Strontium oxidation-reduction potential

The release behavior of the less volatile fission products from overheated fuels was studied in detail in the Sascha experiments (Albrecht, 1987 a). These results demonstrated that the low-volatility elements (e. g. barium, ruthenium, cerium) were essentially released at the highest temperatures realized in the tests, i. e. from the liquid melt. In Fig. 7.11. some of the measured release rates for low-volatility elements are shown and compared with the assumptions made in the NUREG-0772 report. With the exception of barium (and potentially strontium), the release rates of these elements apparently depend only little on the amount of steam supplied. Barium release rates in a pure steam atmosphere have proved to be lower by a factor of nearly 100 than in an Ar + 5% steam atmosphere or in an Ar -H 5% H2 atmosphere. This behavior was assumed to be due to a reduction of the BaO initially present by still non-oxidized Zircaloy, which converted it into the more volatile elemental form. 

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