The Savannah River Site in February completed upgrades to tritium processing facilities at the site’s H-Area that will allow personnel to fill tritium reservoirs for the planned B61-12 nuclear gravity bomb life-extension program, the site said Tuesday.

The upgrades doubled the capacity of one of the site’s tritium lines capacity, according to a press release, and involved “removing dozens of valves, reducing gas flow restrictions and the time required to remove extraneous gas during the loading process.”

The planned B61-12 gravity bomb will homogenize four versions of the oldest deployed U.S. nuclear weapon. South Carolina-based Savannah River will help fill up the tritium reservoir for the weapon’s 3X Assembly, part of B61-12’s new gas transfer system. Tritium, a radioactive hydrogen isotope, increases the efficiency of thermonuclear weapons, increasing their destructive power.

The Department of Energy’s National Nuclear Security Administration (NNSA), which manages civilian nuclear weapons programs, plans to replace the tritium facilities at Savannah River Site’s H-Area Old Manufacturing Facility with a new Tritium Finishing Facility that is supposed to be operational around 2030, site officials have said.

Including Air Force and NNSA work, the B61-12 will cost between roughly $11.5 billion and $13 billion over about 20 years, according to documents from the Energy and Defense departments. The NNSA’s share of the bomb’s cost is about $8 billion, the agency estimates. The F-35A fighter and the planned B-21 Raider stealth bomber will eventually carry B61-12.

After delays related to capacitors used by multiple components of the B61-12, the NNSA expects to complete B61-12 first production unit in November 2021.