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Kudo, Akira*; Fujikawa, Yoko*
JNC TJ8400 2000-010, 67 Pages, 2000/02
JNC-TJ8400-2000-010.pdf:2.17MB
The first and second environmental releases of man-made 
Pu came from nuclear explosions at Alamagordo and Nagasaki in 1945. The release at Nagasaki was more serious than at Alamagordo, because it happened in an area with a high population density. Unfissioned Pu and various fission products have been interacting here with various environmental materials (soils, sediments, and plants) under wet and temperature conditions for more than 45 years. To assess the environmental mobility of Pu, the distributions of radionuclides from this release were investigated at Nishiyama where heavy black rain containing unfissioned plutonium and fission products fell 30 minutes after the nuclear explosion. The vertical distributions of 
Cs and Pu were determined in unsaturated soil cores up to 450cm deep. Most radionuclides were found in the soil column 30cm from the ground surface. However, Pu were detected in the groundwater as well below a depth of 200cm. No Cs was found below 40cm from the ground surface or in groundwater. These observations reveal that about 3% of the total Pu have been migrating in the soil at a faster rate than the remaining Pu. Sharp peak of Cs and Pu, indicating heavy deposition from the Nagasaki local fallout of 1945, were found in sediment cores collected from the Nishiyama reservoir. Pu peaks were unexpectedly discovered in pre-1945 sediment core sections. NO Cs was found. By contrast to the distribution in sediment cores, Cs in tree rings had spread by diffusion from the bark to the center of the tree without holding a fallout deposition record. Most of the Pu was distributed in the tree rings following a similar deposition record to that found in sediment cores. Furthermore, a very small amount of Pu (about 1%) was found unexpectedly in pre-1945 tree rings. The only reasonable ...
; ; ; Isozaki, Tokuju;
PNC TN8450 93-004, 144 Pages, 1993/06
Generally speaking, two kinds of water plumes which have different temperature, salinity and so on are not easily mixturred and have special boundary. So, it is possible to predict ocurrence of special boundary of sea water from observation of temperature, salinity of sea water. Not only marine environmental monitoring such as radioactivity analysis of sea water, sea-bed sediment, marine products but also observation of water current, water direction, surface and ventical observation of water temperature, salinity and so on in Tokai coastal area are carried out with some observation instruments by Environmental Protection Section, Tokai Works, PNC. The results of vertical observation from 1990 to 1991 are recorded in this report.
Katengeza, E.*; Sanada, Yukihisa; Ochi, Kotaro; Iimoto, Takeshi*
no journal, ,
This study aimed at evaluating the vertical distribution of radiocesium in bottom sediment core samples from 45 ponds sampled in 2015-2019 and clarifying the impact of the vertical distribution on the efficiency of decontamination by stripping the top 10 cm of bottom sediments. The relaxation mass depths and depth of sediment containing 90% of the inventory were larger than on land indicating faster downward migration of radiocesium in ponds. This may have been caused by accumulation from the ponds' catchments where radiocesium enrichment occurred. This indicates that local behavior of radiocesium in reservoirs are more important to decontamination outcomes.
Ochi, Kotaro; Abe, Tomohisa; Sasaki, Miyuki; Sato, Rina; Yoshimura, Kazuya; Sanada, Yukihisa
no journal, ,
It is difficult to calculate radiocesium inventories in forests, which cover approximately 60% of the land in Fukushima Prefecture. Conversion coefficients (ADCs) are available for estimating radiocesium inventories from air dose rates, but they are supposed to be applied to flat land, and there are no examples of their validation in forests. In this study, surveys were conducted over a wide area in 2011-2021 and a narrow area in 2019 in both virgin lands and forests. Air dose rates, relaxation mass depth (
), and soil radiocesium inventories were obtained at the same locations. ADCs were calculated based on . The estimated radiocesium inventories and soil radiocesium inventories were not significantly different for both land uses, and this was true for both the wide- and narrow-area surveys. Therefore, it is considered that radiocesium inventories can be easily estimated from air dose rates using ADCs even in forests when sufficient time has passed since the accident.