The cost of modernizing one of the key U.S. nuclear weapons has now at least doubled, according to Sen. Dianne Feinstein (D-Calif.).

The program to keep the B61 warhead current now will cost at least $7.9 billion, according to the Energy Department’s National Nuclear Security Administration (NNSA), which manages the program. The Pentagon’s Cost Analysis Program Evaluation (CAPE) estimates the price tag is even higher: $10 billion, Feinstein says.

The senator, who leads the Senate Appropriations energy and water subcommittee that has jurisdiction over the NNSA, met with agency officials on July 23.

NNSA detailed the need for a revised cost estimate of the B61 program during a hearing earlier this year. And a program official said that without cost constraints on the life-extension program, “the wish list had gotten huge.” The warhead can be used on fighter jets and long-range bomber aircraft. The program is managed at Los Alamos National Laboratory, which is run by Bechtel and Sandia Corp., a Lockheed Martin subsidiary.

The Senate Appropriations Committee would provide $339 million for the life-extension program in fiscal 2013, a reduction of $30 million from President Barack Obama’s request because of “carry-over balances.” And the committee’s report on the fiscal 2013 legislation reflects lawmakers’ concerns about the lack of a valid cost, schedule or scope baseline. The House would provide the full $369 million request.

Feinstein said the recent cost increase will not alter the committee’s view of funding for next year. But it will prompt additional congressional scrutiny.

“We have to find a way to stop this from happening,” Feinstein said. “We’ve asked that we receive monthly reports, that one person be put in charge. ... The purpose of that is to make people solve problems quickly, before they are left and they just continue to grow.”