The U.S. Dept. of Energy has put a $23.5-billion price tag and December 2038 completion deadline on an effort to turn the unfinished shell of an abandoned nuclear megaproject into a plutonium-pit production plant.

The agency on Oct. 15 approved the Savannah River Plutonium Processing Facility Main Process Building’s performance baseline and authorized full construction. The National Nuclear Security Administration (NNSA), a DOE unit, confirmed the $23.5-billion amount to ENR Nov. 9.

The $23.5-billion baseline applies to the Main Process Building, which will modify the partially constructed, roughly 400,000-sq-ft structure originally built for the Mixed Oxide Fuel Fabrication Facility, or MOX, a since-canceled plant intended to convert surplus weapons-grade plutonium into commercial reactor fuel. The new facility is intended to produce at least 50 plutonium pits—the fissile cores of nuclear weapons—per year.

MOX construction began in 2007 with completion originally targeted for 2016.…