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The 2011 Fukushima Daiichi Nuclear Power Plant accident: an analysis over 10 orders of magnitude.

Bristol student theses: Doctoral ThesisDoctor of Philosophy (PhD)

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Abstract

TheMarch2011eventsattheFukushimaDaiichiNuclearPowerPlantrepresentedaradioactivity release of a similar "global severity" as the Chernobyl accident. Following the multiple reactor unit explosions that occurred, a total of 146,520 residents from across Fukushima Prefecture were evacuated from their homes. Today, with many years having passed since the event, there exists a greater commitment than ever to allow for those formerly displaced to return. Central to this resettlement is the combined remediation of the extensive swathe of contaminated land, but also a detailed understanding of the physiochemical nature and associated environmental affinity of the released radionuclides. Regional radiation monitoring was first undertaken using newly-devised aerial and ground-based radiation mapping platforms. From this, it was observed that from an initially quasi-uniform radiocesium distribution in contaminated areas, that significant redistribution of contamination had occurred. For sites that had experienced recent remediation, contamination "hot-spots" were observed to quickly re-establish across such localities, occurring at positions where mobilised particulate would become readily trapped. At locations where no remediation had been performed, contamination was observed to be similarly mobile. These contamination transport results correlate with earlier works examining Cs sorption onto fine-scale clay and mica-type mineral particulates, which forms a ubiquitous and significant component of the Fukushima soil. This mobility is heightened by the regions sub-tropical climate with periodic typhoon events. Alongside the Cs-sorbed material, the coarser particulate contributing to the radioactivity measured during this site-wide monitoring was examined. This material was classified into two groups; (i) particulate on the micron/sub-micron scale obtained from distances of up to 70 km from the site, and (ii) a grouping of larger particles (100’s of µm in diameter), isolated from soils on the boundary of the facility (<2 km). The smaller particulate, found adhered to organic surfaces, was observed to be characteristically angular in form. Sub-micron U composition ejecta, as well as exhibiting a complex internal microstructure, also contained a determinable Cs component. The larger Si-rich particulate, in contrast, was characterised by a variable surface and internal form - in some instances being highly-porous. As well as occurrences of fragments of cement and iron, some of this material also contained micron-scale 235 U-enriched particles. These results provide evidence that correlate with earlier studies, indicating that core material from Unit 2 was released in the accident as well as for the first time reporting the emission of U from the core of reactor Unit 1. The potential environmental implications of such fine and large particulate are investigated and discussed as part of this work, with recommendations detailed associated with the ongoing response and activities of the Japanese Government.

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Original languageEnglish
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Award date19 Jun 2018

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