Interpretation from Sample Analysis Results Obtained in Fukushima Daiichi NPS to Accident Progressions -First Trial-

Abstract

Particles attached on surface of samples collected from the unit 2 of Fukushima Daiichi Nuclear Power Station were analyzed with SEM and TEM in detail. From their composition, microstructure and crystal structure, the formation process of these particles were summarized. From these results, the authors extracted the conditions inside the reactor necessary for particle formation and tried to interpret the inside reactor status during the accident. The results suggested that Si was supplied into core region before fuel melt and that the hot space was formed in the core region in the early stages of the core meltdown. Regarding the status at the time when the bottom side of the reactor pressure vessel was damaged, it was suggested that the in-reactor condition were such that the particles were rapidly cooled from above 1700°C or higher under a steam-rich atmosphere.