Longer Life Seen for Warhead Pits

Tom Z. Collina

An ongoing study by a U.S. nuclear weapons laboratory has found that plutonium parts in warheads can last decades longer than previously thought, with potentially significant implications for multibillion-dollar government programs to maintain nuclear warheads.

The results of the study, which was conducted by Lawrence Livermore National Laboratory in California, have increased scientists’ confidence that the plutonium cores of nuclear warheads, known as pits, “will function as designed up to 150 years after they were manufactured,” said an article in the December issue of Science and Technology Review, the laboratory’s journal.

The findings are drawn from research for a study that was launched in 1997 by Livermore and the Los Alamos National Laboratory in New Mexico to examine how warhead pits change over time. The study provides a scientific basis for estimating their service life. Initial results, which were announced in 2006, showed that the pits would last at least 85 years, compared to the previous estimate of 45 to 60 years.

In a posting on the Livermore website about the most recent findings, Bruce T. Goodwin, the laboratory’s principal associate director for weapons and complex integration, said that “no unexpected aging issues” were seen in plutonium up to the 150-year mark.

During the Cold War, warheads were replaced by new designs well before the end of their operational life, and consequently weapons were rarely kept in the arsenal for more than about 25 years. Questions about how long pits might last beyond that time initially came to the public’s attention in 1989 when the United States’ main pit-production facility, the Rocky Flats Plant in Colorado, was shut down for safety violations after a raid by the FBI. The plant never reopened, and since then, the National Nuclear Security Administration (NNSA), a semiautonomous agency that oversees the nuclear weapons production complex, has tried more than once to secure funding to build a new one.

Under President George W. Bush, for example, the NNSA proposed building a plant known as the Modern Pit Facility, which would have produced 125 to 450 pits per year. (See ACT, May 2004.) Congress canceled the project in 2006.

The Livermore report finding raises questions about the need to build a facility at Los Alamos to support the production of new pits. The proposed plant, called the Chemistry and Metallurgy Research Facility Replacement (CMRR), is estimated to cost between $3.7 and $5.8 billion. The Obama administration, although it still supports the construction of a new pit facility, delayed the project for at least five years in its fiscal year 2013 budget request, saying that the facility was not yet needed.

The House-Senate conference report on the fiscal year 2013 defense authorization bill, which was approved Dec. 21, mandated construction of the facility by 2027, but capped costs at $3.7 billion. The energy and water appropriations bills that the House and Senate appropriations committees passed last year provided no funds for CMRR construction for fiscal year 2013. (The government currently is funded by an interim spending bill that provides money until March 27.) The authorization legislation also required a cost-benefit analysis of reusing existing pits in warheads rather than producing new ones.

According to information that Los Alamos officials distributed on Capitol Hill in June, the CMRR was designed to meet a production requirement of 50 to 80 pits per year. That requirement was last reviewed in 2010 when pits were expected to last 85 years.

Until the CMRR is built, Los Alamos is proposing an interim plan that would produce 20 to 30 pits per year at a total cost of $800 million by using facilities at Los Alamos and other laboratories.

In a Dec. 17 e-mail to Arms Control Today, a Los Alamos spokesman said the Livermore study reaffirms the decision to “pursue a limited manufacturing capability in existing and planned facilities at Los Alamos.” He did not indicate the CMRR facility by name. Experts estimate that Los Alamos could now produce 10 to 20 pits per year in a section of the laboratory known as Technical Area 55.

The NNSA did not respond to a question about how the new estimate for the lifetime of the pits might affect future production requirements. In general, as pits last longer and the nuclear arsenal shrinks, fewer pits would have to be produced each year to deal with potential aging issues. Pits in current warheads are 35 years old or less. Nevertheless, pits may be produced for other reasons, such as to improve the safety and security of a warhead.

The NNSA is also seeking billions of dollars to extend the life of existing warheads, including the B61 bomb, which the Pentagon projects will cost more than $10 billion. (See ACT, December 2012.) The life extension program for the B61, like the ones for other warheads, would reuse the existing pits. Other parts would be rebuilt to match the original design. According to the Livermore journal, the study supports the current NNSA strategy of reusing existing pits in the near term and eventually producing new ones in existing and planned facilities.