Considering water as the primary resource necessary for social life, agriculture, industry, and wealth, the importance of groundwater investigation is clear. Apart from many other pollutants, this work focusses on geogenic uranium (U) and radium (Ra), which both stand for natural radionuclides (NORM) that need to be considered frame of groundwater exploration and monitoring programmes due to their specific mobility and chemo-/radiotoxicity. As investigation of U and – to a lesser extent - Ra is done by an increasing number of scientific working groups, the global dataset is improving continuously. In order to give a summarized overview on available and recent literature, scientific papers, reports, and governmental documents have been reviewed for U-238 mass concentrations and Ra-226 and Ra-228 activity concentrations and collected in tables and global maps. Further natural isotopes of U and Ra have been rarely subject of investigation. The collected data were evaluated and interpreted in frame of an associated scientific publication (see citation). From the available data it can be concluded that high geogenic U occur mainly under oxidizing conditions and carbonate rich groundwater, which might be seen as indicator for elevated U concentrations. Certain geological formations, as for example sedimentary, granitic, and volcanic host rocks, promote high U concentrations in groundwater. For geogenic Ra, the search for definite indications proved difficult, since less clear correlation is given for any observed factor. In a global perspective, the most promising evidence for elevated Ra are highly reducing redox conditions, as well as the occurrence of Fe/Mn mineral phases. Furthermore, barite represents a sink for Ra due to its ability to incorporate Ra isotopes. Dissolution of those mineral phases eventually results in co-dissolution of Ra, when Ra is found in host rocks of investigated aquifers, or downstream of such groundwater reservoirs. Furthermore, cation exchange might enhance Ra mobility process, especially in case of sedimentary aquifers with low sorption capacity and/or aquifers with high salinity. Given those chemical requirements for the occurrence of U and Ra, a negative correlation between mother and daughter nuclide can be established. When knowledge on present geological and geochemical constraints is available, elevated U and Ra concentrations might be predictable, as long as anthropogenic influence is excluded.
The report describes the scientific background and motivation to develop an OECD Guidance Document on the determination on dissolution and dispersion stability of nanomaterials in the environment. It presents the process and approach to develop the GD and summarizes its relevance for risk assessment and regulation of nanomaterials. The “OECD Guidance Document No. 318 for the testing of dissolution and dispersion stability of nanomaterials, and the use of the data for further environmental testing and assessment strategies" is available at the webpages of the OECD Test Guideline Programme. Veröffentlicht in Texte | 176/2020.
For an adequate and valid interpretation of data regarding the environmental fate and behavior of nanomaterials it is essential to describe parameters like dissolution (rate), dispersibility and dispersion stability. Aim of the project was the development of a standardized test method to determine dispersibility and dispersion stability of nanomaterials in simulated environmental media as new OECD Test Guideline. For this objective, both conceptual and experimental work was conducted and an international round robin was initiated and executed to validate the proposed test setup regarding reliability and reproducibility. Two comprehensive expert commenting rounds of the OECD Test Guideline program supported the refinement of the draft within this project. The test method developed in this project was submitted to the OECD Test Guideline program by UBA and published by OECD in October 2017 as new “Test Guideline on dispersion stability of nanomaterials in simulated environmental media (OECD No. 318)”. The presented final report summarizes the experimental work performed to develop the OECD Test Guideline. Veröffentlicht in Texte | 108/2017.
Dieser Bericht präsentiert den Hintergrund, Ablauf und die Inhalte zur Entwicklung eines OECD Leitfadens für die Untersuchung von Löslichkeit und Dispersionsstabilität von Nanomaterialien in der Umwelt und die Nutzung der dadurch gewonnenen Daten für weitere Umweltuntersuchungen und Umweltbewertungsstrategien. Die Löslichkeit(srate) und Dispersionsstabilität werden als die wichtigsten Treiber des Umweltverhaltens und â€Ìschicksals von Nanomaterialien in der Umwelt angesehen. Zur Bestimmung der Dispersionsstabilität von Nanomaterialien in der Umwelt liegt bereits die OECD Prüfrichtlinie (TG) 318 vor. Eine OECD Prüfrichtlinie zur Bestimmung der Löslichkeit(srate) von Nanomaterialien in der Umwelt befindet sich derzeit noch in der Entwicklung. Da noch keine solche OECD Prüfrichtlinie zur Bestimmung der Löslichkeit(-rate) für Nanomaterialien zur Verfügung steht, wurden in den Leitfaden solche Methoden aus Wissenschaft und vorliegenden OECD TG/GDs aufgenommen, die für Nanomaterialien als sinnvoll erachtet werden. Zur Unterstützung der Anwendung der OECD TG 318 sind zusätzliche Informationen zur Präsentation und Interpretation von Daten zur Dispersionsstabilität in den Leitfaden eingebracht worden. Darüber hinaus werden im Leitfaden vorläufige Anleitungen gegeben, wie Heteroagglomeration von Nanomaterialien in der Umwelt bestimmt werden kann. Der vorliegende Bericht stellt neben den Inhalten des Leitfadens und den Ablauf seiner Entwicklung auch seine Bedeutung für die Umweltbewertung von Nanomaterialien dar und gibt einen Ausblick, welche regulatorischen Tragweite dieser in der Zukunft haben kann. Der finale Leitfaden wurde im April 2020 von der OECD Arbeitsgruppe der Nationalen Koordinatoren des OECD Prüfrichtlinienprogramms (WNT) verabschiedet und ist nach Veröffentlichung auf den Internetseiten des OECD Prüfrichtlinienprogramms zu finden. Quelle: Forschungsbericht
technologyComment of chromium production (RoW): Metallic chromium is produced by aluminothermic process (75%) and electroylsis of dissolved ferrochromium (25%) technologyComment of chromium production (RER): Metallic chromium is produced by aluminothermic process (75%) and electroylsis of dissolved ferrochromium (25%) ALUMINOTHERMIC PROCESS The thermic process uses aluminium as a reducing agent for chromium hydroxide. The charge is weighed and loaded into a bin, which is taken to an enclosed room to mix the contents. The firing pot is prepared by ramming refractory sand mixed with water around a central former. After ramming the firing pot, the inner surface is coated with a weak binder solution and dried under a gas fired hood before being transferred to the firing station. The raw material mix is automatically fed at a controlled rate into the firing pot, where the exothermic reaction takes place. When the metal has solidified following the reaction, the firing pot is removed and transferred by crane to a cooling conveyor. On removal from the cooling conveyor (by crane), the firing pot is placed on a stripping bogie for transferral to a stripping booth. Inside the closed booth, the pot casing is hoisted off the solidified metal/slag. The slag is separated from the Chromium metal “button” and sent to a despatch storage area. Water is used to reduce button temperature to below 100 ºC. After cooling the metal button is transferred to other departments on site for cleaning, breaking, crushing and grinding to achieve the desired product size. ELECTROLYTIC PROCESS In the electrolytic process normally high carbon ferrochrome is used as the feed material which is then converted into chromium alum by dissolution with sulphuric acid at temperatures at about 200 ºC. After several process steps using crystallisation filtration ageing, a second filtration and a clarifying operation the alum becomes the electrolyte for a diaphragm cell. Chromium is plated onto stainless steel cathodes until it attains a thickness of ca. 3 mm. The process is very sensitive. The additional de-gassing (heating at 420 °C) stage is necessary because the carbon content of the electrolytic chromium is sometimes too high for further industrial applications. The cooled chromium metal is fragmented with a breaker prior to crushing and drumming. The generated slag can be reused as refractory lining or sold as abrasive or refractory material. Overall emissions and waste: Emissions to air consist of dust and fume emissions from smelting, hard metal and carbide production; other emissions to air are ammonia (NH3), acid fume (HCl), hydrogen fluoride (HF), VOC’s and heavy metals. Emissions to water are overflow water from wet scrubbing systems, wastewater from slag and metal granulation, and blow down from cooling water cycles. Solid waste is composed of dust, fume and sludge, and slag. References: IPPC (2001) Integrated Pollution Prevention and Control (IPPC); Reference Document on Best Available Techniques in the Non Ferrous Metals Industries. European Commission. Retrieved from http://www.jrc.es/pub/english.cgi/ 0/733169
technologyComment of rare earth oxides production, from rare earth oxide concentrate, 70% REO (CN-SC): This dataset refers to the separation (hydrochloric acid leaching) and refining (metallothermic reduction) process used in order to produce high-purity rare earth oxides (REO) from REO concentrate, 70% beneficiated. ''The concentrate is calcined at temperatures up to 600ºC to oxidize carbonaceous material. Then HCl leaching, alkaline treatment, and second HCl leaching is performed to produce a relatively pure rare earth chloride (95% REO). Hydrochloric acid leaching in Sichuan is capable of separating and recovering the majority of cerium oxide (CeO) in a short process. For this dataset, the entire quantity of Ce (50% cerium dioxide [CeO2]/REO) is assumed to be produced here as CeO2 with a grade of 98% REO. Foreground carbon dioxide CO2 emissions were calculated from chemical reactions of calcining beneficiated ores. Then metallothermic reduction produces the purest rare earth metals (99.99%) and is most common for heavy rare earths. The metals volatilize, are collected, and then condensed at temperatures of 300 to 400°C (Chinese Ministryof Environmental Protection 2009).'' Source: Lee, J. C. K., & Wen, Z. (2017). Rare Earths from Mines to Metals: Comparing Environmental Impacts from China's Main Production Pathways. Journal of Industrial Ecology, 21(5), 1277-1290. doi:10.1111/jiec.12491 technologyComment of sodium chloride production, powder (RER, RoW): For the production of dry salt, three different types of sodium chloride production methods can be distinguished namely, underground mining of halite deposits, solution mining with mechanical evaporation and solar evaporation. Their respective products are rock salt, evaporated salt and solar salt: - Underground mining: The main characteristic of this technique is the fact that salt is not dissolved during the whole process. Instead underground halite deposits are mined with traditional techniques like undercutting, drilling and blasting or with huge mining machines with cutting heads. In a second step, the salt is crushed and screened to the desired size and then hoisted to the surface. - Solution mining and mechanical evaporation: In this case, water is injected in a salt deposit, usually in about 150 to 500 m depth. The dissolution of the halite or salt deposits forms a cavern filled with brine. This brine is then pumped from the cavern back to the surface and transported to either an evaporation plant for the production of evaporated salt or transported directly to a chemical processing plant, e.g. a chlor-alkali plant. - Solar evaporation: In this case salt is produced with the aid of the sun and wind out of seawater or natural brine in lakes. Within a chain of ponds, water is evaporated by sun until salt crystallizes on the floor of the ponds. Due to their natural process drivers, such plants must be located in areas with only small amounts of rain and high evaporation rates - e.g. in the Mediterranean area where the rate between evaporation and rainfall is 3:1, or in Australia, where even a ratio up to 15:1 can be found. There are some impurities due to the fact that seawater contains not only sodium chloride. That leads to impurities of calcium and magnesium sulfate as well as magnesium chloride. With the aid of clean brine from dissolved fine salt, these impurities are washed out. As a fourth form on the market, the so-called 'salt in brine' may be found, which is especially used for the production of different chemicals. In this case, the solution mining technique without an evaporation step afterwards is used. This dataset represents the production of dry sodium chloride by underground mining (51%) and by solution mining (49%) with modern solution mining technology (thermo compressing technology). References: Althaus H.-J., Chudacoff M., Hischier R., Jungbluth N., Osses M. and Primas A. (2007) Life Cycle Inventories of Chemicals. ecoinvent report No. 8, v2.0. EMPA Dübendorf, Swiss Centre for Life Cycle Inventories, Dübendorf, CH.
History of the Asse II mine The Asse II mine is one of three facilities constructed on the Asse mountain range in around 1900 for the purpose of salt extraction, which was discontinued in 1964. The mine was subsequently bought by the federal government in 1965 and, from 1967 to 1978, was used for the emplacement of around 47,000 cubic metres of low- and intermediate-level radioactive waste. Research work was carried out until 1995. Following the completion of this work, preparations were made for the mine’s decommissioning. This was to be carried out in accordance with mining law and without proof of long-term safety. In 2009, the facility was brought under the purview of nuclear law in response to demands from society and politics. Since 2013, there has been a legal mandate for the retrieval of the emplaced radioactive waste. According to current knowledge, this is the only way to ensure long-term safety. Salt extraction in the Asse II mine Potash salt was mined in the northern flank of the Asse II mine from 1909 to 1925, when the extraction work was discontinued for financial reasons. The chambers were backfilled during extraction with material arising as part of potash production. The mining of rock salt began in 1916 and continued until 1964. Here, too, mining was discontinued for financial reasons. A total of 131 mining chambers were created in the southern flank and remained open for several decades. The numerous cavities are exposed to geostatic pressure and are now leading to stability problems. Emplacement, research and planned decommissioning under mining law In 1965, the Federal Ministry of Research commissioned the Association for Radiation Reasearch (now known as Helmholtz Zentrum München) to carry out research into the final disposal of radioactive waste in the Asse II mine . The first waste was delivered in 1967. Emplacement was carried out based on the provisions of the Federal Mining Act and the Radiation Protection Ordinance. Around 47,000 cubic metres of low- and intermediate-level radioactive waste were emplaced by the time emplacement finished in 1978. Although the facility was officially operated as a research mine, these emplacement operations effectively constituted the final disposal of almost all low- and intermediate-level radioactive waste from the Federal Republic of Germany from 1971 onwards. In 1987, the “area below the 800 m level” was created beneath the former extraction mine. This area was used to research whether salt was suitable for the storage of heat-generating radioactive waste. The research work ended in 1995. Since 1988, water has been entering the mine in the form of groundwater from the surrounding rock. This water is saturated with rock salt and does not lead to the dissolution of salt in the mine. From 1995 to 2004, the cavities that were still open in the southern flank were backfilled using salt material with a view to stabilising the mine. However, the chosen method did not achieve this aim satisfactorily. In 1997, the former operator presented a framework operating plan for the decommissioning of the Asse II mine. The radioactive waste was to remain in the mine, and no long-term safety demonstration would be carried out. Likewise, no such demonstration was envisaged in the final operating plan presented in 2007. Planned retrieval of radioactive waste In 2008, the Federal Ministry of Research and the environment ministries of the federal government and the State of Lower Saxony decided to treat the Asse II mine as a repository. The mine came under the purview of nuclear law in 2009. As well as stricter requirements for operation, decommissioning and radiation protection, the legislation also requires public participation with regard to the facility’s decommissioning. When the Asse mine came under the purview of nuclear law, the Federal Office for Radiation Protection (BfS) became its operator and was tasked with decommissioning the facility without delay. In 2010, a comparison of multiple decommissioning options showed that the stipulated long-term safety could only be demonstrated by retrieving the radioactive waste from the Asse II mine. In 2013, the Bundestag (the lower house of Parliament in Germany) passed the “Lex Asse” legislation – the “Law on Speeding up the Retrieval of Radioactive Waste and the Decommissioning of the Asse II Mine” – with the backing of a broad political majority. Retrieval was thereby enshrined in the Atomic Energy Act. In 2017, within the framework of the restructuring of final disposal activities, the BGE assumed operating responsibility from the BfS. There were no changes to the legal mandate for the retrieval of radioactive waste from the Asse II mine. In April 2020, the BGE presented its retrieval plan, in which it described how it intended to retrieve the radioactive waste. For further information on the retrieval plan, please refer to the main topic on retrieval (German only) .
For an adequate and valid interpretation of data regarding the environmental fate and behavior of nanomaterials it is essential to describe parameters like dissolution (rate), dispersibility and dispersion stability. Aim of the project was the development of a standardized test method to determine dispersibility and dispersion stability of nanomaterials in simulated environmental media as new OECD Test Guideline. For this objective, both conceptual and experimental work was conducted and an international round robin was initiated and executed to validate the proposed test setup regarding reliability and reproducibility. Two comprehensive expert commenting rounds of the OECD Test Guideline program supported the refinement of the draft within this project. The test method developed in this project was submitted to the OECD Test Guideline program by UBA and published by OECD in October 2017 as new “Test Guideline on dispersion stability of nanomaterials in simulated environmental media (OECD No. 318)”. The presented final report summarizes the experimental work performed to develop the OECD Test Guideline.
What is the objective of the planned decommissioning of the Morsleben repository? It is imperative that the emplaced low- and intermediate-level radioactive waste remains separate from the biosphere – that is, the habitat of plants, animals and humans. As radioactive materials must be prevented from entering the environment, sealing structures are to be built and the shafts are to be sealed. To a large extent, the repository mine will also be backfilled with salt concrete. (See Decommissioning of the Morsleben repository .) Why is costly backfilling of the mine necessary if there are sealing structures? Backfilling the mine will serve to stabilise the rock in the vicinity of the repository. This is important because the surrounding rock prevents the ingress of solutions, acting like a raincoat and performing an important protective function. The mine is currently stable, as shown by extensive geomechanical monitoring. In some areas, however, it must be assumed that the protective function of the salt rock will not remain intact on a permanent basis if no action is taken. The reason for this is that the salt moves a few millimetres a year under the pressure exerted by the rock. Although this movement – known as convergence – is slight, it is detectable. In the long term, convergence results in local excavation-disturbed zones in the rock that harm the stability and impermeability of the salt barrier, and pathways can form that allow the transport of radioactive materials. The decommissioned repository should provide long-term safety and be maintenance-free Backfilled mine workings support the rock, and backfilling prevents the formation of further excavation-disturbed zones. Existing excavation-disturbed zones are healed by creeping movements of salt rock deposits. In the long term, a fully intact barrier forms again and encloses the emplaced waste. It is not only the large mining chambers that are backfilled. Galleries and connections between the individual levels of the repository are also designated as underground excavations. A high degree of backfilling limits dissolution processes Another advantage of backfilling is that it limits dissolution processes within the decommissioned mine workings. Although calculations in the decommissioning plans show that it is unlikely that large quantities of solution or even groundwater will enter the decommissioned Morsleben repository, the possibility has not been ruled out. These solutions could dissolve salt rock that they come into contact with. The more sections of the repository are backfilled, the less this process takes place – and the less the geometry of the mine workings changes. The likelihood of further influxes of solution decreases, and the rock remains stable in the long term. Moreover, damage at ground level due to subsidence, for example, is avoided. What is to be backfilled? The plan is to use salt concrete as the construction material for backfilling. Salt concrete is made up of cement as a binder; concrete additives such as mineral filler; other aggregates such as fine-grained salt rock and quartz sand; and mixing liquid – i.e. water and saline solution. The BGE has already backfilled 27 rock-salt mining chambers with around 935,000 cubic metres of salt concrete, thereby stabilising them, as part of the prevention of mining hazards in the central part . This process provided considerable experience in dealing with the construction material, and this experience is also to be applied to decommissioning. During decommissioning operations, the salt concrete will be prepared off-site as a pumpable mixture. On the premises of the Bartensleben shaft, the concrete will be transferred to a salt conveyor system that transports it underground through pipelines that pass through the shaft. Once underground, the salt concrete will be pumped into the respective mine workings via backfilling boreholes. In the process, the liquid concrete will have to cover a distance of several kilometres. A total of three piping systems will be provided for this purpose. Current plans involve the pumping of some 4 million cubic metres of salt concrete. In addition to salt concrete as a construction material, the process will also use magnesia cement for the seals as well as smaller quantities of other construction materials. How is backfilling to be carried out? All of the planned backfilling measures aim to ensure the long-term safety of the Morsleben repository as effectively as possible. Taking account of possible changes in geology and stability, the individual measures must fulfil a number of different purposes. During decommissioning planning, these purposes were used to determine not only the material to be used but also the different degrees of backfilling. The degree of backfilling varies depending on the nature of the cavity and on the intended purpose of backfilling. The material stabilises and/or reduces the size of the cavity. Each of the underground excavations is assigned to a backfilling category. The exceptions are the Marie and Bartensleben shafts, which constitute their own decommissioning measure in combination with the shaft closures and are completely backfilled with multiple coordinated materials – primarily gravel, bitumen and bentonite. What backfilling categories are there? Backfilling category I This includes mine workings in which sealing structures are built. Over 30 seals will be constructed in galleries and connections between the levels of the Bartensleben and Marie mines. Backfilling category II This category encompasses all open areas of the repository mine that are to undergo geomechanical stabilisation. Category II areas will be backfilled as completely as possible in order to achieve the necessary supporting effect. This work is intended to preserve the rock’s integrity or to further improve it in the long term, and corresponds to the backfilling that was already carried out as part of the prevention of mining hazards in the central part. Backfilling category III This includes all mine workings that are not assigned to another category. The degree of backfilling for each rock salt excavation in this category is determined on an individual basis, taking account of optimisation aspects. On average, the galleries and connections between the levels belonging to backfilling category III will be backfilled to a degree of 65% of the relevant pit area. Backfilling category IV This category encompasses all potash deposits of the Bartensleben and Marie pits, including the associated galleries and connections to adjacent levels. Potash salt is slightly soluble, and the backfilling measures are intended to limit the dissolution of potash salt deposits and the precipitation of minerals from the resulting solution (reprecipitation) in the event of an influx of solution. In order to limit the volume available for solutions, all potash deposits are therefore to be backfilled as completely as possible. However, the spatial conditions will mean that this is not possible in all locations – and this fact is accounted for in the safety assessments. Backfilling process The sequence of operations for backfilling the mine workings is precisely specified from both logistical and mining perspectives. In principle, backfilling will be carried out from the bottom to the top and from the outer areas of the repository mine inwards, progressing towards the Bartensleben shaft. Work will not begin on a new level until the backfilling measures for the underlying level are completed. The backfilling of the Marie mine will begin at the same time as work on the Bartensleben mine. Here, too, backfilling will be carried out from the bottom to the top and from the outside inwards, progressing towards the Marie shaft. According to current plans, it will take around 15 years to complete the backfilling of the mine workings. Main topic: stability Decommissioning of the Morsleben repository Short information about the Morsleben repository
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