QUENCH is a series of experiments being performed at the Forschungszentrum Karlsruhe, to investigate quenching with water and cooling with steam of oxidized and partially degraded fuel rod bundle. Test QUENCH-07 was performed to address the effects of chemical behavior and degradation of B4C absorber rods, especially the oxidation of B4C, its interaction with stainless steel, formation and composition of gaseous reaction products and the impact of absorber rod degradation on surrounding rods. An unexpected feature of the experiment was the strong oxidation during the cooldown phase accompanied by an increased release of all gaseous species. Temperature escalation and hydrogen release during cooldown were observed for the first time in any steam cooled QUENCH experiment. Since not only the absorber rod was a novel feature but also the steam flow rate during cooldown was smaller in comparison with previous tests, it is not yet clear whether this escalation can be attributed to the effect of B4C.

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