Deep Geological Repositories For Nuclear Waste Research Articles

Migration behavior of Se(IV) and Re(VII) in muscovite for potential application in deep geological nuclear waste repositories

Migration behavior of Se(IV) and Re(VII) in muscovite for potential application in deep geological nuclear waste repositories

Identification of key thermal couplings affecting the bentonite behaviour in a deep geological nuclear waste repository

Deep geological nuclear waste repositories use the multi-layer Engineered Barrier System (EBS) to isolate nuclear waste from the environment. The key component of the barrier is densely compacted bentonite, closely resembling claystone. Therefore, to ensure safety, we need a numerical model for the bentonite and the barrier that predicts EBS behaviour during transient thermal, hydraulic, mechanical and chemical conditions. The paper identifies key mechanisms and processes affecting the bentonite in the barrier due to temperature changes (thermal couplings) based on advanced fully-coupled Finite Element Method simulations. The paper investigates 1) non-isothermal infiltration experiment on FEBEX bentonite (Villar and Gomez-Espina, 2009) and, 2) Centro de Investigaciones Energeticas Medioambientales y Tecnologicas (Ciemat) test (Martin et al., 2006), presenting 10 simulation configurations that are set up by inactivating one thermal coupling/variable at a time. The difference between these simulations and the baseline model results, examined in terms of the net mean stress (swelling pressure), suction and fluid flow, give insights into the significance of investigated coupling. Results suggest that thermal couplings related to vapour density, viscosity, water retention curve, and molecular diffusivity are among the most influential. The study additionally highlights the importance of water transport as liquid and gas, and water evaporation and condensation.

Thermochemical Effect on Swelling Pressure and Microstructure of Monovalent and Divalent Indian Bentonites

Abstract During the long-term operation of deep geological nuclear waste repositories, the swelling properties of compacted bentonites can be affected by canister temperature and electrolyte concen...

An Open-Access Stress Magnitude Database for Germany

Abstract. The stress field in the Earth's crust plays a central role in the site-selection process for a deep geological repository for high-level nuclear waste. Site selection and construction planning must take into account several factors that are influenced by the stress state. These include the excavation damage zone, the hydraulic permeability of the host rock, the self-sealing capacity, the effects of seismic events and the possible reactivation of faults as migration pathways for fluids and radionuclides. Likewise, the initial stress state is of central importance for the long-term studies to prove site safety over 1 Ma. To obtain a continuous description of the current 3D stress state, 3D geomechanical numerical models are used. These models have to be calibrated with data on stress magnitudes to obtain robust predictions. One of the central goals of the SpannEnD project (Spannungsmodell Endlagerung Deutschland, http://www.spannend-projekt.de, last access: 31 October 2021) was to build the first comprehensive and publicly accessible stress magnitude database for Germany, including a quality ranking of the data compiled from different methods. This database is the logical extension of the database of the World Stress Map project, in which so far only information on stress orientations and the stress regime has been compiled systematically. We present this first compilation of stress magnitude data published and made available by Morawietz et al. (2020). The stress data density is generally low and heterogeneous, so that a model calibration at the scale of a site model is not possible. Therefore, the main objective of the SpannEnD project is to develop a 3D geomechanical numerical model for the whole of Germany. The resulting 3D stress field will provide the basis for regional and local models in a later phase of the site selection process. Details on this are presented in three complementary contributions in this symposium by Reiter et al., Röckel et al. and Ahlers et al. The new Geology Data Act (Geologie-Datengesetz) now allows access to considerably more data, which will be incorporated into an update of the database after assessment according to the defined quality criteria. This database extension will improve the reliability of the predictions of the geomechanical models on different spatial scales.

Electrical-sedimentary anisotropy of landforms adjacent to postglacial faults in Lapland

Postglacial faults (PGFs) are common SW-NE-trending features in the northern part of the Fennoscandian shield being attributed to former high-magnitude (Mw ≈ 7–8.2) earthquakes (Arvidsson, 1996). These are of interest for the long-term seismic hazard of deep geological nuclear waste repositories. The PGFs are still seismically active; and many of the deformation features, such as paleolandslides, are spatially coextensive within these earthquake zones. Based on the 14C-datings of landslide-buried organic materials, three postglacial seismic episodes (≈9.7–11, ≈5–6, and 1.3–1.8 ky ago) have been found in western Finnish Lapland. Because the model predictions by Wu et al. (1999) suggested that the onset of fault instability started at 15 ky and that the maximum fault instability was reached at 13–10 ky in Fennoscandia, we postulate that not only subaerial but also subglacial types of deformations may have been associated with the past seismic events. Here, we present LiDAR DEM observations and sediment electromagnetic anisotropy data on the landforms, such as the rim-ridged/arcuate Pulju moraine (Kujansuu, 1967), roundish (liquefaction) bowls, postdepositional (liquefaction) deformations on streamlined landforms, as well as hummocky ridge fields of massflow sediments. The sediments in the Pulju moraine and massflow ridges displayed clear anisotropy, indicating lateral transportation in subglacial wet-based environment. Instead, sediments in the bowl-shaped morphologies next to PGFs and deformed ice-stream flutings tended to be isotropic, suggesting postdepositional and vertical liquefaction processes. Based on the LiDAR morphology and sedimentary anisotropy data, these landforms may be linked to past earthquakes.

Uptake of radioiodide by Paenibacillus sp., Pseudomonas sp., Burkholderia sp. and Rhodococcus sp. isolated from a boreal nutrient-poor bog

Radionuclides, like radioiodine (129I), may escape deep geological nuclear waste repositories and migrate to the surface ecosystems. In surface ecosystems, microorganisms can affect their movement. Iodide uptake of six bacterial strains belonging to the genera Paenibacillus, Pseudomonas, Burkholderia and Rhodococcus isolated from an acidic boreal nutrient-poor bog was tested. The tests were run in four different growth media at three temperatures. All bacterial strains removed iodide from the solution with the highest efficiency shown by one of the Paenibacillus strains with >99% of iodide removed from the solution in one of the used growth media. Pseudomonas, Rhodococcus and one of the two Paenibacillus strains showed highest iodide uptake in 1% yeast extract with maximum values for the distribution coefficient (Kd) ranging from 90 to 270L/kg DW. The Burkholderia strain showed highest uptake in 1% Tryptone (maximum Kd 170L/kg DW). The Paenibacillus strain V0-1-LW showed exceptionally high uptake in 0.5% peptone +0.25% yeast extract broth (maximum Kd>1,000,000L/kg DW). Addition of 0.1% glucose to the 0.5% peptone +0.25% yeast extract broth reduced iodide uptake at 4°C and 20°C and enhanced iodide uptake at 37°C compared to the uptake without glucose. This indicates that the uptake of glucose and iodide may be competing processes in these bacteria. We estimated that in in situ conditions of the bog, the bacterial uptake of iodide accounts for approximately 0.1%–0.3% of the total sorption of iodide in the surface, subsurface peat, gyttja and clay layers.

Environmental and health impacts of February 14, 2014 radiation release from the nation's only deep geologic nuclear waste repository

The environmental impact of the February 14, 2014 radiation release from the nation's only deep geologic nuclear waste repository, the Waste Isolation Pilot Plant (WIPP) was assessed using monitoring data from an independent monitoring program conducted by the Carlsbad Environmental Monitoring & Research Center (CEMRC). After almost 15 years of safe and efficient operations, the WIPP had one of its waste drums rupture underground resulting in the release of moderate levels of radioactivity into the underground air. A small amount of radioactivity also escaped to the surface through the ventilation system and was detected above ground. It was the first unambiguous release from the WIPP repository. The dominant radionuclides released were americium and plutonium, in a ratio that matches the content of the breached drum. The accelerated air monitoring campaign, which began following the accident, indicates that releases were low and localized, and no radiation-related health effects among local workers or the public would be expected. The highest activity detected was 115.2 μBq/m3 for 241Am and 10.2 μBq/m3 for 239+240Pu at a sampling station located 91 m away from the underground air exhaust point and 81.4 μBq/m3 of 241Am and 5.8 μBq/m3 of 239+240Pu at a monitoring station located approximately one kilometer northwest of the WIPP facility.CEMRC's recent monitoring data show that the concentration levels of these radionuclides have returned to normal background levels and in many instances, are not even detectable, demonstrating no long-term environmental impacts of the recent radiation release event at the WIPP. This article presents an evaluation of almost one year of environmental monitoring data that informed the public that the levels of radiation that got out to the environment were very low and did not, and will not harm anyone or have any long-term environmental consequence. In terms of radiological risk at or in the vicinity of the WIPP site, the increased risk from the WIPP releases is exceedingly small, approaching zero.

Radiation release at the nation's only operating deep geological repository--an independent monitoring perspective.

Recent incidents at the nation's only operating deep geologic nuclear waste repository, the Waste Isolation Pilot Plant (WIPP), resulted in the release of americium and plutonium from one or more defense-related transuranic (TRU) waste containers into the environment. WIPP is a U.S. Department of Energy mined geologic repository that has been in operation since March, 1999. Over 85,000 m3 of waste in various vented payload containers have been emplaced in the repository. The primary radionuclides within the disposed waste are 239+240Pu and 241Am, which account for more than 99% of the total TRU radioactivity disposed and scheduled for disposal in the repository. For the first time in its 15 years of operation, there was an airborne radiation release from the WIPP at approximately 11:30 PM Mountain Standard Time (MST) on Friday, February 14, 2014. The radiation release was likely caused by a chemical reaction inside a TRU waste drum that contained nitrate salts and organic sorbent materials. In a recent news release, DOE announced that photos taken of the waste underground showed evidence of heat and gas pressure resulting in a deformed lid, in material expelled through that deformation, and in melted plastic and rubber and polyethylene in the vicinity of that drum. Recent entries into underground Panel 7 have confirmed that at least one waste drum containing a nitrate salt bearing waste stream from Los Alamos National Laboratory was breached underground and was the most likely source of the release. Further investigation is underway to determine if other containers contributed to the release. Air monitoring across the WIPP site intensified following the first reports of radiation detection underground to ascertain whether or not there were releases to the ground surface. Independent analytical results of air filters from sampling stations on and near the WIPP facility have been released by us at the Carlsbad Environmental Monitoring & Research Center and confirmed trace amounts of 241Am and 239+240Pu, at ratios reflecting the suspect waste stream. The highest activity detected offsite was 115.2 μBq/m3 for 241Am and 10.2 μBq/m3 for 239+240 Pu. These concentrations in air were very small, localized, and below any level of public health or environmental concern.

Numerical analysis of canister movements in an engineered barrier system

The mid-term safety of deep geological nuclear waste repositories is based in part on the presence of a buffer, the main role of which is to isolate the environment from radionuclides. A design evaluation of such a repository is necessary to assess the potential vertical canister movement inside the drift that could reduce the buffer efficiency. A thermo-hydro-mechanical (THM) simulation is performed in a vertical cross-section of the drift. The THM couplings are described, and their influences on the mid-term (300 years) response of the engineered barrier system (EBS) are revealed. This study uses an advanced constitutive model to simulate the THM processes that occur in a specific EBS design case. The near-field simulations of the nuclear waste canister are performed in a two-dimensional finite element configuration that considers the effect of gravity. The focus of this study is on the mechanical behaviour of the buffer, which consists of two different forms of bentonite. Such an approach allows realistic consideration of the effect of the wetting and drying of the buffer material in non-isothermal conditions. Due to a specific design that includes bentonite blocks and pellets, the canister is observed to heave slightly during the re-saturation period, which extends up to 100 years.

Engineered materials as potential geocatalysts in deep geological nuclear waste repositories: A case study of the stainless steel catalytic effect on nitrate reduction by hydrogen

The reduction of NO3- in natural waters is commonly promoted by biological activity. In the context of deep geological nuclear waste repositories with potentially high H2 pressure, abiotic redox reactions may be envisaged. Here, the catalytic effect of “inert” metallic surfaces, in part used for nuclear waste canisters, on NO3- reduction under H2 pressure is evaluated. The study is focused on stainless steels by testing the 316L and Hastelloy C276 steels. A parametric kinetic study (0<P(H2)<10bar, 0.1<[NO3-]<10mM, 90<T°<150°C, 4<pHin situ<9) reveals that NO3- reduction, in the presence of stainless steel 316L and Hastelloy C276, proceeds via a pH-independent reaction requiring H2 as an electron donor. No corrosion of these steels is observed indicating a true catalytic process. The reaction is inhibited in the presence of PO43-. Activation energies assuming a first-order reaction in the 90–150°C temperature range are found to be 46kJ/mol for stainless steel 316L and 186kJ/mol for Hastelloy C276, making the reaction efficient at lower temperature and on a human time scale.Nitrate sorption at the metallic surface being thought to be the limiting step, sorption and competitive sorption isotherms of several oxyanions were performed at 90°C on 316L. Nitrate and PO43- are more strongly sorbed than SO42-, likely as inner sphere complexes, and in a large pH range, from acidic to pH 9. The Langmuir–Hinshelwood formalism best fits the kinetic data. The nature of the surface complex, and the competition for sorption between NO3- and PO43- account for the macroscopic features of NO3- reduction by H2 observed at the steel surface. It should be stressed that some engineered materials such as stainless steels should be considered both as geological material and as geocatalysts as they could remain in the environment over an extremely long period of time.

Natural organic matter (NOM)-clay association and impact on Callovo-Oxfordian clay stability in high alkaline solution: Spectromicroscopic evidence

The understanding of chemical association between natural organic matter (NUM) and clay minerals is of paramount importance to predict the long term stability of host rock formations for deep geological nuclear waste repositories. Synchrotron-based soft X-ray spectromicroscopy demonstrates a strong association between K-rich clay phases (illite) and NOM in the Callovo-Oxfordian argillite (Meuse-Haute Marne, or MHM site, France) and a weaker association in the Opalinus clay (Benken, Switzerland). C(ls) spectra show no significant depth dependent variation in the MHM site 1447-516m). Alteration experiments under oxidizing conditions and high pH of the Callovo-Oxfordian clay indicate a passivation of chemically reactive sites by NOM that is responsible for the kinetic hindered clay dissolution/ transformation. These experiments lead to a significant release of humic/fulvic acid colloids in the alkaline solution with time dependent variation in size and functional group content.