[Code of Federal Regulations] [Title 31, Volume 3] [Revised as of July 1, 2005] From the U.S. Government Printing Office via GPO Access [CITE: 31CFR540.315] [Page 220] TITLE 31--MONEY AND FINANCE: TREASURY CHAPTER V--OFFICE OF FOREIGN ASSETS CONTROL, DEPARTMENT OF THE TREASURY PART 540_HIGHLY ENRICHED URANIUM (HEU) AGREEMENT ASSETS CONTROL REGULATIONS--Table of Contents Subpart C_General Definitions Sec. 540.315 Uranium-235 (U235). The term uranium-235 or U235 means the fissile isotope found in natural uranium.