Radioactive Waste Disposal Facility Research Articles

A long term baseline and variability of natural radionuclides in groundwater at the Vaalputs low-level radioactive waste disposal facility, Namaqualand, South Africa: regional implications

Abstract Vaalputs is the only South African nuclear waste disposal facility; it is licensed to dispose of low and intermediate level radioactive waste. Possible disposal of long-lived waste, potentially including spent fuel rods, prompted a study to establish a baseline of naturally-occurring radionuclides from the U and Th decay chains in the groundwater of Vaalputs. This baseline was created by investigating a dataset containing 25 years of analyses of the groundwater at the Vaalputs site. The behaviour over time, of 23 radionuclides in groundwater samples from 13 annually and three quarterly sampled boreholes, was evaluated and integrated in order to establish changing trends in the activities of radionuclides, the relative contributions of individual radionuclides to total radiation levels and how these were influenced by groundwater conditions. 238U levels showed a natural anomaly in the near-field of the disposal site that was attributed to the underlying basement rocks (granites) which are anomalously enriched in U. A set of duplicate samples from 2009 determined that the activity ratio of 234U/238U in the groundwater of Vaalputs is 4.1; this is ascribed to more rapid leaching of 234U relative to 238U, because of increased crystal structural damage around sites surrounding 234U atoms. High levels of 226Ra, unsupported by 238U, were found in groundwater from boreholes on the western side of the property: this groundwater yielded low values for 234U/238U, lower pH and stronger oxidizing conditions than groundwater from the rest of the area. The absence of overlying sedimentary rocks, which tend to ameliorate the effects of high radiation from granites by absorption, is suggested as the reason for the different geochemical conditions of the groundwater from boreholes in the west. This suggestion may apply to those boreholes elsewhere in Namaqualand with low published concentrations of 238U, but exceptionally high levels of α -and β-emitters. 232Th and its daughter radionuclides yielded radiation levels far below the guideline of 1 Bq.L-1 specified by the World Health Organization; this result is in line with the known low mobility of Th in groundwater systems.

Spatiotemporal changes in hydrogeochemistry of coastal groundwater through the construction of underground disposal facility for low and intermediate level radioactive wastes in Korea

This study was objected to assess active changes in hydrochemistry of coastal groundwater through the construction of underground low- and intermediate-level radioactive waste (LILRW) disposal facility. Groundwater monitoring data from the construction stage of the facility beginning in 2010 to the operation stage in 2017 revealed seawater intrusion (SWI) into the inland area with significant spatiotemporal variation and subsequent changes in hydrochemical reactions. Groundwater was divided into three groups based on the temporal changes in the seawater mixing ratio. Group 1 showed an increasing trend with some delayed responses to SWI and an ion-exchange dominant process. Group 2 represented dynamic changes of hydrochemical reactions in time toward to a new equilibrium condition along SWI and refreshing. In this group, simultaneous increases in SO4 and Ca, depletion of δ34SSO4, and a slight decline in the SI of gypsum suggest that precipitation and re-dissolution of gypsum occurred during the transition of SWI. These changes are probably attributable to the balance change between seawater and fresh groundwater inflows, and subsequently to preferential flow paths developed in the fractured aquifer. Group 3 groundwater demonstrated a rapid and direct connection with seawater since the beginning of construction of the LILRW facility. In summary, SWI process and subsequent hydrogeochemical reactions in the coastal groundwater varies significantly in time and in space, thus continuous monitoring of groundwater chemistry is warranted for safety management of the underground LILRW facility.

Development of Artificial Neural Network-Based Model for Prediction of Temperature Field in Host Rock of a Geological Disposal Facility for Radioactive Waste

Development of Artificial Neural Network-Based Model for Prediction of Temperature Field in Host Rock of a Geological Disposal Facility for Radioactive Waste

The importance of surface ruptures and fault damage zones in earthquake hazard assessment: a review and new suggestions

Abstract Large earthquakes (M W > c. 6) generate surface ruptures and strong ground motions, resulting in extensive property damage and loss of lives. The earthquake damage and causality levels depend, for example, on the earthquake magnitude, seismic wave characteristics, the distance from the epicentre, the depth of earthquake and the foundation of related area . However, these factors cannot all be known for future earthquakes, because the exact times and locations of earthquakes cannot be predicted with the current technology. Thus, it is only possible to prepare for earthquakes by implementing anti-seismic design codes based on the local geological conditions. With accurate information about the locations of active faults or potential surface ruptures and deformation patterns, earthquake-prone areas could be avoided during site selection, especially for important facilities such as nuclear power plants and high-level radioactive waste disposal facilities. In this study, we investigated several factors for earthquake hazard estimation, focusing on the fault damage zones and respect distances. Fault damage zones around faults are mainly controlled by fault types, tip modes, exposed locations and slip senses along the fault. The characteristics of geological faults and earthquake ruptures show asymmetrical displacements and damage patterns, making it difficult to estimate respect distances and surface deformations. Therefore, both the respect distance and fault damage zone should be considered when identifying safe regions. This information will facilitate earthquake hazard assessment and appropriate site selection to reduce earthquake hazards in earthquake-prone areas.

Анализ подходов к консервации и ликвидации скважин на участке недр «Енисейский» (Красноярский край, Нижнеканский массив)

Rock mass is considered as a natural barrier impeding the release of radioactive waste into the environment, being part of a multi-barrier system designed to ensure the safety of deep disposal facilities for radioactive waste (DDF RW). A number of regulatory documents [1] and recommendations [2, 3] states the importance of the geological medium, namely, its characteristics for the long-term safety of RW disposal. Current stage of URL development project is specifically focused on providing the opportunities for geological research covering target RW disposal horizons solely via borehole methods before the entire complex of underground excavations is formed. Due to long-term operation of wells and their initial design features, the state of some of these wells has appeared to be unsatisfactory requiring reconstruction. In addition, in accordance with certain legislative requirements, all wells shall be abandoned after relevant operations have been completed. The article discusses the reconstruction and abandonment of wells drilled at the Yeniseiskiy site. It demonstrates the feasibility of proposed designs providing the opportunities for further expansion of studies to investigate the state of rocks under natural conditions and to arrange for monitoring. The paper provides an evaluation and comparative analysis of plugging materials proposed to be applied under well abandonment operations.

О системном подходе к выбору барьеров безопасности для захоронения РАО классов 3 и 4

The article describes different designs and materials of engineered safety barriers (ESB) for radioactive waste disposal facilities, systematizes the functions and technical specifications of EBS and based on a system approach proposes safety barrier materials and designs for the disposal of radioactive waste class 3 and 4.

NORM inventory forecast for Australian offshore oil and gas decommissioned assets and radioactive waste disposal pathways

This research establishes a decommissioning timeline for the existing oil and gas facilities across all of the Australian offshore oil and gas production basins. Minimal data exist in the public domain to estimate these decommissioning timelines and, more importantly, the significant waste volumes generated; including potentially hazardous wastes such as naturally occurring radioactive material (NORM). At this time there is no approved onshore radioactive waste disposal pathway in Australia to accommodate this material. Applying an estimation methodology, based on Norwegian decommissioning data with regional activity factors, allows a NORM waste forecast to be established for the decommissioning of Australian oil and gas offshore infrastructure. The total NORM disposal burden is estimated to be in the range of 223–1674 tonnes for decommissioning activity to 2060, with over 68% of this material generated between 2018 and 2025. Due to the sparsity of public domain data this forecast is deemed to be uncertain and excludes the NORM contamination anticipated to be present in subsea export pipelines, trunklines and well production tubing. Current regulations governing the categorisation and disposal of radioactive wastes across Australia are complex and regionally dependent. This regional variation makes the implementation of a national radioactive waste disposal facility more difficult, and encourages the export of radioactive wastes overseas for final disposal. Exporting of radioactive wastes potentially presents a higher risk compared with in-country disposal and is likely not an effective long-term proposition. A comprehensive NORM data collection and quantification assessment programme, spanning all onshore and offshore oil and gas infrastructure, needs to implemented to drive and verify a NORM waste management strategy for the wave of facility decommissioning projects that are fast approaching.

A preliminary study of the engineering properties of dorbank

Dorbank, a naturally indurated, pedogenic layer, is found over vast expanses of arid and semi-arid parts of southern Africa. Although considered a nuisance to local farmers, dorbank is relatively easy to rip from the soil profile to clear the way for agricultural developments. Its strategic position just beneath the topsoil in the soil profile, as well as its consistency which is often close to that of rock, raises the question of its engineering capabilities. In this study the properties of unbound, mechanically crushed dorbank gravels were investigated in the context of exploiting dorbank for road-building purposes. Moreover, the study investigated the pedogenic variance of dorbank for possible indicators of engineering quality. Dorbank samples were taken from three different regions in the Karoo - the vicinity of Vanrhynsdorp, Aggeneys and the Vaalputs radioactive waste disposal facility near Springbok. Samples were subjected to two stages of investigation. Firstly, the pedogenic nature of dorbank was determined. Different morphologies of dorbank and their relation to the soil type in which they were found were described, whereafter cementing agents were selectively dissolved from dorbank while noting the resulting effect on its structural strength. Polished dorbank sections were additionally analysed with scanning electron microscopy (SEM), coupled with energy-dispersive x-ray (EDX) spectroscopy to identify minerals that are deleterious to roadworks and to understand the chemical enrichment of dorbank by cementing agents. Secondly, the unbound granular qualities of dorbank were tested to establish its use as a material in the structure of a flexible pavement or as a gravel wearing coarse. Dorbank samples were crushed with a small jaw crusher from which the particle size distribution (PSD), the flakiness index (FI), pH, electrical conductivity (EC), Atterberg limits, linear shrinkage (LS), maximum dry density (MDD), optimum moisture content (OMC), soaked California Bearing Ratio (CBR) and direct shear strength (DST) of remoulded samples were determined. The strength and durability of particles that fell within the 13.2 to 19.0 mm size fraction were evaluated with the Treton impact test, the aggregate pliers test (APT) and the accelerated weathering test (AWT). Dorbank samples presented as platy and as massive morphologies in transported sandy soils. Platy dorbanks were found to occur in silty sands, and massive dorbanks in medium to coarse sands. Dorbanks were often found overlying calcrete horizons and containing calcerous veins, which cause adverse discontinuities in the macro- and micro-morphology of dorbank. From the selective dissolution test with NaOH and HCl, and with quantitative SEM-EDX analyses, samples were confirmed to be petroduric in nature. Dorbank fell short of the South African road-base material requirements, particularly due to its low CBR and low durability. Furthermore, dorbanks were found to be almost cohesionless from the DST results (c' = 3 to 7 kN/m2) and non-plastic from the Atterberg limit test results. The aggregate strength and grading coefficient of dorbank from the Vanrhynsdorp and Vaalputs regions satisfy the requirements for use as a gravel wearing coarse, although possible corrugating, ravelling and a high re-gravelling frequency and dustiness can be expected. Finally, the study concluded that platy dorbank performs better in strength tests, but weather more quickly in the accelerated weathering test. The lack of cohesion and its non-plastic behaviour are likely due to the suppression of the activity of clay, which in turn is due to cementation and the aggregation of clay minerals. Further investigation of dorbank gravels, modified with the addition of fines, is suggested.

Use of interaction matrices to formalise the development of conceptual models of contaminant transport in the biosphere and the translation of those conceptual models into mathematical models

In developing models of the biosphere for use in assessing the impacts on human health and the environment of releases of contaminants from disposal facilities for solid radioactive wastes or from contaminated legacy sites, there is a need to demonstrate that the models adopted are both comprehensive and appropriate to the assessment context. To achieve this end, it is useful to develop a structured approach to conceptual model development and it is here proposed that interaction matrices (IMs) provide a suitable framework. This process can provide a conceptual model expressed in terms of either a single IM or a nested set of IMs. The focus of the work described herein is the development of a transparent approach to translating such a set of IMs into a mathematical model, which is typically expressed as a set of ordinary differential equations complemented by algebraic expressions. Some remarks are also made on appropriate approaches to obtaining numerical solutions of these equations in circumstances where simplifications of the general equations can be justified. Overall, the intent is to provide background and guidance by providing a formal basis for the process in generalised terms.

Underground Research Laboratory in “the Yenisei” Section of the Nizhnekansky Massif of the Krasnoyarsk Region

The issues of the construction and operation of an underground research laboratory for the purpose of substantiating the long-term safety of the deep radioactive waste disposal facility in the Russian Federation from the perspective of scientific support are considered. The basic principles are stated and the key directions of a long-term program of scientific research, including in an underground laboratory, are justified for assessing and substantiating the safety of an object at all stages of its life cycle

Investigation of novel composites to be used as backfill materials in radioactive waste disposal facilities

The current work aims at the preparation and characterization of novel composite materials of acrylic acid/charcoal/montmorillonite (MMT) (PAACM and AMC). They are characterized using SEM, EDX, and TGA. The work handled the removal of cesium and strontium ions, as a model radioactive waste, their concentrations were determined using ICP. The experimental results showed that PAACM composite has a sorption capacity of 11.49 mg/g for Cs+ and 10.99 mg/g for Sr2+, but for AMC, the composite has a sorption capacity of 21.59 mg/g Cs+ and 26.68 mg/g for Sr2+. High thermal stability even at 700 °C the net weight loss is 1% for both composites.

The Core Agenda of Public Debate on the Cigéo Project in France

원자력 발전은 상대적으로 저렴한 발전비용으로 우리나라 경제성장의 밑거름이 되었던 에너지원으 로 알려져 있으나 방사성 폐기물 처리에 대해서는 논란이 지속적으로 발생하고 있다. 본 연구에서는 프랑스의 고준위 방폐장인 Cigéo의 설치에 대한 정책 수립과정과 공론화 과정을 살펴보고, 시맨틱네트워크 분석(Semantic Network Analysis)을 통해 프랑스의 고준위 방폐장 건설과정에서 제시되었던 여러 가지 핵심적인 의제들을 파악하였다. 분석결과 연결중심성이 높은 상위 10위의 주제어는 토론사업, 폐기물, 저장, 공공의, 질문, 위험, 시민, 참여, 부지 등이다. 프랑스의 사례를 볼 때 우리나라의 고준위 방폐장 설치단계에서 다양한 정책행위자들의 참여와 토론을 유도하고, 현세대와 미래세대간의 형평성을 고려해야 하는 한편, 사전적으로 관련 법제도를 정비해야 한다는 정책적 시사점을 제시할 수 있다.Nuclear power generation has been the cornerstone of economic growth due to low generation costs in Korea, but the disposal of radioactive waste continues to be controversial. Looking back on the controversy at the time of the establishment of low-level radioactive waste disposal facilities, it is expected that the establishment of high-level radioactive waste disposal facilities will lead to enormous social conflicts, urgently seeking social consensus. In this study, we examined the process of establishing the policy and public debate on the installation of Cigeo, a high-level radioactive waste disposal facility in France. In addition, through SNA (semantic network analysis), we identified several key agenda items which had been presented during the installation process, including debate, business, waste, storage, public, question, danger, citizen, participation, and site. Based on the case of Cigeo, we suggested several policy implications that it is necessary to promote participation and discussion of various policy actors and to consider intergenerational equity as well as preemptive legal action.

Evaluation of durability and radiation shielding property of heavyweight filling material for application in radioactive disposal facilities

Environmental problems caused by municipal and industrial waste are serious worldwide. In particular, landfill of recyclable industrial waste due to a lack of technology is a serious loss of resources. Heavyweight waste glass is an industrial waste that has been studied by many researchers for use as a fine aggregate. Until now, the heavy metal is removed through complex pretreatment. However, in this study, the waste glass was recycled through a simple crushing process without pretreatment. We investigated the fundamental properties, durability, and shielding property of filling material containing waste glass. The test results show that the durability and shielding property were all better than in ordinary mortar. Also, the reduction in strengths, and the expansion due to ASR, can be solved by using a mineral admixture. In conclusion, mortar containing a mineral admixture and waste glass is considered to be viable as filling material in radioactive waste disposal facilities.

Natural systems evidence for the effects of temperature and the activity of aqueous silica upon montmorillonite stability in clay barriers for the disposal of radioactive wastes

Natural systems data can provide important constraints upon the performance and longevity of montmorillonite in clay engineered barriers in a geological disposal facility for radioactive wastes. Here, natural systems evidence for the effects and impacts of temperature and the activity of aqueous silica upon montmorillonite stability and behaviour in compacted clays has been evaluated. An assessment of the effect of temperature showed that montmorillonite may be stable to temperatures as high as 300 °C under appropriate chemical conditions. Although illitization is often the focus of smectite transformation considerations, reaction of montmorillonite may form beidellite, saponite and quartz, rather than illite, in the absence of excess K+.Thermodynamic modeling of clay stability using three different thermodynamic databases showed that stability fields for montmorillonite exist from 0 to 140 °C, but at low values of silica activity, a stability field for illite replaced that for montmorillonite. Pore fluid chemical and mineralogical data for sediments from a range of ODP sites from offshore Japan showed a trend from montmorillonite + amorphous silica stability at temperatures up to 60 °C to that for illite + quartz at higher temperatures. However, even over very long timescales (≫1 Ma), smectite did not transform appreciably to illite under thermodynamically-favourable conditions at temperatures <80 °C. Natural systems evidence showed that silica released from montmorillonite during clay mineral transformation reactions may cement clay grains as sheets of microcrystalline quartz, thereby increasing stiffness and brittle behaviour. This process occurred at temperatures in excess of 70 °C but may be significant only over million-year timescales.

Determination of diffusion coefficient of 137Cs at unsaturated zone of DH-2 site soil under δ = 1.41 g.cm−3 condition

Radiocesium is one of the reference radionuclide on low-level radioactive waste disposal system. For the safety assessment of environment around the disposal facility, it needs to be studied their characters on the candidate site of radioactive waste disposal facility. Diffusion coefficient is important to be studied especially on the unsaturated zone lies between the foundation of facility and the saturated zone. In this experiment, soil samples were taken out from the logging result of DH-2 hole of SP-4 site on the 7 m depth from surface. Work was done in the diffusion column by gravitation method under density condition was 1.41 g.cm−3. The diffusion coefficient is determined in one dimension using non-steady diffusion method with variation of diffusion time and has obtained the smallest of Da value of 137Cs in the soil sample was 1.76 E-12 m2s−1 at the 6 months of diffusion time. The results show that the longer of length diffusion time, the smaller diffusion value was obtained.

Identification of Sandstone Layer beneath the Demonstration Disposal Site at Nuclear Serpong Area Using Resistivity Geo-electrical Method

The depth, thickness and expanse of sandstones or sandy material in site candidate of the disposal demo in Serpong nuclear area (SNA) need to be identified. This is considered because sandstones as ground water aquifers will potentially serve as a medium for transporting radionuclides from waste to biosphere. For design optimization and safety assessment of radioactive waste disposal facility so as not to endanger the public and environment, it is necessary to identify the sandstone layer data. This study was conducted with primary data at SNA using the Wenner configuration of resistivity geoelectricity method on five lines. Data processing and modeling is done through RES2DINV software to obtain the resistivity value of rocks that represent sandstone beneath the surface. In the line 1, the sandstone is at a depth of 6 m and 10 m with a resistivity value of 2,13 – 9,40 Ωm. In the line 2, the sandstone is at a depth of 12,5 m and 17,5 m with a resistivity value of 0,51 – 1,43 Ωm. In the line 3, the sandstone is at a depth of 18 m with a resistivity value of 0,70 – 3,28 Ωm. In the line 4, the sandstone is at a depth of 30 m with a resistivity value of 3,97 – 8,48 Ωm and in the line 5, sandstone is at a depth of 16 m with a resistivity value of 1,12 Ωm. Based on the results of the assessment, all the lines meet the safety requirements of radioactive waste disposal because there is a sufficient barrier zone between the base of the repository and the sandstone as groundwater aquifer, line 1 has a thickness of 4 m and 8 m, line 2 has a thickness of 10,5 m and 15,5 m, line 3 has a thickness of 16 m, line 4 has a thickness of 28 m and line 5 has a thickness of 14 m.

Hydrogenotrophic methanogenesis dominates at high pH

One potential design for a geological disposal facility (GDF) for intermediate level radioactive waste (ILW) involves the use of a cement base grout which will establish a highly alkaline environment for extended time periods [1]. Methane generation by colonising microbes could impact the long-term performance of the facility by influencing gas pressures and potentially leading to the migration of 14C to the biosphere [1]. Sediments acquired from a wide-range of anthropogenic alkaline sites in the UK were used to develop acetoclastic and hydrogenotrophic methanogen enrichment cultures over a broad range of pH values (7.0–12.0). The generation of methane from hydrogen and acetate was assessed to determine the dominant methanogenic pathways. Archaeal community analysis via Illumina MiSeq was employed to describe the populations involved and the acetoclastic inhibitor methyl fluoride was utilised to confirm the lack of acetate-dependent methane generation under alkaline conditions. High pH (pH&gt;9.0) microcosms employing alkaline sediments were dominated by hydrogen-consuming methanogens of the orders Methanobacteriales and Methanomicrobiales, with no acetate consumption detected under these conditions. In contrast, neutral pH microcosms employing control sediments were dominated by acetoclastic methanogens of the order Methanosarcinales and demonstrated high acetate consumption rates. The rate of acetate consumption and proportion of acetoclastic methanogens decreased in a linear fashion as the pH within cultures was increased, however hydrogen consumption rates remained stable up to pH 11.0. The data shown suggests hydrogenotrophic methanogenesis is the dominant methanogenic pathway at high pH which could have important consequences on gas pressures within a GDF.

Study on Practical Application of Optimization Method for Radioactive Waste Disposal Facility Design Based on Probabilistic Approach: Discussion on Procedure for Setting Radionuclide Migration Parameters

Study on Practical Application of Optimization Method for Radioactive Waste Disposal Facility Design Based on Probabilistic Approach: Discussion on Procedure for Setting Radionuclide Migration Parameters

Radiation Damage Effects in Chlorite Investigated Using Microfocus Synchrotron Techniques

A detailed understanding of the mechanisms and effects of radiation damage in phyllosilicate minerals is a necessary component of the evaluation of the safety case for a deep geological disposal facility (GDF) for radioactive waste. Structural and chemical changes induced by α-particle damage will affect the performance of these minerals as reactive barrier materials (both in the near and far-field) over time scales relevant to GDF integrity. In this study, two examples of chlorite group minerals have been irradiated at α-particle doses comparable to those predicted to be experienced by the clay buffer material surrounding high-level radioactive waste canisters. Crystallographic aberrations induced by the focused 4He2+ ion beam are revealed via high-resolution, microfocus X-ray diffraction mapping. Interlayer collapse by up to 0.5 A is prevalent across both macrocrystalline and microcrystalline samples, with the macrocrystalline specimen displaying a breakdown of the phyllosilicate structure into loosely ...

Importance of root uptake of 14CO2 on 14C transfer to plants impacted by below-ground 14CH4 release

14C-labelled methane (14CH4) released from deep underground radioactive waste disposal facilities can be a below-ground source of 14CO2 owing to microbial oxidation of 14CH4 to 14CO2 in soils. Environmental 14C models assume that the transfer of 14CO2 from soil to plant occurs via foliar uptake of 14CO2. Nevertheless, the importance of 14CO2 root uptake is not well understood. In the present study, below-ground transport and oxidation of 14CH4 were modeled and incorporated into an existing land-surface 14CO2 model (SOLVEG-II) to assess the relative importance of root uptake and foliar uptake on 14CO2 transfer from soil to plants. Performance of the model in calculating the below-ground dynamics of 14CH4 was validated by simulating a field experiment of 13CH4 (as a substitute for 14CH4) injection into subsoil in a wheat field in the UK. The proposed model simulation was then applied to 14C transfer in a hypothetical ecosystem impacted by continuous 14CH4 input from the water table (bottom of 1-m thick soil), which simulated continuous release of 14CH4 from a deep underground radioactive waste disposal facility. The contrast between the results obtained from the model calculation that assumed different distributions of roots (rooting depths of 11 cm, or 97 cm) and methane oxidation (characterized by e-folding depths of 5 cm, 20 cm, or 80 cm) in the soil provided insight into the relative importance of root uptake and foliar uptake pathways. In the shallowly rooted ecosystem with rooting depth of 11 cm, foliar uptake of 14CO2 was significant, accounting for 80% of the 14C accumulation (as organic 14C) in the plant (leaf compartment). By contrast, in a deeply rooted ecosystem (rooting depth of 97 cm), where the root penetrated to depths close to the water-table, more than half (63%) the 14C accumulated in the plant was transferred via the root uptake pathway. We found that 14CO2 root uptake (thus 14C accumulation in the plant) in this ecosystem depended on the distribution of methane oxidation in the soil; all 14C accumulated in the plant was transferred by the root uptake pathway when methane oxidation occurred at considerable depths (e-folding depths of 20 cm, or 80 cm) in the soil. The high level of 14CO2 root uptake was ascribed to the oxidation of added 14CH4 (i.e., production of 14CO2) in the deep part of the soil and the subsequent high level of root uptake of the deep soil-water containing 14CO2. These results indicate that 14CO2 root uptake contributes significantly to 14CO2 transfer to plants if 14CH4 oxidation occurs at great depths and roots penetrate deeply into the soil. It is recommended that current environmental 14C models must be refined to consider the importance of the root uptake pathway to ensure that dose estimates of 14CH4 release from deep underground waste disposal facilities are accurate.