SWELLING AND INERT GAS DIFFUSION IN IRRADIATED URANIUM

Technical Report · Sat Oct 31 04:00:00 EST 1959

OSTI ID:4260561

Barnes, R S; Churchman, A T; Foreman, A J.E.; Plail, O S; Pugh, S F; Walton, G N; Curtis, G C; Eldred, V W; Enderby, J A; Wyatt, L M

The increases in volume which occur when uranium is irradiated are of considerable importance in nuclear engineering since they impose a ceiling to irradiation levels and efficiency. These limitations may be overcome to some extent by principles of design or by the development of improved materials based on an understanding of the fundamental processes involved in swelling. Much of the swelling encountered is a result of the formation of fission products. In particular, bubbles of the inert gases may form and grow at elevated temperatures, and the factors which control these processes are of outstanding interest. Experiments designed to determine changes in density and dimensions in uranium on irradiation at temperatures below about 800 deg C are described and results reported. Severe swelling occurrcd at the higher temperatures. The total amount of gaseous fission products released from specimens during irradiation was small unless swelling reached a critical value. Further changes in volume may occur in uranium if it is annealed above the irradiation temperature after removal from the pile; the presence of irradiation, other than to produce the rare gases is not essential for swelling. Two investigations, involving material of about 0.4 and 0.2% burnup, respectively, are described. In both cases annealing treatments were carried out at temperatures between 550 and 1,000 deg C, and sufficient bubbles to account for the swellings observed were generally detected on subsequent metallographic examination. Factors involved in the nucleation and growth of such bubbles are considered in the light of the results. The emission of xenon and krypton from uranium into a stream of carrier gas during irradiation has been measured. For foils which were thick compared with the recoil range there was evidence that some type of diffusion process was operating in addition to surface recoil. The apparent diffusion coefficients were found to be greater than those detrrmined in out-of-pile experiments and possible reasons for this are put forward. The rate of escape of inert gases from uranium during short out-ofpile anneals in vacuo, after irradiation to 0.15% burnup or less, followed approximately a diffusion law, and diffusion constants were estimated for various temperatures in the range 400 to 900 deg C. Activation energies obtained in this way were low, suggesting grainboundary diffusion. The part played by diffusion as a factor in swelling is discussed and the effect of bubble formation on the apparent diffusion constants is considered. Methods of calculation, which in some cases have given increases in volume in reasonable accord with observation, have been developed, and improvements in knowledge of the properties of uranium, particularly under creep conditions, are leading to better agreement. The remaining anomalies may be accounted for in a number of ways which are discussed. (auth)

• Research Organization: Atomic Energy Research Establishment, Harwell, Berks, Eng.; United Kingdom Atomic Energy Authority, Sellafield, Cumb., Eng.
• NSA Number: NSA-13-006769
• OSTI ID: 4260561
• Report Number(s): A/CONF.15/P/81
• Country of Publication: Country unknown/Code not available
• Language: English

Related Subjects

ACTIVATION ENERGY
ANNEALING
BUBBLES
BURNUP
DENSITY
DIFFUSION
EXCITATION
EXPANSION
FISSION PRODUCTS
FOILS
GRAIN BOUNDARIES
HIGH TEMPERATURE
INERT GASES
IRRADIATION
KRYPTON
MEASURED VALUES
METALLOGRAPHY
METALLURGY AND CERAMICS
NUCLEATE BOILING
NUMERICALS
QUANTITATIVE ANALYSIS
RADIATION EFFECTS
RECOILS
TEMPERATURE
THICKNESS
URANIUM
VACUUM
VARIATIONS
VOLUME
XENON