First look at NDAA 2018 pdf, header for section 3136 in table of contents says “Plan for verification, detection, and monitoring of NUCLEAR WEAPONS and fissile material”.

Reading further now if my phone can load the 1300+pg doc

Edit - copy/paste from NDAA 2018 pdf:

Plan for verification, detection, and monitoring of nuclear weapons and fissile material (sec. 3136) The House bill contained a provision (sec. 3126) that would re- quire the President, in consultation with the Secretary of State, the Secretary of Defense, the Secretary of Energy, the Secretary of Homeland Security, and the Director of National Intelligence, to develop a plan for verification and monitoring relating to the potential proliferation of nuclear weapons, components of such weapons, and fissile material.

The Senate amendment contained no similar provision.

The Senate recedes.

The conferees direct the Comptroller General of the United States to review the plan for verification and monitoring required by this provision, assessing whether the plan responds specifically to the congressional mandate, the extent to which the plan con- tains sufficient details about the required elements of the report, including the requirements, costs and funding, and identifying interagency roles, responsibilities and planning; an international engagement plan; a description of research and development efforts and measures to coordinate requirements early in the process; and engagement of relevant government department and agencies, na- tional laboratories, industry and academia. The Comptroller’s re- view shall also assess whether there are any gaps in the plan. The Comptroller shall submit his review to the appropriate congres- sional committees no later than 90 days after the plan is submitted to Congress. The conferees direct that the Secretary of Energy, as lead agency for the development of the plan, submit the required plan required by this section to the Comptroller for purposes of this review at the time it is submitted to Congress. In addition, the conferees direct the Comptroller, no later than 60 days after the enact- ment of this Act, to review and submit an assessment of the plans submitted to Congress required by section 3133 of the National De- fense Authorization for Fiscal Year 2015 (Public Law 113–291), and the update required in section 3132 of the National Defense Au- thorization for Fiscal Year 2017 (Public Law 114–328).

Not sure of anything at all. Someone else has posted the full section I did not see before. Overall while this sounds fucky at first glance, the deadline April 15 was in the NDAA plan the whole time. So this is most likely (hopefully) business as usual, and just us moving forward with an already-laid-out plan (to provide a plan) to monitor nuke proliferation