Modelling the mitigation speeds of 137Cs, 90Sr and 131I in the topsoils and assessment of the radiological hazards.

Fate modelling of artificial radionuclides (ARs) in top soils are necessary to assess the radiological effects to population. Among ARs, 137Cs, 90Sr and 131I are very important since the large abundances in the environment. In this study, the fates of 137Cs, 90Sr and 131I in the surface soil layers were simulated by the soil model which was developed by the Canadian Centre for Environmental Modelling and Chemistry (CEMC). The scenario that 137Cs, 90Sr and 131I contaminated in topsoil in the exclusion of Fukushima Daiichi nuclear power plant (NPP) accident was evaluated. The results show the expected time for the minimum hazardous level of exposure. It is 115.5 days after the exposure, when the total effective dose is 1 mSv y-1 in which 0.46 mSv y-1 from ingestion and 0.54 mSv y-1 from gamma exposure. Hazard levels due to exposure progresses are varied in order gamma exposure (82.14%) > ingestion (17.47%) > inhalation (0.39%). The hazard levels from radionuclides are varied in order 137Cs (63.34%) > 131I (33.48%) > 90Sr (3.18%).

Gross alpha/beta and radionuclide activity concentrations in soil, plant and some fruits around the Tehran Research Reactor.

Human activities usually have some contamination as effluents from chemical industries and radionuclides from nuclear reactors. For assessing the probable radioactive contamination in vicinity of Tehran Research Reactor, The gross alpha and beta radioactivity concentrations in soil, pine and cedar leaves and some selected fruits (fig, apple, berry and pomegranate) were investigated using an alpha/beta spectrometer during 2021-2022. Also, the concentrations of artificial and natural radionuclides in samples were investigated by the method of gamma spectroscopy. The gross alpha activity concentrations in soil, pine and cedar leaves and some selected fruits samples are from 0.05 to 0.35 Bq/gr and 0.07-0.31 Bq/gr and 0.04-0.18 Bq/gr, respectively. The gross beta activity concentrations in soil, pine and cedar leaves and some selected fruit samples are from 0.73 to 4.25 Bq/gr and 0.21-3.97 Bq/gr and 1.01-2.71 Bq/gr, respectively. Average activities concentration of natural radionuclide 232Th, 238U and 40K in soil, pine and cedar leaves and some selected fruits are 31.89-16.23-582.73 Bq/kg and 1.84-0.99-84.60 Bq/kg and 1.98-1.09-72.08 Bq/kg respectively. From artificial radionuclides, just 137Cs is recognized in soil sample and the range of 137Cs concentration in surface soils was observed to vary in the range 0.85-2.21 (Bq/kg). The result showed that the Tehran Research Reactor activities not have increased the environmental radioactivity and radiation level in the area.

A prototype tracing-technique to assess the mobility of dispersed earthworm casts on a vegetated hillslope using caesium-134 and cobalt-60.

Soil transport on fully vegetated land surfaces is typically detachment limited. Rates of soil and nutrient transport, and ultimately long-term landscape evolution, are controlled by processes that supply soil material for entrainment and transport. Despite their on-going nature, many such processes operate at low rates and have not been subject to detailed investigation. We present preliminary findings from a prototype tracing approach to quantify one such process; namely to determine the relative mobility of sediment from earthworm casts on a fully vegetated hillslope surface. A 0.6 ∗ 0.5 m bounded area of pasture was prepared and fifteen intact earthworm casts representing 203 g of soil were labelled with an estimated 216 Bq of caesium-134 (134Cs) activity and evenly distributed across the upslope half of the plot, 0.3-0.6 m from the downslope outlet. A further 15 intact casts representing 190.7 g of soil were labelled with 224 Bq of cobalt-60 (60Co) activity and distributed between 0.3 and 0.0 m from the same outlet. All labelled casts were exposed to natural weather events over 76 days, during which time 186.3 mm of rainfall generated 16 runoff samples. A mass balance was used to partition labelled sediment from the unlabelled material. A total of 27.17 g of 60Co-labelled casts, equivalent to 14.2% of the original mass deployed, was recovered from a distance of ≤0.3 m from their original locations. In contrast, 8.77 g of 134Cs-labelled casts, equivalent to 4.3% of the original mass deployed, was recovered from a distance ≥0.3 m from their original locations. Some runoff-derived samples recorded an over-enrichment of radionuclide material, which suggests that intact casts may sorb more material than the original assumption predicts. Ways in which sorption can be more accurately quantified to improve the accuracy of the tracing approach are outlined.

Characteristics of artificial radionuclides in sedimentary soil cores from a volcanic crater lake.

The distributions of 137Cs, 237Np, and 239+240Pu activity concentrations in sedimentary soil cores of the volcanic crater-lake have been studied. The 240Pu/239Pu atom ratios measured by MC-ICP-MS and mutual activity ratios were examined. These results were used to evaluate the sedimentation characteristics of the crater-lake (Baengnokdam of Mt. Halla, Korea). The 137Cs, 237Np, and 239+240Pu activity concentrations showed similar distribution patterns and one maximum peak was observed in each sediment core, except at St.10. For all sediment cores, the activity concentrations were in the range 1.03 × 100-1.92 × 102 Bq·kg-1 dw for 137Cs, 7.56 × 10-3 - 7.15 × 100 mBq·kg-1 dw for 237Np, and 5.20 × 10-3 - 5.13 × 100 Bq·kg-1 dw for 239+240Pu, respectively. The averaged 240Pu/239Pu atomic ratio (0.159) was slightly less than the global fallout ratio (0.176). The averaged inventories were estimated to be 9.21 × 103±5.34 × 103 Bq·m-2 for 137Cs, 2.27 × 102±1.58 × 102 Bq·m-2 for 239+240Pu, and 3.22 × 10-1±1.78 × 10-1 Bq·m-2 for 237Np. The averaged 239+240Pu/137Cs and 237Np/239+240Pu activity ratios were 2.21 × 10-2 and 2.21 × 10-3, respectively. The mean sedimentation rates calculated using 239+240Pu activity concentrations at the central area (St.30 - St.45) and at all stations (St.5 - St.75) were estimated to be 0.844 cm yr-1, and 0.767 cm yr-1, respectively. In addition, the sedimentation rates calculated using 210Pb and 226Ra were 0.856 cm yr-1 at depths of 0-35 cm and 0.204 cm yr-1 at depths of 35-55 cm. These results imply that the sedimentation in Baengnokdam was relatively slow (0.204 cm yr-1) until about 44 years ago and then became faster (0.856 cm yr-1) to the present. The excess 210Pb dating is consistent with the sedimentation rate calculated from the vertical 239+240Pu profile.