Radionuclide Migration Research Articles

Insights into the thermo-hydraulic properties of compacted MX80 bentonite during hydration under elevated temperature

In high-level radioactive waste geological repositories, compacted bentonite undergoes coupled thermo-hydraulic processes due to heat released from a central waste canister and groundwater imbibition from the surrounding host rock. An understanding of these processes is essential for long-term simulations of radionuclide migration and canister corrosion, which requires an understanding of temperature effects on the coupled thermo-hydraulic properties governing these processes. In this study, a tank-scale radial infiltration test was used to investigate water imbibition processes in compacted bentonite under a central heater temperature of 200 °C that simulates high thermal gradients in a repository. Interpretation of this test focuses on evaluation of the liquid water wetting front during hydration and the interpretation of the temperature-dependent transient soil water retention curve (SWRC), thermal conductivity function (TCF), and hydraulic conductivity function (HCF). The SWRC during imbibition follows a temperature-dependent wetting path. Temperature effects on the hydraulic conductivity of bentonite in saturated conditions had the greatest effect on the shape of the HCF, with minimal temperature effects at higher suctions. The transient thermal conductivity data matched well with a new TCF linked with the SWRC shape. Although the bentonite layer was restrained, local deformations during hydration may have affected the shapes of the TCF and HCF.

Radionuclide Transport Simulations Supporting Proposed Borehole Waste Disposal in Israel

A scientific collaboration between the U.S. and Israel is underway to assess the suitability of a potential site for subsurface radioactive waste disposal in the Negev Desert, Israel. The Negev Desert has several favorable attributes for geologic disposal, including an arid climate, a deep vadose zone, interlayered low-permeability lithologies, and carbonate rocks with high uranium-sorption potential. These features may provide a robust natural barrier to radionuclide migration. Geologic and laboratory characterization data from the Negev Desert are incorporated into multiphase flow and transport models, solved using PFLOTRAN, to aid in site characterization and risk analysis that will support decision-making for waste disposal in an intermediate-depth borehole design. The lithology with the greatest uranium sorption potential at the site is phosphorite. We use modeling to evaluate the ability of this layer to impact uranium transport around a proposed disposal borehole. The current objective of the simulations is focused on characterizing hypothetical leakage from waste canisters and subsequent uranium migration under three infiltration scenarios. Here, we describe a hydrogeologic model based on data from a local exploratory borehole and present results for uranium flow and transport simulations under varying infiltration scenarios. We find that under the current climate conditions, it is likely that uranium will remain in the near-field of the borehole for thousands of years. However, under a hypothesized extreme climate scenario representing an increase in infiltration by a factor of 300x above present-day values, uranium may break through the phosphorite layer and exit the base of the model domain (~200 m above the water table) within 1000 years. Simulation results have direct implications for the planning of nuclear waste disposal in the Negev Desert, and specifically in intermediate-depth boreholes.

The homogenisation behaviour of BCV bentonite – A laboratory and numerical study

Bentonite is considered as a suitable sealing material for radioactive waste geological repositories because of its high swelling capacity and low permeability. Regardless of the construction procedure and initial form of the bentonite, i.e. blocks, pellets, powder or combinations and mixtures thereof, the placement of the bentonite barrier results in initial heterogeneities which could potentially form preferential pathways for the migration of radionuclides. This study focused on the laboratory investigation of the homogenisation of Czech BCV bentonite. The analysis comprised the performance of four sets of tests on dual-density samples composed of two layers of bentonite compacted to various dry densities. Each set of tests considered two identical samples saturated from different sides under constant volume conditions. Homogenisation was investigated through the measurement of swelling pressure on both sides of the samples and via the determination of the final density distribution in a vertical profile from the post-mortem analysis. The results confirmed a substantial degree of homogenisation, with only a small density gradient revealed by the post-mortem analysis. The density distribution profiles indicated a gradual change in the vertical direction with no distinct border between the original layers. A higher degree of homogenisation was found in the samples with a higher overall density and, consequently, a higher swelling potential. No clear effect of the direction of saturation on homogenisation was identified from the density profiles. The final swelling pressures corresponded well to swelling pressures obtained on single-density samples with density equal to the global density of the dual-density samples. The numerical modelling represented well the final swelling pressures and the swelling pressure evolution curves for both the single- and dual-density samples (including the distinct experimentally-observed swelling pressure peak when the dual-density sample was saturated from the high-density end). More accurate results were obtained while considering the porosity and the degree of saturation-dependent permeability. However, the model did not fully capture the homogenisation of the dual-density samples in terms of the dry density profiles. While the tendency towards homogenisation was predicted correctly, two distinct density zones were evident in the simulations, while the experiment revealed a gradual density distribution.

Sorption behavior studies of Cs and its migration in soil samples around Visakhapatnam, India.

Meeting the requirement of high specific activity of radioisotopes and carrying out comprehensive research and development activities in the nuclear field, different nuclear facilities, including their waste disposal facilities, are going to be operational at Visakhapatnam, India. Due to environmental processes, the engineered disposal modules may lose their structural integrity and may release some radioactivity to the geo-environment. The subsequent migration of radionuclides reaching the geological environment will be governed by the distribution coefficient (Kd). Cs was chosen for the sorption study in two soil samples (soil-29 and 31) and to estimate the Kd in all the 40 soil samples through the laboratory batch method at the new campus of DAE, Visakhapatnam, India. Different soil chemical parameters like pH, organic matter, CaCO3, and cation exchange capacity were determined in 40 soil samples and their effect on Cs sorption was investigated. The effect of solution pH and initial concentration of Cs on sorption was also studied. The results show that the sorption of Cs increases with increasing pH. The Cs sorption was well explained by Freundlich and Dubinin-Radushkevich (D-R) isotherm models. Site-specific distribution coefficients (Kd) were also estimated and the values were found to vary from 75 ± 1 to 540 ± 12 L kg-1. The observed wide variation in Kd could be due to large variations in the physico-chemical properties of collected soil. The competitive ions effect study suggests that K+ has higher interference for Cs+ sorption as compared to Na+. The present study results will help assess the environmental impact due to Cs release in any unforeseen scenario and in planning effective remediation strategies.

The Use of Microfluidic Platforms with Raman Spectroscopy for Investigating the Co-Precipitation of Metals and Radionuclides in Carbonates

In the context of long-term safety assessments of deep geological repositories for radio-active wastes, a rigorous understanding of the retention of radionuclides such as 226Ra due to co-precipitation with carbonate and sulphate minerals is important for a realistic prediction of radionuclide migration behaviour in the repository near and far field. The co-precipitation of 226Ra in sulphate minerals, in particular barite, has been studied experimentally and numerically in detail throughout the last decade to establish the thermodynamic properties and mixing behaviour of its solid solutions over a wide range of temperatures. However, so far, few studies have been dedicated to the incorporation of 226Ra into carbonates, and little is known about the mixing behaviour of 226Ra and calcium carbonate phases such as calcite, aragonite, or vaterite. The aim of the work presented here was to develop and explore innovative microfluidic experiments in combination with in situ Raman spectroscopy that can be used to investigate co-precipitation processes of radionuclides in carbonate minerals, using stable Ba as a chemical analogue for 226Ra in the first step, due to their similar ionic radii. Different microfluidic set-ups were developed to address co-precipitation in bulk solution as well as in confinement or under diffusive flow regimes. It could be shown by XRD and SEM-EDX analyses that high amounts of Ba can be incorporated into the lattice of calcite when formed via an amorphous precursor phase, suggesting that the formation of calcium carbonates can contribute to the retention of 226Ra in the repository environment, which will be verified in future studies using the presented microfluidic platforms.

Composition and structure of marls from the Sumer Formation as an environment for geological disposal of radioactive waste

When selecting a site for the construction of a repository for high-level radioactive waste (HLW), the mineral composition of the geological environment is of primary importance. The content and type of the clay component and its structure have important implications for the insulating and sorption properties of the host rock and migration of radionuclides. In such previous studies in Bulgaria for site selection of the geological disposal of HLW the Lower Cretaceous marls (argillites) of the Sumer Formation (Western Pre-Balkans) were considered as ones of the prospective formations. This paper presents data about grain size distribution and mineral composition of the marls (argillites) at depths of 50 m and 400 m. A study was conducted on the structure of samples taken at a depth of 800 m from the Golyamo Pestene borehole. The obtained results are compared in order to clarify the homogeneity of the formation in depth. An increase in the clay fraction and the illite contained in it are observed in depth – from 22% at 18 m to 29% at 400 m, additionally, there is a slight increase in the carbonate content from 13.9% in samples up to 50 m to 26.9% on samples of 400 m. Data are presented on the volume, surface area, size and distribution of pores in the marls from 200 m depth (P-5 “Golyamo Peshtene”), which are necessary in assessing the migration of radionuclides from the repository. The majority of pores (82.4%) have a radius below 0,1 μm. A comparison is made of the mineral composition and structure of the argillites (marls) with similar clay rocks in Western Europe, where underground research laboratories have been constructed for in-situ study of the host rock.

Localization and chemical speciation of europium(III) in Brassica napus plants

For the reliable safety assessment of repositories of highly radioactive waste, further development of the modelling of radionuclide migration and transfer in the environment is necessary, which requires a deeper process understanding at the molecular level. Eu(III) is a non-radioactive analogue for trivalent actinides, which contribute heavily to radiotoxicity in a repository. For in-depth study of the interaction of plants with trivalent f elements, we investigated the uptake, speciation, and localization of Eu(III) in Brassica napus plants at two concentrations, 30 and 200 µM, as a function of the incubation time up to 72 h. Eu(III) was used as luminescence probe for combined microscopy and chemical speciation analyses of it in Brassica napus plants. The localization of bioassociated Eu(III) in plant parts was explored by spatially resolved chemical microscopy. Three Eu(III) species were identified in the root tissue. Moreover, different luminescence spectroscopic techniques were applied for an improved Eu(III) species determination in solution. In addition, transmission electron microscopy combined with energy-dispersive X-ray spectroscopy was used to localize Eu(III) in the plant tissue, showing Eu-containing aggregates. By using this multi-method setup, a profound knowledge on the behavior of Eu(III) within plants and changes in its speciation could be obtained, showing that different Eu(III) species occur simultaneously within the root tissue and in solution.

Analysis of radionuclide retention by the cement hydrate phase portlandite: A novel modelling approach

Cement is a widely used material for conditioning and confining radioactive waste; thus, the analysis of its sorption properties as well as of those of its main hydration products is crucial to assess radionuclide migration under disposal conditions.In this study, the sorption of radioisotopes with different chemical properties (137Cs, 133Ba, 109Cd, 152Eu, 238Pu, 75Se and 36Cl) in portlandite suspended in 20 mM Ca(OH)2 (pH = 12.5 ± 0.2) was analyzed by means of batch sorption isotherms. In the range of the concentrations investigated, all the radionuclides showed a linear adsorption isotherm. Almost quantitative adsorption was observed for Eu, Pu and Cd, with a very high logarithm of the distribution coefficient, Kd [g·mL−1] (log(Kd) > 5). The adsorption of the cations Cs and Ba was significantly smaller, with a log(Kd) of approximately 2 and 0.3 respectively. The two anionic species analyzed were Cl− and SeO32−: whereas Cl did not show any retention, selenite showed a Log(Kd) of approximately 1.8. The precipitation of Se is observed for aqueous concentrations higher than 1·10−4 M, being the precipitation of CaSeO3(s) predicted by thermodynamic calculations.The electrokinetic surface potential of portlandite was analyzed as a function of pH (10–13.5) and with and without the presence of alkalis (0.2 M Na) to gather the basic information needed for understanding radionuclide/solid interactions and sorption modelling. The portlandite charging behaviour could be explained assuming calcium as the main ion determining the potential. This is the first time that a surface model for portlandite is proposed.A simplified double layer modelling approach was proposed to describe experimental data, identifying the most probable sorbing species under the geochemical conditions generated by portlandite, and all the adsorption isotherms could be satisfactorily reproduced the model.

Surface charge property governing co-transport of illite colloids and Eu(III) in saturated porous media

The transport of colloids and radionuclides is sophisticated because of the variety of charge properties between colloidal particles and host subsurface media, which causes great difficulty in establishing a reliable model of radionuclides migration by taking the colloid phase into consideration. In this work, the co-transport of illite colloids (IC) and Eu(III) in the quartz sand and iron-coated sand porous media was investigated by column experiments to address the predominant mechanism of charge properties on co-transport. Results showed that Eu(III) transport was driven by the illite colloids and electrostatic interaction was critical in governing the co-transport patterns. The promotion of Eu(III) transport by IC was attenuated in the iron-coated sand systems; more IC-Eu(III) complexes were retained uniformly in the column. The pore throat shrinkage caused by electrostatic attachment between aggregated IC and iron oxides exacerbated the physical straining and size exclusion effect of IC-Eu(III) complexes. An aggravated irreversible retention of IC-Eu(III) was detected in iron-coated sand column due to the electrostatic attraction of IC-Eu(III) to host media. The findings are essential for improving the understanding on the potential transport, retention and release risk of colloids associated radionuclides, and imply that the positively charged permeable reactive barrier is an effective strategy to reduce the transport risk of colloid associated radionuclides.

Coupled flow and transport modelling of a large-scale in situ migration experiment with 14 C-labelled natural organic matter colloids in Boom Clay

Abstract Twenty-five years ago, a unique long-term and large-scale in situ experiment with 14 C-labelled natural organic matter (NOM) was set up at the HADES underground research facility in Mol (Belgium) to study its migration behaviour. Natural organic matter plays an important role in the mobility of various safety-relevant radionuclides, which is critical in the context of Safety & Performance Assessment (SA/PA) calculations for a possible nuclear waste repository. The objective of this work is to enlarge the confidence in current NOM transport models by validating them with the in situ experiment, which is still continued to this day. Stepwise adding more complexity to the model resulted in a 10-parameter model with which excellent fits to the data are obtained. The model considers two different fractions that are transported by advection and diffusion and can be subject to both irreversible and reversible immobilization processes. The associated fitted parameter values compare well with values determined on small-scale migration experiments. This builds confidence in the NOM transport model, which in turn contributes to the confidence in the outcome of the radionuclide migration calculations performed in the context of SA/PA. These results again highlight the incredible value of such long-running experiments at underground research facilities like HADES.

Study on the Atmospheric Diffusion of Airborne Radionuclide under LOCA of Offshore Floating Nuclear Power Plants Based on CALPUFF

Studying the migration and diffusion of radionuclides plays an important role in emergency decision making and accident mitigation of floating nuclear power plants. Based on the CALPUFF model, this paper simulates the spatial distribution and concentration distribution of airborne radionuclides 131I diffusion under the conditions of sailing and power supply under LOCA (Loss-of-Coolant Accident) of the floating nuclear power plant, and the influence of four meteorological parameters, namely wind speed, cloudiness, temperature and air pressure, on the migration was analyzed using sensitivity analysis. The results show that the wind direction affects the diffusion direction of 131I, and the concentration of 131I decreases with the increase in the diffusion distance; under the same conditions, the radionuclides diffuses farther and the affected area is larger under the sailing condition. Wind speed is the dominant factor affecting the diffusion of radionuclides, followed by the cloud amount parameter, temperature parameter, and air pressure parameter. The research results can provide theoretical support for emergency responses to nuclear accidents in offshore floating nuclear power plants.

Do transient hydrological processes explain the variability of strontium-90 activity in groundwater downstream of a radioactive trench near Chernobyl?

The Chernobyl Pilot Site (CPS) was created in 2000 in order to study radionuclide migration processes to the geosphere from radioactive material of the Red forest buried in a trench. In this article, the data collected in the CPS up to 2015 are analyzed to identify the links between hydrological conditions and release of strontium-90 (90Sr) from the trench. Then, a flow-and-transport model is used for simulating distribution of 90Sr both in the unsaturated and saturated zones downstream of the trench. The results show that the 90Sr activity in groundwater is strongly transient in time, due to the high inter-annual variability of both the recharge rate and the groundwater level (some particularly wet winters resulted in saturation of the bottom part of the trench). In addition, the parameters that govern the sorption of 90Sr in trench material appear to vary significantly in space (the retardation factor ranges from 10 to 50 depending on the location). This spatiotemporal variability could hide some critical processes, e.g., related to a long-term trend, and needs to be characterized through an appropriate sampling frequency.

Modelling simultaneous transport of natural and anthropogenic radionuclides in fractured media — Diffusion into the heterogeneous layered rock matrix for an arbitrary length decay chain

Transport models used for assessing the safety of radioactive waste repositories hosted in fractured bedrock typically do not consider fluxes of naturally occurring radionuclides in the rock and their further migration in flow-bearing fractures. A consistent model that simultaneously describes the transport of radionuclides from both natural and anthropogenic sources has been developed, where decay chains and rock heterogeneity are accounted for. The model accounts for advective flow in the fracture, a decay chain of arbitrary length, and diffusion into and out of the adjacent rock matrix composed of different geological layers. The proposed solution has been verified against a previously published steady state case which considers a homogeneous rock matrix of infinite extent where porewater ingrowth is not accounted for. The model is also applied to some different calculation examples for both transient and limiting steady state cases to represent typical applications of the model as well as to illustrate the effect of different parameters and processes on the transport of natural radionuclides in fractured rocks. This study presents a novel and powerful tool to simulate migration of both anthropogenic and natural radionuclides in and from crystalline rocks to the biosphere. The presented modelling is essential in safety and performance assessment of deep geological disposal of radioactive waste in fractured rocks. The obtained analytical solution can be used to compare relative fluxes of natural and anthropogenic radionuclides, which is useful for validation of the radionuclide transport parameters obtained from field and laboratory experiments.

Influence of Rock Structure on Migration of Radioactive Colloids from an Underground Repository of High-Level Radioactive Waste

Studies of leaching of vitrified simulated high-level radioactive waste (HLW) evidence that most of actinides or their simulators enter leaching water in a colloidal form. In this paper, we consider a mechanism of colloid-facilitated migration of radionuclides from an underground repository of HLW located at a depth of a few hundreds of meters in fractured crystalline rocks. The comparison between data of field and laboratory measurements showed that the bulk permeability of the rock massif in field tests is much greater than the permeability of rock samples in laboratory experiments due to an influence of a network of fractures in the rock massif. Our theoretical analysis presents evidence that this difference can take place even in a case when the network is not continuous, and the fractures are isolated with each other through a porous low-permeable matrix of the rock. Results of modelling revealed a possibility of mechanical retention of radionuclide-bearing colloid particles in the frame of rock during their underground migration.

Влияние потенциального оледенения на безопасность подземного хранилища радиоактивных отходов на участке «Енисейский» (Красноярский край)

The paper evaluates the impact of potential glaciation on the migration of radionuclides from an underground radioactive waste repository to be sited at the Yeniseiskiy site. The problem was solved by mathematical modeling methods. The study considers a 3D model of groundwater flow and radionuclide migration taking into account the heterogeneous rock permeability. Groundwater dynamics equation was solved by the successive overrelaxation method, equation governing radionuclide migration was integrated by the alternating directions method using the Douglas’ scheme. The paper describes the influence of freeze-thaw cycles on rock permeability at the site taking into account available experimental data on samples collected from different rocks. Simulation showed that in the most unfavorable case glaciation could lead to a twofold increase of time-averaged velocity of radioactive plume propagation from the repository.

АНАЛИЗ ЗАВИСИМОСТЕЙ РАСПРЕДЕЛЕНИЯ РАДИОНУКЛИДОВ ОТ СПОСОБА ПЕРЕРАБОТКИ НЕФТЕСОДЕРЖАЩИХ ОТХОДОВ

In this paper main regularities of distribution of radionuclides in dependence of the method of treatment of oil-containing wastes have been analyzed. Calculation of limit values of the specific effective activity of natural radionuclides have been carried out. Results of experiments are showing that during the burning of oil sludges samples the analyzed radionuclides behave the same in all cases. The relationship between migration coefficients and ash content has been also established. For the samples with more high ash content during the burning the coefficients of migration of radionuclides into the remaining ashes were high than for the samples with the lower values of ash. Estimation of migration of natural radionuclides 226Ra, 232Th and 40Kin the processes of treatment of oil-containing wastes (burning, extraction of oil products, distillation of the diesel fraction) has been carries out. It was determined that during the carrying out of these processes the radionuclides are concentrated in more solid processes products: in ash, solid residue and bitumen fraction. As result, it increases their specific effective activity. The dependence of the coefficients of migration of radionuclides from the ash and the con tent of the mechanic impurities during the treatment by the methods of burning and extraction of oil products has been also received. Using of the results of work is allowing us to select the most appropriate methods of treatment of oil-containing wastes and to reach significant reduction of radioactive nuclides negative impact to the humans and to the environment.

Assessment of radionuclides in the "soil-plant" chain of uranium mining regions (literature review)

It is well known that as a result of the activities of the mining industry, radionuclides and chemicals with active mutagenic and carcinogenic effects can be extracted to the surface. Disposal products, such as radioactive waste and others, may cause particular danger. In this regard, this requires regular monitoring of radioactive waste storage sites and the degree of migration of radionuclides and heavy metals in environmental objects. This review article considers the uranium ore region’s current data for the content of radionuclides in soil, vegetation, and their migration in the “soil-plant” chain.

Impact of MOX fuel use in light-water reactors: long-term radiological consequences of disposal of high-level waste in a geological repository

ABSTRACT As a series of studies to evaluate impact of mixed-oxide (MOX) fuel in light-water reactors (LWRs), post-closure long-term safety for various vitrified high-level radioactive waste (HLW) arising from the different fuel cycle intends to recycle Pu are examined. In this study, four fuel cycle scenarios with different ratio of spent MOX generated and two reprocessing options for each fuel cycle scenario are considered. One reprocessing option considers disposal of vitrified HLW generated separately from the reprocessing of spent UO2 fuel and MOX fuel (separated HLW), and the other is blended vitrified UO2-MOX HLW (blended HLW) generated during reprocessing whereby MOX spent fuel is diluted by UO2 spent fuel. First, the radionuclide inventories of those vitrified HLWs are discussed. Next, radionuclide migration analyses for geological disposal of those vitrified HLWs are evaluated. It has revealed that the disposal of blended HLW will not have an adverse effect on the long-term radiological impact compared to separated HLW. Results of this study can be used as a basis for considering the blending option as a viable alternative approach in the future for managing MOX fuel used in light-water reactors.

A Comparative Study on Heterogeneity of Clay Rocks Using Pore‐Scale Diffusion Simulations and Experiments

AbstractAccurate modeling and simulation of radionuclide migration in clay rocks such as the Opalinus Clay (OPA) play a key role in the safety assessment of deep geological repositories for nuclear wastes. At the continuum scale, the representative elementary volume (REV) is a fundamental constraint to quantify the effective diffusivity, which is a key parameter in reactive transport (RT) models. Therefore, an accurate estimation of the REV is essential for a meaningful continuum‐scale RT simulation in heterogeneous clay rocks. This study presents a comprehensive analysis of the heterogeneities of porosity and effective diffusivity in clay rocks by using the classical sampling theory and pore‐scale simulations. First, in this study, the two‐dimensional representative elementary area is correlated with the REV for porosity via a characteristic length. Next, it is shown that the REV for diffusivity is larger than the REV for porosity. Moreover, these two REVs can be correlated using Archie's law. In such a way, the REV for diffusivity can be determined by the developed correlations through analyzing two‐dimensional microstructures, thus significantly reducing the computational cost. Finally, the applicability of our approach for clay rocks is validated by experimental data on the diffusion of tritiated water in the heterogeneous sandy facies of OPA. From both the experimental data and the modeling prediction, the REV for diffusivity in the sandy facies of OPA is in the order of cubic centimeters. This study provides critical insights into the diffusion in heterogeneous clay rocks toward an enhanced predictability of radionuclide migration.

Influence of tectonic perturbations on the migration of long-lived radionuclides from an underground repository of radioactive waste

We studied the influence of tectonic perturbations on the transport of potentially mobilized radionuclides in groundwater from a deep-mined repository of solid high-level radioactive waste. The study was carried out by the method of mathematical modeling. Key parameters of the model correspond to the site of a potential federal repository in Russia. The groundwater flow domain is delimited on one side by a water divide (i.e., boundary of the catchment basin) and on the other side by the river bank. 2D simulations of groundwater flow and radionuclide migration are carried out along a vertical cross-section normal to the water divide. The groundwater flows through the rock massif, which encloses the repository, and discharges into the adjacent river. It is supposed that tectonic activity may form a fault which is parallel to the river bank. We analyzed how repository safety depends on the time of the fault emergence and on the distance between the repository and the fault. The results of our simulations suggest that: (1) emergence of a fault due to tectonic perturbations is not inevitably associated with a substantial growth of radionuclides released from the repository to the environment; (2) influence of the fault on the repository safety depends on the distance between the fault and the repository as well as on the time interval between the repository development and the fault emergence; (3) the influence of the fault on the repository safety can depend substantially on local elevations of the relief at the repository site.