Presentation Radiocaesium distributions in sediments within the 30 km area from the Fukushima Dai-ichi Nuclear Power Station in 2013-2014

福田, 美保  ,  山崎, 慎之介  ,  青野, 辰雄  ,  吉田, 聡  ,  長沼, 翔  ,  久保, 篤史  ,  島田, 啓資  ,  高澤, 伸江  ,  保坂, 拓志  ,  佐藤, 憲一郎  ,  山口, 征矢  ,  伊藤, 友加里  ,  石丸, 隆  ,  神田, 穣太

The Fukushima Dai-ichi Nuclear Power Stations (FDNPS) accident on March 2011 cause released large amount of artificial radionuclides including 134Cs and 137Cs (radiocaesium) into environment (e.g. ocean, atmosphere and land). As of May 2013, radiocaesium activities in seawater had exponentially decreased over 10 time values compared to the pre-FDNPS accident by TEPCO’s monitoring data. On the other hand, these in sediment had decreased slowly than those in seawater and large fluctuation. However, there is still some controversy of transistion process from seawater to sediment and behavior after accumulation for radiocaesium. In the Fukushima coastal area, marine sedimentary environment depend on several factors such as freshwater and terrestrial material input via river and seabed topography. The aim of this study is to elucidate temporal variation and behavior of radiocaesium activities in sediment collected within the 30 km from the FDNPS during 2013-2014.  The 134Cs activities in upper layer of sediment (0-3 cm) ranged from 3.0 to 200 Bq kg-1-dry and radiocaesium activity ratio, which were corrected on March 11, 2011, were from 0.82 to 1.2. The 134Cs inventories in sediments were between 276 and 4229 Bq m-2. 134Cs inventories at NP1 and M01 stations, which are location of water depth range of 50-100 m had decreased over time. In contrast, these at NP3 and I02 stations, which are located on the area of deeper than a depth of 100 m had increased. In the north Fukushima area, there are a continental slope in water depth range of 50-120 m and outer continental shelf in deeper than a depth of 110 m. It is suggested that the pore water including radiocaesium penetrated deeper and lateral transport due to strength of bottom current had contributed to decreased 134Cs inventories in depth range of 50-100 m.
XIX International Union for Quaternary Research (INQUA)

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