; and (2) an estimate of the cost of meeting such milestones during the four fiscal years following that fiscal year. . (b) Clerical amendment The table of contents for the Atomic Energy Defense Act is amended by inserting after the item relating to section 4408 the following new item: Sec. 4409. Estimation of costs of meeting defense environmental cleanup milestones required by consent orders. . 3122. Extension of suspension of certain assessments relating to nuclear weapons stockpile Section 3255(b) of the National Nuclear Security Administration Act ( 50 U.S.C. 2455(b) ) is amended by striking fiscal year 2018 or 2019 and inserting any of fiscal years 2018 through 2023 . 3123. Repeal of requirement for review relating to enhanced procurement authority Section 4806 of the Atomic Energy Defense Act ( 50 U.S.C. 2786 ) is amended— (1) by striking subsection (e); and (2) by redesignating subsections (f) and (g) as subsections (e) and (f), respectively. 3124. Determination of effect of treaty obligations with respect to producing tritium Not later than February 15, 2020, the Secretary of Energy shall— (1) determine whether the Agreement for Cooperation on the Uses of Atomic Energy for Mutual Defense Purposes, signed at Washington July 3, 1958 (9 UST 1028), between the United States and the United Kingdom, permits the United States to obtain low-enriched uranium for the purposes of producing tritium in the United States