Lell, R.; Grimm, K.; McKnight, R.; Shaefer, R.; Division, Nuclear Engineering & INL. ZPPR-20 phase D : a cylindrical assembly of polyethylene moderated U metal reflected by beryllium oxide and polyethylene., report, September 30, 2006; (https://digital.library.unt.edu/ark:/67531/metadc899618/m1/1/: accessed November 12, 2018), University of North Texas Libraries, Digital Library, digital.library.unt.edu; .