Experimental simulations of gas-driven eruptions: kinetics of bubble growth and effect of geometry

(i) Experiments have been made on the incidence and time of onset of decompression sickness in mice exposed in single or repeated exposures to raised pressures of nitrogen or helium . If a first (conditioning) exposure to pressure is followed 5 min later by a second (test) exposure, the incidence of sickness is considerably higher than that for either exposure alone, or for a single exposure equal in length to the sum of the other two exposures. The same result is obtained if the conditioning exposure is to saturation. Sickness produced by repeated exposures has a shorter latency of onset than after single exposures. These results are explicable on the basis of asymptomatic bubble formation after decompression. (ii) This latent susceptibility to decompression sickness, as revealed by the test exposure, initially increases with time after decompression, reaches a maximum, and then declines. The rate of decline is faster than can be accounted for on the basis of the decay and local reabsorption of bubbles. It is suggested that gas bubbles are also removed by passage from the tissues through the venous system to the lungs. (iii) The degree to which very short second exposures to pressure (lasting only a few seconds) give rise to the symptoms of decompression sickness cannot be explained on the basis of the kinetics of bubble growth. These symptoms could also arise from compression by the second exposure of bubbles in the tissues, allowing them to enter the venous system and pass to the lungs, where, if expanded by decompression before elimination, they give rise to severe decompression sickness. (iv) These observations are in direct conflict with the principles on which current decompression tables are based. The relative success of the latter must be attributed to the empirical manner in which the tables have been constructed and modified in the light of experience.The results support the theory that separated gas may be present in symptomless decompressions and raise the question of gas transport to the lungs as a factor which should be taken into account in the design of decompression tables.

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Direct observations of radiation-enhanced transformations in glass

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100075543 ◽

1983 ◽

Vol 41 ◽

pp. 354-355

Author(s):

J. F. DeNatale ◽

D. G. Howitt

Keyword(s):

Glass Matrix ◽

Diffusion Mechanism ◽

Bubble Formation ◽

Silicate Glasses ◽

Phase Decomposition ◽

Direct Observations ◽

Thin Foils ◽

Oxygen Bubble ◽

Electron Energy Loss ◽

Kinetics Of

The electron irradiation of silicate glasses containing metal cations produces various types of phase separation and decomposition which includes oxygen bubble formation at intermediate temperatures figure I. The kinetics of bubble formation are too rapid to be accounted for by oxygen diffusion but the behavior is consistent with a cation diffusion mechanism if the amount of oxygen in the bubble is not significantly different from that in the same volume of silicate glass. The formation of oxygen bubbles is often accompanied by precipitation of crystalline phases and/or amorphous phase decomposition in the regions between the bubbles and the detection of differences in oxygen concentration between the bubble and matrix by electron energy loss spectroscopy cannot be discerned (figure 2) even when the bubble occupies the majority of the foil depth.The oxygen bubbles are stable, even in the thin foils, months after irradiation and if van der Waals behavior of the interior gas is assumed an oxygen pressure of about 4000 atmospheres must be sustained for a 100 bubble if the surface tension with the glass matrix is to balance against it at intermediate temperatures.

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Irradiation behavior of pyrolytic silicon carbide

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100074288 ◽

1983 ◽

Vol 41 ◽

pp. 72-73

Author(s):

R. J. Lauf

Keyword(s):

Silicon Carbide ◽

Fission Products ◽

Thermodynamics And Kinetics ◽

Neutron Fluences ◽

Fuel Particles ◽

Sic Coatings ◽

Irradiation Behavior ◽

Kinetics Of ◽

Htgr Fuel

Fuel particles for the High-Temperature Gas-Cooled Reactor (HTGR) contain a layer of pyrolytic silicon carbide to act as a miniature pressure vessel and primary fission product barrier. Optimization of the SiC with respect to fuel performance involves four areas of study: (a) characterization of as-deposited SiC coatings; (b) thermodynamics and kinetics of chemical reactions between SiC and fission products; (c) irradiation behavior of SiC in the absence of fission products; and (d) combined effects of irradiation and fission products. This paper reports the behavior of SiC deposited on inert microspheres and irradiated to fast neutron fluences typical of HTGR fuel at end-of-life.

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