CHEMICAL FORM AND RELEASE OF FISSION PRODUCTS AT ELEVATED TEMPERATURE
From experimental release data at temperatures above 1500 degrees C, Dr. ANDRIESSE derives a theory for the fission products release. The release is described in terms of intragranular diffusion, driven by small gradients of concentration and temperature. About one half of the fission product atoms diffuse interstitially with a relatively low activation energy; as they are larger than the interstitial holes they diffuse with a positive excess entropy, which is a strong function of their size. The other half diffuses substitutionally with a relatively high activation energy. Other transport processes, like diffusion along grain boundaries and cracks, are faster than this intragranular diffusion and thus do not limit the release. It is speculated that all fission products are released as single atoms, except the lanthanides, the yttrium, the zirconium and the niobium. The use of such a theory might be, e.g. that some deliberately introduced disorder in the UO-2 matrix could reduce the excess entropy of the diffusion and thereby possibly reduce the release of large interstitial atoms.
Bibliographic Reference: EUR 10345 EN (1985) MF, 33 P., BFR 150, BLOW-UP COPY BFR 200, EUROFFICE, LUXEMBOURG, POB 1003
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Record Number: 1989124104700 / Last updated on: 1987-01-01
Available languages: en