Research Suggests Warhead Plutonium Pits Last Longer

By David Ruppe
Global Security Newswire

WASHINGTON — Recent research by a U.S. laboratory suggests that plutonium contained in U.S. nuclear warheads may be reliable significantly longer than previously expected, which some experts say reduces the urgency for developing new warheads (see GSN, Feb. 8).

A senior Energy Department official said yesterday, though, that there is not yet government consensus on the finding, and that the Bush administration’s emerging Reliable Replacement Warhead effort still would be useful for hedging against unexpected problems with aging warheads in future decades, as well as for other reasons.

Confidence is high in the reliability of the current U.S. nuclear weapons stockpile, National Nuclear Security Administration chief Linton Brooks told the Strategic Forces Subcommittee of the House Armed Services Committee. He said that ongoing research has convinced him that U.S. scientists are keeping up with the effects of aging warheads.

“Right now, our best estimates [of the lifespan of warhead plutonium] are somewhere between 45 and 60 years, and that sounds like a long time, but remember, the last pit we made was made in the 1980s,” Brooks said. After that, “The properties have changed to the point where you lack confidence that what you saw when you were testing is what you’d see now.”

He then alluded to recent but yet unreleased department-funded research that suggests the plutonium in warheads may age even better than previously expected.

“It may turn out to be that it’s 60-plus. We’re doing accelerated aging tests to find that out,” he said.

The oldest warhead in the arsenal is said to be in the 40s.

An initial assessment by the Lawrence Livermore National Laboratory of the minimum age at which pits need to be replaced, published in 2003 in JOM, formerly the Journal of Metals, was 45 to 60 years.

The additional research by the laboratory finds longevity for the warheads’ plutonium cores could extend well past 60 years, according to Raymond Jeanloz, a professor earth and planetary science and of astronomy at the University of California, Berkeley.

“The remarkable finding is that key materials making up the nuclear explosive package are far more stable and predictable than anyone would have anticipated. Recent developments reinforce the conclusion that plutonium pits and the U.S. stockpile are stable over periods of at least 50 to 60 years and probably much, much longer,” he said at an Arms Control Association panel discussion last month.

Jeanloz, who chairs the National Academy of Science’s International Security and Arms Control Committee, argued the finding suggests there should be no great urgency to proceed with the Reliable Replacement Warhead program. The initiative was first funded last fiscal year, as an effort to develop new warheads with greater reliability over the long-term, among other attributes.

Having more reliable and more-easily manufactured and serviced warheads in the arsenal should allow the United States to keep fewer in reserve, administration officials have said.

“The key motivation for RRW would … be to support the decision to significantly reduce the arsenal,” Jeanloz said. “Without that reduction, however, there is no widely accepted motivation as of yet for an RRW program. … Plutonium aging does not force us to a decision point at present.”

Following the hearing yesterday, Brooks told Global Security Newswire that there is not government consensus yet on the new finding.

“Our official position is 45 to 60 years. I think that many believe that Raymond is right, that it’s going to be on the high end of that. But I don’t think we know yet.  There’s supposed to be a statement later this year,” he said.

The administration has requested $27.7 million for the Reliable Replacement Warhead program to continue early research work in fiscal 2007, and additional millions to fund other programs such as an increased pit production capability that would enable new warheads to be produced as soon as 2012.

The department is requesting $6.41 billion for all nuclear stockpile activities for fiscal 2007.

The United States is estimated by nongovernmental analysts to have approximately 10,000 nuclear weapons deployed and in reserve, and the Bush administration in May 2004, without confirming that number, said that it would reduce the total “by nearly half” by 2012, with no more than 2,200 deployed at any given time.

The Reliable Replacement Warhead program could enable further stockpile reductions, Brooks has said, by developing a capacity for developing and building warheads with new capabilities more rapidly. 

“The reduced stockpile the president approved in 2004 still retains a significant non-deployed nuclear stockpile as a hedge against technical problems or geopolitical changes. Once we demonstrate [through the Reliable Replacement Warhead program] that we can produce warheads on a timescale in which geopolitical threats could emerge, we would no longer need to retain extra warheads to hedge against unexpected geopolitical changes,” Brooks said in a written statement to the committee yesterday.

Goals of the program set by a joint committee made up of Defense and Energy representatives in 2004, Brooks said yesterday in his printed statement to the committee, include “revitaliz[ing] our weapons design community to meet the challenge of being able to adapt an existing weapon within 18 months and design, develop, and begin production of a new design within three to four years of a decision to enter engineering development.”

The program could bring other benefits to the U.S. arsenal, he said, such as improved warhead safety and security, reduced danger to the environment, and a reduced need to resume live weapons testing to address a stockpile problem.

Jeanloz last month argued that of all the suggested benefits of the program, the only credible rationale for investing in it is to shrink the arsenal, and that the recent research on plutonium longevity undermined that rationale. 

“To be sure, new phenomena may appear in the future, but these will be uncovered through ongoing work such as accelerated aging experiments. Meanwhile, the technical conclusion is that we do have time for a thorough and well-informed discussion of U.S. nuclear weapons policy,” he said.

Brooks told the committee yesterday the Reliable Replacement Warhead program could further reduce uncertainties about aging nuclear weapons that might emerge in 20 years.

“Why should we take that risk? Because, if there were a problem, then we’re faced with either an unreliable stockpile or what would be a hugely traumatic event of after 20 years resuming nuclear testing,” he said.

“The Reliable Replacement Warhead idea is to drive us farther away from those [risk] margins so that we have less concern,” Brooks said.

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