Difference in oxidation behavior of heterogeneous BWR fuel assembly under steam-starved condition

永江 勇二 ; 山下 晋   ; 倉田 正輝 

Nagae, Yuji; Yamashita, Susumu; Kurata, Masaki

BWR has heterogeneous configuration of fuel assembly, especially control blade. Growth and reduction behavior of oxidation depend on steam fraction. The oxidation behavior affects the reaction between SUS and Zry in an early stage of accident progression. According to ANSYS-fluent using oxidation growth and reduction models depending on steam fraction, oxidation behavior drastically change above 1200C. Steam fraction on the surface of channel box covered by control blade decreases up to steam-starved condition around 1200C, which means oxidation growth rate decreases depending on steam fraction. Oxidized layer grows continuously even steam-starved condition using a model of oxidation behavior independent of steam fraction. According to experimental integral tests without pre-oxidation, a reaction between SUS-BC and Zry occurs under low steam flow rate because the reaction rate is higher in the case of thin oxidized layer. Almost full oxidization occurs on the surface of Zry under a sufficient steam flow condition, except for thin oxidation at a top part of the test body. The reaction between control rod and Zry occurs at the top part. In addition, an observation of oxidation behavior in an integral test with pre-oxidation show us that a thickness of oxidized layer in a part of Zry covered by control blade is thinner and the interaction between SUS-BC and Zry begins even pre-oxidation. The model will be implemented into JUPITER code developed by Nuclear Science and Engineering Center.