Design Options for HLW Repository Operation Technology: Part V—Preliminary Study and Small Scale Experiments on the Method of Removal of Buffer Material With Salt Solution

2010 ◽  
Author(s):  
Satohito Toguri ◽  
Takashi Ishii ◽  
Jiho Jang ◽  
Mitsunobu Okihara ◽  
Kengo Iwasa ◽  
...  
Keyword(s):  
Radioactive Waste ◽  
Salt Solution ◽  
Scale Model ◽  
Disposal Site ◽  
Small Scale ◽  
High Level Radioactive Waste ◽  
Buffer Material ◽  
Basic Characteristics ◽  
High Level ◽  
Design Options

The Nuclear Safety Commission of Japan stipulates that “When closing a waste disposal site, the validity of safety assessment results should be verified using the data obtained in the construction and operation phases as well. The retrieval of high-level radioactive waste should be made continuously possible during the period before the verification of the validity.”[1] Retrieving high-level radioactive waste requires the removal of the bentonite-based buffer around the emplaced overpack. In this study, focus was placed on a method for reducing the cohesion of bentonite, a major component of the buffer by dipping the buffer in fluid salt solution and dissolving the material into a slurry using fluid salt solution for removal (method of making a slurry). In order to examine the feasibility and the basic characteristics of the method, element tests were conducted using a small specimen of buffer and fluid salt solution (NaCl solution). In order to verify the feasibility of the infiltration and jetting of fluid salt solution, small-scale model tests were conducted using a specimen composed of 1/14-scale overpack and buffer. It was made clear that the infiltration and jetting of fluid salt solution was feasible as a method for removing a buffer.

scholarly journals Thermal Conductivity of Compacted GO-GMZ Bentonite Used as Buffer Material for a High-Level Radioactive Waste Repository

2018 ◽  
Vol 2018 ◽  
pp. 1-11 ◽  
Author(s):  
Yong-Gui Chen ◽  
Xue-Min Liu ◽  
Xiang Mu ◽  
Wei-Min Ye ◽  
Yu-Jun Cui ◽  
...  
Keyword(s):  
Thermal Conductivity ◽  
Radioactive Waste ◽  
Water Content ◽  
Radioactive Waste Disposal ◽  
Dry Density ◽  
Gmz Bentonite ◽  
High Level Radioactive Waste ◽  
Buffer Material ◽  
High Level ◽  
Crucial Parameter

In China, Gaomiaozi (GMZ) bentonite serves as a feasible buffer material in the high-level radioactive waste (HLW) repository, while its thermal conductivity is seen as a crucial parameter for the safety running of the HLW disposal. Due to the tremendous amount of heat released by such waste, the thermal conductivity of the buffer material is a crucial parameter for the safety running of the high-level radioactive waste disposal. For the purpose of improving its thermal conductivity, this research used the graphene oxide (GO) to modify the pure bentonite and then the nanocarbon-based bentonite (GO-GMZ) was obtained chemically. The thermal conductivity of this modified soil has been measured and investigated under various conditions in this study: the GO content, dry density, and water content. Researches confirm that the thermal conductivity of the modified bentonite is codetermined by the three conditions mentioned above, namely, the value of GO content, dry density, and water content. Besides, the study proposes an improved geometric mean model based on the special condition to predict the thermal conductivity of the compacted specimen; moreover, the calculated values are also compared with the experimental data.

scholarly journals Microscopic and spectroscopic investigations of uranium(VI) reduction by <i>Desulfosporosinus hippei</i> DSM 8344

2021 ◽  
Vol 1 ◽  
pp. 155-156
Author(s):  
Stephan Hilpmann ◽  
Robin Steudtner ◽  
Björn Drobot ◽  
René Hübner ◽  
Frank Bok ◽  
...  
Keyword(s):  
Radioactive Waste ◽  
Reduction Process ◽  
Opalinus Clay ◽  
Disposal Site ◽  
Luminescence Spectroscopy ◽  
Worst Case ◽  
High Level Radioactive Waste ◽  
Sulfate Reducing ◽  
High Level

Abstract. Clay formations are potential host rocks for the long-term storage of high-level radioactive waste in a deep geological repository. Bentonites are supposed to serve as backfill material, not only for a final disposal site in clay formations but also in crystalline rock. For a long-term safety assessment, various aspects must be taken into account. Besides geological, geochemical and geophysical considerations, naturally occurring microorganisms also play a crucial part in the environment of such a repository. In the event of a worst-case scenario when water enters the disposal site, they can interact with the radionuclides and change for example the chemical speciation or the oxidation state (Lloyd et al., 2002). Desulfosporosinus spp. are an important representative of anaerobic, sulfate-reducing microorganisms, which are present in clay formations as well as in bentonites. Various studies have shown that they play a major role in the microbial communities of these surroundings (Bagnoud et al., 2016; Matschiavelli et al., 2019). A closely related microorganism to the isolated species is Desulfosporosinus hippei DSM 8344, which was originally found in permafrost soil (Vatsurina et al., 2008). This bacterium was used to investigate its interactions with uranium(VI) especially regarding the reduction to the less mobile uranium(IV). Time-dependent reduction experiments in artificial Opalinus Clay pore water (Wersin et al., 2011) (100 µM uranium(VI), pH 5.5) showed the removal of about 80 % of the uranium(VI) from the supernatants within 48 h. Corresponding UV/Vis measurements of the dissolved cell pellets exhibited an increasing proportion of uranium(IV) in the cell-bound uranium. Calculations with the inclusion of extinction coefficients led to a ratio of 39 % uranium(IV) after 1 week. Therefore, a combined sorption-reduction process is a possible interaction mechanism. Time-resolved laser-induced luminescence spectroscopy verified the presence of two uranium(VI) species in the supernatant. A comparison with reference spectra led to an assignment to a uranyl(VI) lactate and a uranyl(VI) carbonate complex. The species distribution showed a decrease of the proportion of the lactate species with time, whereas the proportion of the carbonate species remained almost constant. Uranium aggregates are formed on the cell surface during the process, as determined by transmission electron microscopy (TEM). Furthermore, uranium occurs inside and outside the cells as well as vesicles containing uranium. These findings help to close existing gaps in a comprehensive safeguard concept for a repository for high-level radioactive waste in clay rock. Moreover, this study provides new insights into the interactions of sulfate-reducing microorganisms with uranium(VI).

scholarly journals Scale-model test for disposal pit of high-level radioactive waste and theoretical evaluation of self-sealing of bentonite-based buffers

2020 ◽  
Vol 57 (4) ◽  
pp. 608-615
Author(s):  
Hideo Komine
Keyword(s):  
Radioactive Waste ◽  
Model Test ◽  
Experimental Work ◽  
Model Tests ◽  
Interstitial Space ◽  
Scale Model ◽  
Theoretical Evaluation ◽  
High Level Radioactive Waste ◽  
High Level

Bentonite is attracting greater attention in Japan and some other countries as a buffer for use in repositories of high-level radioactive waste (HLW). Bentonite-based buffers for HLW disposal are expected, because of their swelling deformation, to fill spaces between buffers and walls of disposal pits or between buffers and waste containers designated as overpack. Bentonite has a self-sealing capability. This study conducts scale-model tests simulating the relation between the buffer and interstitial space. It also investigates the validity of theoretical equations for swelling presented by Komine and Ogata (published in 2003 and 2004) to evaluate buffer self-sealing capabilities by comparing calculated and experimentally obtained results of scale-model tests. Results of the experimental work and calculations described herein highlight bentonite’s self-sealing capability and demonstrate the high applicability of these Komine and Ogata equations to quantify filling of interstitial spaces by bentonite-based buffer swelling.

The role of microorganisms in the bentonite barrier of high-level radioactive waste repositories

2020 ◽  
Author(s):  
Nicole Matschiavelli ◽  
Magdalena Dressler ◽  
Tom Neubert ◽  
Sindy Kluge ◽  
Ariette Schierz ◽  
...  
Keyword(s):  
Radioactive Waste ◽  
Thermophilic Bacteria ◽  
Disposal Site ◽  
Dissolution Behavior ◽  
Strictly Anaerobic ◽  
Dependent Manner ◽  
Metabolic Potential ◽  
High Level Radioactive Waste ◽  
Geochemical Parameters ◽  
High Level

&lt;p&gt;The global production of 12,000 metric tonnes of high-level radioactive waste (HLW) every year is a big challenge with respect to its safe long-term storage. In the favored multi-barrier system, bentonite is discussed as a geo-technical barrier in many disposal programs worldwide. The bentonite seals the space between the canister containing the HLW and the surrounding host rock, thereby fulfilling two major tasks: 1) slow down the process of corrosion when water enters the disposal site, and 2) hinder the discharge of radionuclides into the bio-geosphere in case of a leaking canister. Due to their metabolic activity, microorganisms could significantly influence the properties of the bentonite barrier. In order to investigate the metabolic potential of naturally occurring microorganisms, we conducted anaerobic bentonite-slurry experiments containing uncompacted bentonite and a synthetic Opalinus Clay pore water solution. Within one-year incubation at 30 and 60&amp;#160;&amp;#176;C, lactate- or H&lt;sub&gt;2&lt;/sub&gt;-stimulated microcosms at 30 &amp;#176;C showed the dominance and activity of strictly anaerobic, sulfate-reducing and spore-forming microorganisms. Consequently, hydrogen sulfide gas was generated in the respective set ups, leading to the formation of fractures and iron-sulfur precipitations. Experiments that incubated at 60 &amp;#176;C, showed the dominance of thermophilic bacteria, independent of the presence of substrates. The respective set-ups showed/revealed no significant changes in the analyzed bio-geochemical parameters. The obtained results clearly show that indigenous microorganisms evolve in a temperature- and substrate-dependent manner. The formed metabolites can potentially affect the dissolution behavior of minerals and ions within the bentonite as well as corrosion processes and require further investigations.&lt;/p&gt;

scholarly journals Geochemical and microtextural properties of veins in a potential high-level radioactive waste disposal site

2021 ◽  
pp. 104490
Author(s):  
Ervin Hrabovszki ◽  
Emese Tóth ◽  
Tivadar M. Tóth ◽  
István Garaguly ◽  
István Futó ◽  
...  
Keyword(s):  
Radioactive Waste ◽  
Waste Disposal ◽  
Radioactive Waste Disposal ◽  
Disposal Site ◽  
Waste Disposal Site ◽  
High Level Radioactive Waste ◽  
High Level

scholarly journals On the temperature in a final disposal site for high-level radioactive waste

2021 ◽  
Vol 1 ◽  
pp. 99-100
Author(s):  
Ute Maurer-Rurack ◽  
Guido Bracke ◽  
Eva Hartwig-Thurat ◽  
Artur Meleshyn ◽  
Torben Weyand
Keyword(s):  
Radioactive Waste ◽  
Outer Surface ◽  
Site Selection ◽  
Temperature Limit ◽  
Disposal Site ◽  
Final Disposal ◽  
High Level Radioactive Waste ◽  
High Level ◽  
Host Rocks ◽  
Respective Host

Abstract. The Site Selection Act stipulates a precautionary temperature limit of 100 ∘C on the outer surface of the containers with high-level radioactive waste (HLRW) in the final disposal site. This precautionary temperature limit should be applied in preliminary safety analyses provided that the maximum physically possible temperatures in the respective host rocks have not yet been determined due to pending research. Increasing temperatures in the deep geological underground, caused by the heat generation of the HLRW, can trigger thermal, hydraulic, mechanical, chemical and biological processes (THMCB) in the respective host rocks of a final disposal site and thus endanger safety. Furthermore, high temperatures may hamper the feasibility to retrieve and recover HLRW from a final disposal site. Such processes are described in detail in databases for features, events and processes (FEP) databases. Single components or barriers of a final disposal facility may require specific design temperatures for the preservation of their features once a concept for long-term safety of a final disposal site is established; however, the interactions of all relevant processes of a concept for a final disposal site must be considered when a specific temperature limit for the outer surface of the containers is derived. This temperature limit may vary for particular safety and final disposal concepts in the host rock: salt, clay and crystalline rock. The conclusion is that temperature limits regarding the outer surface of the containers should be derived specifically for each safety and disposal concept and should be supported by a solid safety analysis. Temperature limits without reference to specific safety concepts or the particular design of the final disposal site likely narrow down the possibilities for optimisation and could adversely affect the site selection process in finding the best suitable site.

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