PHYSICO-CHEMICAL STUDIES OF Fe--Cr--Al-CLAD FUEL SYSTEMS.

Reactions which can occur between oxidation-resistant Fe - CR - AL base alloys and UO{sub 2} at 500 to 1200 deg C are discussed. Aluminum in the Fe - Cr - Al-base cladding reduces the UO{sub 2} in the cermet fuels at 1000 to 1200 deg C. The U dissolves and diffuses through the cladding and is converted to an oxide. Oxygen combines with Al forming Al{sub 2}O{sub 3} which inhibits Al diffusion into the UO{sub 2}. The diffusion for Al in Cr leads to the development of a Cr barrier and reduces the Al - UO{sub 2} interaction and eliminates surface contamination. Free U as substoichiometric UO{sub 2-x} diffuses through 0.38 mm cladding within 100 hrs at 1000 deg C or in 6 hrs at 1200 deg C. At 1000 deg C, U solubility in Fe - Cr - Al-base alloy is 0.1 to 0.2% and its diffusion coefficient is in the range of 10{sup -9} to 10{sup -10} cm{sup 2}/cm. (F.S.)