[3J09-13] Debris 1

[3J11] Investigation of re-distribution of B in SUS304-B₄C alloy under high temperature steam simulating BWR severe accident

*Shinnosuke Sakuma¹, Ayumi Itoh¹, Shintaro Yasui¹, Yoshinao Kobayashi¹, Kenichi Ito², Mutsumi Hirai², Masato Mizokami² (1. Tokyo Tech, 2. TEPCO HD)

Keywords:Fukushima Daiichi nuclear power station accident, BWR, Control rods, SUS304-B4C

The isothermal annealing experiment was performed with the SUS304-B₄C alloy under Ar + steam atmosphere at 1100 ℃ for 1-4 h to investigate the distribution behavior of boron in the Fukushima Daiichi Nuclear Power Plant Unit 2. Metallographic analysis of the specimens after the test revealed that the boron existed as (Fe,Cr)₂B intermetallic compound in the bulk and (Fe,Cr)-B-O oxide was formed on the surface due to the chemical reaction between oxygen from steam and boron diffused from the bulk, which was not expected in thermodynamics evaluation before the test and was newly observed phenomena. Consequently, this study provided new insights into the formation of boron in the fuel debris and contribution to improving the accuracy of the re-criticality evaluation.