Plutonium pits are a critical core component of a nuclear weapon. To ensure the reliability, safety, and security of nuclear weapons without underground nuclear testing; weapons go through a surveillance process, where they are regularly taken apart, examined, and tests run on their components.
Most of the weapons are reassembled and returned to the stockpile; however, some of the inspections are so thorough that the pit and other components are destroyed during evaluation. In order for this weapon to reenter the stockpile, a replacement pit is needed.
NNSA lost the capability to manufacture replacement pits since the Rocky Flats Plant closed in fiscal year 1992. For the W88 warhead, this was a concern because there were not enough W88 pits to replace ones that were destroyed during the surveillance process.
By 2007, NNSA reconstituted its ability to manufacture pits, which is now done at Los Alamos National Laboratory. The W88 warhead was able to be re-assembled, certified and accepted into the stockpile with a newly manufactured pit without conducting an underground nuclear test. Certification was possible because of NNSA's powerful experimental tools, supercomputers, and improved computer models. NNSA manufactured a limited number of pits for the W88 from 2007-2012.