologies, methods, and procedures to build pits." At the time, Technical Area 55, the Laboratory's plutonium science and manufacturing facility, was—it still is—one of the few fully functional plutonium facilities in the DOE complex and the only one capable of taking on this mission.

In 2003, LANL produced the first pit with the requisite quality pedigree, Qual-1, needed for quality control and testing purposes. Before LANL's pits could enter the stockpile, the Laboratory needed to verify that the quality and performance of its pits equaled or exceeded the quality and performance of those from Rocky Flats—a daunting task in the era of no nuclear testing. This requirement was driven, in large measure, by one of the Laboratory's new pit manufacturing processes—casting—whereby the plutonium is melted and poured to make a pit. At Rocky Flats, pits were manufactured using a wrought process—the plutonium was rolled flat and then pressed into a pit. The wrought process requires significantly more time, labor, and facility space.

casting furnace

The casting furnace used for the last W88 plutonium casting.

Following the production and certification of Qual-1, the Laboratory developed and nondestructively evaluated its next Qual pits to ensure consistency in their structural, chemical, and metallurgical quality. In the end, the quality and performance of LANL's cast pits were deemed to be on par with pits manufactured at Rocky Flats. After nearly a decade of development, Qual-1 and the Qual pits that followed repeatedly demonstrated the Laboratory's ability to manufacture fresh plutonium pits.

By 2007, the Laboratory produced its first production pit: Prod-1. Prod-1 was the first pit incorporated into the nuclear stockpile as a replacement pit for a W88 warhead. In 2007, the program had also achieved a 10-pits-per-year capacity, as required by the NNSA and Congress. In that same year, the program manufactured 17 Prod pits, of which 12 met LANL's and NNSA's quality standards—a 70 percent success rate. The pits that did not meet all the quality standards were recycled.

Pit manufacturing is a "use it or lose it" endeavor precisely because it requires constant production to maintain quality and increase efficiency.

By 2009, the program achieved a 100 percent success rate—an increase in efficiency of 30 percent—with every pit produced demonstrating the quality standards required for incorporation into the stockpile. In addition to improving efficiency, the Laboratory decreased the cost of its 10-pits-per-year capacity by nearly 30 percent.

Perfect Pits from Lessons Learned

The Plutonium Sustainment Program has learned two major lessons.

First, "practice makes perfect pits," says Putnam. Significant interruptions to the production cycle increase the risks of introducing deviations into the manufacturing process, which can lead to production errors, resulting in a considerable increase in the scrap rate, that is, a higher number of unusable pits. In addition, efficiency is lost. Pit manufacturing is a "use it or lose it" endeavor precisely because it requires constant production to maintain quality and increase efficiency.

Says Tim George, acting associate director for Plutonium Science and Manufacturing, "Making pits is a process and an exercise in capability. If that capability is not used, it atrophies—becomes 'rusty.'"

Furthermore, manufacturing is needed to provide training opportunities for new staff who replace those who leave or retire.

Molten plutonium in a crucible

Molten plutonium in a crucible. Before LANL's cast pits could enter the stockpile, the Laboratory needed to verify that their quality and performance equaled or exceeded the quality and performance of the wrought pits produced at Rocky Flats.

While it is ideal to manufacture pits start to finish—to complete the process without interruption—it is possible for the program to maintain its manufacturing ability by, for example, building surplus pits and disassembling them. Over the next few years, the program plans to build or assemble four to six pits a year for various experiments and later disassemble them to practice production and to maintain a capability for the future.

The second lesson learned, according to Putnam, is that "a risk taken tends to become a risk realized." When risks—or sacrifices—to the pit manufacturing program are taken, unfavorable realities are the likely result. For example, in the spring of 2011, temporary cuts to the equipment maintenance budget led to a temporary failure of the plutonium casting furnaces, costing five weeks of production time and $1 million for recovery efforts.

Pit manufacturing personnel

Pit manufacturing personnel perform an operational check on equipment used in the fabrication of the final W88 pit.

Pit Manufacturing Process

"Pit manufacturing is an art," Putnam asserts. By learning from experienced subject-matter experts at Rocky Flats, LANL, and Lawrence Livermore National Laboratory, the Plutonium Sustainment Program was able to learn the process and then improve it.

To manufacture a single pit, the program today relies on nearly 700 employees, of which approximately 300 are dedicated full time to pit manufacturing. These employees, from scientists and administrators to technical and clerical support, bring their unique knowledge, skills, and experiences to the process. For example, practiced operators craft the pit using processes of plutonium purification, casting, machining, welding, assembly, and nondestructive evaluation, including radiographic testing and chemical and metallurgical analyses.

Future of Pit Manufacturing

Following the completion of the 29th pit, the Plutonium Sustainment Program will maintain the capability to development other types of pits and weapons components for future stockpile stewardship endeavors. These new pits will be used to support SSP activities and to develop and demonstrate the ability to manufacture different pit designs that are represented in the current stockpile. "We've broadened our portfolio. We're not just pit manufacturing anymore. We're involved in many aspects of sustaining the capability to work with significant quantities of plutonium and manufacture other weapons components that require plutonium," says Putnam.

The Laboratory will reach a future production capacity of 50 to 80 pits per year by maintaining the physical infrastructure and capability to produce pits, modifying the program's equipment, and obtaining the right levels of skilled staff and an appropriate budget. LANL will already be in the pit-development cycle when NNSA issues the next order for pits. At that time, the Plutonium Sustainment Program will have the staff, systems, and equipment required to produce what NNSA wants

"It's the highly committed, highly dedicated people doing this work who have made the program so successful. Their trade skills, education, and attention to detail make the LANL pit manufacturing staff one of the country's most valuable assets," says George.

–Marisa Sandoval

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