(a) In General.—Except as provided in subsection (b), amounts appropriated pursuant to a DOE national security authorization for operation and maintenance or for plant projects may, when so specified in an appropriations Act, remain available until expended.

(b) Exception for Program Direction Funds.—Amounts appropriated for program direction pursuant to a DOE national security authorization for a fiscal year shall remain available to be obligated only until the end of that fiscal year.