Out-of-pile experimental programs

Laboratory investigations like those described exemplarily above (as well as numerous others conducted in many laboratories) have provided valuable information on the basic mechanisms of the release of fission products from overheated nuclear fuel. Insight has been gained into the vaporization behavior of volatile and less volatile fission products, into the chemical forms of the released species, into the impact of environmental conditions (e. g. redox potential), etc. However, these experiments were often carried out under experimental conditions which are not 

Similar experimental conditions to those in the Sascha experiments, that is a flowing steam-hydrogen atmosphere at atmospheric pressure, were used in the ORNL high temperature tests, the principal aim of which was to determine the impact of specific accident conditions on the behavior of fuel and fission products. In the early ORNL high-temperature experiments (HT series), fuel rod segments fabricated of power-reactor irradiated fuel and encapsulated in Zircaloy cladding were heated for a short time (a few minutes) to temperatures up to 1900 K in atmospheres of various composition. The results obtained in these tests were the main basis for the assessment of fission product release from overheated fuels made in the NUREG-0772 report (US NRC, 1981). 

UO2 specimens containing fission product simulants were subjected to heating similar to that used in the Sascha experiments discussed above. All tests were carried out at atmospheric pressure for 2 to 60 minutes at the test temperature different atmospheres (in particular different ratios of H2 H2O) have been used in different tests of the series. 

The execution and the results of the HI experiments which were conducted over the temperature range 1400 to 2000 °C (1700 to 2300 K) were published in a number of reports and, as far as the question of release kinetics from the fuel is concerned, summarized by Osborne et al. (1987). These tests mainly aimed at the study of the release behavior of the volatile fission products krypton, iodine and 

At temperatures beyond about 1800 °C (2100 K), fuel liquefaction begins to play an important role in the vaporization of volatile fission products. The next step is 

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