In a sprawling building atop a mesa in New Mexico, workers labor around the clock to fulfill a vital mission: producing America’s nuclear bomb cores.

The effort is uniquely challenging. Technicians at Los Alamos National Laboratory must handle hazardous plutonium to create the grapefruit-size cores, known as pits. They do so in a nearly 50-year-old building under renovation to address aging infrastructure and equipment breakdowns that have at times disrupted operations or spread radioactive contamination, The New York Times found.

Now, the laboratory is under increasing pressure to meet the federal government’s ambitions to upgrade the nation’s nuclear arsenal. The $1.7 trillion project includes everything from revitalizing missile silos burrowed deep in five states, to producing new warheads that contain the pits, to arming new land-based missiles, bomber jets and submarines.

But the overall modernization effort is years behind schedule, with costs ballooning by the billions, according to the Congressional Budget Office. In 2018, Congress charged Los Alamos with making an annual quota of 30 pits by 2026, but by last year it had produced just one approved for the nuclear stockpile. (Officials have not disclosed whether more have been made since then.)

That pace has put the lab — and especially the building called Plutonium Facility 4, or PF-4 — under scrutiny by Trump administration officials.