Experimental investigation of nonisothermal interaction between Fe-Zr melt and stainless steel forming "metallic debris" in Fukushima Daiichi Nuclear Power Station

Ito, Ayumi*; Kanno, Tatsuya*; Iwama, Takayuki*; Ueda, Shigeru*; Sato, Takumi ; Nagae, Yuji 

In the Fukushima Daiichi Nuclear Power Station Unit 2, the formation of a metallic pool, mainly comprising Fe and Zr, has been proposed as a mechanism contributing to the failure of the reactor pressure vessel. This study focuses on material interactions during the early core degradation that led to metallic pool formation in the late phase of the in-vessel degradation process. Initially, two compositions, Fe-87Zr and Fe-15Zr (at%), were heated to the liquidus temperature of 1723 K, dropped onto SS at lower temperatures, and the metallographic structure of the reaction products was examined. Subsequently, the Fe-87Zr melt at temperatures ranging from 1723 to 1873 K was dropped onto oxidized SS to evaluate the influence of the oxide layer on degradation. This study confirmed that the liquidus temperatures of all intermetallic compounds were below 2000 K, and the metallic debris could be a source of the "metallic pool formation" predicted by recent severe accident analysis.