This isn’t an issue I’ve really worked on, but I found “this June 1995 report”:http://pogoarchives.org/m/nss/doe-cong-rpt-heu-naval-fuel-19950600.pdf a little while ago on POGO’s site and thought it might be of interest. Prepared by the Director of Naval Nuclear Propulsion and titled _Report on Use of Low Enriched Uranium in Naval Nuclear Propulsion_, the report seems to have been cited in a few places (I first found a reference in “this”:http://cns.miis.edu/npr/pdfs/81mahip.pdf Spring 2001 NPR piece), but it’s not the easiest thing to track down via Google.

Anyway, the report states that “Naval [reactor] cores use fuel enriched to a minimum of 93%” U-235. That’s the highest official USFG figure I ran across during a quick search; “IPFM”:http://fissilematerials.org/library/gfmr10.pdf describes fuel containing 97.4% U-235 as “the standard for U.S. submarine fuel.”