Solute diffusion in dilute alloys

The first and basic step in gas release is single gas atom diffusion. The lattice location of rare gas atoms in the UO2 lattice and the mechanism of this diffusion process are discussed. Trapping of single gas atoms is important for out-of-pile laboratory work and helps to explain much of the scatter in the reported data. It is less important in-pile due to irradiation induced resolution. The experimental techniques used to measure gas diffusion and release are critically discussed. The available data on fission gas bubble mobility are reviewed. The reliable knowledge is scarce. The effect of burn-up (change in O/M-ratio, in-growth of fission products) is treated. The relative contributions of single gas atom diffusion, fission gas bubble mobility, sweeping and inter-granular bubble growth are discussed for the cases of highly rated fast breeder fuel and moderately rated water reactor fuel. It is argued that single gas atom diffusion is contributing essentially to release in LMFBR fuel, whereas t...

Gas release mechanisms in UO2—a critical review

Colossal carbon supersaturation in austenitic stainless steels carburized at low temperature

Ten measurements of the isotope effict for diffusion of Fe/sup 55/ and Fe/sup 59/ in pure single cryatals of silver and copper were made over approximately a 300 deg C temperature interval below the melting point. The measured isotope effect was found to be about 2/3, significantly less than the value of unity expected from conventional reaction rate theory. It is shown from Vineyard's extension of reaction rate theory that the measured isotope effect is to a good approximation a product of the Bardeen-Herring correlation factor and the fraction of the total translational kinetic energy associated with the diffusing tracer in a tracervacancy exchange. It is shown that the ring, interstitialcy, crowdion, and relaxion mechanisms are not responsible for diffusion in the systems studied. The three-frequency theory of correlation for vacancy diffusion in fcc lattices is extended to show that the relative frequency factors are vacancy exchange. It is shown that the ring, interstitialcy, crowdion, and relaxion mechanisms are not responsible for diffusion in the systems studied. The three-frequency completely specified by a knowledge of the correlation factor and the diffusion coefficients. An expression for the difference in the Arrhenius Q and the activation energy due to the temperature dependencemore » of the correlation factor is derived. This theory is shown to be inconsistent with the observed isotope effect if many-body effects are neglected. It is shown that a "long-range" repulsive interaction between the vacancy and impurity would be necessary if the measured isotope effect is to be explained purely in terms of correlation. (auth)« less

M.C. Naik

Papers

Diffusion of carbon in stainless steels

Lattice and grain boundary diffusion of chromium in superalloy Incoloy-800

Temperature dependence of diffusivity of xenon in high dose irradiated UO 2

Release of xenon from low-dose irradiated thoria pellets

Mass transport of chromium and nickel in monel-400