Uranium self-diffusion

Uranium self-diffusion in UN has quite recently been measured by Reimann et al. (333) based on an assumed pressure-temperature relation for constant composition. The results obtained, however, would indicate that the composition of the sample was not constant during the measurement. They presumed from the pressure dependence of D that uranium diffusion in UN is based on the vacancy mechanism. 

Murch GE, Bradhurst DH, de Brain HJ (1975) Oxygen self-diffusion in non-stoichiometric uranium dioxide. Phil Mag 32 1141-1150... 

Self-diffusion of uranium has been reported in the 1102 + phase but almost all data deal with stoichiometric or nearly stoichiometric UO2-... 

The self-diffusion of uranium in nonstoichiometric U02+,t has been reported by Hawkins and Alcock (309), Marin et al. (308) and Marin and Contamin (298), as summarized in Fig. 24. The agreement of the data is again poor, as in the case of stoichiometric composition, but a tendency may be discerned of increasing D value of uranium with increase of. x. This suggests that the diffusion of uranium may occur through uranium vacancies, and hence, uranium vacancies may exist in the 1702 +, phase along with oxygen interstitials. 

In-pile self-diffusion of uranium in stoichiometric UO2 and UC has been measured by Hoh and Matzke 3J6). The diffusion coefficients obtained at a nominal irradiation temperature of 900°C and a fission rate of 1 x 10 //cm indicated that radiation-enhanced diffusion was higher by a factor of 10 to lO than determined by extrapolation of thermal diffusion coefficients. They suggested that the data are of immediate relevance to the understanding and the prediction of such quantities as in-pile sintering and densification, diffusion-controlled creep, and fission gas behavior in the outer zones of the fuel. 

The self-diffusion of uranium in stoichiometric UC which was doped with Fe is increased as compared to undoped UC at all temperatures studied (1380 to 2200°C). The increase was most pronounced (by more than a factor of 100) at low temperatures [1974Mat]. Simultaneously, pronounced grain-boundary penetration was observed at low temperatures. 

By means of the isotopic exchange reaction between uranium dioxide powders with a normal content, and carbon dioxide gas enriched in 1 0, the self-diffusion of oxygen in the stoichiometric and non-stoichiometric dioxide was measured. For essentially stoichiometric UO2, the diffusion of oxygen at 550 to 780C was... 

An important example of pressure diffusion (1) is the current worldwide competition to perfect a low-cost gas centrifuge capable of industrial-scale separation of the and U, gaseous hexafluoride isotopes. To date, atomic bomb and atomic power self-sufficiency has been limited to major powers since the underdeveloped countries have neither the money nor an industrial base to build the huge multi-billion dollar gaseous diffusion (2) plants currently required for uranium enrichment. In these plants, typified by the U.S. Oak Ridge Operation, and Up6 are separated by forcing a gaseous mixture of the... 

---