High Sorption and Selective Extraction of Actinides from Aqueous Solutions

The selective elimination of long-lived radioactive actinides from complicated solutions is crucial for pollution management of the environment. Knowledge about the species, structures and interaction mechanism of actinides at solid–water interfaces is helpful to understand and to evaluate physicochemical behavior in the natural environment. In this review, we summarize recent works about the sorption and interaction mechanism of actinides (using U, Np, Pu, Cm and Am as representative actinides) on natural clay minerals and man-made nanomaterials. The species and microstructures of actinides on solid particles were investigated by advanced spectroscopy techniques and computational theoretical calculations. The reduction and solidification of actinides on solid particles is the most effective way to immobilize actinides in the natural environment. The contents of this review may be helpful in evaluating the migration of actinides in near-field nuclear waste repositories and the mobilization properties of radionuclides in the environment.

Long-term storage of information about nuclear waste. 100 000 years and beyond

In the 20th century, intertwined with the topic of “final nuclear repository”, the ethical requirement to warn about the danger of radioactive radiation over a period of 1 million years was debated. In the meantime, a narrative is beginning to gain acceptance – also in public – that postulates that a repository should be described in terms of content and location in such a way that future generations are capable of making their own informed decisions. After all, nuclear waste consists of materials ranging from dangerous to precious. From the concept of sustainability and responsible usage of resources comes the demand to not isolate, bury and forget nuclear waste in the biosphere forever, but rather to leave the information about it in such a way that even if the transmission of information is interrupted, it can be reconstructed by a technically industrialized civilization. The materials that we store in the depths, especially in places where one would not expect them geologically, could represent valuable resources for future generations. The following questions arise: What time horizons are we talking about? In what form can information exist for so long? What language or symbols do we use for this? Who are the addressees? Conventional information carriers are unsuitable for these purposes. Even the most durable, even with optimal storage, have a shelf life that is orders of magnitude below the temporal safety requirements of nuclear waste repositories. In this lecture, the latest technologies and methods for long-term storage of information are introduced. Ceramic-based data carriers. Ceramic-based data carriers with a durability extending to millions of years even under the most extreme conditions. Originating from the Memory of Mankind project in Hallstatt, Austria, a research program is being carried out at the Vienna University of Technology for data carriers which, in addition to an extremely long durability, also have a high data density. Data formats. There is no guarantee that the digital formats used today will be readable in the near or distant future. Information that is intended for addressees in thousands of years must therefore be recognized as such and be directly legible. Data formats must be intuitively decodable and readable. And finally, universal icons are needed for a “manual”, in order to describe the location and contents of a nuclear waste repository to a distant technical civilization.

Comparing two concepts of the OECD-NEA RK&M Initiative (2011–2019): The Set of Essential Records and the Key Information File

In the last decade, the Nuclear Energy Agency (NEA) of the OECD​​​​​​​ co-ordinated an international initiative to develop understanding and guidelines related to the longer-term preservation of records, knowledge and memory (RK&M) regarding radioactive waste repositories, the so-called “RK&M Initiative”. Their final report (NEA, 2019) can be read as a general guide to the RK&M preservation topic. In terms of practical support, the group prepared an RK&M preservation toolbox, comprising 35 different preservation mechanisms. Amongst those are classical, much discussed tools such as “archives”, “surface markers” or “land use control”, hitherto less discussed tools such as “international regulations”, “small time capsules” or “clear and planned responsibilities”, and two entirely new concepts: the Set of Essential Records (SER) and the Key Information File (KIF). In the current contribution, I present these two concepts, pointing out their role both in the wider RK&M preservation context (i.e. in the toolbox as a whole) and in the narrower “documents” context. My main focus is a comparative approach, addressing the peculiarities of the KIF and the SER concepts by working out the differences between the two. It becomes apparent that the KIF is far from being a condensation of the SER, but in fact KIF and SER are independent concepts: in terms of their authors/creators, their target audiences, and first and foremost their functioning, i.e. “how” they contribute to RK&M preservation.

Swelling Characteristics of Compacted Claystone-Bentonite Mixtures

High-density claystone mixtures have been suggested as liners in radioactive waste repositories. However, this material can also be used as a liner in landfills. This study focuses on swelling characteristics of compacted claystone-bentonite at a low density for landfill applications. Claystone was taken from the Banjarbakula landfill project in Banjarbaru. The bentonite used is a commercially available bentonite from Indonesia. Claystone was mixed with 5, 10, 15, and 20% of bentonite on a dry weight basis. The mixture was statically compacted with moisture contents of 10, 15, and 20% to achieve a dry density of 16 kN/m3. A swell-load test was carried out using conventional oedometer equipment to obtain the swelling potential and swelling pressure of the samples. The results show that the swelling potential and swelling pressure increased with an increase in bentonite contents. At a bentonite content of more than 10%, both increased significantly. This research also revealed a linear relationship between swelling potential and swelling pressure.

Thermally Induced Bentonite Alterations in the SKB ABM5 Hot Bentonite Experiment

Pilot sites are currently used to test the performance of bentonite barriers for sealing high-level radioactive waste repositories, but the degree of mineral stability under enhanced thermal conditions remains a topic of debate. This study focuses on the SKB ABM5 experiment, which ran for 5 years (2012 to 2017) and locally reached a maximum temperature of 250 °C. Five bentonites were investigated using XRD with Rietveld refinement, SEM-EDX and by measuring pH, CEC and EC. Samples extracted from bentonite blocks at 0.1, 1, 4 and 7 cm away from the heating pipe showed various stages of alteration related to the horizontal thermal gradient. Bentonites close to the contact with lower CEC values showed smectite alterations in the form of tetrahedral substitution of Si4+ by Al3+ and some octahedral metal substitutions, probably related to ferric/ferrous iron derived from corrosion of the heater during oxidative boiling, with pyrite dissolution and acidity occurring in some bentonite layers. This alteration was furthermore associated with higher amounts of hematite and minor calcite dissolution. However, as none of the bentonites showed any smectite loss and only displayed stronger alterations at the heater–bentonite contact, the sealants are considered to have remained largely intact.

Uranium carbonate complexes demonstrate drastic decrease in stability at elevated temperatures

Quantitative understanding of uranium transport by high temperature fluids is crucial for confident assessment of its migration in a number of natural and artificially induced contexts, such as hydrothermal uranium ore deposits and nuclear waste stored in geological repositories. An additional recent and atypical context would be the seawater inundated fuel of the Fukushima Daiichi Nuclear Power Plant. Given its wide applicability, understanding uranium transport will be useful regardless of whether nuclear power finds increased or decreased adoption in the future. The amount of uranium that can be carried by geofluids is enhanced by the formation of complexes with inorganic ligands. Carbonate has long been touted as a critical transporting ligand for uranium in both ore deposit and waste repository contexts. However, this paradigm has only been supported by experiments conducted at ambient conditions. We have experimentally evaluated the ability of carbonate-bearing fluids to dissolve (and therefore transport) uranium at high temperature, and discovered that in fact, at temperatures above 100 °C, carbonate becomes almost completely irrelevant as a transporting ligand. This demands a re-evaluation of a number of hydrothermal uranium transport models, as carbonate can no longer be considered key to the formation of uranium ore deposits or as an enabler of uranium transport from nuclear waste repositories at elevated temperatures.