Low-level Radioactive Contamination Research Articles

Advancing environmental monitoring: A comparative analysis of sequential radiochemical methods for precise alpha-particle spectrometry analysis of 241Am in soil and marine sediment samples

Environmental monitoring of alpha-emitting radionuclides is crucial for assessing the long-term impacts of nuclear activities and understanding ecosystem dynamics. Thus, long-term marine environmental monitoring needs a precise analytical method for determining isotopes in sediment and soil samples. Because 241Am is the first decay product of 241Pu, its activity in the environment will grow during the next 50 years. This study aims to compare and evaluate different sequential radiochemical methods for 241Am analysis, focusing on their precision and accuracy, to establish a more rapid, refined and reliable approach for environmental monitoring. Four radiochemical methods for 241Am determination in soil and marine sediment samples were compared using alpha-particle spectrometry. This sensitive technique plays a key role in quantifying low-level radioactive contaminants in sediment and soil samples. The procedure was optimised using reference materials prepared by IAEA: sediment (IAEA-300, IAEA-384 and IAEA-385) and soil (IAEA-327 and IAEA-375), and digestion, radiochemical separation, and purification on anion exchange resin (AG 1X8) and chromatographic resins (UTEVA, TRU) were used. The effectiveness of the Ca-oxalate precipitation method for iron removal was also evaluated. We used microcoprecipitation on neodymium fluoride (NdF3) to prepare measurement sources. As a significant outcome, we suggested the potential exclusion of co-precipitation (method D) in the determination of the 241Am isotope in sediment and soil samples. This recommendation aligns with our goal of developing a precise sequential radiochemical method for alpha-particle spectrometry. Our approach offers a valuable and optimised tool for monitoring the environmental impact of nuclear activities and accidents, particularly in marine ecosystems.

Determination of long distance transport of Cs+, Co2+ and Zn2+ ions in vascular plants by autoradiography and gamma-spectrometry

Heavy metals and radionuclides can enter the food chain via cereals and vegetables grown in contaminated soils. In the case of microelements such as zinc, studies have not focused only to assessing its environmental risk, but also to enhancing its uptake by plants as an important growth-limiting factor. In our study, digitalized autoradiograms of whole plants of celery (Apium graveolens L.), tobacco (Nicotiana tabacum L.) and sunflower (Helianthus annuus L.) grown in hydroponic nutrient media spiked with 137CsCl, 60CoCl2 and 65ZnCl2 were used for quantitative determination of uptake, long-distance transport and distribution of Cs+, Co2+ and Zn2+ ions in plant tissues. Results from autoradiography and gammaspectrometry of plants showed, that cesium was translocated to aboveground part of the plants with the shoot-to-root ratio 1.0 : 0.6. On the contrary, cobalt and zinc were more immobilized in roots, with the shoot-to-root ratio up to 1.0 : 3.8. The highest concentration of cesium, cobalt and zinc, expressed in specific radioactivity per unit of leaf surface (Bq/cm2) was found in top, rapidly growing leaves, the lowest concentration in the oldest leaves in low position. Detection limits 3, 2 and 14 Bq/cm2 by using X-ray film
 for 137Cs, 60Co and 65Zn, respectively were obtained. These data correspond to detection limits 10.5 pg Cs+/cm2, 7.2 pg Co2+/cm2 and 785 pg Zn2+/cm2 at specific radioactivity of commercially available 137CsCl, 60CoCl2 and 65ZnCl2. Resolutions 1-2 mm was sufficient for visualization of metal uptake and distribution in roots, stalks, leaves and leaf venation. Obtained data are part of quantitative study of uptake and translocation of both low level-radioactive contamination in plants and microelements applied as fertilizers.

Measurement of the Background Activities of a 100Mo-enriched Powder Sample for an AMoRE Crystal Material by Using a Single High-Purity Germanium Detector

The Advanced Molybdenum-based Rare process Experiment (AMoRE) searches for neutrino-less double-beta (0{\nu}\b{eta}\b{eta}) decay of 100Mo in enriched molybdate crystals. The AMoRE crystals must have low levels of radioactive contamination to achieve low background signals with energies near the Q-value of the 100Mo 0{\nu}\b{eta}\b{eta} decay. To produce low-activity crystals, radioactive contaminants in the raw materials used to form the crystals must be controlled and quantified. 100EnrMoO3 powder, which is enriched in the 100Mo isotope, is of particular interest as it is the source of 100Mo in the crystals. A high-purity germanium detector having 100% relative efficiency, named CC1, is being operated in the Yangyang underground laboratory. Using CC1, we collected a gamma spectrum from a 1.6-kg 100EnrMoO3 powder sample enriched to 96.4% in 100Mo. Activities were analyzed for the isotopes 228Ac, 228Th, 226Ra, and 40K. They are long-lived naturally occurring isotopes that can produce background signals in the region of interest for AMoRE. Activities of both 228Ac and 228Th were < 1.0 mBq/kg at 90% confidence level (C.L.). The activity of 226Ra was measured to be 5.1 \pm 0.4 (stat) \pm 2.2 (syst) mBq/kg. The 40K activity was found as < 16.4 mBq/kg at 90% C.L.

Visualization of Low-Level Gamma Radiation Sources Using a Low-Cost, High-Sensitivity, Omnidirectional Compton Camera.

We present experimental protocols for visualizing various low-level gamma radiation sources in the ambient environment. Experiments were conducted by using a low-cost, high-sensitivity, omnidirectional, gamma-ray imaging Compton camera. In the laboratory, the position of a sub-MeV gamma radiation source such as 137Cs can easily be monitored via omnidirectional gamma-ray imaging obtained by the Compton camera. In contrast, a stationary, wall-mounted dose rate monitor cannot always successfully monitor such a source. Furthermore, we successfully demonstrated the possibility of visualizing the radioactivity movement in the environment, for example, the movement of a patient injected with 18F-fluorodeoxyglucose (18F-FDG) in a nuclear medicine facility. In the Fukushima field, we easily obtained omnidirectional gamma-ray images concerned with the distribution on the ground of low-level radioactive contamination by radioactive cesium released by the Fukushima Daiichi nuclear power plant accident in 2011. We demonstrate clear advantages of using our procedure with this camera to visualize gamma-ray sources. Our protocols can further be used to discover low-level gamma radiation sources, in place of stationary dose rate monitors and/or portable survey meters used conventionally.

Radioisotope Identification and Nonintrusive Depth Estimation of Localized Low-Level Radioactive Contaminants Using Bayesian Inference.

Obtaining the in-depth information of radioactive contaminants is crucial for determining the most cost-effective decommissioning strategy. The main limitations of a burial depth analysis lie in the assumptions that foreknowledge of buried radioisotopes present at the site is always available and that only a single radioisotope is present. We present an advanced depth estimation method using Bayesian inference, which does not rely on those assumptions. Thus, we identified low-level radioactive contaminants buried in a substance and then estimated their depths and activities. To evaluate the performance of the proposed method, several spectra were obtained using a 3 × 3 inch hand-held NaI (Tl) detector exposed to Cs-137, Co-60, Na-22, Am-241, Eu-152, and Eu-154 sources (less than 1μCi) that were buried in a sandbox at depths of up to 15 cm. The experimental results showed that this method is capable of correctly detecting not only a single but also multiple radioisotopes that are buried in sand. Furthermore, it can provide a good approximation of the burial depth and activity of the identified sources in terms of the mean and 95% credible interval in a single measurement. Lastly, we demonstrate that the proposed technique is rarely susceptible to short acquisition time and gain-shift effects.

A Bayesian Approach for Remote Depth Estimation of Buried Low-Level Radioactive Waste with a NaI(Tl) Detector.

This study reports on the implementation of Bayesian inference to improve the estimation of remote-depth profiling for low-level radioactive contaminants with a low-resolution NaI(Tl) detector. In particular, we demonstrate that this approach offers results that are more reliable because it provides a mean value with a 95% credible interval by determining the probability distributions of the burial depth and activity of a radioisotope in a single measurement. To evaluate the proposed method, the simulation was compared with experimental measurements. The simulation showed that the proposed method was able to detect the depth of a Cs-137 point source buried below 60 cm in sand, with a 95% credible interval. The experiment also showed that the maximum detectable depths for weakly active 0.94-μCi Cs-137 and 0.69-μCi Co-60 sources buried in sand was 21 cm, providing an improved performance compared to existing methods. In addition, the maximum detectable depths hardly degraded, even with a reduced acquisition time of less than 60 s or with gain-shift effects; therefore, the proposed method is appropriate for the accurate and rapid non-intrusive localization of buried low-level radioactive contaminants during in situ measurement.

Динаміка вмісту 137Cs у компонентах раціону диких ратичних тварин у лісах Житомирського Полісся

Наведено результати визначення питомої активності 137Cs у тих частинах деревних порід, чагарників, чагарничків і грибів, які є основним кормом для козулі європейської у лісах Житомирського Полісся. Визначено основні «критичні» періоди протягом року, які характеризуються найвищими рівнями вмісту радіонуклідів у кормах і в організмах дикого кабана і козулі європейської. Для всіх досліджуваних видів рослин, що входять до складу раціонів дикого кабана та козулі європейської, характерні значні сезонні коливання концентрації 137Сs у різних органах рослини, які можуть використовувати як корм тварини (коренях, річних пагонах, листі), а також у частинах органів (верхня, середня та нижня частини пагона). В осінній та весняний періоди виявлено підвищену концентрацію 137Сs у верхівках пагонів та коренях рослин. Влітку найбільшу активність 137Сs зафіксовано у надземній фітомасі. Представлено сезонні коефіцієнти переходу 137Cs з ґрунту в корма дикого кабана та козулі європейської у «критичні» періоди радіоактивного забруднення їх організмів. Запропоновано заходи щодо оптимізації термінів відстрілу диких ратичних тварин.

Assessment of self-help methods to reduce potential exposure to radiological contamination after a large-scale radiological release.

After the release of radioactive materials from a large radiological dispersal device (e.g., dirty bomb), improvised nuclear detonation, or nuclear power plant accident, up to hundreds of square miles may be contaminated. A portion of this area will be evacuated; however, people living in the portion that is not evacuated yet is still contaminated with low-levels of radioactive contamination will be asking for ways they can reduce their exposure. Whether cleaning activities can significantly reduce exposure is not fully understood. In this effort, the ability of cleaning activities to remove cesium (137Cs) was studied. The removal efficacy of cleaning with a commercial product, Simple Green®, was compared to cleaning with water for hard surfaces typically seen in residences. The removal efficacy of laundering fabric material surfaces was also determined for a range of conditions (e.g., fabric material type, wash temperature). During these studies, assessments of the implications of these activities (e.g., cross-contamination, resulting waste streams) were also completed. Simple Green and water were effective for removing 137Cs from plastic laminate and vinyl flooring (93.4-96.8%) but were not effective for removing 137Cs from painted wallboard and wood (7.3-68.1%). It was also determined that there was no significant difference between the two cleaners on all of the surfaces, except plastic laminate, for which Simple Green was slightly more effective. Laundering was effective for removing 137Cs contamination from polyester and cotton swatches and cotton comforters (up to 96.8% in the single swatch testing).

Enzyme polymorphism of antioxidant system in chronically irradiated Scots pine populations

Background. The Chernobyl accident caused dramatic and long-term increases in ambient radiation doses to many forest environments. Sites still exist in the Bryansk region of Russia, 25 years after the Chernobyl accident, where radioactive contamination significantly exceeds background. There is growing evidence that effects of chronic radiation exposure lead to population-level impacts. Isozymes polymorphism assessment is thought to be promising since it sensitive enough, may integrate the impacts of harmful agents in the environment, and provide meaningful information on biological damage The aims of this study were to examine whether Scots pine trees have experienced stress in areas with relatively low levels of radioactive contamination and, if so, to quantify such an impact.Materials and methods. Scots pine (Pinus sylvestris L.), the dominant tree species in North Eurasia boreal forests, was chosen as a test organism for an assessment of the possible effects from the radioactive contamination. Four study sites were chosen in the most contaminated areas of the Bryansk region of Russia. This area was significantly contaminated by Chernobyl fallout with an initial 137Cs ground deposition level more than 1 MBq/m 2 in some locations (Ramzaev et al., 2008). Sites are uniform in climate and the physical and chemical properties of soils, forest stand is homogeneous, and pine trees occupy a large part of phytocenosis. Dose rates at the study sites ranged from 0.37 to 1.21 μGy/h, compared to 0.10 μGy/h at control site. Pine cones were collected in December of 2009–2010. Specific activities of radionuclides in soil samples were measured, and doses to the pine trees’ generative organs were estimated. Antioxidant enzymes polymorphism (superoxide dismutase (SOD, KF 1.15.1.1), glutathione reductase (GR, KF 1.6.4.2), and glutathione peroxidase (GPX, KF 1.11.4.2)) was investigated by vertical electrophoresis.Results. The study sites did not differ substantially in soil properties, or chemical content of soil or pine cones (Geras'kin et al., 2011; Geras'kin et al, 2008). The main contribution to the radioactive contamination was from 137Cs with activity concentrations at the contaminated sites (averaged through 0–15 cm soil layer) ranging from 2.4 to 56.3 kBq/kg of soil. These activity concentrations exceed those at the referent site by factors of 47–1081 (Geras'kin et al., 2011). Annual absorbed doses rates changes from 7.0 to 130 mGy/year compared to 0.14 mGy/year at reference site. The average frequency of mutations in three enzymes significantly (r = 99 %, p 0.01) increases with increasing absorbed dose by generative plant organs. Indices of phenotypic diversity in the populations studied are significantly different from the control. Proportion of rare morphs dramatically increases in populations inhabiting areas contaminated with radionuclides, which is associated with the emergence of new alleles in several enzyme systems (null alleles, allele 0.80 in the GPX-1 and 0.95 in the GPX-2). The observed and expected heterozygosity in affected populations increase along with the level of contamination sites (r = 99 %, p 0.01).Conclusions. These data show that chronic, low level radiation exposure (7–130 mGy/year) results in an increase in frequency of mutations in the endosperm and the seed embryos and modify the genetic structure of Scots pine populations. These data suggest that a high level of mutations occurs in the progeny of these pine populations and that their diversity is conditioned by radiation exposure. Thus, in spite of their low values, dose rate observed can be considered as a factor capable of modifying the genetic structure of populations.

Disaster Preparation: Lessons from Japan

On 11 March 2011, the earthquake and tsunami in Japan claimed thousands of lives, disrupted the lives of hundreds of thousands, and destroyed regional power and transportation infrastructure. Backup systems intended to maintain cooling for three operating nuclear reactors and the spent-fuel pools failed. Experts in various technical fields from Japan, the United States, and around the world worked to understand and mitigate the consequences of unplanned releases of radioactivity. As a team of U.S. health and medical subject matter experts deployed to Japan in the early days after the tsunami, we have identified the elements that remain most challenging in preparing for future disasters. ![Figure][1] Support. The U.S. Navy delivers relief supplies to an evacuation center in northern Japan. CREDIT: MASS COMMUNICATION SPECIALIST 1ST CLASS BEN FARONE, US NAVY/WIKIMEDIA COMMONS Given the reality of the uncertainty in the physical state of the Fukushima reactors, the ability to make accurate predictions based on models was limited. We found that the absence of such information led to suspicion by the public that data were not being reported. Information was being provided by a variety of sources, including international news media. Cultural differences and national sovereignty must be understood and respected when determining how to present, disseminate, and discuss information. Although the public was justifiably concerned about possible radiation health effects, we believe that lack of understanding of radiation and its effects resulted in unnecessary fear. The misunderstanding extended to the purpose of potassium iodide (KI), which should not be distributed indiscriminately, but rather used to protect those with active thyroids, particularly infants, young adults, and teens who are at risk from the exposure resulting from internal contamination. There was also uncertainty about the best KI dosage and administration schedule, partly because Japanese dosage guidance differed from that provided by the United States. Fortunately, in this case KI prescriptions were reduced to very few people, primarily those working close to the reactors. We also observed differences in risk tolerance. Compared with those far from the site, a local population may choose to accept a modestly greater risk from low-level radioactive contamination in order to restore their economy and way of life. Cultural differences also may alter the acceptable level of risk (such as the amount of iodine normally contained in the diet) or how to balance risk and benefit. Less stringent requirements can be acceptable for adults, compared with infants and children, although conflicting protective action guidelines create public confusion. When evacuation is initiated, it is crucial to identify the criteria that must be met before residents are permitted to return. Each decision requires the assessment of competing risks at a time when outcomes are uncertain. For example, initially imposing a travel warning and limiting entry of people and removal of food products from a 50-mile zone around the radiation source were sensible. However, there are risks in mass movements of people, including transportation accidents, trauma from disrupting lives, separating people from their normal support structure (including care for chronic medical conditions), and diverting personnel who might be needed elsewhere. If evacuation is maintained for too long, there can be serious health (including mental health), family, and economic consequences. In rapidly evolving situations, scientists who advise decision-makers must think like clinicians and make decisions based on the best information available at the time. 1. The contents in this manuscript are from the authors and do not represent U.S. government policy or opinion. [1]: pending:yes

Radioactivity in Oily Sludge and Produced Waste Water from Oil: Environmental Concerns and Potential Remedial Measures

Produced water separated from oil is usually returned to the environment and could permeate through the water table. If such water is contaminated with radioactive substances, it could create a definite threat to the water supply, especially in arid regions where ground water and overhead streams are sources of potable water. Low-level radioactive contamination of oily sludge is equally hazardous and also leads to detrimental pollution of water resources. We investigated the distribution of 226Ra, 40K and 228Ac in produced waste water and oily sludge and found abnormal levels of radioactivity. A total of 90 ground wastewater samples were collected from different sites for a period of one year. The presence of these radionuclides was identified by their characteristic gamma rays. The detection system consisted of a high-purity germanium detector. Our results show that about 20% of the samples exhibited 20–60 Bq/L radioactivity and ~6% of the samples exceeded 60 Bq/L. Roughly 70% of the experimental samples fell in the range of 2–20 Bq/L, which still exceeded the maximum admissible drinking-water limit 0.2 Bq/L.

DNA damage in barn swallows ( Hirundo rustica) from the Chernobyl region detected by use of the comet assay

We investigated levels of DNA damage in blood cells of barn swallows ( Hirundo rustica) inhabiting the Chernobyl region to evaluate whether chronic exposure to low-level radioactive contamination continues to induce genetic damage in free-living populations of animals. Blood samples were obtained from barn swallows collected at sites with different background levels of radiation, including a relatively uncontaminated area. The extent of DNA damage was evaluated using the alkaline (pH = 12.1) comet assay, a robust and sensitive electrophoresis-based technique widely employed in research ranging from biomonitoring to clinical studies. We found that levels of DNA damage, as indexed by the extent of DNA migration, were increased in barn swallows living in areas surrounding Chernobyl when compared to swallows sampled at low-level sites. The results we obtained are consistent with previous findings on this same species, which showed that swallows breeding in areas heavily contaminated with radionuclides have increased mutation rates, higher oxidative stress and incidence of morphological aberrations and tumors. Overall, these results indicate that chronic exposure to radioactive contaminants, even 20 years after the accident at the Chernobyl nuclear power plant, continues to induce DNA damage in cells of free-living animals.

A chromatographic system for removal of radioactive 85Kr from xenon

Extremely low count rates of useful events in detectors of neutrino or weakly interacting exotic particles require using detector working media with low levels of radioactive contaminants. Liquid xenon, highly purified and filtered using advanced semiconductor industry technologies serves as an attractive target for several modern experiments searching for cold dark matter, double beta decay, and detection of low energy neutrino. Separation of xenon from trace amounts of 85Kr cannot be achieved with commercially available gas purifiers. We have developed an automated system for purification of xenon from trace amounts of krypton. The system has been used to purify 25 kg of xenon to the level of < 3 ppt of krypton. The purified xenon will be used for the two-phase emission detector, XENON10, to search for WIMP dark matter in the Gran Sasso Underground Laboratory.

Birds prefer to breed in sites with low radioactivity in Chernobyl

Low-level radioactive contamination may affect choice of breeding site and life-history decisions if (i) radioactivity directly affects body condition or (ii) it affects resource abundance that then secondarily influences reproductive decisions. We tested the effects of radioactive contamination on nest-site choice and reproduction in a community of hole nesting birds by putting up nest boxes in areas differing in levels of background radiation. Great tit Parus major and pied flycatcher Ficedula hypoleuca significantly avoided nest boxes in heavily contaminated areas, with a stronger effect in flycatchers than in tits. These preferences could not be attributed to variation in habitat quality or resource abundance, as determined by analyses of habitat use and the relationship between radiation and life-history characters. Likewise, none of these effects could be attributed to individuals of a specific age breeding in the most contaminated areas. Laying date and clutch size were not significantly related to dose rate in either species. Hatching success was depressed by elevated radioactive contamination, interacting with habitat in the great tit and with laying date in the pied flycatcher. Interspecific differences in effects of radiation on nest-site choice suggest that species respond in a species-specific manner to radiation, perhaps related to differences in migratory habits. We suggest that individual body condition rather than secondary effects of radiation on resource abundance account for the effects on nest box use and hatching success.

LOW-ACTIVITY RADIOACTIVE MATERIALS MANAGEMENT AT THE U.S. DEPARTMENT OF ENERGY

The U.S. Department of Energy (U.S. DOE) is making significant progress with the cleanup of its legacy radioactively-contaminated facilities and sites left from research and development and production of nuclear materials and weapons. Sites like Rocky Flats, Battelle Columbus Laboratories, Fernald, Mound, Brookhaven National Laboratory, Hanford, and Oak Ridge are faced daily with decisions related to disposition of waste and radioactive material. One key to this success is the disposition of waste arising from cleanup. Most of the generated waste volume has very low levels of radioactive contamination. The waste includes contaminated soil, debris from demolition, or scrap metal and equipment. The cost of disposing of large volumes of waste can be prohibitive, so there is incentive to find innovative ways to disposition wastes. This paper describes the current status of policy development in this area, such as development of a draft programmatic environmental impact statement and monitoring of related rulemaking at the U.S. Nuclear Regulatory Commission. The paper also provides an overview of draft U.S. DOE guidance on control and release of property with residual radioactive material, and site-specific applications of DOE guidance.

建屋表面を対象とした低レベル放射能汚染の自動測定装置の開発

建屋表面を対象とした低レベル放射能汚染の自動測定装置の開発

Population monitoring: experience with residents exposed to uranium mining/milling waste

More emphasis should be placed upon using biomarkers to address potential health risk among populations exposed to high concentrations of environmental toxicants. Among these studies, those which integrate exposure measurements with analyses of validated biomarkers may provide more reliable information for risk assessment and disease prevention. We have used a multidisciplinary approach to elucidate potential health hazards in a population living around uranium mining/milling facilities. The study included 24 target and 24 control residents who were matched for age and gender and selected based on time of residence in the study areas and proximity to mining/milling sites. Environmental samples were analyzed for uranium-238 ( 238 U) concentrations and lead isotope ratios using inductively coupled plasma-mass spectrometry (ICP-MS) procedures, and blood samples were collected for cytogenetic analysis. We found that the 238 U concentrations in soil samples were significantly higher than those in the control areas. In addition, the concentrations in the surface soil were significantly higher than in the subsurface soil ( p<0.05) from target areas indicating environmental contamination by the mining/milling activities. Lead isotope data from soil samples taken near a railroad transfer location was significantly different from those of other sites, indicating contamination by non-native ore transported from sources outside of the region to local milling facilities for processing. Therefore, local residents have been exposed to low levels of radioactive contamination from the mining/milling activities on a daily basis for many years. From our cytogenetic analysis, the target population had more chromosome aberrations than the controls, although the differences were not significant ( p<0.05). However, using our challenge assay, cells from the target population had a significantly abnormal DNA repair response, compared to cells from the same control population. In conclusion, the observed environmental contamination by uranium is consistent with the observed genotoxic effects in the target residents. Therefore, the residents have increased health risk and some of the health problems will most likely be related to exposure to the radioactive contaminants. Since the chromosome aberration frequency revealed increased, but not significant differences between the exposed and the control populations, we conclude that the health risk among the exposed residents is similar to those among nuclear workers.

A dosimetric determination of 137Cs ingestion from global fallout and the related risks to Japanese.

137Cs released from atmospheric nuclear detonation tests has been transported worldwide in the environment and finally taken up by humans through various pathways. In particular, ingestion pathways are important for evaluating the human health risks caused by the chronic global low-level radioactive contamination. In this research, the mathematical model for the evaluation of the dietary intake of 137Cs and the related risks to Japanese are proposed by coupling the previously published global 137Cs distribution model with the regional models such as various food ingestion models and the model of the domestic and international supply. Predictions from the proposed model were compared with the monitoring data of 137Cs in Japanese total diet as an attempt at validation. The major findings obtained in this research include that the proposed model is promising for evaluating the risk to Japanese health caused by the dietary intake of global radioactive fallout 137Cs, the 137Cs is taken up by Japanese mostly through farm products, the ingestion of 137Cs through imported foods is increasing, the risk to the Japanese health of inducing cancer by 137Cs internal exposure reached a maximum in 1963, gradually decreasing to the lowest present level, and the risk to infants is the highest.

地球規模フォールアウト｀１３７´Ｃｓの日本人による経口摂取評価モデルの不確実性解析

Most of model estimation of the environmental contamination includes some uncertainty associated with the parameter uncertainty in the model. In this study, the uncertainty was analyzed in a model for evaluating the ingestion of radionuclide caused by the long-term global low-level radioactive contamination by using various uncertainty analysis methods: the percentile estimate, the robustness analysis and the fuzzy estimate. The model is mainly composed of five sub-models, which include their own uncertainty; we also analyzed the uncertainty. The major findings obtained in this study include that the possibility of the discrepancy between predicted value by the model simulation and the observed data is less than 10%; the uncertainty of the predicted value is higher before 1950 and after 1980; the uncertainty of the predicted value can be reduced by decreasing the uncertainty of some environmental parameters in the model; the reliability of the model can definitively depend on the following environmental factors: direct foliar absorption coefficient, transfer factor of radionuclide from stratosphere down to troposphere, residual rate by food processing and cooking, transfer factor of radionuclide in ocean and sedimentation in ocean.

Adsorption Decontamination of Radioactive Waste Solvent by Activated Alumina and Bauxites

An adsorption process utilizing activated alumina and activated bauxite adsorbents was evaluated as a function of operating parameters for the removal of low level radioactive contaminants from organic waste solvent generated in the fuel reprocessing facilities and support operations at Savannah River Site. The waste solvent, 30 vol% tributyl phosphate in n-paraffin diluent, was degraded due to hydrolysis and radiolysis reaction of tributyl phosphate and n-paraffin diluent, producing fission product binding degradation impurities. The process, which has the potential for removing these activity-binding degradation impurities from the solvent, was operated downflow through glass columns packed with activated alumina and activated bauxite adsorbents. Experimental breakthrough curves were obtained under various operating temperatures and flow rates. The results show that the adsorption capacities of activated alumina and activated bauxite were in the order of 10{sup 4} and 10{sup 5} dpm/g of adsorbent, respectively. The performance of the adsorption process was evaluated in terms of dynamic parameters (i.e., adsorption capacity, the height and the efficiency of adsorption zone) in such a way as to maximize the adsorption capacity and to minimize the height of the mass transfer or adsorption zone.