A leaked report from a nominally independent office within the National Nuclear Security Administration offers a trove of new details about the cost estimate for a plan the agency must sell to Congress to start producing nuclear-warhead cores in South Carolina.

Last week, Energy Secretary Rick Perry said he would officially cancel the Mixed Oxide Fuel Fabrication Facility (MFFF) — intended to deweaponize 34 metric tons of surplus weapon-usable plutonium — and convert the unfinished building into a factory capable of annually making 50 fissile warhead cores called plutonium pits by 2030.

Perry cited authority given to him by Congress to cancel the facility if he could prove an alternative, called dilute and dispose, could deweaponize the plutonium for half the cost of finishing the MFFF. Perry said dilute and dispose would cost about $20 billion while MFFF would cost about $50 billion.

Now, a 37-page report from the NNSA’s Cost Estimation and Program Evaluation office, obtained by the Union of Concerned Scientists and posted online Monday, fills in some of the details.

In inflation-adjusted terms, dilute and dispose would cost about $20 billion from 2019 through 2050, the CEPE office estimated in the study. That averages about $645 million per year.

Nearly $8 billion would be spent at the Los Alamos National Laboratory in New Mexico, which would process plutonium pits into plutonium oxide ahead of further downblending at the Savannah River Site’s K-Area. Savannah River would take the next biggest share of dilute and dispose costs at around $6 billion, according to the internal NNSA report. The Waste Isolation Pilot Plant (WIPP), which would receive the processed plutonium, bears the third-largest share of the costs at about $1.2 billion inflation-adjusted dollars, the report says.

Transportation costs to WIPP from the Savannah River Site — an expense Rep. Mike Simpson (R-Idaho) has demanded the NNSA tally before it even thought of canceling the MFFF — would ring in at about $650 million over the life of the project. That includes both transportation and the criticality control overpack containers “and other containers” that would hold the material during the ride, according to the report.

Simpson and his colleagues on the House Appropriations Committee have their first opportunity to reject or accept the NNSA’s estimates today during a markup of the agency’s 2019 budget bill. The legislation, approved for a vote last week days before the agency announced its pit decision, funds MFFF and zeroes out the NNSA’s request for dilute and dispose.