[en] Simulated fuel rod burst-oxidation experiment in steam was performed in order to make clear the cladding embrittlement behavior due to inner surface oxidation during a LOCA. It was found that the main factor influencing the cladding embrittlement due to inner surface oxidation is absorbed hydrogen. Ring compression test at 100⁰C showed that cladding with more than 200 -- 300 wt.ppm of absorbed hydrogen are brittle when the oxidation temperature is above 1000⁰C. When the oxidation temperature ranges from 932⁰C to 972⁰C, claddings with more than 500 -- 750 wt.ppm of absorbed hydrogen are brittle. Hydrogen absorbed in the cladding precipitated in the vicinity of prior-β grain boundaries as fine hydride. Hydrogen absorption peak located in the range 15 to 45 mm from the center of rupture opening. It was suggested that the hydrogen absorption behavior is strongly influenced by inner surface atmosphere, especially hydrogen-steam volume ratio (V sub(H₂)/V sub(H₂O)). (author)