Identification of Carbon in Glassy Cesium-Bearing Microparticles Using Electron Microscopy and Formation Mechanisms of the Microparticles

Abstract

The author previously proposed that glassy cesium-bearing microparticles [resulting uniquely from the Fukushima Daiichi nuclear power station (FDNPS) accident] may have been formed by melting and atomization of glass fibers (GFs) of the high-efficiency particulate air filter in the standby gas treatment system line due to the flame and blast during the hydrogen explosion in Unit 3. Assuming that this hypothesis is correct, Type A could contain or accompany carbon, which ignites spontaneously above 623 K, because of the limited time to be heated up, the inclusion of carbon in the binder applied on the GF surface, and the closely located charcoal filter. As previous studies have not identified carbon, the present analyses were performed with an electron probe microanalyzer to determine whether Type A contains carbon. The results show that Type A contained carbon originating from the binder. Some nonspherical particles were accompanied by Type A, and the film surrounding Type A contained more carbon, which is thought to originate from the charcoal filter. These results cannot be explained by the other mechanisms proposed so far and can be explained consistently only by the author’s proposed hypothesis. Although it may be premature to determine Type A formation mechanisms, this information enables one to limit the temperature conditions of Type A formation.

Keywords:

• Fukushima Daiichi NPS accident
• glassy cesium-bearing microparticle
• hydrogen explosion
• HEPA filter
• carbon spontaneous ignition

Acknowledgments

The author would like to express his sincere appreciation to Ikken Sato of the Japan Atomic Energy Agency (JAEA) for his technical comments on the thermohydraulics in the primary containment in Unit 3. The author would like to thank Hiroki Hagiwara and Masaaki Kobata of JAEA for their measurements and technical comments on the insoluble Cs-bearing microparticles with the EPMA. Special thanks are also due the Nippon Muki Co. Ltd. for providing the results of the ultrapure water elution test of the GF filter medium and their interpretation.