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Theoretical Investigations of Fission Product Deposition from Flowing Gas Streams

Ernest R. Venerus and M. Necati Ozisik

Nuclear Science and Engineering

Volume 26 / Number 1 / September 1966 / Pages 122-130


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Deposition of fission products from an isothermal laminar gas stream to the surfaces of a circular tube is theoretically investigated for a source releasing a radioactive precursor into the gas stream at a uniform rate at the origin. A slug velocity profile is assumed. In solving the partial differential equations of the problem, two different models are examined as boundary conditions to couple the equations. The first model, which is referred to as the Resistance Model, is applicable when the surface concentration of the deposited precursor is small or removal of particles from the surface is negligible; and it is equivalent to assuming a fictitious unknown resistance to mass transfer at the wall surface. The boundary value problem of mass transfer based on the resistance model has been solved for the transient conditions and analytical relations are derived for the concentration of fission products in the gas stream and on the tube surface. In the second model, which is referred to as the Transport Model, a more detailed account is taken of the actual physical transport process in the immediate vicinity of the conduit surface. The removal of precursor from the surface is related to the adsorption energy of the precursor and the temperature of the surface. Removal from the gas stream in the immediate vicinity of the conduit surface is described by a stream removal coefficient which is obtained from the kinetic theory of gases. The boundary value problem based on the transport model has been solved for the steady state condition only. The transport model has been applied to experiments on deposition of radioactive isotopes from laminar gas streams and adsorption energies for some radioactive isotopes are determined. Correlation of the transport model with experiments provides a useful means for obtaining the adsorption energies of radioactive isotopes on metal surfaces.

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