Residual plutonium migration in soil of Nagasaki

Abstract

The residual 239+240Pu concentration in the Nagasaki soil was observed 36 years after the plutonium atomic bombing of Nagasaki in 1945. The highest level of 239+240Pu contamination was discovered in the soil at the edge of the Nishiyama reservoir, a level about 10–30 times higher than in other areas of Nagasaki. In the Nishiyama district, 97% of the total plutonium in the soil was retained to a depth of 0.3 m, but the remaining 3% was dispersed over a 0.3‐ to 2.25‐m depth at approximately 0.037 Bq/kg of dry soil. The mean 239+240Pu migration rate in the Nishiyama soil for 36 years was estimated at 1.25 mm yr−1, compared to the infiltration rate of rainwater of 2500 mm yr−1.

Aging Effect of 137Cs Obtained from 137Cs in the Kanto Loam Layer from the Fukushima Nuclear Power Plant Accident and in the Nishiyama Loam Layer from the Nagasaki A-bomb Explosion

“…Core sample A was a 2.25-m-long core taken in 1981 from point A, core sample B was a 4.5-m-long core collected in 1984 from point B, and core sample C was a 0.3-m-long taken in 1981 from point C. These points were observed to have heavy fallout deposits produced by the atomic bomb in 1945. 15 To prevent cross contamination, the soil cores were carefully excavated by hand from the center of a 0.5-m-diameter soil pedestal. The soil core samples (cores A, B, and C) were carefully quarried with a sharp knife from the 0.5-m-diameter pedestal.…”

“…11 On the other hand, on August 9, 1945, a plutonium A-bomb exploded 500 m above Urakami in Nagasaki city at 11:02 LT. Half an hour after the detonation, large quantities of fission products and unfissioned plutonium in the form of fallout reached the ground (the so-called black rain). The greatest Pu and 137 Cs depositions were found at Nishiyama in an eastern suburb of Nagasaki city, 2.8 km east of the hypocenter, [12][13][14][15][16][17][18] strongly suggesting that the local fallout was not deposited as dust or aerosol particles, but as precipitate. 16 The Tokyo metropolitan area belongs to the Kanto loam region, which mainly consists of clays derived from weathered volcanic ash.…”

“…We obtained the content of deposited 137 Cs and the 10-cm-depth profile of 137 Cs in Kanto loam of the ETMA seven months after the Fukushima accident, and compared it to the vertical profiles of 137 Cs in the loam 36 -38 years later after the detonation of the Pu A-bomb reported by Mahara and Miyahara 15 and Mahara.…”

“…The Nishiyama and Tokyo metropolitan areas are located in the Nishiyama and Kanto loam areas, respectively, and the soil of both areas is derived from volcano activity. Mahara and Miyahara 15 and Mahara 14 determined the relative contributions of the local fallout from the Nagasaki A-bomb and the global fallout from nuclear-weapon tests to the total concentration of 137 Cs, 90 Sr, and 239 Pu in the Nishiyama soil 36 and 38 years after the Nagasaki A-bomb. On the other hand, Igarashi et al 19,20 studied the migration of stable Sr, Co, and Cs through the unsaturated Kanto loamy soil by using various field tracer experiments under the direct influence of natural rainfall and evapotranspiration.…”

Speciation of 137Cs and 129I in Soil After the Fukushima NPP Accident

“…This is considerably less than the rainwater infiltration rate of 2.5 m y 1 . Furthermore, 137 Cs was not detected in the groundwater of the Nishiyama area, suggesting that 137 Cs has not yet migrated to the groundwater table [14]. We collected 4 L of shallow groundwater in the Kashiwa city in the ETMA on August 17, 2012.…”