The Pentagon and the National Nuclear Security Administration (NNSA) are still “sorting out” exactly how many nuclear-weapon triggers the military needs and by when, the head of the civilian agency said in congressional testimony Wednesday.

Law requires the semiautonomous Department of Energy nuclear-weapons agency to make 80 pits a year by 2030 — a goal the agency last year acknowledged it would miss by at least two to five years.

“Is 80 the magic number?” Sen. Angus King (D-Maine) asked senior NNSA officials during a hearing of the Senate Armed Services Committee’s strategic forces subcommittee, which he chairs. “Is 80 the number we project we’ll need?”

“That’s a good question,” Jill Hruby, administrator of the NNSA, told King. “So we’re working really closely now with the Department of Defense, NNSA and the Department of Defense, to look at the outyear requirements and to see how we can satisfy the program of record in ways that we’re all comfortable with that mean a safe, secure, reliable and effective weapon program.”

The NNSA still plans to build a pair of plutonium pit plants to furnish the arsenal for much of the rest of this century, during which existing pits — which according to public estimates have a lifetime of 75 years to 80 years, if not longer — will become too old to reliably trigger explosions of the intended destructive power.

The NNSA expects to begin making about 30 pits annually at the Los Alamos National Laboratory in 2036 or so. A companion pit plant, to be built at the Savannah River Site from the partially completed Mixed Oxide Fuel Fabrication Facility plutonium recycling plant, will not come online until 2032 or 2035, the NNSA told Congress in June.

The Pentagon, and the NNSA, had previously framed the need for 80 pits a year as a hard requirement for completing the ongoing modernization of the U.S. nuclear arsenal inside of the 30-year window that opened in 2016 during the Obama administration. Congress has since codified the deadline in law.

In Wednesday’s hearing, Hruby told lawmakers that, despite the challenges with the Savannah planned River Plutonium Processing Facility, none of the pits in the arsenal are close to aging out. If need be, Hruby said, the NNSA could use existing pits to complete future nuclear-weapon life-extensions — though that would mean shorter stints for weapons in the field, compared with using new pits.

“[W]e are establishing pit production as a hedge against plutonium aging and pit aging,” said Hruby in an unprompted address to King. “[O]ur pits are not today at any kind of an aging cliff so we can reuse pits, we just don’t like that plan because we may have to take them out [of other nuclear weapons] before the end of the life of the weapon system.”