Fission Fragment Recoil Effects on Zirconium Oxidation

Fission fragment recoil effects on zirconium oxidation in pure oxygen were studied at 1 atm pressure and 250 deg C. Specimens were oxidized under the following conditions: reactor radiations including recoils, reactor radiations in the absence of recoils, and no radiation. Irradiation experiments were conducted in a maximum thermal neutron flux of 8.5 x 1011 neutrons/cm 2-sec. Specimen surfaces subject to fission fragments were exposed to an estimated average recoil intensity of 6 x 108 particles/cm 2-sec, the average particle energy being about 32 Mev or approximates 40% of the initial energy. It was concluded from electron and optical microscopy studies of the specimens that the normal oxide film on surfaces exposed to recoils underwent a phase transformation with fine particle size, although the possibility that the normal oxide developed a fine particle size of random orientation was not ruled out. From estimates of oxide thickness based on interference colors and from a limited amount of weight gain data, it was concluded that the oxide film on surfaces exposed to fission fragments was thicker than surfaces exposed to reactor radiation alone. The amount of corrosion as indicated by the oxide thickness and weight data was at least a factor of ten less than that expected in a solution of uranyl sulfate producing an equivalent recoil intensity. However, the data obtained do not provide sufficient information to establish the mechanism of the effects of fission fragment recoils on zirconium oxidation.