The Department of Energy announced in May that it will spend at least $7.6 billion to build new facilities to manufacture plutonium cores, known as pits, for nuclear weapons. Given the shrinking US stockpile, the probable usability of many pits from retired weapons, and the lack of new weapons on the drawing board, why are new pits required at all?

The Trump administration’s nuclear posture review released in February calls for DOE to build 20 new pits a year beginning in 2024 and increase production to 80 pits annually by 2030. The document said that a sustained pit-manufacturing capability is required “to avoid stockpile age-out, support life extension programs, and prepare for future uncertainty.”

If a US nuclear weapon were ever detonated, high explosives would implode the grapefruit-sized pit as it is flooded with neutrons from a generator. Fissioning of the plutonium would then generate x rays that implode the secondary, fusion–fission stage of the weapon.

LOS ALAMOS NATIONAL LABORATORY

The US lost its ability to produce pits in large numbers in 1989, when the Rocky Flats Plant near Denver, Colorado, was shut down after the Federal Bureau of Investigation and Environmental Protection Agency investigated environmental violations at the site. Up to 1200 pits per year were manufactured there—“Dr. Strangelove numbers,” says Los Alamos National Laboratory (LANL) director Terry Wallace. Since then, only 30 pits for weapons have been fabricated—all at LANL, the sole US facility with production capability. Weapons-quality pit production ceased in 2012, when LANL began modernizing its 40-year-old facilities, although several practice pits have since been fabricated. The oldest pits in the stockpile—which now numbers 3882, according to DOE’s National Nuclear Security Administration (NNSA)—date to 1978.

The NNSA plans to split its pit operations between LANL and the Savannah River Site in South Carolina. The controversial plan would include repurposing a plant being built to produce mixed oxide (MOX) fuel from surplus plutonium for commercial reactors to instead fabricate 50 pits per year. South Carolina’s congressional delegation opposes termination of the MOX plant due to the economic benefits it would bring to the region. Under the NNSA plan, LANL will retain its status as the center of plutonium R&D.

Opponents of new pit production, such as the watchdog Los Alamos Study Group, say pit production isn’t necessary to address aging or stockpile needs. Instead, says the group’s executive director Greg Mello, the plans “arise from a combination of ideology, contractor influence, and pork-barrel politics.” And Jay Coghlan, director of the antinuclear group Nuclear Watch New Mexico, says pit-production requirements have been driven by proposals from the labs for new interoperable warhead types that would fit both US Navy and US Air Force missiles. The Trump posture review included no mention of such a warhead. Critics suspect the military wants a pit-manufacturing capability simply because Russia has one.

Long lifetimes predicted Section: Choose Top of page ABSTRACT Long lifetimes predicted << Running the numbers The opponents of pit production point to scientific studies that strongly suggest that aging won’t affect the functioning of pits until at least the 2060s and perhaps much longer. Most notable is a 2006 report by JASON, a group of independent science advisers to the government. Its report said that the pits in most types of weapons will last at least 85 years, so the oldest pits shouldn’t need replacements before 2063. A 2008 memo signed by the secretaries of energy and defense went further and declared that “depending on warhead type, the best estimate of minimum pit life is 85–100 years.” Even so, the memo stated, “degradation from plutonium aging still introduces uncertainty in overall system performance,” and “as the stockpile continues to age, the United States must plan to replace considerable numbers of pits in stockpiled weapons.” A 2012 study by Lawrence Livermore National Laboratory identified no unexpected aging issues with plutonium for at least 150 years. Yet in 2014 then secretary of defense Chuck Hagel told lawmakers that the effects of aging plutonium were a factor in establishing the need for new pit production. The basis for his concern, however, was classified. An NNSA spokesperson says the JASON study “validated the framework used for evaluating pit lifetimes” but notes that the study’s lifetime estimates applied to most, but not all, weapon types. The effects of aging and the lifetimes for a warhead system vary from one type of weapon to another, the spokesperson notes. The 2012 lab study also called for further research to more fully understand the pit-aging process. Although factors other than aging were used to set the production requirement of 80 pits per year, they are classified, the NNSA official says. “We disagree significantly” with the JASON findings, says LANL director Terry Wallace; he notes that pit aging extends to how plutonium interacts with other components of the pit and weapon. Siegfried Hecker, a plutonium expert who was LANL director from 1986 to 1997, also takes issue with the JASON conclusions, which he says led to a “dramatic decline” in research on pit aging. Hecker maintains that despite differences, scientists at LANL and Lawrence Livermore National Laboratory were pressured to reach a consensus on aging that could be reviewed by JASON, and key aging issues were left unresolved. He also notes that since the JASON review, a reinterpretation by LANL researchers of results from underground experiments suggests the need to revise pit lifetime estimates.