Masami Fukui

Factors affecting interaction of radioiodide and iodate species with soil

Abstract The uptake of radioiodide and iodate species by soil dried at 100 °C (particle size of less than 0.25 mm) was studied in laboratory batch experiments for three major groups of variables: (i) experimental conditions (ambient temperature, liquid-to-solid ratio and contact time), (ii) solid phase conditions (grain size and washing treatment), and (iii) liquid phase conditions (pH, and concentrations of electrolytes and carrier). Effects of the presence of soluble and insoluble organic matter were also investigated in relation to radioiodine uptake by the soil. Plural uptake mechanisms were considered for iodide species, while a simple anion exchange process for iodate.

Vertical distributions of trace metals in natural soil horizons from Japan. Part 1. Effect of soil types

To predict the long-term behavior of trace metals in a soilprofile, we studied the vertical distributions of barium, zinc,copper, chromium, nickel, cobalt, lead, and the principalmetals, aluminum, iron and manganese, in three soils withdeveloped horizons obtained from rural areas in Japan. Totalelement analysis and selective extraction tests with variousreagents were conducted to clarify the extractability of themetals at each sampling depth.Soil-b (Dystric Cambisols) had the highest extractability ofelements although the vertical distributions of its traceelements were similar to those of soil-d (Umbric Andosols),which had to lowest metal extractability of the three soils.Soil-KUR (Orthic Acrisols or Dystric Cambisols) was the oldest of the three soils and showed downward movement of some tracemetals (chromium and nickel) and principal elements (Fe and Mn)that was probably induced by long-term weathering.The extractability of manganese, zinc and barium with water washigher than other metals examined in all three soils. Lead andcobalt in soil-b and soil-KUR also were considered to have highextractability under long-term weathering processes. Zinc andlead accumulated near soil surface showed higher extractabilitywith every reagent used than those in deep layers of the three soils.

Adsorptive solute transport in fractured rock: analytical solutions for delta-type source conditions☆

Abstract Solutions for adsorptive solute transport equations in a single fracture-rock system were derived under two different delta-type source conditions. One was the delta-type, flux injection condition. The correspondent solution can be used for the analysis of experimental column breakthrough curves obtained by injecting the tracer into the rock fracture. The other was the delta-type, resident fluid injection condition. The solution can be used for the crude estimation of pollutant migration from the underground radioactive waste repository. In formalizing the resident fluid injection, an initial distribution of solute between solution and solid phase was assumed in order to satisfy the mass balance between injected and detected solute. Each of the two solutions was also expressed in two ways reflecting the flux and the resident fluid detection. Solutions expressed in terms of the flux detection correspond to the effluent concentration measured experimentally by a fraction collector system. On the other hand, solutions expressed in terms of the resident fluid detection describe spatial distribution of the solute in the fluid. Since considerably long tailings of breakthrough curves are often observed in column tracer experiments using fractured rocks effects of some parameter values on the tailing were also discussed. It was shown that the adsorption of solute rock matrix caused longer tailing. It was also shown that the resident fluid injection caused longer tailing of breakthrough curves than the flux injection condition.

Analysis of trace actinide elements in soil organic matter: Optimization of sample processing to improve chemical separation of U and Pu

Chemical separation yield of actinide elements from soil samples containing high amounts of organic matters was often low as compared to that for samples containing low organic matters. We compared chemical yield of uranium and plutonium from organic-rich Japanese soil and humic acid samples which were subjected to three different pretreatment procedures ((1) pulverization only, (2) dry-ashing at 510 °C after pulverization, and (3) 680 kGy gamma-ray irradiation after pulverization) prior to acid digestion. Separation of U and Pu was performed by U-TEVA resin and AG1-X8 anion exchange resin, respectively. For organic samples, pretreatment procedures governed the yield of actinide elements significantly. Chemical separation yield of U was low (6±1%) for Aldrich humic acid sample after dry-ashing at 510 °C. For such samples, gamma-ray irradiation improved the yield of U to 35±22%. Recovery of Pu was lower for some organic soil samples which were dry-ashed at 510 °C (27±2%) as compared to those which were not dry-ashed (62±10%).

Analysis of radioactive cesium and cobalt adsorption to rocks using the two-site kinetic model equations

The present study shows that equations of the two-site kinetic model, which have been applied to trace-metal and pesticide adsorption to soil, could also be used to simulate diffusion-controlled adsorption behaviour of 60Co and 137Cs to rock powder (diameter less than 105 × 10−5m), pieces (diameter 2 × 10−3m ∼ 3 × 10−3m) and slabs (0.05 m × 0.05 m × 0.01 m) of chert, shale and granodiorite in saline water. The adsorption rate coefficient was dependent on sizes of rocks and rock pore structures but was independent of distribution coefficients. The desorption rate coefficient was dependent on sizes of rocks, rock pore structures and distribution coefficients. The difference in adsorption and desorption rate coefficients between rock powder, pieces, and slabs was zero to two orders of magnitude for 137Cs and zero to three orders of magnitude for 60Co. Theoretical relationships between parameters of the two-site kinetic model and the Fickian diffusion model were also developed. Effective diffusion coefficients could be evaluated from the fitted rate parameter values of the two-site kinetic model. Observed characteristics of rate parameters agreed well with the theoretical equation. Dependence of adsorption and desorption rate coefficients and equilibrium distribution coefficient of 137Cs and 60Co on solid to liquid ratios were insignificant for rock powder. Applying rate parameter values obtained in this study to field conditions, it was concluded that kinetics of adsorption may often become important in predicting field-scale solute transport.

Anomalous 235U/238U ratios and metal elements detected in the black rain from the Hiroshima A-bomb.

Abstract— Contents of black rain from the A-bomb are important to clarify the health and environmental hazard caused by nuclear warfare. We analyzed the only existing physical remains of the black rain from Hiroshima A-bomb (Little Boy), a plastered wall with black streaks. Excess 137Cs and anomalous 235U/238U ratios detected in the black residues on the wall confirmed that the black streaks on the wall originated from Little Boy. The results also showed that excess 235U could be used as a fingerprint to clarify the distribution of materials discharged from Little Boy into the environment. High concentrations of lead and zinc, which may have caused a degree of heavy metal pollution in the area where the rain fell, were also detected in the black rain sample.

VERTICAL DISTRIBUTION OF TRACE METALS IN NATURAL SOIL HORIZONS FROM JAPAN PART 2: EFFECTS OF ORGANIC COMPONENTS IN SOIL

The association of Al, Mn, Fe, Ba, Zn, Cr, Ni, Co and Pb withsoil organic matter (SOM) was investigated in three Japanesesoils. Organically bound metals were assayed by elementalanalysis of a fraction extracted with acidified hydrogenperoxide (H2O2) and the humic acid extracted withalkaline reagent, from soil sampled at various depths of solums.A Dystric Cambisol showed higher extractability with acidifiedH2O2 for most of the metals than a Humic Andosol and an Orthic Acrisol. A Humic Andosol had more metals associated with humicacid than the other two soils.Cu showed high extractability with acidified H2O2 andalso significant association with humic acid, while Pb showedhigh extractability with acidified H2O2 but itsassociation with humic acid was relatively low among the metalsinvestigated. As humic acid is highly resistant to weathering,retention of Cu with SOM may last longer than that of Pb.The binding of metals with SOM probably has contributed to theaccumulation of some metals in organic-rich shallow horizons of soil. Such metals were Zn, Cu, Ni and Pb in a Dystric Cambisol,Cu in a Humic Andosol, and Pb and Cu in an Orthic Arisol.

222Rn concentrations and variations in unconfined groundwater

Abstract The variation and the distribution of 222 Rn concentrations were investigated in unconfined groundwater to obtain information as to the establishment of representative concentration measurement and the effect of meteorological parameters on the concentration. Vertical distributions of concentration increase in unconfined groundwater were clearly obtained in summer rather than in winter due to the stability of water density, although the spatial distributions of concentration were observed in a restricted area. The continuous extraction of groundwater causes pronounced increase of the concentration, thus it was necessary to drain more than 1 m 3 of water to get the representative concentration, which coincides with that of deep groundwater of the same geology. The concentration diluted by the precipitation recovers to the former level within a week.

Analysis of the migration of instantaneously injected cesium in artificial fractures of Lac du Bonnet granite, Manitoba, Canada

Abstract Breakthrough curves of 137 Cs and tritiated water injected instantaneously into artificial fractures in Lac du Bonnet granite were analyzed using the analytical solution for a single rock-fracture system and assuming the linear sorption isotherm of the solute. Parameters of nuclide diffusion and sorption in rock matrices, obtained by fitting, varied depending on the flow velocity in the fractures. According to theoretical calculations, different fracture flow velocities lead to different diffusion distances of nuclides in matrices at the same injection volume. As microscopic inhomogeneity is considered to exist in the rock matrix, the average diffusion-sorption characteristics of the matrix within the diffusion distance may have varied with the fracture flow velocity. Surface sorption was marked in fractures that had relatively high matrix sorption-diffusion capacities. The phenomenon was interpreted using the theoretical relationships developed between the surface sorption, matrix sorption and pore diffusion coefficient, and the porosity of matrices. The effect of the nonlinear sorption of solute was examined by numerically solving model equations that incorporate the nonlinear isotherm. This incorporation may contribute to the reduction of deviations between theoretical and experimental BTCs.

Variations in adsorption mechanisms of radioactive cobalt and cesium in rocks

Variations in adsorption mechanisms of 60Co and 137Cs in metamorphosed shale and chert, and granodiorite were examined under aerobic conditions in terms of different adsorption periods, salinity of solution and solid to liquid ratios. The mechanisms were investigated by means of selective extraction tests using: (1) distilled water; (2) 1 N ammonium acetate (pH 7), (3) 0.1 M hydroxylamine hydrochloride (pH 3.5); and (4) 0.2 M ammonium xalate + 0.2 M oxalate (pH 2.5). The increase in relative amounts of 137Cs and 60Co extracted by ammonium acetate was observed in the first 1-month period of adsorption. Then the conversion of the nuclides from ammonium acetate extractable to non-extractable was observed, which continued on the order of several years. It indicates that under aerobic conditions, remobilization of the nuclides once adsorbed to geologic media will become less probable as time elapses. Solid to liquid ratios and salinity of solution of the adsorption experiments did not influence the adsorption mechanisms of 60Co and 137Cs.