Radioactive Waste Disposal Facility Research Articles

Phenotypic Characterisation of Shewanella oneidensis MR-1 Exposed to X-Radiation.

Biogeochemical processes mediated by Fe(III)-reducing bacteria such as Shewanella oneidensis have the potential to influence the post-closure evolution of a geological disposal facility for radioactive wastes and to affect the solubility of some radionuclides. Furthermore, their potential to reduce both Fe(III) and radionuclides can be harnessed for the bioremediation of radionuclide-contaminated land. As some such sites are likely to have significant radiation fluxes, there is a need to characterise the impact of radiation stress on such microorganisms. There have, however, been few global cell analyses on the impact of ionizing radiation on subsurface bacteria, so here we address the metabolic response of S. oneidensis MR-1 to acute doses of X-radiation. UV/Vis spectroscopy and CFU counts showed that although X-radiation decreased initial viability and extended the lag phase of batch cultures, final biomass yields remained unchanged. FT-IR spectroscopy of whole cells indicated an increase in lipid associated vibrations and decreases in vibrations tentatively assigned to nucleic acids, phosphate, saccharides and amines. MALDI-TOF-MS detected an increase in total protein expression in cultures exposed to 12 Gy. At 95 Gy, a decrease in total protein levels was generally observed, although an increase in a putative cold shock protein was observed, which may be related to the radiation stress response of this organism. Multivariate statistical analyses applied to these FT-IR and MALDI-TOF-MS spectral data suggested that an irradiated phenotype developed throughout subsequent generations. This study suggests that significant alteration to the metabolism of S. oneidensis MR-1 is incurred as a result of X-irradiation and that dose dependent changes to specific biomolecules characterise this response. Irradiated S. oneidensis also displayed enhanced levels of poorly crystalline Fe(III) oxide reduction, though the mechanism underpinning this phenomenon is unclear.

Large scale in-situ experiments on sealing constructions in underground disposal facilities for radioactive wastes – Examples of recent BfS- and GRS-activities

This paper shows examples of in-situ constructions and laboratory tests that have been designed and implemented by BfS and GRS in order to demonstrate the technical feasibility of special constructions for the sealing of drifts and shafts in different salt formations.Since it is often not possible to directly verify the long-term functionality (for times scales envisaged in long-term safety assessments) of such constructions, an overall understanding of the main chemical and physical processes involved needs to be developed. Such an understanding is required in order to extrapolate the evolution of a sealing system with a sufficient degree of reliability. Laboratory tests and large-scale in-situ tests are necessary and integral parts of the procedures for enhancing the process understanding.Based on a safety case, BfS has developed a robust decommissioning concept for the closure of the low- and intermediate-level waste disposal facility Morsleben (ERAM) which also takes into account the retention of radionuclides by combined effects of different sealing components.GRS has contributed to this concept with laboratory tests and modelling of the long-term behaviour of the sealing material “salt concrete” foreseen for the sealing constructions in Morsleben. Salt concrete is based on the cement Portlandite i.e., on CaO. Furthermore GRS has also investigated the MgO based “sorel concrete” employed by BfS for the Asse project. The chemical corrosion path and the subsequent permeability changes for both concretes have been investigated with test procedures developed in the GRS laboratory. GRS has also developed a new Self-Sealing material “Selbst Verheilender Versatz – SVV” (SVV, German for Self Sealing Backfill) and tested in laboratory and in-situ experiments. With this material it is possible to achieve an instantaneous and long-lasting permeability reduction within the complex system consisting of the sealing construction and the Excavation Demaged Zone (EDZ) upon brine intrusion.The presentation demonstrates details of the concepts and highlights results from the BfS in-situ experiments in Morsleben and the preceding GRS laboratory and in-situ tests.

Decreasing Kd uncertainties through the application of thermodynamic sorption models

Radionuclide retardation processes during transport are expected to play an important role in the safety assessment of subsurface disposal facilities for radioactive waste. The linear distribution coefficient (Kd) is often used to represent radionuclide retention, because analytical solutions to the classic advection–diffusion-retardation equation under simple boundary conditions are readily obtainable, and because numerical implementation of this approach is relatively straightforward. For these reasons, the Kd approach lends itself to probabilistic calculations required by Performance Assessment (PA) calculations. However, it is widely recognised that Kd values derived from laboratory experiments generally have a narrow field of validity, and that the uncertainty of the Kd outside this field increases significantly. Mechanistic multicomponent geochemical simulators can be used to calculate Kd values under a wide range of conditions. This approach is powerful and flexible, but requires expert knowledge on the part of the user.The work presented in this paper aims to develop a simplified approach of estimating Kd values whose level of accuracy would be comparable with those obtained by fully-fledged geochemical simulators. The proposed approach consists of deriving simplified algebraic expressions by combining relevant mass action equations. This approach was applied to three distinct geochemical systems involving surface complexation and ion-exchange processes. Within bounds imposed by model simplifications, the presented approach allows radionuclide Kd values to be estimated as a function of key system-controlling parameters, such as the pH and mineralogy.This approach could be used by PA professionals to assess the impact of key geochemical parameters on the variability of radionuclide Kd values. Moreover, the presented approach could be relatively easily implemented in existing codes to represent the influence of temporal and spatial changes in geochemistry on Kd values.

Note: Establishing α-particle radiation damage experiments using the Dalton Cumbrian Facility's 5 MV tandem pelletron.

Evaluating the radiation stability of mineral phases is a vital research challenge when assessing the performance of the materials employed in a Geological Disposal Facility for radioactive waste. This report outlines the setup and methodology for efficiently allowing the determination of the dose dependence of damage to a mineral from a single ion irradiated sample. The technique has been deployed using the Dalton Cumbrian Facility's 5 MV tandem pelletron to irradiate a suite of minerals with a controlled α-particle ((4)He(2+)) beam. Such minerals are proxies for near-field clay based buffer material surrounding radioactive canisters, as well as the sorbent components of the host rock.

Shear Strength Behavior of Mont Terri Opalinus Claystone in Fault Zone

The paper summarizes the results of direct shear strength tests carried out on Opalinus Claystone deriving from a fault zone, at the site of Mont Terri (North-Western Switzerland). In Mont Terri an Underground Rock Mechanical Laboratory is conducting studies aimed at specifying the rock mechanical parameters of the rock surrounding, which is at the same time the potential host rock of a highly active radioactive waste disposal facility. The samples for the tests were derived from blocks and cores collected from the main fault zone, during the excavation of a tunnel, named: Full scale Emplacement demonstration experiment Gallery (FE Gallery). Direct shear strength tests were carried out on 50x50 mm samples undergoing a 1 MPa constant normal load, where the natural shear plane was parallel to the direction of the shear. The orientation of the bedding planes in the samples was recorded and the maximal shear strength and residual shear stress were determined. The maximal shear strength values obtained from the tests fell in the interval 0.34-0.78 MPa, while the residual values fell between 0.31 and 0.72 MPa. The effect on the shear strength of different angles defined by the bedding and the shear plane of the samples was also examined. The bedding of the samples enclosed different angles with the shear plane, ranging from 0 to 49 degrees.

Shear strength behavior of Mont Terri Opalinus Claystone in fault zone

The paper summarizes the results of direct shear strength tests carried out on Opalinus Claystone deriving from a fault zone, at the site of Mont Terri (North-Western Switzerland). In Mont Terri an Underground Rock Mechanical Laboratory is conducting studies aimed at specifying the rock mechanical parameters of the rock surrounding, which is at the same time the potential host rock of a highly active radioactive waste disposal facility. The samples for the tests were derived from blocks and cores collected from the main fault zone, during the excavation of a tunnel, named: Full scale Emplacement demonstration experiment Gallery (FE Gallery). Direct shear strength tests were carried out on 50x50 mm samples undergoing a 1 MPa constant normal load, where the natural shear plane was parallel to the direction of the shear. The orientation of the bedding planes in the samples was recorded and the maximal shear strength and residual shear stress were determined. The maximal shear strength values obtained from th...

Effect of limestone fillers on microstructure and permeability due to carbonation of cement pastes under controlled CO2 pressure conditions

In underground concrete structures such as radioactive waste disposal facilities, the concrete is subjected to higher CO2 partial pressure than in the atmosphere and/or higher pressure gradient of liquid in which CO2 is dissolved. Under these conditions CO2 transport, which governs the carbonation, occurs both by diffusion and advection. This study aims at developing a new experimental method to carbonate cement-based materials by applying an elevated pressure gradient of pure CO2 to the specimens at 65% relative humidity (RH). The proposed method was used to investigate the effects of limestone fillers on changes in microstructure and permeability due to carbonation. The experiments were performed on two hardened cement paste samples with different water/powder and limestone filler replacement ratios. Samples were subjected to an elevated CO2 pressure of 6bar at the upstream side. The CO2 uptake was measured in the up- and downstream sides by precise mass flow meters. Carbonated samples were analyzed by a series of methods including SEM, MIP and N2-adsorption to characterize the microstructural changes; phenolphthalein spraying, XRD, TGA and water permeability measurements to study alterations in chemical compositions and transport properties.Results showed that the carbonation of samples at 65% RH was considerably fast during the first few experimental hours, while carbonation rate significantly decreased thereafter due to the increase of internal RH. However, by alternating carbonation with drying periods, as proposed here, carbonation rates remained high during the complete experiment. Our study evidenced that, in addition to portlandite, also C–S–H was partly carbonated under the studied conditions resulting in gradual profiles of these phases. Limestone filler replacement promoted the CO2 uptake because calcite precipitates preferentially on limestone particles than on portlandite and C–S–H phases as the latter inhibits further carbonation. C–S–H carbonation was more enhanced in samples without limestone fillers which resulted in a BET specific surface area increase. On the other hand, in samples with limestone fillers, BET specific surface area decreased because of porosity and pore size decreases. The carbonation induced changes in the microstructure which resulted in a significant decrease in water permeability. As a consequence of larger BET specific surface area, higher porosity and pore size reductions, the decrease in permeability was more pronounced in the sample without limestone fillers.

Characterization of low-molecular-weight organic acids isolated from the Toarcian argillite pore water (Tournemire site, France)

Bacterial activity in the near-field environment of radioactive waste disposal facilities in deep argillaceous rocks is currently under investigation. Bacterial development could be enhanced by the availability of low-molecular-weight organic acids (LMWOA) dissolved in the pore water of clayey rocks. This study firstly aimed at isolating and characterizing the LMWOA of the Toarcian argillite from the Tournemire Underground Research Laboratory (France, Aveyron). It also aimed at assessing the disturbing effects that could be induced by a disposal facility on the type and release of LMWOA (exposure to oxygen, alkaline pH, temperature increase). Under the experimental conditions investigated at 60°C, the mean dissolved organic carbon (DOC) is about 15 mg L−1 with a LMWOA proportion of 35 %. The main LMWOA are composed of formate, fumarate, propionate, acetate, and lactate. DOC is mainly influenced by both temperature and pH increases, whereas the LMWOA type nature and release are more specifically affected by the exposure to oxygen.

중·저준위 방사성폐기물 처분시설 안전성평가를 위한 입력데이터 설정 및 관리에 대한 고찰

(Received November 26, 2014 / Revised December 19, 2014 / Approved December 22, 2014)The systematic quality assurance activities on documents of the safety assessment are required for the safety case of the low- and intermediate-level radioactive waste disposal facility. In this paper, quality assurance system focused on the input data including the site characterization, groundwater flow, system design and monitoring are prepared and discussed. Rule for the input data selection is suggested and applied for the safety assessment which is based on the in-situ/experiment observations, final facility design and waste pileup plan, engineered barrier, field monitoring, recent biosphere, and radio-nuclide inventory. The reduction of data uncertainty will be expected to contribute to the safety of disposal facility further.

Equilibrium isotherm and kinetics modeling of U(VI) adsorption by natural soil systems

This research examined the adsorption capability of natural soils of different origin for U(VI) at soil–water interface and the mechanism involved. Adsorption kinetics study indicates that adsorption followed the pseudo-second order kinetics irrespective of soil types and was not solely controlled by the diffusion step rather surface complexation and ion-exchange plays major role. Study of adsorption isotherms indicates adsorption involves chemisorption and soil with high Fe and Mn content better fit to Langmuir model. The study provides a better insight for site selection for radioactive waste (uranium) disposal facilities as well as soil suitable for back fill or permeable reactive barrier to inhibit migration of U(VI).

A feasibility study on the criticality control method using radioactive vitrified forms for spent fuel storage

Vitrification form is an immobilization method for the radioactive wastes that are generated from various facilities such as nuclear power plants. Currently, the resultant vitrified forms are classified as radioactive wastes and therefore they should be disposed of in radioactive waste disposal facilities; but this disposal method is costly. In this study, a re-use method for various vitrified forms as the criticality control material was proposed for the replacement of the conventional neutron absorber in spent fuel storages. First, a nuclear fuel storage design was proposed for PLUS7 and WH 17×17 fuel assemblies. In addition, the criteria of the effective boron densities were established. For the verification of the criticality control ability, the multiplication factors in the storages were estimated with the 43 vitrified forms which have been developed in various countries. The results showed that most of the vitrified forms, except for a few cases, can be utilized for the criticality control materials. The proposed method uses the vitrified forms as neutron absorbers in the spent fuel storages without any chemical additions. Therefore, it can contribute to an increase in the efficient disposal of radioactive waste, as well as the providing economic benefits.

A two-stage approach to defining an affected community based on the directly affected population and the sense of community

Studies have demonstrated the inadequacy of relying on existing administrative boundaries or simple proximity to define an affected community. The proposal and siting of hazardous facilities can have a range of impacts upon people across wide areas, with some more affected than others as a result of living with the physical impacts of construction or the fear associated with perceived risk. We term those most affected the directly affected population and propose a two-stage model for identifying an affected community which places those most affected at the centre of the definition. The second stage is to identify the relationships those most affected have with the wider elements of the sense of community to discover the existing community or communities which are affected. Illustrated by the siting of a low-level radioactive waste disposal facility at Dounrey in the north of Scotland, we show that elements of the lived community experience may have very different shapes, extents and conflicting interests which pose challenges for their incorporation into a siting process. The two-stage model presented in this paper, by placing those most directly affected at the centre and working from there out into the existing communities, identifies issues early in any siting process to improve their incorporation and amelioration.

Rock alteration in alkaline cement waters over 15 years and its relevance to the geological disposal of nuclear waste

The interaction of groundwater with cement in a geological disposal facility (GDF) for intermediate level radioactive waste will produce a high pH leachate plume. Such a plume may alter the physical and chemical properties of the GDF host rock. However, the geochemical and mineralogical processes which may occur in such systems over timescales relevant for geological disposal remain unclear. This study has extended the timescale for laboratory experiments and shown that, after 15years two distinct phases of reaction may occur during alteration of a dolomite-rich rock at high pH. In these experiments the dissolution of primary silicate minerals and the formation of secondary calcium silicate hydrate (C–S–H) phases containing varying amounts of aluminium and potassium (C–(A)–(K)–S–H) during the early stages of reaction (up to 15months) have been superseded as the systems have evolved. After 15years significant dedolomitisation (MgCa(CO3)2+2OH−→Mg(OH)2+CaCO3+CO32−(aq)) has led to the formation of magnesium silicates, such as saponite and talc, containing variable amounts of aluminium and potassium (Mg–(Al)–(K)–silicates), and calcite at the expense of the early-formed C–(A)–(K)–S–H phases. This occured in high pH solutions representative of two different periods of cement leachate evolution with little difference in the alteration processes in either a KOH and NaOH or a Ca(OH)2 dominated solution but a greater extent of alteration in the higher pH KOH/NaOH leachate. The high pH alteration of the rock over 15years also increased the rock’s sorption capacity for U(VI). The results of this study provide a detailed insight into the longer term reactions occurring during the interaction of cement leachate and dolomite-rich rock in the geosphere. These processes have the potential to impact on radionuclide transport from a geodisposal facility and are therefore important in underpinning any safety case for geological disposal.

Field‐Scale Sulfur Hexafluoride Tracer Experiment to Understand Long Distance Gas Transport in the Deep Unsaturated Zone

A natural gradient SF6 tracer experiment provided an unprecedented evaluation of long distance gas transport in the deep unsaturated zone (UZ) under controlled (known) conditions. The field‐scale gas tracer test in the 110‐m‐thick UZ was conducted at the U.S. Geological Survey's Amargosa Desert Research Site (ADRS) in southwestern Nevada. A history of anomalous (theoretically unexpected) contaminant gas transport observed at the ADRS, next to the first commercial low‐level radioactive waste disposal facility in the United States, provided motivation for the SF6 tracer study. Tracer was injected into a deep UZ borehole at depths of 15 and 48 m, and plume migration was observed in a monitoring borehole 9 m away at various depths (0.5–109 m) over the course of 1 yr. Tracer results yielded useful information about gas transport as applicable to the spatial scales of interest for off‐site contaminant transport in arid unsaturated zones. Modeling gas diffusion with standard empirical expressions reasonably explained SF6 plume migration, but tended to underpredict peak concentrations for the field‐scale experiment given previously determined porosity information. Despite some discrepancies between observations and model results, rapid SF6 gas transport commensurate with previous contaminant migration was not observed. The results provide ancillary support for the concept that apparent anomalies in historic transport behavior at the ADRS are the result of factors other than nonreactive gas transport properties or processes currently in effect in the undisturbed UZ.

New characterization methods for monitoring small resonant frequency variation: Experimental tests in the case of hydrogen detection with uncoated silicon microcantilever-based sensors

The uncoated silicon microcantilever (USMC) operated in the dynamic mode is a new concept in the field of microcantilever-based chemical sensors. Due to the absence of a sensitive layer, this kind of microsensor can only be used for specific applications where it is known that only one chemical species may be varying in concentration, such as monitoring hydrogen release in radioactive waste disposal facilities. Usually, the relative variation of the USMC resonant frequency expected for low concentrations (≤2%) of hydrogen in nitrogen is below 50ppm. As a result, the measurement of both the resonant frequencies, fr, and the quality factor, Q, by classical methods, based on the gain spectrum (resonant peak and −3dB bandwidth), is not sufficiently accurate. In this paper, new measurement methods for monitoring fr and Q variations are proposed: (1) variation of gain and phase at fixed frequencies and (2) polynomial approximations of gain and phase spectra. The performance study of these characterization methods shows that monitoring fr by using phase linearization yields the best signal-to-noise ratio (e.g., 100 at 0.6% of H2 in N2), with 0.02% as a limit of detection for hydrogen.

The environmental impact assessment process for nuclear facilities: A review of the Lithuanian practice and experience

The only one nuclear power plant (NPP) in the Republic of Lithuania – Ignalina NPP has been shutdown and entered the phase of decommissioning. Decommissioning activities, along with dismantling works, include construction and operation of a new spent nuclear fuel and radioactive waste management, storage and disposal facilities. The new NPP in Lithuania, if such would be constructed, are to be located adjacently to the existing plant. Current and future planned nuclear activities in Lithuania are concentrated in a single location, in the northeast of the country near the state borders with the Republic of Latvia and the Republic of Belarus. Number of different projects and participants involved, necessity to control and limit overall impact on the environment require for planning and coordination of activities and impacts, including consideration and updating of outcomes from the previous environmental impact assessment (EIA) studies. Regulatory review and coordination of EIA documents also demands substantial time resources, impacts schedule of activities and therefore must be properly planned and managed. The paper describes approach and progress in EIA for nuclear activities in Lithuania and examines experience gained in preparation, review and coordination of EIA studies. Emphasis is placed on approach that has been used to deal with cumulative radiological impact because acceptability of this impact is one of primary goal in demonstration of acceptability of the newly planned nuclear activities.

Public perception of ultimate disposal facilities for radioactive waste and carbon dioxide: results from a cross-national comparison

The public perception of ultimate disposal facilities for Radioactive Waste (RW) and carbon dioxide (CO2) is crucial for the selection, construction and operation of such sites. This paper presents a cross-national comparison of the public perceptions of ultimate disposal facilities for RW and CO2 in the Czech Republic, Germany and Lithuania. The results of the comparison revealed similarities and differences in public perceptions in the three countries, as well as similarities and differences in the public perception of the two issues of RW and CO2 disposal. Key lessons learnt from the comparisons are that (a) public knowledge about RW and CO2 disposal is still low, (b) misconceptions about RW and CO2 disposal are widespread, (c) risk perceptions of CO2 disposal sites among the public might be influenced by risk perceptions of RW disposal sites and (d) the social context of public perceptions should be taken into account.

Comparison of monitoring programmes of ultimate disposal facilities for radioactive waste and carbon dioxide

Reliable and cost-effective monitoring is an important part of making geological repositories safe, effective, and acceptable for radioactive waste disposal and carbon dioxide (CO2) storage. The major objectives of monitoring should include the evolution of disposal systems compared to the baseline data of the undisturbed site, as well as the validation of the assumptions and results of the safety assessment. Hence, monitoring is performed in support of safety assessment activities concerning geological, hydrogeological, geo-mechanical, and geochemical data. For a monitoring programme, initial information should be available during the site characterisation stage, and should be updated as site-specific data are provided during site construction and operation. Monitoring activities need to be continued for as long as necessary after the closure of the repository or storage site in order to provide public confidence, ascertain the integrity of the repository, and confirm its behaviour as predicted by the safety assessment.

Mechanical interpretations of the homogeneous nature of bentonite due to swelling

Abstract To achieve the high sealing capability required for the bentonite engineered barriers used in geological disposal facilities for radioactive waste, the bentonite should be highly compacted. Previous investigation of methods to enable such compaction has revealed that the construction methods used have an impact on the density distribution. However, these investigations focused on achieving the required average dry density in the bentonite barriers and little attention has been paid to the distribution of dry density. As a result, there has been a lack of understanding of how the construction method used affects this distribution, which is highly pertinent to the evaluation of the long-term performance of bentonite engineered barriers. This paper first describes the residual density distribution after resaturation and then highlights how swelling behaviour can be studied and evaluated based on elasto-plastic theory. The conceptual understanding is that the buffer does not swell to achieve an entirely homogeneous density, but will reach an equilibrium state with a remaining gradient.

Comparison of cost estimates of final disposal facilities for carbon dioxide and high-level radioactive waste

This paper presents new research and new cost calculations for carbon dioxide (CO2) disposal in Cuba and Lithuania, as well as lessons from the comparative assessment of CO2 and high-level Radioactive Waste (RW) disposal costs in several countries. Nuclear power and CO2 Capture and Disposal (CCD) are key greenhouse gas mitigation options, both entailing the long-term, geological disposal of wastes. This paper presents the related economic calculations and draws lessons from their inter-comparison. The paper compares the costs of geological disposal of CO2 and RW in several countries by applying the same unit: US cent/Kilowatt Hour (kWh). CO2 disposal costs were estimated for Lithuania and Cuba, while RW disposal costs were assessed and compared for Lithuania, Switzerland, India and the Republic of Korea. In both cases, costs vary across a wide range in the countries analysed, but the variations are consistent with published estimates for other countries with similar geological and economic conditions.