High-level Waste Storage Research Articles

Dissolution Behavior of Simulated Spent Nuclear Fuel in LiCl-KCl-UCl3 Molten Salt

Considering the necessity of the development of methods to reduce the burden of storage and disposal of high-level radioactive waste, in this study, we propose a nuclide separation technique using molten salt immersion. The dissolution behavior of simulated spent nuclear fuels (SSFs) immersed in a LiCl-KCl-UCl3 (LKU) molten salt at 500°C was investigated using a combination of thermodynamic and experimental studies. Surrogates of transuranic elements (TRUs), that is, rare earth elements (REs), in the SSFs were dissolved into the molten salt without any damage to the UO2 structure of the SSFs. The results suggest that the LKU salt technique can be used to separate REs and, potentially, TRUs from actual spent nuclear fuels (SNFs). It is thought that this technique is advantageous over the conventional TRU recovery techniques because the majority of the SNFs (i.e., UO2) remained stable, thus reducing the process burden. Several SNF treatment process options using this technique were suggested. This study will serve as a guide for future studies on the management of high-level waste discharged from nuclear reactors.

Adsorption of barium and radium on montmorillonite: A comparative experimental and modelling study

The widely favored option for the safe storage of high-level radioactive waste is a multi-barrier disposal system with clay-based geotechnical barriers e.g. bentonite. Montmorillonite as a major constituent of bentonite (up to 90 wt.-%) is an important sink for potentially released radionuclides. The adsorption of 226Ra and Ba on Na-montmorillonite (SWy-2) was investigated as function of pH (edges) and of Ba concentration (isotherms) at different ionic strengths. Ba is often used as a chemical analogue for 226Ra due to their closely related physical and chemical properties e.g. the formation of complete Ba/Ra solid solutions. The experimental Ba/Ra adsorption data could be quantitatively described by considering cation exchange reactions on the planar sites of montmorillonite. To describe the pH dependent adsorption of Ba and Ra at high ionic strength and high pH, an additional reaction involving surface complexation was necessary. The fitted selectivity coefficients (Kc) for the cation exchange of Ba and Ra with respect to Na are very similar at low ionic strength (0.02 M), whereas at higher ionic strength (0.3 M), Ra appears to be more selective.

Confidence gap or timid trust building? The role of trust in the evolution of the nuclear waste governance in Germany

Nuclear waste disposal represents one of the biggest socio-economic challenges of this century and probably for many centuries to come. It is a highly complex issue due to the interrelated technical, material, social, economic and political dimensions as well as the real or perceived risks involved. Distrust in technology, institutions, industry and even experts and decision-making processes are some of the reasons for opposition to nuclear waste disposal strategies. Our contribution analyses the dynamics of trust and distrust in Germany over the evolution of the search for a nuclear waste repository site in the last 40 years, identifies major turning points and explores the main factors that shaped trust/distrust relations over time. Site selection conflicts have often provoked ‘confidence gaps’ and site selection policies depend heavily on relationships based on mutual recognition and trust. We select key factors considered necessary to build trust in institutions and siting selection procedures and review recent changes in the institutional setting, including the establishment of a National Civil Society Board and the attempt to design more participatory procedures. Twenty-one stakeholders and experts were asked to rate some of the identified factors necessary for building trust and whether the measures carried out so far are sufficient to enhance trust in the relevant institutions and procedures and increase public confidence. Without a trust-building process for the siting, development and operation of a risky asset, a short-term attenuation of long-lasting conflicts is unlikely. The legacy of the past still plays an inhibiting role. In addition to expert judgement, evidence was derived from document analysis and participatory observation in the works of the German ‘Commission on the Storage of High-level Radioactive Waste’ and of the ‘National Civil Society Board’ as well as of events of regulator and operator.

NIMBY問題で当事者に対する優位的正当化が抑制されるとき―地層処分場を焦点とした「誰がなぜゲーム」における将来世代の呈示―

NIMBY問題で当事者に対する優位的正当化が抑制されるとき―地層処分場を焦点とした「誰がなぜゲーム」における将来世代の呈示―

The remote-controlled spectrometric system for searching and characterization of high-level radioactive waste

In 2003, the work on environmental rehabilitation of the former coastal technical base of the Russian Navy in Gremikha town, with technical and financial support of the State Atomic Energy Corporation “Rosatom” and the French Alternative Energies and Atomic Energy Commission had begun. In 2017, the task of searching, characterization and packaging in transport containers for export to the long-term storage of high-level waste containing 152Eu was set as part of this program. These wastes were presented as fragments of reactor control and safety system rods of first generation nuclear submarine reactors and were placed in temporary storage containers mixed with other radioactive waste and construction garbage on the territory of the Gremikha branch of the North-West Center “SevRAO”. To accomplish the task, the spectrometric system “Gamma-Pioneer” was developed and made at National Research Center “Kurchatov Institute”. The system consist of a collimated spectrometric gamma-ray CdZnTe detector 500 mm3 volume, a dosimeter for continuous measurement of ambient equivalent dose rate at the instrument location and a color video camera with zoom lens. The device is placed in a protective frame and installed as an attachment implements on robot Brokk-90. Communication between the measuring system and the control computer is carried out using USB extender and 100 meters cable. The video camera is connected to the control computer via Ethernet. To search for the most active sources of gamma radiation, an equivalent dose rate calculation program using the results of measured instrumental spectra was developed. The characterization of the extracted fragments was carried out by activity evaluation of the main radionuclides polluting the samples under investigation. The paper describes design and operating principles of the system, as well as methods for the equivalent dose rate calculation and the activity evaluation of the fragments of reactor control and safety system rods based on spectral measurements obtained using the developed radiometric system

Stability of Microbial Community Profiles Associated with Compacted Bentonite from the Grimsel Underground Research Laboratory.

To assess the microbiology and corrosion potential of engineered components of a deep geological repository for long-term storage of high-level nuclear waste, the Materials Corrosion Test is being conducted at the Underground Research Laboratory in Grimsel, Switzerland. Modules containing metal coupons surrounded by highly compacted MX-80 bentonite, at two dry densities (1.25 and 1.50 g/cm3), were emplaced within 9-m-deep boreholes, and the first modules were retrieved after 13 months of exposure. Bentonite and associated module materials were sampled, and microbial communities and their distributions were assessed using 16S rRNA gene sequencing and phospholipid fatty acid (PLFA) analysis. Borehole fluid was dominated by amplicon sequence variants (ASVs) affiliated with Desulfosporosinus and Desulfovibrio, which are putatively involved in sulfate reduction. The relative abundance of these ASVs was lower for samples from inside the borehole module, and they were almost undetectable in samples of the inner bentonite layer. The dominant ASV in case and filter sample sequence data was affiliated with Pseudomonas stutzeri, yet its relative abundance decreased in the inner layer samples. Streptomyces sp. ASVs were relatively abundant in all bentonite core sample data both prior to emplacement and after 13 months of exposure, presumably as metabolically inactive spores or extracellular "relic" DNA. PLFA concentrations in outer and inner layer bentonite samples suggested cellular abundances of 1 × 106 to 3 × 106 cells/g, with similar PLFA distributions within all bentonite samples. Our results demonstrate consistent microbial communities inside the saturated borehole module, providing the first evidence for microbial stability under conditions that mimic a deep geological repository.IMPORTANCE The Materials Corrosion Test in Grimsel Underground Research Laboratory, Switzerland, enables an evaluation of microbiological implications of bentonite clay at densities relevant for a deep geological repository. Our research demonstrates that after 13 months of exposure within a granitic host rock, the microbial 16S rRNA gene signatures of saturated bentonite clay within the modules were consistent with the profiles in the original clay used to pack the modules. Such results provide evidence that densities chosen for this emplacement test are refractory to microbial activity, at least on the relatively short time frame leading to the first time point sampling event, which will help inform in situ engineered barrier system science. This study has important implications for the design of deep geological repository sites under consideration for the Canadian Shield.

Ceramic Matrix Composites Based on Lanthanum Orthophosphate for Disposal of High-Level Radioactive Waste

Ceramic matrix composites for solidification and disposal of actinide-rare-earth fraction of high-level waste (HLW) were prepared by sintering of nanosized powders of 0.8LaPO4–0.2Al2O3, 0.8LaPO4–0.2Y2O3 and 0.8LaPO4–0.2ZrO2 obtained from 0.8LaPO4 · nH2O–0.2Al(OH)3, 0.8LaPO4 · nH2O–0.2Y(OH)3 and 0.8L-aPO4 · nH2O–0.2ZrO(OH)2 precursors. These powders-precursors were synthesized via sol-gel technique. After heat treatment at 850°C powders of 0.8LaPO4–0.2Al2O3, 0.8LaPO4–0.2Y2O3 and 0.8LaPO4–0.2ZrO2 were obtained. Further powdered compositions were stepwise sintered to prepare ceramic composites which were supposed to be used as matrices for storage of HLW. Rate of La3+, Al3+, Y3+ and Zr4+ leaching from ceramic matrix composites in strength aqueous solutions of NaCl and Na2SO4 simulating underground brine typical for proposed location of HLW geological repository was estimated.

ANALYSIS OF THE USE OF DEPLETED URANIUM AS A PROTECTIVE MATERIAL FOR RADIOACTIVE WASTE MANAGEMENT

An analysis of the use of depleted uranium as a protective material for containers for the storage of high-level waste. By its protective properties, it surpasses all known materials used in protection against ionizing radiation. The article analyzes the possibility of improving the container used at the ChNPP for the storage of HLW KTZV0,2. Developed models and calculations carried with the possible addition of depleted uranium to the composite of concrete, as well as the possibility of using, instead of lead, segments of depleted uranium in containers with the addition of an additional protective layer. Calculations have shown that the use of depleted uranium in protective containers for HLW allows reducing the total number of containers. That required for temporary storage of HLW in ChNPP repositories, which makes it possible to optimize the scheme of radioactive waste management at ChNPP during the work on the decommissioning and conversion of the Shelter object on an environmentally safe system. The application of depleted uranium as an impurity to the concrete composite and the use of it as an additional metal protection in containers KTZV-0,2, considered by us, showed that:there is a decrease in the dose rate from 2 to 4 times, depending on the addition of the percentage to the concrete composite;the efficiency of the protective properties of the use of uranium is increased compared with lead in the application of depleted uranium in the form of metal plates. This allows you to increase the activity of VAB in the container to 3.95E + 18 Bq, compared with lead.

NIMBY施設をめぐる討議が正当性と受容意図に及ぼす効果―高レベル放射性廃棄物の地層処分場を焦点とした"誰がなぜゲーム"における承認–受容モデル―

NIMBY施設をめぐる討議が正当性と受容意図に及ぼす効果―高レベル放射性廃棄物の地層処分場を焦点とした"誰がなぜゲーム"における承認–受容モデル―

Molten-Salt Reactor for Nuclear Fuel Cycle Closure on All Actinides

It is proposed that a specialized molten-salt reactor facility for burning long-lived actinides be located in direct proximity to a pilot-demonstration center. A full-scale ZhSR-S with thermal power 2400 MW will make it possible to burn all transuranium elements released during the reprocessing of spent VVER-1000 nuclear fuel and part of the regenerated plutonium and in the process produce 1 GW of electricity and radioisotope products. The inclusion of a specialized reactor facility for burning transuranium elements from the spent nuclear fuel of VVER-1000 reactors into the nuclear energy system as an integral element will make it possible to solve the problem of closing the nuclear fuel cycle for actinides and reduce the volume and lower the cost of the long-term storage and subsequent disposal of high-level wastes produced in reprocessing.

Association of Eu(III) and Cm(III) onto an extremely halophilic archaeon.

In addition to geological, geochemical, and geophysical aspects, also, microbial aspects have to be taken into account when considering the final storage of high-level radioactive waste in a deep geological repository. Rock salt is a potential host rock formation for such a repository. One indigenous microorganism, that is, common in rock salt, is the halophilic archaeon Halobacterium noricense DSM15987T, which was used in our study to investigate its interactions with the trivalent actinide curium and its inactive analogue europium as a function of time and concentration. Time-resolved laser-induced fluorescence spectroscopy was applied to characterize formed species in the micromolar europium concentration range. An extended evaluation of the data with parallel factor analysis revealed the association of Eu(III) to a phosphate compound released by the cells (F2/F1 ratio, 2.50) and a solid phosphate species (F2/F1 ratio, 1.80). The association with an aqueous phosphate species and a solid phosphate species was proven with site-selective TRLFS. Experiments with Cm(III) in the nanomolar concentration range showed a time- and pCH+-dependent species distribution. These species were characterized by red-shifted emission maxima, 600-602nm, in comparison to the free Cm(III) aqueous ion, 593.8nm. After 24h, 40% of the luminescence intensity was measured on the cells corresponding to 0.18μg Cm(III)/gDBM. Our results demonstrate that Halobacterium noricense DSM15987T interacts with Eu(III) by the formation of phosphate species, whereas for Cm(III), a complexation with carboxylic functional groups was also observed.

Sorption of Am(III) on clays and clay minerals: A review

The problem connected to the long-term storage of high-level nuclear waste has initiated an extensive search for suitable host rock formations and backfill materials to guarantee an isolation of hazardous nuclear elements from the biosphere for thousands of years. Besides other alternatives, clays and clayey materials have been in the focus of various sorption studies. With respect to long-term predictions of migration processes, the transuranium elements and fission products are of particular interest. The present review gives a detailed summary of sorption studies conducted during the past decades describing the impact of various geochemical parameters on the immobilization of Am(III) by different clays and clay minerals.

Risk analysis of high level radioactive waste storage tank based on HAZOP

High-level radioactive liquid waste tanks have the possibility of releasing radioactivity, and thus it is of great importance to identify hazards in such storage tanks and take measures to improve their safety. In this paper, a hazard and operability (HAZOP) methodology is used to identify the hazards in a double-shell stainless-steel tank for high-level radioactive liquid waste storage for which a risk matrix was implemented to assess the risks posed by the hazard. First, during the HAZOP process, appropriate process parameters and guidewords were selected to describe the deviation of the storage tank, and the causes and possible consequences of deviations as well as existing protection measures were analyzed. The risk matrix then was used to evaluate the risk level of the deviation identified, combined with the consequences of the deviation as well as the associated likelihood of its occurrence. Results showed that primary tank leaks and hydrogen combustion or explosion in tanks are undesirable risks, and thus corresponding countermeasures were put forward. The analysis results could be used to provide guidance for safe operation of, and rectification of hidden dangers in, high-level radioactive liquid waste storage tanks.

Comparison of solvent extraction and extraction chromatography resin techniques for uranium isotopic characterization in high-level radioactive waste and barrier materials

The development of Deep Geological Repositories (DGP) to the storage of high-level radioactive waste (HLRW) is mainly focused in systems of multiple barriers based on the use of clays, and particularly bentonites, as natural and engineered barriers in nuclear waste isolation due to their remarkable properties.Due to the fact that uranium is the major component of HLRW, it is required to go in depth in the analysis of the chemistry of the reaction of this element within bentonites. The determination of uranium under the conditions of HLRW, including the analysis of silicate matrices before and after the uranium-bentonite reaction, was investigated. The performances of a state-of-the-art and widespread radiochemical method based on chromatographic UTEVA resins, and a well-known and traditional method based on solvent extraction with tri-n-butyl phosphate (TBP), for the analysis of uranium and thorium isotopes in solid matrices with high concentrations of uranium were analysed in detail.In the development of this comparison, both radiochemical approaches have an overall excellent performance in order to analyse uranium concentration in HLRW samples. However, due to the high uranium concentration in the samples, the chromatographic resin is not able to avoid completely the uranium contamination in the thorium fraction.

Risk discourses and governance of high-level radioactive waste storage in Taiwan

Policy scholars have indicated that the quality of the solution to a perceived social problem depends on the adequacy of its framing. This paper examines how policy stakeholders and local residents frame the issue of the radioactive waste storage facility in Taiwan, the limits of institutional mechanisms in decision-making processes, and the implications of the deliberative forums undertaken by the national Stop Nukes Now organisation. The controversy illustrates the problems of a knowledge gap and the top-down procedures as well as the challenges that Taiwan faces in becoming a nuclear-free country. This case demonstrates civic society organisations’ efforts to challenge the ‘social–technical divide’ and technical experts’ prior definition of the ‘problems’ and selection of a ‘solution’. Deliberative forums enable the participation of affected communities to shape public discourses, which helps to strengthen public communication, improves citizen consciousness of nuclear waste issues, and attempts to link wider communities and public interests.

Kinetic Properties of the Passive Film on Copper in the Presence of Sulfate-Reducing Bacteria

Copper specimens were exposed to Sulfate-Reducing Bacteria (SRB) for 10 months under the conditions corresponding to the final disposal of high-level nuclear waste. In-situ electrochemical impedance spectroscopy (EIS) measurements were carried out to characterize the surface-environment interface after various times of exposure. The EIS results are interpreted in terms of the Point Defect Model (PDM), in order to obtain kinetic information on the formation of the Cu2S passive film. The standard rate constant and the rate constants for the surface reactions revealed that the Cu2S layer is a p-type semiconductor. The diffusion constant for cation vacancies in the barrier layer and the average bulk cation vacancy concentration in the barrier layer were found to be on the orders of 10−13 cm2⋅s−1 and 1022 cm−3, respectively, i.e., both slightly higher than reported in literature for corresponding electrochemically developed Cu2S layers. The electric field strength was approximately 3⋅105 Vcm−1 at all measurement points. These results are presented and discussed in this work in the light of storage of high-level nuclear waste.

Hydration and Diffusion Mechanism of Uranyl in Montmorillonite Clay: Molecular Dynamics Using an Ab Initio Potential

Permanent geological repositories lined with bentonite, a montmorillonite-containing clay, is one of the options considered for the storage of high-level radioactive waste. If the fuel rods were dissolved by a water leak, the clay would exchange its cations with the radioactive cations, slowing down their diffusion to the environment. We present an ab initio force field for the uranyl–montmorillonite interaction based on the hydrated ion model, i.e., recognizing the [UO2(H2O)5]2+ as the cationic species. This new interaction potential was used to run molecular dynamics simulations of the hydrated clay system. The uranyl aqua ion formed outer-sphere complexes with the clay layers, in agreement with EXAFS data. The hydrate is strongly bound, forming 1.4 hydrogen bonds between the first shell and clay oxygens. Uranyl–clay interaction sites were identified as groups of three Mg substitutions. Increasing the uranyl concentration enhances mobility due to partial surface coverage. Uranyl diffuses by means of a h...

About the Possibility of Disposal of HLRW in Deep Boreholes in Germany

Using deep boreholes for the final disposal of high-level radioactive waste (HLRW) can take advantage of multiple geologic barriers as safety features and aims for the safe containment of radionuclides by containment-providing rock zones (CPRZ). The great depth efficiently prolongs or hinders radionuclide transport and also impedes proliferation. Finally, there may be a time benefit with regard to technical implementation and costs. Due to the phase-out from nuclear energy in Germany the number of boreholes could be less than 100. A simplified, generic safety concept, and the requirements for the diameter of boreholes and containers are derived in this paper. Furthermore, the operational safety of emplacement, the retrieval of waste and sealing of the boreholes is discussed. It is outlined that boreholes can be sealed quickly and over long distances with proven technologies, for example, using the creep properties of salt rock formations. This concept is assessed for its compliance with the safety requirements of the German Federal Ministry for the Environment, Nature Conservation, Building and Nuclear Safety (BMUB), and the requirements and criteria for site selection defined by the German commission on “Storage of high-level radioactive waste”. The retrievability of HLRW is assessed to be technically feasible based on today´s knowledge, but recoverability after closure cannot be guaranteed for long time spans. Further developments in details of the concept of deep borehole disposal (DBD), a demonstration of its technical feasibility and an assessment of operational and long-term safety are still necessary to make DBD an approved option.

Experiments on thermo-hydro-mechanical behaviour of Opalinus Clay at Mont Terri rock laboratory, Switzerland

Repositories for deep geological disposal of radioactive waste rely on multi-barrier systems to isolate waste from the biosphere. A multi-barrier system typically comprises the natural geological barrier provided by the repository host rock – in our case the Opalinus Clay – and an engineered barrier system (EBS). The Swiss repository concept for spent fuel and vitrified high-level waste (HLW) consists of waste canisters, which are emplaced horizontally in the middle of an emplacement gallery and are separated from the gallery wall by granular backfill material (GBM). We describe here a selection of five in-situ experiments where characteristic hydro-mechanical (HM) and thermo-hydro-mechanical (THM) processes have been observed. The first example is a coupled HM and mine-by test where the evolution of the excavation damaged zone (EDZ) was monitored around a gallery in the Opalinus Clay (ED-B experiment). Measurements of pore-water pressures and convergences due to stress redistribution during excavation highlighted the HM behaviour. The same measurements were subsequently carried out in a heater test (HE-D) where we were able to characterise the Opalinus Clay in terms of its THM behaviour. These yielded detailed data to better understand the THM behaviours of the granular backfill and the natural host rock. For a presentation of the Swiss concept for HLW storage, we designed three demonstration experiments that were subsequently implemented in the Mont Terri rock laboratory: (1) the engineered barrier (EB) experiment, (2) the in-situ heater test on key-THM processes and parameters (HE-E) experiment, and (3) the full-scale emplacement (FE) experiment. The first demonstration experiment has been dismantled, but the last two ones are on-going.

Measurement of Biot's coefficient for COx argillite using gas pressure technique

A complete poromechanical study has been carried out on COx argillite which is currently foreseen by Andra (in France) for the storage of high-level and long-life nuclear waste. The main goal of this study was to measure Biot's coefficient for samples cured at different relative humidity. To overcome the difficulties which occur with water as the fluid to control the pore pressure of argillite, a new technique has been used with gas injection (argon) was intended to measure the coefficient in this contribution. The results unambiguously showed that Biot's tensor components were isotropic, and equal to 1 for partially saturated samples. They revealed to be independent on the level of confining pressure or pore pressure. Unexpected results were however obtained for the dry materials for which the components, larger than 1, were measured, depending on the level of pore pressure. It was therefore suspected that an additional swelling phenomenon occurred with argon due to its adsorption in the micropores of argillite. Complementary experiments were thus carried out with helium leading to the coefficients virtually equal to 1 for the dry material, as helium does not adsorb at ambient temperature. Hence, it evidenced that there was a swelling deformation due to argon adsorption leading to apparent Biot's coefficients greater than 1.