Duplex coated fuel particles consist of two discontinuous layers of pyrolytic coating. Theoretical advantages of the layered construction appear substantiated in irradiation tests. The inner coating is applied at temperatures of 1400 C to 1750 C, and the high-density, more graphitic final coating is applied at 1800 to 2200 C. Coating micro-structure may be varied from a rough-surfaced highly oolitic conical pyrolytic to a smooth, glossy fine coned pyrolytic. The force necessary to crush these particles is inversely proportional to pyrolytic cone length. Irradiation of Duplex particles at temperatures up to 1200 C and bum-up s to 30 atom percent show a steady Kr88 of 10-5.