June 29, 2021

US pit production: Why we can wait, and why we should wait

Frank von Hippel is a senior research physicist and professor of public and international affairs emeritus with Princeton’s Program on Science & Global Security which he co-founded. His following remarks were made at SCELP's June 29, 2021 press conference calling for a Programmatic Environmental Impact Statement on the US pit-production program.


1. US pits are 40-50 years old. It is believed that they will last till at least 100 years.  The National Nuclear Security Administration (NNSA) has launched a ten-year accelerated-aging program to see how much longer. One preliminary result is 150 years.

2. NNSA’s priority is in fact not to produce replacement pits but rather new pits to make the warheads of DOD’s strategic ballistic missiles less susceptible to plutonium dispersal accidents.  Unless the US decides to return to Cold War levels of three warheads per ICBM, however, there are already a sufficient number of such warheads for US intercontinental ballistic missiles. If NNSA would reveal its proposed pit for DOD’s replacement SLBM warheads, it is possible legacy pits would be available for those warheads as well.

3. Given the lack of a demonstrated immediate need for new pits, the US can afford, without harming national security, to wait ten years for a new longevity estimate for US Cold War pits and also for more information on the pit requirements for NNSA’s proposed new SLBM warheads.

4. It also would be wise and cost effective to wait to see whether the pilot pit production facility at Los Alamos works before replicating it at the Savannah River Site.

How long will the legacy pits last? Virtually all of the pits in current US operational warheads were made in the 1980s during the last Cold War cycle of new warhead production before production at the US pit production facility in Rocky Flats, Colorado was shut down in 1989 for environmental infractions. Almost all the pits in US warheads are therefore 40-50 years old.

In 2006, a JASON group review of work on accelerated pit aging research done at NNSA’s Los Alamos and Livermore National Laboratories found,

“Most primary types have credible minimum lifetimes in excess of 100 years as regards aging of plutonium; those with assessed minimum lifetimes of 100 years or less have clear mitigation paths that are proposed and/or being implemented.”

On this basis, the earliest date that replacements would be required would be in the 2080s, more than a half century hence.

The JASON group recommended extending accelerated pit aging work until failure mechanisms emerged.  Accelerated aging studies by a Livermore group did push the estimated life past 150 years but a second Congressionally-commissioned JASON group review found in 2019,

in general, studies on Pu aging and its impacts on the performance of nuclear-weapon primaries have not been sufficiently prioritized [by NNSA] over the past decade.

In December 2020, the Senate Appropriations Committee ordered NNSA

to develop a comprehensive, integrated ten-year research program for pit and plutonium aging…The plan shall be submitted to the Committees on Appropriations of both the House and the Senate no later 180 days after enactment of this act.

Does the US need additional W87 pits? NNSA proposes to replace the 200 W78 warheads deployed on the 400 US Minuteman III intercontinental ballistic missiles (ICBMs) with W87-1 warheads, because the W-78s are more susceptible to plutonium dispersal accidents.  But DOD already has 340 nondeployed W87 warheads of the design which NNSA would like to produce.  The 200 W78s therefore could be replaced immediately by existing W-87s.

DOD would need additional ICBM warheads only if the US decided to load the Minuteman IIIs or their proposed successor intercontinental ballistic missiles (ICBMs), the Ground Based Strategic Deterrent (GBSD), to their full carrying capacity of three warheads each.  That would require a total of 3x400 = 1200 warheads. If the US kept its 600 W78 warheads6 in reserve for such an emergency, it would have 1140 total deployable ICBM warheads.  

Do we need new pits to replace all the warheads on the submarine-launched ballistic missiles (SLBMs)?  NNSA completed the life extension of approximately 1500 W76 warheads in 2019 and is on course to extend the lives of approximately 400 W88 warheads for a total of about 1900 SLBM warheads.  Currently, approximately half of these warheads are deployed.  But NNSA would like to replace all of them with warheads resistant to plutonium dispersal accidents.  The Navy, which has not suffered a plutonium dispersal accident in its history, resisted for three decades but finally, acquiesced. The Trump Administration announced that the first replacement warhead, the W93, would be, equipped with a pit that had already been tested with insensitive high explosive before the US ended its nuclear testing in 1992.  For some reason, NNSA has not specified the pit but the most likely is the pit for the W89, a warhead that was tested but not deployed because of the end of the Cold War.  According to one report, the pit was from the W-68, a previous SLBM warhead that was produced by the thousands in the 1970s.  Those pits are still available in storage at NNSA’s Pantex Plant in Texas, where more than 10,000 pits are in storage.

Is the US capable of simultaneously building two pit-production facilities? In 1996, DOE tasked Los Alamos to produce 31 W88 pits at its PF-4 plutonium facility. Production of the W88 pits had been cut off in mid-course by the shutdown of the Rocky Flats facility. Los Alamos struggled and finally produced the 31 pits over six years (2007-2012) with a peak production of 11 in 2007, even though NNSA had asked Los Alamos to demonstrate pit production at a rate of 20 pits/year.  In 2013, DOE shut down pit production at Los Alamos because of safety violations. Restart is currently scheduled for 2023 and production at a rate of 30 pits per year is scheduled for 2026. It remains to be seen whether and when, after 30 years of struggling and failing to produce pits safely, these goals can be achieved.

Los Alamos contains the reservoir of US expertise on pit production. Should it not be required to demonstrate at home a pilot facility that works before designing a second production facility at Savannah River?  NNSA recently admitted that production of 50 pits per year at the Savannah River Site, which will face a tremendous technical challenge given that the site has no pit-production experience, already has slipped by two to five years from 2030 to 2032-5 and that the cost estimate has already doubled, to over $11 billion.

Given that the requirement for new pits has not been established, why not wait to see whether the planned pit-production production line works at Los Alamos first?


* Based on Frank N. von Hippel, “Comments on National Nuclear Security Administration’s Draft Environmental Impact Statement for Plutonium Pit Production at the Savannah River Site in South Carolina,” 19 May 2020 and “Why a decision on a second US plutonium-pit-production factory should be delayed,” Bulletin of the Atomic Scientists, 12 June 2020, https://thebulletin.org/2020/06/why-a-decision-on-a-second-us-plutonium-pit-production-factory-should-be-delayed/.

[1] Steve Fetter and Frank von Hippel,“Does the United States Need a New Pit Production Facility?” Arms ControlToday, May 2004, Table 1, https://www.armscontrol.org/act/2004-05/features/does-united-states-need-new-plutonium-pit-facility.

[2] Pit Lifetime, JASON groupreview done for the National Nuclear Security Administration (2006) https://fas.org/irp/agency/dod/jason/pit.pdf.

[3] Livermore National Laboratory,“Plutonium at 150 years,” (2012) https://www.llnl.gov/news/plutonium-150-years.

[4] JASON letter report, 23 November2019, https://fas.org/irp/agency/dod/jason/pit-aging.pdf.

[5] Explanatory Statement for Energy andWater Development and Related Agencies Appropriations Bill, 2021, pp. 128-129, https://www.appropriations.senate.gov/imo/media/doc/EWRept.pdf

[6] Hans M. Kristensen and Matt Korda,“United States nuclear weapons, 2021,” Table 1, footnote 4, https://www.tandfonline.com/doi/pdf/10.1080/00963402.2020.1859865?needAccess=true.  

[7] R.E. Kidder, Assessment of theSafety of U.S. Nuclear Weapons and Related Nuclear Test Requirement~:

APost-Bush Initiative Update,Lawrence Livermore National Laboratory, UCRL-LR-109503, 1991, https://fas.org/programs/ssp/nukes/testing/kidderucrllr109503.pdf.

[8] “W89,” https://en.wikipedia.org/wiki/W89.

[9] Dr. Charlie Verdon, ActingAdministrator, National Nuclear Security Administration,  House Armed Services Committee, Subcommitteeon Strategic Forces Hearing: “FY22 Budget Request for Nuclear Forces and AtomicEnergy Defense Activities,” https://armedservices.house.gov/hearings?ID=E382890A-2CE2-4141-B0A6-F899B9D2A8B0, in response to a question fromchairman Jim Cooper, at 1 hour, 28 minutes.

[10] U.S. Department of Energy budget request for Fiscal Year 2022, NNSA volume 1,28 May 2021, p. 157, https://www.energy.gov/sites/default/files/2021-06/doe-fy2022-budget-volume-1-v4.pdf.

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