United States. Government Accountability Office. Nuclear Nonproliferation: National Nuclear Security Administration Has Improved the Security of Reactors in its Global Research Reactor Program, but Action Is Needed to Address Remaining Concerns, report, September 17, 2009; (https://digital.library.unt.edu/ark:/67531/metadc299085/m1/1/: accessed November 21, 2018), University of North Texas Libraries, Digital Library, digital.library.unt.edu; .