29 research outputs found
Kinetics of helium bubble formation in nuclear materials
The formation and growth of helium bubbles due to self-irradiation in
plutonium has been modelled by a discrete kinetic equations for the number
densities of bubbles having atoms. Analysis of these equations shows that
the bubble size distribution function can be approximated by a composite of:
(i) the solution of partial differential equations describing the continuum
limit of the theory but corrected to take into account the effects of
discreteness, and (ii) a local expansion about the advancing leading edge of
the distribution function in size space. Both approximations contribute to the
memory term in a close integrodifferential equation for the monomer
concentration of single helium atoms.
The present boundary layer theory for discrete equations is compared to the
numerical solution of the full kinetic model and to previous approximation of
Schaldach and Wolfer involving a truncated system of moment equations.Comment: 24 pages, 6 figures, to appear in Physica
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Role of gas pressure and lateral stress on blistering
Both gas pressure in bubbles and lateral stress have been suggested as primary causes of blistering. An analysis of both mechanisms is presented, and the conditions for blistering are examined. To realistically predict the gas pressure in bubbles, a recently derived high-density equation of state for helium is utilized
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Stress-induced deformation of metals during fast-neutron irradiation
From European conference on irradiation embrittlement and creep in fuel cladding and core components; London, UK (9 Nov Theoretical models for the deformation of metals subjected simultaneously to external loads and fast-neutron irradiation are discussed. The following models have been analyzed in detail: dislocation climb; climb controlled glide; and nucleation, growth, and unfaulting of dislocation loops. It is shown that the strains produced only by the climb of dislocations are equal to the isotropic swelling strains plus the thermal creep strains due to climb of dislocations. No irradiation-induced creep results from the climb of dislocations or growth of loops. The climb controlled glide of dislocations is a viable irradiation creep mechanism for low fluences at all temperatures or for all fluences at high temperatures. At low temperatures the hardening occurs by the elastic interaction of loops and dislocations. It is shown that the climb controlled glide of dislocations through the loop structure can explain the transient irradiation creep behavior. Steady-state creep, however, at low temperatures is explained by the stressaffected nucleation of dislocation loops. Comparison of the theoretical prediction with the experimental results suggests that stress not only influences the orientation of the loop nuclei but also enhances the interstitial loop nucleation and reduces the vacancy- loop nucleation. In addition, various mechanisms are discussed briefly for the effects of stress on the irradiationinduced swelling of metals. Since irradiation creep and swelling both occur by partial segregation of vacancies and interstitials it was concluded that the two phenomena are closely related. (auth
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