Axial variations of oxide layer growth and hydrogen uptake of BWR fuel claddings under steam starvation conditions

坂本 寛*; Adachi, Mika*; 徳島 二之*; 青見 雅樹*; 柴田 裕樹 ; 永江 勇二 ; 倉田 正輝 

Sakamoto, Kan*; Adachi, Mika*; Tokushima, Kazuyuki*; Aomi, Masaki*; Shibata, Hiroki; Nagae, Yuji; Kurata, Masaki

Steam oxidation tests under steam-starved and non-steam-starved conditions were conducted up to 1573 K using prototypic BWR fuel assembly (four fuel pins and fuel channel box) with approximately 750 mm length. Significant suppression of oxide layer growth and enhancement of hydrogen uptake were found at the downstream positions under the steam-starved conditions. To understand the results obtained in the tests using the prototypic BWR fuel assembly, three separate-effects tests were conducted to obtain a fundamental understanding of mechanism of oxygen and hydrogen uptake and its axial variations and evaluation of hydrogen solubility in oxygen-dissolved Zircaloy-2. It is retrieved that the fuel channel box contributes to the axial variations of oxide layer growth and hydrogen uptake of the fuel pins by acting as a source of hydrogen and a sink of oxygen. The evaluation of hydrogen uptake and release requires a detailed estimation of steam oxidation with time at each elevation.