| Autor: |
V.W. Storhok, D.L. Keller, W. Chubb, R.F. Hilbert |
| Rok vydání: |
1972 |
| Předmět: |
|
| Zdroj: |
Materials Science and Engineering. 9:293-300 |
| ISSN: |
0025-5416 |
| DOI: |
10.1016/0025-5416(72)90045-6 |
| Popis: |
The external diametral swelling rates of uranium oxides, nitrides and carbides at temperatures of up to 1900°C are presented. Under similar conditions, the swelling rates are seen to increase from approximately 0.2 percent per 1020 fissions per cm3 at 1200°C to 10–30 percent per 1020 fissions per cm3 at 1900°C. This exponential or Arrhenius relationship of swelling rates to temperature is consistent with a diffusional creep model of swelling of fuels by fission gas pressures at these temperatures. Arguments are presented which show that diffusional creep processes are required in the formation of even the smallest of gas bubbles. Mechanisms are suggested by which gas bubble growth by diffusional creep can continue to form bubbles of larger sizes without invoking difficult bubble migration processes. The kinetic nature of high-temperature fission gas swelling requires the existence of a rate process dependent upon fuel properties. It is apparent that the most probable rate-controlling processes are the coupled processes of diffusion of gas atoms to clusters and of diffusion of vacancies, primarily Schottky vacancies, to both atoms and clusters. The driving force for vacancy flow to the sites of gas atoms is initially the lattice strain energy of the individual gas atoms and subsequently the “pressure” of gas atoms in “clusters” or “bubbles”. This dynamic driving force is reduced by the passive, temperature-independent force called “surface tension”, but the former is always in excess to provide kinetic action toward the equilibrium described by “surface tension”. |
| Databáze: |
OpenAIRE |
| Externí odkaz: |
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