In Jun

ABSORBED INTERNAL DOSE CONVERSION COEFFICIENTS FOR DOMESTIC REFERENCE ANIMALS AND PLANT

This paper describes the methodology of calculating the internal dose conversion coefficient in order to assess the radiological impact on non-human species. This paper also presents the internal dose conversion coefficients of 25 radionuclides (³H, ?Be, 14 C, 40 K, 51 Cr, 54 Mn, 59 Fe, 58 Co, 60 Co, 65 Zn, 90 Sr, 95 Zr, 95 Nb, 99 Tc, 106 Ru, 129 I, 131 I, 136 Cs, 137 Cs, 140 Ba, 140 La, 144 Ce, 238 U, 239 Pu, 240 Pu) for domestic seven reference animals (roe deer, rat, frog, snake, Chinese minnow, bee, and earthworm) and one reference plant (pine tree). The uniform isotropic model was applied in order to calculate the internal dose conversion coefficients. The calculated internal dose conversion coefficient (μGyd -1 per Bqkg -1 ) ranged from 10 -6 to 10 -2 according to the type of radionuclides and organisms studied. It turns out that the internal does conversion coefficient was higher for alpha radionuclides, such as 238 U, 239 Pu, and 240 Pu, and for large organisms, such as roe deer and pine tree. The internal dose conversion coefficients of 239 Pu, 240 Pu, 238 U, 14 C, 3 H and 99 Tc were independent of the organism.

Root uptake of radionuclides following their acute soil depositions during the growth of selected food crops.

Greenhouse experiments were performed to investigate the root uptake of radionuclides following their acute soil deposition during the growth of several food crops. For this purpose, the soil under the standing plants was contaminated without any direct contamination of their stems or leaves. The intention of this design was to differentiate foilar uptake and root uptake subsequent to a radionuclide deposition during the vegetation period. Soil-to-plant transfer of a radionuclide was quantified with its aggregated transfer factors specified for the time periods from deposition until harvest (T(ag)(a), m(2)kg(-1)). Deposition time-dependent T(ag)(a) values of Mn, Co, Sr and Cs for selected crop species were measured in an acid sandy soil. For rice and Chinese cabbage, HTO experiments were also carried out using this soil. Particularly for rice, experiments with various paddy soils were also performed for (90)Sr and (137)Cs. The obtained T(ag)(a) values varied considerably with the radionuclides, plant species, and times of deposition. Recommendations about, and limitations in, the use of the T(ag)(a) values were discussed.

RADIATION DOSE TO HUMAN AND NON-HUMAN BIOTA IN THE REPUBLIC OF KOREA RESULTING FROM THE FUKUSHIMA NUCLEAR ACCIDENT

This paper describes the radiation doses to human and non-human biota in the Republic of Korea, as a result of the Fukushima nuclear accident. By using the measured airborne activity and ground deposition, the effective and thyroid doses of five human age groups (infant, 5 years, 10 years, 15 years and adult) were estimated by the ECOSYS code, and the whole body absorbed dose rate of the eight Korean reference animals and plants (RAPs) was estimated by the K-BIOTA (the Korean computer code to assess the risk of radioactivity to wildlife). The first-year effective and thyroid human doses ranged from 5.7E-5 mSv in the infant group to 2.0E-4 mSv in the 5 years group, and from 5.0E-4 mSv in the infant group to 3.4E-3 mSv in the 5 years group, respectively. The life-time (70 years) effective and thyroid human doses ranged from 1.5E-4 mSv in the infant group to 3.0E-4 mSv in the 5 years group, and from 6.0E-4 mSv in the infant group to 3.5E-3 mSv in the 5 years group, respectively. The estimated maximum whole body absorbed dose rate to the Korean RAPs was 6.7E-7 mGy/d for a snake living in soil (terrestrial biota), and 2.0E-5 mGy/d for freshwater fish (aquatic biota), both of which were far less than the generic dose criteria to protect biota from ionizing radiation. Also, the screening level assessment for ERICAs (Environmental Risks from Ionizing Contaminants: Assessments and management) limiting organisms showed that the risk quotient (RQ) for the estimated maximum soil and water activity was significantly less than unity for both the terrestrial and freshwater organisms. Conclusively, the radiological risk of the radioactivity released into the environment by the Fukushima nuclear accident to the public and the non-human biota in the republic of Korea is considered negligible.

Transport behavior and rice uptake of radiostrontium and radiocesium in flooded paddy soils contaminated in two contrasting ways

In order to investigate the transport behavior and rice uptake of radiostrontium and radiocesium in flooded rice fields, lysimeter experiments with two paddy soils were performed in a greenhouse. A solution containing (85)Sr and (137)Cs was applied in two different ways - being mixed with the top soil 27 d before transplanting or being dropped to the surface water 1d after transplanting. Rice uptake was quantified with two kinds of transfer factor - TF(m) (dimensionless) and TF(a) (m(2)kg(-1)-dry) for the pre- and post-transplanting depositions, respectively. For brown rice, the TF(m) values of (85)Sr and (137)Cs differed between the soils by factors of 2 (1.6×10(-2) and 2.5×10(-2)) and 7 (2.2×10(-2) and 1.5×10(-1)), respectively. Corresponding factors by the TF(a) values were 2 (2.5×10(-4) and 4.4×10(-4)) for (85)Sr and 3 (1.1×10(-3) and 2.9×10(-3)) for (137)Cs. Straws had several times higher TF(m) and TF(a) values of (85)Sr than of (137)Cs. The surface-water concentrations were substantially higher for the TF(a) than for the TF(m), indicating the possibility of a much higher plant-base uptake for the TF(a). In the TF(a) soils, (137)Cs and, to a lesser degree, (85)Sr were severely localized towards the soil surface, probably leading to an increased root uptake. The activity loss due to plant uptake and water percolation was generally inconsiderable. Time-dependent K(d) values of (85)Sr measured in a parallel experiment ranged from 20 to 170, whereas (137)Cs had much higher K(d) values. The use of TF(a) values instead of TF(m) values turned out to be a reasonable approach to the evaluation of a vegetation-period deposition.

A dynamic model to estimate the activity concentration and whole body dose rate of marine biota as consequences of a nuclear accident.

This paper describes a dynamic compartment model (K-BIOTA-DYN-M) to assess the activity concentration and whole body dose rate of marine biota as a result of a nuclear accident. The model considers the transport of radioactivity between the marine biota through the food chain, and applies the first order kinetic model for the sedimentation of radionuclides from seawater onto sediment. A set of ordinary differential equations representing the model are simultaneously solved to calculate the activity concentration of the biota and the sediment, and subsequently the dose rates, given the seawater activity concentration. The model was applied to investigate the long-term effect of the Fukushima nuclear accident on the marine biota using (131)I, (134)Cs, and, (137)Cs activity concentrations of seawater measured for up to about 2.5 years after the accident at two locations in the port of the Fukushima Daiichi Nuclear Power Station (FDNPS) which was the most highly contaminated area. The predicted results showed that the accumulated dose for 3 months after the accident was about 4-4.5Gy, indicating the possibility of occurrence of an acute radiation effect in the early phase after the Fukushima accident; however, the total dose rate for most organisms studied was usually below the UNSCEAR (United Nations Scientific Committee on the Effects of Atomic Radiation)s bench mark level for chronic exposure except for the initial phase of the accident, suggesting a very limited radiological effect on the marine biota at the population level. The predicted Cs sediment activity by the first-order kinetic model for the sedimentation was in a good agreement with the measured activity concentration. By varying the ecological parameter values, the present model was able to predict the very scattered (137)Cs activity concentrations of fishes measured in the port of FDNPS. Conclusively, the present dynamic model can be usefully applied to estimate the activity concentration and whole body dose rate of the marine biota as the consequence of a nuclear accident.

Approach to non-human species radiation dose assessment in the Republic of Korea

This paper describes the approach to non-human species radiation dose assessment in Korea. As the tentative reference organisms, one plant and seven animals were selected based on the new International Commission on Radiological Protection recommendation issued in 2007, and the size of the selected organisms was determined from the corresponding Korean endemic species. A set of 25 radionuclides was considered as a potential source term of causing radiological damage to organisms. External and internal dose conversion coefficients for the selected organisms and radionuclides were calculated by the uniform isotropic model or Monte Carlo simulation. Concentration ratios of some endemic species are being measured in laboratory experiments, in parallel with the review of existing data.

Effects of the simultaneous application of potassium and calcium on the soil-to-Chinese cabbage transfer of radiocesium and radiostrontium

Pot experiments were carried out in a greenhouse to investigate how effectively the transfer of radiocesium and radiostrontium from soil to Chinese cabbage could be reduced by applying K and Ca simultaneously to the soil. The sources of these elements were KCl and Ca(OH)(2) at agrochemical grades. Varying dosages of K and Ca were tested for an acid loamy soil treated with a mixed solution of (137)Cs and (85)Sr at two different times - 3 d before sowing and 32 d after sowing. For the pre-sowing deposition, the soil-to-plant transfer of (137)Cs decreased sharply with increasing dosages of K and Ca (K/Ca, g m(-2)) from 4.8/46 up to 22.4/215 but the (85)Sr transfer had the greatest reduction at a dosage of 12.8/123. At this dosage, an about 60% reduction occurred for each radionuclide. Plant growth was inhibited from the dosage of 22.4/215, above which all the plants died young. Both dosages of 4.8/46 and 12.8/123 tested following the growing-time deposition produced around 95% reductions for (137)Cs and 50% reductions for (85)Sr. In the second year after the 12.8/123 applications, the effects for (85)Sr were almost the same as in the first year, whereas those for (137)Cs were diminished slightly for the pre-sowing deposition and markedly for the growing-time deposition. Considerably (K) or slightly (Ca) higher doses than 12.8/123 would be allowable for the maximum TF reductions achievable without a growth inhibition.

Time-dependent transfer of 137Cs, 85Sr and 65Zn to earthworms in highly contaminated soils

The transfer characteristics of (137)Cs, (85)Sr and (65)Zn to earthworms (Eisenia andrei) in soils with different amounts of the radionuclides have been investigated. The time-dependent whole-body concentration ratios (CR) were derived for worms in artificially contaminated soils with three different activity concentrations. Two parameters of a first order kinetic model, the equilibrium concentration ratio (CR(eq)) and the effective loss rate constant (k), were estimated by a comparison of experimental CR results with model predictions. The estimated CR(eq) (Bq/kg fresh worm per Bq/kg dry soil) ranged from 3.9 × 10(-4) to 4.1 × 10(-3) for (137)Cs, 1.39 × 10(-3) to 2.94 × 10(-2) for (85)Sr, and 1.39 × 10(-3) to 5.0 × 10(-2) for (65)Zn, and consistently decreased with increasing soil activity concentration but the trend was not statistically significant. The CR(eq) for (137)Cs was one to two orders of magnitude lower than previously reported CR(wo-soil) values (based on field data with much less contaminated soil), that for (85)Sr was comparable with other reported values and for (65)Zn was less two to three orders of magnitude lower than CR(wo-soil) values for stable zinc. The estimated k (d(-1)) values ranged from 9 × 10(-2) to 1.4 × 10(-1) for (137)Cs, 7 × 10(-2) to 2 × 10(-1) for (85)Sr, and 6 × 10(-2) to 1.8 × 10(-1) for (65)Zn, and did not show a relationship with soil activity concentration. The effect of CR(eq) on the total dose rate was insignificant for (137)Cs or (65)Zn because external dose rates to the soil dwelling earthworms due to these radionuclides were much greater than the internal dose rate. In contrast, the total dose from (90)Sr was determined by the internal dose rate and therefore proportional to the CR(eq).

Radioecological studies in Korea atomic energy research institute, KAERI.

Regarding the assessment of the terrestrial food chain dose to man, radioecology may be the field that is focused on the transfer of radionuclides from environmental media to food crops. In Korea, the environmental transfer of radionuclides to staple food crops have been investigated at Korea Atomic Energy Research Institute (KAERI) for the last 25 y mainly through radiotracer experiments in greenhouses. As a result, several hundreds of parameter values for the prediction of the radionuclide transfer have been produced. Many of them appear in two recent publications of International Atomic Energy Agency. This paper outlines the KAERIs past radioecological work and introduces the ongoing research and future plans.

Long-Term Predictions of the 90Sr and 137Cs Concentrations in Rice for Their Acute Deposition at Different Times of the Year

transfer. The 90Sr and 137Cs concentrations (Bq kg−1-brown rice) at the first harvest following each deposition were in the range of 4.2 × 10−4−1.8 × 1.8 × 10−2 and 1.2 × 10−4−1.8 × 10−1 , respectively, being higher for the growing-season depositions than for the non growing-season depositions. The highest concentrations came from the deposition on September 1 for both owing to their highest seed-translocation factors. At the second harvest, the ranges for 90Sr and 137Cs were 3.0 × 10−4−4.2 × 10−4 and 7.9 × 10−5−1.2 × 104, respectively. Between the second and 50th harvests, the concentrations decreased by a factor of about 18 for 90Sr and 17 for 137Cs as a result of a reduced root uptake. The time-integrated concentrations (Bq · d kg−1−white rice) of 90Sr and 137Cs for a 50 years’ dietary consumption were in the range of 9.6 × 10−1−4.1 × 100 and 1.6 × 10−1-3.2 × 101, respectively. The use of the empirical data might enhance the accuracy of the prediction considerably. The present results may be used for a quick prediction at the time of a real accident.