Radionuclide Transport Model Research Articles

Modeling of long-term radiological and toxicological impacts of the uranium mill tailings on groundwater and surface water

Modeling predictions are presented of radionuclide transport processes in the zone of influence of the Zahidne uranium mill tailings situated at the Prydniprovsky Chemical Plant (PChP), Kamianske. The groundwater transport model was developed using the NORMALYSA software. Refined estimates of parameters of water exchange in the zone of uranium mill tailing (obtained from field studies and modeling of groundwater flow processes) were used to parameterize the model for radionuclide transport in groundwater. Calibration of the radionuclide transport model using monitoring data on radioactive contamination of groundwater in 2005 - 2021 allowed to estimate the sorption distribution coefficient (Kd) for the most hazardous contaminants 238,234U isotopes (Kd = 8 ± 2 l/kg) and estimate the rate of uranium migration in groundwater. According to modeling, during the next 800 to 1100 years, uranium concentration in wells in the zone of influence of uranium mill tailing (at 500 - 800 m distance) will be determined mainly by the contamination of the alluvial aquifer, which was formed during the operation period of the uranium mill tailing. According to modeling predictions, usage of groundwater (partial drinking water consumption, irrigation) outside the PChP site downstream of the uranium mill tailing will result in doses exceeding the relevant reference level (annual effective dose > 1 mSv/year) in 380 - 440 years, while the toxicological impact will result in the exceeding of the acceptable hazard index for uranium (HI > 1) in 200 - 260 years. Modeling results indicate the importance of restricting the use of groundwater downstream of the uranium mill tailing within the PChP industrial site and, in the longer term, beyond its boundary. At the same time, contamination of the Konoplyanka River due to the migration of radionuclides from the uranium mill tailing does not pose unacceptable radiological and toxicological risks for the considered scenario (irrigation, fish consumption) due to the dilution of contaminants in surface waters.

The value of simplified models of radionuclide transport for the safety assessment of nuclear waste repositories: A benchmark study

In order to assess sites for a deep geological repository for storing high-level nuclear waste safely in Germany, various numerical models and tools will be in use. For their interaction within one workflow, their reproducibility, and reliability version-controlled open-source solutions and careful documentation of model setups, results and verifications are of special value. However, spatially fully resolved models including all relevant physical and chemical processes are neither computationally feasible for large domains nor is the data typically available to parameterize such models. Thus, simplified models are crucial for the pre-assessment of possible sites to narrow down the list of suitable candidates for which detailed site investigations and fully resolved models will be done at a later stage. Still, the accuracy of these simplified models is of importance as the pre-assessment of suitable sites will be based on them. In this study, we compare the modelling capabilities of TransPyREnd, a one-dimensional transport code based on finite differences, specifically developed for the fast estimation of radionuclide transport by the German federal company for radioactive waste disposal (BGE), with OpenGeoSys, which is a modelling platform based on finite elements in up to three spatial dimensions. Both codes are used in the site selection procedure for the German nuclear waste repository. The comparison of the model results of TransPyREnd and OpenGeoSys is augmented by comparisons with an analytical solution for a homogeneous material. For the purpose of numerical benchmarking, we consider a geological profile located in southern Germany as an example where the hypothetical repository is located in a clay-stone formation. TransPyREnd and OpenGeoSys yield overall similar results. However, both codes use different discretizations which impact is the highest for strongly sorbing compounds, while the difference gets negligible for less sorbing and more diffusive compounds as higher diffusion tends to blur the initial conditions. Overall, the OpenGeoSys model is more exact whereas the TransPyREnd model has considerable faster run times. We found in our example, that significant substance amounts are only leaving the host rock formation, if apparent diffusion is high, for which case both codes give similar results, while relative differences are considerable for strongly sorbing compounds. However, in the latter case no significant substance amount of radionuclides leaves the host-rock formation, thus deeming the differences in the model results minor for the overall safety assessments of sites.

The Lagrangian Atmospheric Radionuclide Transport Model (ARTM) – sensitivity studies and evaluation using airborne measurements of power plant emissions

Abstract. The Atmospheric Radionuclide Transport Model (ARTM) operates at the meso-γ scale and simulates the dispersion of radionuclides originating from nuclear facilities under routine operation within the planetary boundary layer. This study presents the extension and validation of this Lagrangian particle dispersion model and consists of three parts: (i) a sensitivity study that aims to assess the impact of key input parameters on the simulation results, (ii) the evaluation of the mixing properties of five different turbulence models using the well-mixed criterion, and (iii) a comparison of model results to airborne observations of carbon dioxide (CO2) emissions from a power plant and the evaluation of related uncertainties. In the sensitivity study, we analyse the effects of the stability class, roughness length, zero-plane displacement factor, and source height on the three-dimensional plume extent as well as the distance between the source and maximum concentration at the ground. The results show that the stability class is the most sensitive input parameter as expected. The five turbulence models are the default turbulence models of ARTM 2.8.0 and ARTM 3.0.0, one alternative built-in turbulence model of ARTM, and two further turbulence models implemented for this study. The well-mixed condition tests showed that all five turbulence models are able to preserve an initially well-mixed atmospheric boundary layer reasonably well. The models deviate only 6 % from the expected uniform concentration below 80 % of the mixing layer height, except for the default turbulence model of ARTM 3.0.0 with deviations of up to 18 %. CO2 observations along a flight path in the vicinity of the lignite power plant Bełchatów, Poland, measured by the Deutsches Zentrum für Luft- und Raumfahrt (DLR) Cessna aircraft during the Carbon Dioxide and Methane Mission (CoMet) campaign in 2018 allowed for evaluation of model performance for the different turbulence models under unstable boundary layer conditions. All simulated mixing ratios are of the same order of magnitude as the airborne in situ data. An extensive uncertainty analysis using probability distribution functions, statistical tests, and direct spatio-temporal comparisons of measurements and model results help to quantify the model uncertainties. With the default turbulence setups of ARTM versions 2.8.0 and 3.0.0, the plume widths are underestimated by up to 50 %, resulting in a strong overestimation of the maximum plume CO2 mixing ratios. The comparison of the three alternative turbulence models shows good agreement of the peak plume CO2 concentrations, the CO2 distribution within the plumes, and the plume width, with a 30 % deviation in the peak CO2 concentration and a less than 25 % deviation in the measured CO2 plume width. Uncertainties in the simulations may arise from the different spatial and temporal resolutions of simulations and measurements in addition to the turbulence parametrisation and boundary conditions. The results of this work may help to improve the accurate representation of real plumes in very unstable atmospheric conditions through the selection of distinct turbulence models. Further comparisons at different stability regimes are required for a final assessment of model uncertainties.

Numerical modelling of groundwater radionuclide transport with finite difference-based method of lines

Numerical modelling of groundwater radionuclide transport with finite difference-based method of lines

Parallelization of numerical solutions of shallow water equations by the finite volume method for implementation on multiprocessor systems and graphics processors

An overview of approaches to parallelization of grid-based numerical methods for solving shallow water equations for multiprocessor systems and graphics processors is presented. A multithreaded approach for shared-memory computing systems implemented on the basis of the OpenMP programming interface and a geometric decomposition approach with message-passing using the MPI library for distributed-memory computers are described. Multithreading for programming GPUs based on the OpenACC software interface is considered. For the COASTOX-UN system of two-dimensional modeling of hydrodynamics, sediment and radionuclide transport in river systems and coastal areas of the seas, the parallelization of its hydrodynamic model COASTOX-HD was carried out. In the developed numerical model, the shallow water equations are solved by finite-volume numerical methods on unstructured computational grids with triangular cells of variable size. The parallelization is implemented using a hybrid MPI+OpenACC approach targeting multiprocessor systems and GPUs. For multiprocessor computers, geometric decomposition and MPI-based messaging are used, and for GPUs, multithreading is implemented using OpenACC directives. The performance of the developed parallel hydrodynamic model was evaluated during the calculation of typical problems of hydrodynamics of shallow water bodies, river flood, and tsunami wave run-up on the coast on a Dell Precision Workstation 7920 multi-core workstation with two 20-core Intel Xeon Gold 6230 processors and NVIDIA Quadro RTX 5000 and NVIDIA GeForce RTX 3080 graphics cards. It is shown that the developed model has significantly accelerated the simulation on the considered multiprocessor system and the considered GPUs. The acceleration on GPUs depends on the size of the computational grid, increasing to saturation with an increase in the number of grid cells. It is established that for the developed parallel model, whose numerical schemes are related to algorithms with low computational intensity, the memory bandwidth of the NVIDIA architecture GPUs is a more important limiting factor of acceleration than their performance.

Development of public exposure scenarios for land sites with residual radioactive contamination

The article considers the experience of development of public exposure scenarios for land sites with residual radioactive contamination on the example of three sites located in Moscow and St. Petersburg. The study was intended to identify the anticipated groups of land users and select parameters for calculating radiation doses. Exposure scenarios regarding use of land sites for living or working were described by such parameters as duration of the stay, staying indoors or outdoors, physical activity, etc. Exposure pathways for selected users were identified using the conceptual site model approach. For calculations within a number of scenarios, geomigration modeling of radionuclide transport in the environment was performed using the GeRa code. Exposure doses for population groups were calculated using the Ecorad-Aqua software module. Doses were calculated for each exposure pathway. The study demonstrates that the proposed scenario “Office worker” can be applied to various sites that are planned for placing administrative, industrial, scientific, commercial buildings and structures, scenario “Construction worker” – for sites with construction and excavation activities underway. The parameters of the “Resident” scenario allow for its application for the multiapartment residential development in large cities. In the future, it is practical to develop a typical scenario for an outdoor worker whose activity is to provide care and maintenance of the site. These scenarios can be used as ready-made solutions for calculating radiation doses for the population from residual radioactivity at the nuclear sites under decommissioning and remediated areas. Estimates of annual effective doses for the population are needed for decommissioning and remediation planning and determination of the values of radiation factors in the relevant projects.

Local atmospheric transport behaviors of representative radionuclides during the Fukushima accident: A 200-m-resolution cross-scale study from site to 20 km

Modeling of local atmospheric radionuclide transport is essential for nuclear emergency response. However, very few studies of the Fukushima Dai-ichi nuclear power plant (FDNPP) accident have focused on this topic because of the complex meteorology and the cross-scale transport behaviors from the site to 20 km of the FDNPP. In this study, both the local meteorology and transport behaviors were investigated at high resolution (200 m) using ensembles of different meteorology and models. Four wind fields calculated from onsite observations and three regional-scale meteorological fields (i.e., the 1-km ECMWF, 3-km and 1-km NHM-LETKF), and two transport models: the RIMPUFF Lagrangian puff model and the SPRAY particle model were considered and combined with each other. These eight simulations and their ensemble mean were analyzed based on onsite observations of wind and gamma dose rates, and local-scale observations of 137Cs concentration. Results revealed that at the site, the Onsite wind field which captured the frequently changing wind, best reproduced the onsite gamma dose rates with the grid resolution of 200 m. At the local scale (up to 20 km), the observations present a smoother temporal change. The wind fields assimilated with Japanese domestic observations presented advantageous performance, and the 1-km NHM-LETKF achieved the best score of the factor of 5 metric of 0.49 for the simulated 137Cs concentration. The SPRAY coupled with the three-dimensional (3D) convolution method and RIMPUFF showed better performance in simulating the onsite gamma dose rate and the local-scale concentration, respectively. The ensemble mean achieved robust metrics, better simulated the baseline of onsite gamma dose rates, and reproduced more peaks of local-scale concentration at the expense of peak value deviation.

Development of a model for radionuclide transport in streams for biosphere assessment purpose

As a part of the overall safety assessment for a geological disposal of radioactive waste, models for different ecosystems are used to evaluate doses to humans and biota from possible radionuclide discharges to the biosphere. In previous safety assessments, transport modelling of radionuclides in running waters such as streams has been much simplified to the extent that only dilution of the inflow of radionuclides has been considered with no regard of any other interactions.Hyporheic exchange flow (HEF) is the flow of surface water in streams that enters the subsurface zone and, after some time, returns to the surface. HEF has been studied for decades. Hyporheic exchange and the residence time in the hyporheic zone are key parameters controlling the transport of radionuclides in a stream. Furthermore, recent studies have shown that HEF can reduce the groundwater upwelling area and increase the upwelling velocity in areas closest to the streambed water interface.In this paper, the development of an assessment model describing radionuclide transport with consideration of HEF and deep groundwater upwelling along streams is presented. An approach to parameterising the hyporheic exchange processes into an assessment model is based on a comprehensive study that has been performed in five different Swedish catchments. Sensitivity analyses are performed to explore the effect with consideration of the inflow of radionuclides with regard to HEF and deep groundwater upwelling in a safety assessment perspective. Finally, we include some suggestions for the application of the assessment model to long-term radiological safety assessments.

Feasibility of neural network metamodels for emulation and sensitivity analysis of radionuclide transport models

In this paper we compare the outputs of neural network metamodels with numerical solutions of differential equation models in modeling cesium-137 transportation in sand. Convolutional neural networks (CNNs) were trained with differential equation simulation results. Training sets of various sizes (from 5120 to 163,840) were used. First order and total order Sobol methods were applied to both models in order to test the feasibility of neural network metamodels for sensitivity analysis of a radionuclide transport model. Convolutional neural networks were found to be capable of emulating the differential equation models with high accuracy when the training set size was 40,960 or higher. Neural network metamodels also gave similar results compared with the numerical solutions of the partial differential equation model in sensitivity analysis.

Some considerations on the dependence to numerical schemes of Lagrangian radionuclide transport models for the aquatic environment

Lagrangian models present several advantages over Eulerian models to simulate the transport of radionuclides in the aquatic environment in emergency situations. A radionuclide release is simulated as a number of particles whose trajectories are calculated along time and thus these models do not require a spatial discretization (although it is always required in time). In this paper we investigate the dependence of a Lagrangian model output with the grid spacing which is used to calculate concentrations from the final distribution of particles, with the number of particles in the simulation and with the interpolation schemes which are required because of the discrete nature of the water circulation data used to feed the model. Also, a Lagrangian model may describe the exchanges of radionuclides between phases (liquid and solid), which is done in terms of transition probabilities. The dependence of these probabilities with time step is analyzed as well. It was found that the optimum grid size used to calculate concentrations should be carefully checked, and that temporal interpolation is more significant than spatial interpolation to obtain a more accurate solution. A method to estimate the number of particles required to have a certain accuracy level is proposed. Finally, it was found that for low sediment concentrations and small radionuclide kd, exact equations for the transition probabilities should be used; and that phase transitions introduce a stability condition as in Eulerian models.

Синтез и выщелачивание боросодержащих стекол для РАО в условиях глубинного захоронения

The study focuses on the synthesis and characterization of three boron-containing glasses, namely, two borosilicate glasses and one borophosphate glass containing mockup RW elements (Se, Sr, Mo, Cs, La, U, etc.) and radionuclides (99Tc, 239Pu, 241Am). It explores the glass-forming elements (Li, B, Na, Si, P, etc.), mockup RW and radionuclides and their leaching from the synthesized glasses in model underground water assuming the presence of barrier bentonite at temperatures of 25, 90 and 150°C. The study evaluates the changes in the elemental composition and density of the leached layer formed upon incongruent dissolution of glasses, as well as the time-dependent changes in the element concentrations of the leachates assuming different temperatures. For boron-containing glasses, it presents the evaluated concentrations of leachate saturation with glass-forming and RW elements under deep disposal conditions. These findings can be used in experimental and computational modeling of radionuclide transport under deep RW disposal conditions.

Recultivation of soils contaminated with radionuclides by phytomelioration

The use of aqueous solutions of ammonium nitrate and microorganisms in the proposed method will intensify the transition of radionuclides into soluble forms for assimilation by the root system of plants, obtaining maximum biomass of plants accumulating radionuclides, and significantly reducing the growing season. The process of obtaining biomass using the above technology makes it possible to repeat this method of purification many times, including within one seasonal period, until the content of radionuclides in the soil reaches acceptable values, after which the soil becomes suitable for agricultural use. The purpose of the study. Consider the transition of radionuclides into soluble forms for assimilation by the root system of plants. Material and Methods. To substantiate the possible directions of soil reclamation, we propose a conceptual model of radionuclide transport in the agrocenosis, on the basis of which a functional scheme for recultivation of soils contaminated with radionuclides has been developed. The collected biomass and the root system of plants must be disposed of. Due to the fact that large volumes of mass are subject to disposal, it is subjected to heat treatment - drying.

Численное моделирование миграции нуклидов в конструкциях и ближней зоне приповерхностного пункта захоронения радиоактивных отходов

The paper considers a numerical model of radionuclide transport in the structural elements of a near-surface radioactive waste disposal facility (NSDF). It presents a calculation of a nuclide flow from the NSDF into the underlying rocks and groundwater considering three characteristic groups of radionuclides: long-lived weakly absorbable, long-lived absorbable and relatively short-lived (with a half-life of up to 31 years). The study demonstrates how the sorption properties of the engineered barriers, their geometric characteristics, as well as the features of radioactive waste package layout may influence radionuclide releases from the waste disposal facility into groundwater.

Uncertainty and sensitivity analysis of radionuclide migration through fractured granite aquifer

The radionuclide migration in the high-level radioactive waste (HLW) disposal is usually predicted by numerical simulations for risk analysis of radionuclide contamination in a large scale of time and space. However, the uncertainties in radionuclide migration models and their associated parameters significantly affect the simulation results. In the present study, we first selected certain parameters and output data as independent parameters and risk metrics and performed a series of radionuclide transport models at a research site in Northwestern China. The models considered radionuclide migration in the equivalent porous medium with the mechanism of nuclide decay in an arbitrary-length decay chain, adsorption, advection, diffusion, and dispersion. Then 3000 Monte Carlo (MC) simulations were performed to carry out a set of uncertainty and global sensitivity analysis by coupling an uncertainty quantification tool with a radionuclide migration simulator. The results indicated that both hydraulic gradient and hydraulic conductivity significantly influenced the risk metrics. Thus, it is critical to obtain hydraulic gradient and hydraulic conductivity data under the same economic conditions. We applied the multivariate adaptive regression spline (MARS) method to generate response surface models representing the relationships among independent parameters and risk metrics. Calculations of the risk metric distribution ranges revealed that the peak release doses would appear at 0.40 and 0.79 million years, and their values will be in the range of 4.7 × 10−7–1.93 × 10−6 Sv/a. Uncertainty and sensitivity analysis results of radionuclide contamination in the fractured granite upon which HLW is disposed can improve simulation and prediction accuracy for radionuclide migration.

On the inclusion of forest exposure pathways into a stylized lake-farm scenario in a geological repository safety analysis

Geological disposal of radioactive waste has been recognized as the ‘reference solution’ to ensure the safety required for the present and future society and environment. To study the possible exposure pathways from groundwater to humans, radioactive transport modelling is used. One of the ecosystems that may play a significant role when assessing the dose conversion factor (i.e. the dose resulting from a nominal release of 1 Bq/year of each radionuclide) for humans is forest. In this paper we have developed a model of a lake-farm system with a forest component. The biosphere system used in this study represents a typical agricultural scenario in Finland, amended with a typical forest. A lake is assumed to form due to post-glacial land uplift. The main features of this future lake have been obtained from our probabilistic shoreline displacement model. Both deterministic calculations and sensitivity analysis were carried out to simulate the model. The deterministic simulation demonstrates the behaviour of the studied radionuclides (36Cl, 135Cs, 129I, 237Np, 90Sr, 99Tc and 238U) and the proportions of different exposure pathways to humans. Particularly for 135Cs and 129I, forest pathways make a notable contribution to the dose conversion factor. The sensitivity analysis was done using two methods: EFAST and Sobol’. With both methods, the parameters related to the farm contribute the most to the variance of the dose conversion factor for humans. The study demonstrates that the exposure pathways related to forest products may make a considerable contribution to the dose conversion factor in a lake–farm–forest system. It is also confirmed that an advanced sensitivity analysis for a radionuclide transport and dose assessment model on such a landscape scale is feasible even with moderate computational efforts.

The Lagrangian Atmospheric Radionuclide Transport Model (ARTM) — development, description and sensitivity analysis

Atmospheric dispersion models are applied to describe and predict the dispersion of emitted plumes. Here, we describe the Lagrangian Atmospheric Radionuclide Transport Model (ARTM) 2.8.0 which was developed to simulate the atmospheric dispersion of the emissions of nuclear facilities under routine operation for regulatory purposes over annual time scales. ARTM includes a diagnostic wind field model and a particle dispersion model. It simulates size-dependent wet and dry deposition, plume rise and γ-cloud shine of radioactive exhaust plumes in the simulation domain. This work presents an extensive overview of the different components of the model and of the physical and mathematical concepts of ARTM. We investigate the dependence of the plume dispersion in terms of plume volume, position of maximum concentration and dry deposition rates on key input parameters such as atmospheric stability, surface roughness, zero plane displacement height, source height and the particle size in the case of particulate matter tracers. The results indicate a strong dependence of plume volume and position of the maximum concentration on the stability as well as a minor influence on surface roughness. The source height above ground level has a low impact on the plume volume as the zero plane displacement only slightly affects the position of maximum concentration. Strong turbulence under unstable conditions tends to reduce the impact of sedimentation and decreases deposition in general. This computational model serves to advance the understanding of the dispersion of radioactive plumes in the boundary layer.

Sediment and Radioactivity Transport in the Bohai, Yellow, and East China Seas: A Modeling Study

This paper is concerned with the development of a radionuclide dispersion model for the nuclear power plants in the Bohai, Yellow, and East China seas (BYECS) characterized by high turbidity and multi-scale circulations, focusing on the comparison of dispersion processes of 137Cs depending upon, in particular, the suspended sediment concentration and erosion/sedimentation processes. The simulations were carried out using a multi-fraction sediment transport model embedded in the semi-implicit Eulerian–Lagrangian finite-element coupled wave-circulation model linked with the model of radionuclide transport, which describes the key radionuclide transfer processes in the system of water–multi-fraction sediments. In contrast to the Eulerian models used for hydrodynamics and sediment transport processes, the Lagrangian technique was applied to simulate the transport of radionuclides. The simulation results for total suspended concentration agreed with in situ measurements and the Geostationary Ocean Color Imager data. The results of the simulation of hypothetical releases of 137Cs from four nuclear power plants (NPPs) placed in BYECS essentially differ from the real release of activity in the Pacific Ocean shelf due to the Fukushima Daiichi accident, which took place at the same time and released activity that was similar. The total amount of bottom contamination of 137Cs in releases from the Sanmen, Hanbit, and Hongyanhe NPPs was about 40% of dissolved component, and the total amount of suspended component was about 20% of dissolved component, in contrast with the Fukushima Daiichi accident, where the particulate component was only 2%. The results demonstrate the importance of erosion processes in the budget of 137Cs in shallow areas around the Sanmen and Hanbit NPPs, where strong wind and tidal currents took place.

Stochastic machine learning modeling for the estimation of some uncertain parameters. Case study: Retardation factor in a radionuclide transport model

In the present work, we define a stochastic model using machine learning techniques to generate random fields of some uncertain parameters. The proposed stochastic model is based on Bayesian inference and aims at reconstituting the parameters of interest and their credible intervals. The main goal of this work is to define a model that estimates the values of the uncertain parameters known only by their distribution probability functions and some observed spatial measurements. We note that this type of parameters may be associated with some mathematical models usually traduced by non-linear differential equations. In our case, we study the uncertainty of the retardation factor in a radionuclide transport model. To achieve a more realistic parameter estimation, Markov сhain Monte Carlo (MCMC) algorithms are applied. We demonstrate that the obtained results confirm the feasibility of our proposed model and lead to a new understanding of contaminants' behavior.

An Adjoint Sensitivity Model for Radionuclide Transport in Heterogeneous Discrete Fractured Porous Formation in Steady‐State Regime

The development of the adjoint state method for the system of partial differential equations (PDEs) describing radionuclide transport in heterogeneous discrete fractured porous media in steady-state regime is presented in this study for both continuous and discrete adjoint approaches. The continuous adjoint approach has its own advantage in the sense that the adjoint system can be derived in terms of PDEs which can be solved analytically for specific performance measures. These PDEs can then be used to obtain a physical interpretation of the adjoint state functions. The discrete adjoint approach permits a simpler mathematical treatment based on the use of the same matrix (or its transpose) of the linear system of the discretized transport equations referring to from hereon as the forward problem. Analytical solutions for both the forward problem and its associated adjoint problem have been derived for radionuclide transport in layered formations including a fracture using an analytical inversion of tridiagonal matrices. A set of 14 formulas of sensitivity coefficients with respect to pertinent system parameters has been derived and presented in integral forms. Analytical results have been compared with numerical results and have shown excellent agreements. The discrete adjoint approach has been coupled with the differential sensitivity analysis method and applied to a real field case involving the performance assessment of a site currently being considered for underground nuclear storage in northern Switzerland, Zürich Nordost. The results show that when a fracture is present in the vicinity of waste repository, the state parameter controlling flow through the fracture, referred to herein as fracture transmissivity, is among the important parameters which should be considered in sensitivity analysis studies.

Opening Fukushima floodgates: Modelling 137Cs impact in marine biota

A numerical model was applied to simulate the transport of 137Cs released with the waters which were used to cool Fukushima reactors. These stored waters will be released to the Pacific Ocean according to Japanese government plans. The radionuclide transport model is Lagrangian and includes radionuclide interactions with sediments and an integrated dynamic foodweb model for biota uptake. Calculations made from a conservative approach indicate that expected concentrations in sediments and marine fish would be orders of magnitude below those detected after Fukushima accident and also lower than those resulting from global fallout background.