Hydrogen absorption by zircaloy cladding in inner-surface oxidation

Rod-burst/oxidation tests and zircaloy tube oxidation tests in a stagnant steam or a mixed gas of steam and hydrogen environment were made to examine hydrogen absorption by zircaloy cladding in inner-surface oxidation under a hypothetical LOCA condition in LWRs. Hydrogen is absorbed by zircaloy cladding oxidized at above 9500C, depending on hydrogen fraction in mixed gas of steam and hydrogen. Absorbed hydrogen content increases with exposure time to steam. Tetragonal zirconia with monoclinic form is observed in the specimen with relatively high content of absorbed hydrogen. In a simulated fuel rod, hydrogen absorption is influenced by rupture opening area and steam flow rate outside the cladding, for hydrogen generated by zirconium-steam reaction at the location severely oxidized is absorbed at other location in a rod where hydrogen absorption easily occurs. (author)