Radioactive Waste Sites Research Articles

Transdisciplinary research on the safety case for nuclear waste repositories with a special focus on uncertainties and indicators

In the search for a repository site for high-level radioactive waste in Germany, the perception of safety and trust in the actors are central to public acceptance. In communicating safety, methods of safety assessment and the role of uncertainties need to be addressed. Given the complexity of the issue, there is a need for indicators that are suitable both for assessing the long-term safety of repositories and for communicating with the general public. Similarly, there is a requirement to communicate uncertainties in an accessible manner. The TRANSENS project provides basic research in nuclear waste management (NWM) and utilizes a transdisciplinary approach: Non-experts who are not directly affected by the site selection process and who have no stated interest in NWM are involved in the research process, as are practice actors. A series of four transdisciplinary workshops was specifically designed to explore the perspectives of individuals with a high level of disciplinary knowledge but no system knowledge of NWM. Participants were selected from doctoral students in science and technology who had no prior knowledge in this area. Two of these workshops address the questions stated above and are presented here. The article describes the considerations underlying the workshop planning and implementation phases, and the content developed in the workshops on indicator selection and visualisation of uncertainties. The participants compiled a list of desirable indicator properties, which showed a high degree of congruence with the relevant literature. A proposal for a database to collect, administer and assess uncertainties shows similarities with the approach followed by the German implementer and complements it with an interactive visualisation. Transdisciplinary work is resource-intensive and its use in a research context must be carefully considered for each individual application. A transdisciplinary approach was successfully used for the purposes of method validation, method optimisation and the development of disciplinary impulses. An application of transdisciplinary approaches for optimising the Safety Case of nuclear repositories is feasible.

Cliff Retreat Rates Associated with a Low-Level Radioactive Waste Disposal Facility in Los Alamos, New Mexico, USA

We present an analysis and interpretation of potential cliff stability at a low-level waste disposal facility at Los Alamos National Laboratory, New Mexico, using cliff morphologic and fracture characteristics coupled with carbon-14 surface exposure dating. Our study is important as it directly bears on the licensing criteria for low-level radioactive waste sites. We find that future characteristic cliff failures will likely not breach disposal pits and shafts over the 1000-year minimum regulatory period. Further, we find, using a multivariate regression model, that slope angle and cliff face aspect are sub-equal in importance to predict regions of high risk of failure when combined with surface exposure ages and assuming that old exposure ages are most indicative of stability (instability) and therefore can aid decision making in final design implementation.

Accelerator mass spectrometry measurements of 233U in groundwater, soil and vegetation at a legacy radioactive waste site

Low-level radioactive wastes were disposed at the Little Forest Legacy Site (LFLS) near Sydney, Australia between 1960 and 1968. According to the disposal records, 233U contributes a significant portion of the inventory of actinide activity buried in the LFLS trenches. Although the presence of 233U in environmental samples from LFLS has been previously inferred from alpha-spectrometry measurements, it has been difficult to quantify because the 233U and 234U α-peaks are superimposed. Therefore, the amounts of 233U in groundwaters, soils and vegetation from the vicinity of the LFLS were measured using accelerator mass spectrometry (AMS). The AMS results show the presence of 233U in numerous environmental samples, particularly those obtained within, and in the immediate vicinity of, the trenched area. There is evidence for dispersion of 233U in groundwater (possibly mobilised by co-disposed organic liquids), and the data also suggest other sources of 233U contamination in addition to the trench wastes. These may include leakages and spills from waste drums as well as waste burnings, which also occurred at the site. The AMS results confirm the historic information regarding disposal of 233U in the LFLS trenches. The AMS technique has been valuable to ascertain the distribution and environmental behaviour of 233U at the LFLS and the results demonstrate the applicability of AMS for evaluating contamination of 233U at other radioactive waste sites.

Effects of carbonate on ferrihydrite transformation in alkaline media.

Alkaline media widely exist in natural and engineered systems such as semiarid/arid areas, radioactive waste sites, and mine tailings. In these settings, the commonly occurring iron (oxyhydr)oxides differed in their ability to influence the fate of nutrients and contaminants. Due to the substantially increased atmospheric carbon dioxide (CO2) concentration, carbonate stands to increase in these media. However, how increasing carbonate affects the transformation of poorly crystalline iron (oxyhydr)oxides (e.g., two-line ferrihydrite) under alkaline conditions still remains unclear. Here, kinetics of ferrihydrite transformation were evaluated at pH ∼10 as a function of [carbonate] = 0-286 mM using synchrotron-based X-ray and vibrational spectroscopic techniques. The results showed that carbonate slowed down ferrihydrite transformation slightly and suppressed goethite formation, but promoted hematite formation regardless of its concentration. At low carbonate concentration (11.42 mM), the effect of carbonate on product formation was obvious due to the weak inner-sphere complex; however, at high carbonate concentration (80-286 mM), the effect was retarded because of the adsorption equilibrium of carbonate as well as the initial carbonate adsorption followed by desorption. Moreover, carbonate modified the morphology of hematite from rhombic to ellipsoidal to honeycomb and goethite from rod-like to needle-like to spindle-like due to the inner-sphere adsorption-desorption of carbonate and adsorption of hydroxyl ions on reactive sites of iron (oxyhydr)oxides in alkaline media. The results suggest that the concurrently increasing carbonate with enhanced atmospheric CO2 could control the transformation and occurrence of iron (oxyhydr)oxides in natural and engineered environments and have important implications for the biogeochemical cycles of iron and carbon.

Рецензия на горно-геологическую часть обоснования строительства подземного хранилища радиоактивных отходов

The city district “Closed Administrative-territorial formation of the city of Zheleznogorsk” has appointed and organized public discussions on the materials of the justification of the license (including environmental impact assessment materials) for activities in the field of nuclear energy use “Creation of a second-class RW storage facility at FSUE GCK”. The mining and geological materials on the construction site of an underground repository of radioactive waste (RW) of the second hazard class in Zheleznogorsk of the Krasnoyarsk Territory are considered. The purpose of the construction of the storage facility is to ensure the storage of second-class radioactive waste at the site of the mining and chemical plant in volumes that meet the needs of the enterprise until the national operator is ready to handle radioactive waste. The review is a response to an offer to discuss supposedly public materials of open access. The subject of public discussions was conducted in the form of a survey. It is proposed to carry out the initial stage of the justification of the object on the basis of the Law “On Subsoil”. The following conclusion is made: the target horizon after the conservation of the object is likely to be flooded, primarily along vertical collector trunks; heterogeneous backfilling of the internal free space of trunks and horizontal workings with finished concrete lining with crushed/granular natural bentonite will not help; in reality, the volume of water in the burial zone will significantly determine the characteristics and the inexhaustible resource of the overlying water supply layers of rocks, rather than rocks of the target range, and even without recharge from other sources, the flooded PGZRO will quickly turn into a supplier of hot water and radiolytic gases. The opinion is expressed that it is unacceptable to turn a temporary storage facility into a permanent disposal site for radioactive waste.

Assessment of Radioecologically Relevant Radionuclides 14C, 99Tc, and 129I in Vitrified High-Level Nuclear Wastes from Spent Fuel Reprocessing

A method is proposed for quantifying the specific activities of radioecologically significant radionuclides, including 14C, 99Tc, and 129I, in vitrified high-level wastes. The conditions for the separation and purification of these radionuclides from potential interfering components are optimized and the yield coefficients and purification factors are determined. The quantification of 14C entails a three-fold distillation in CO2 followed by the measurement of the 14C counting rate in the purified solution by liquid scintillation spectrometry. 129I was determined by dissolving a sample in HNO3, five-fold extraction, and the subsequent measurement of the 129I counting rate in the purified solution using liquid scintillation spectrometry. The determination of 99Тс included dissolving a sample in the presence of ClO–, double extraction-chromatographic separation of 99Тс with an adsorbent impregnated with methyltrioctylammonium nitrate, followed by the determination of its activity by inductively coupled plasma–mass spectrometry. We have applied this approach to a simulator of vitrified high-level waste, labeled with radionuclides, and achieved satisfactory results. This approach will be instrumental in the analysis of the accumulated vitrified high-level wastes at the “Mayak” Production Association (Mayak PA). The results will be important for modeling the engineering safety barriers of a deep disposal site for radioactive wastes.

Geowissenschaftliche Methoden – Datenbank (GeM-DB) – a basis for planning surface exploration programs

Abstract. In phase II of the German site selection procedure for a final repository site for high-level radioactive waste, identified siting regions will be explored above ground. For each siting region, different geoscientific data exist, resulting in various exploration requirements as results of the representative preliminary safety analysis. The exploration requirements, i.e. exploration objectives (Kneuker et al., 2020) and parameters, are based on a legal foundation, especially sections 22–24 of StandAG (2017). The exploration requirements in turn define the methods to be used for surface exploration of siting regions to collect all data needed for the further-developed preliminary safety analyses at the end of phase II. Commissioned by the Federal Company for Radioactive Waste Disposal (BGE), the Federal Institute for Geosciences and Natural Resources (BGR) is developing a database, GeM-DB, which allows the search for different geophysical and geoscientific exploration methods. Among the exploration methods are airborne, ground and borehole methods as well as investigations on obtained samples, e.g. from drill cores. The database entries consist of a general description, different attributes and an evaluation of the suitability and applicability for (1) the different host rocks (claystone, crystalline rock and rock salt) and (2) the exploration objectives deriving from the legal foundations, especially the exclusion criteria, minimum requirements and geoscientific weighing criteria as stated in sections 22–24 of StandAG (2017). This link is the key element of the database and a unique compilation of the collective knowledge of BGR experts. Certain filters and selection options allow queries of the database content, for instance to generate host rock-specific sequences of exploration methods. These sequences of methods can be used as a basis for the exploration programmes to be planned by the BGE.

International Atomic Energy Agency (IAEA) support for the management of site investigations for radioactive waste disposal facilities

Abstract. Providing safe, secure and environmentally acceptable radioactive waste disposal is a national responsibility that requires a long-term commitment, adequate resources and the involvement of multiple stakeholders. The choice of a particular disposal concept and its detailed design will depend on several factors, such as the properties of the waste inventory to be disposed of, national circumstances and strategic preferences. A concept is likely to evolve iteratively as one or more sites are investigated and the repository design is refined to reflect local conditions. In this context, the International Atomic Energy Agency (IAEA) recently published technical guidance on the management of site investigations for radioactive waste repositories. A key objective of the publication Management of Site Investigations for Radioactive Waste Disposal Facilities (IAEA, 2023) is to ensure that site investigation efforts in Member states have firm foundations based on a clear understanding of data and information requirements. The publication was developed to reflect the experiences and knowledge from a range of disposal programmes, and it is intended to support initiation of well-planned and focused site investigations in Member states with a need to develop and site radioactive waste disposal facilities. A siting process is intended to result in the identification of a suitable location for any nuclear installation, including a deep geological repository, and ultimately to receive authorisation to construct and operate the facility. To achieve this objective, it will be necessary to ensure that the combination of site properties and engineered barrier properties provides requisite levels of safety for the inventory under consideration (IAEA, 2015). The siting process and associated site investigations for a radioactive waste disposal facility follow a stepwise process, irrespective of whether the early stages of siting start with investigating and screening the national territory or whether the iterative investigation process starts with a more focused approach, e.g. volunteer sites, sites with already well-known characteristics, sites with existing nuclear facilities or similar ones (IAEA, 2023). Site investigations should follow a graded approach in an iterative manner, reflecting a phased approach to decision-making and the development of disposal facilities (IAEA, 2011). At each stage in the siting process the disposal system is to be evaluated based on the data and information available at that time. Following an assessment, a gap analysis comparing requirements to knowledge about the site would identify process model and data uncertainties affecting confidence in the implementation of the disposal concept at the site. Furthermore, the IAEA also recently launched a project to develop guidance reflecting good practices in Member states' programmes for establishing site selection criteria and applying a decision-making framework as part of a siting process.

Geostatistical and hydrogeochemical characterization of a probable borehole disposal site for radioactive waste in Accra, Ghana

Geostatistical and hydrogeochemical characterization of a probable borehole disposal site for radioactive waste in Accra, Ghana

Design of an autonomous navigation system for emergency disposal robots at radioactive waste sites under extreme climatic conditions

There are many factors of environmental hazards that endanger the lives of personnel at radioactive waste sites after sudden extreme weather disasters, and the use of robotic substitutes can effectively safeguard the lives of personnel. For the situation where the environmental information of radioactive waste sites is unknown and there are many variables, an autonomous navigation system of emergency disposal robots with strong resilience and stability is designed. First, an algorithm based on the Rao-Blackwellized particle filtering theory is used in the autonomous navigation system to achieve more accurate robot positioning and map building through four processes: prediction, correction, resampling, and map building. Second, the traditional path planning algorithm combined with road information is added to Hopfield neural network to achieve deep analysis of complex road conditions. Finally, the intelligent voice interaction function is added to the navigation system to realize the robot’s interaction and real-time monitoring and feedback. The experimental results show that the emergency disposal robot has high accuracy in positioning, navigation, obstacle avoidance, etc., can respond quickly in unexpected situations and can carry out effective voice interaction.

Bürgerbeteiligung im langfristigen Endlagerungsprozess: Künftige Aufgaben und angemessene Beteiligungsformen

The central importance of public participation in the search for a repository site for high-level radioactive waste is already recognized both in Germany and in other countries. In this paper, we argue that public participation will have to play a role after site selection as well, especially in the political and sociotechnical decisions in the next stages of the final disposal process. The form of citizen participation should correspond to the specific tasks and follow the principles of safety and justice. In order to show in which cases these principles apply and which form of participation would then be appropriate, we analyze three aspects of participation (co-determination, co-design, and involvement) and look at two cases: the decision on the sealing of the repository and the design of compensations.

Contaminant release, mixing and microbial fluctuations initiated by infiltrating water within a replica field-scale legacy radioactive waste trench

Numerous legacy near-surface radioactive waste sites dating from the mid 20th century have yet to be remediated and present a global contamination concern. Typically, there is insufficient understanding of contaminant release and redistribution, with invasive investigations often impractical due to the risk of disturbing the often significantly radiotoxic contaminants. Consequently, a replica waste trench (~5.4 m3), constructed adjacent to a legacy radioactive waste site (Little Forest Legacy Site, LFLS), was used to assist our understanding of the release and mixing processes of neodymium (Nd) — a chemical analogue for plutonium(III) and americium(III), two significant radionuclides in many contaminated environments. In order to clarify the behaviour of contaminants released from buried objects such as waste containers, a steel drum, representative of the hundreds of buried drums within the LFLS, was placed within the trench. Dissolved neodymium nitrate was introduced as a point-source contaminant to the base of the trench, outside the steel drum. Hydrologic conditions were manipulated to simulate natural rainfall intensities with dissolved lithium bromide added as a tracer. Neodymium was primarily retained both at its point of release at the bottom of the trench (>97 %) as well as at a steel container corrosion point, simulated through the emplacement of steel wool. However, over the 8-month field experiment, advective mixing initiated by surface water intrusions rapidly redistributed a small proportion of Nd to shallower waters (~1.5–1.7 %), as well as throughout the buried steel drum. Suspended particulate forms of Nd (>0.2 μm) were measured at all depths in the suboxic trench and were persistent across the entire study. Analyses of the microbial communities showed that their relative abundances and metabolic functions were strongly influenced by the prevailing geochemical conditions as a result of fluctuating water depths associated with rainfall events. The site representing steel corrosion exhibited divergent biogeochemical results with anomalous changes (sharp decrease) observed in both dissolved contaminant concentration as well as microbial diversity and functionality. This research demonstrates that experimental trenches provide a safe and unique method for simulating the behaviour of subsurface radioactive contaminants with results demonstrating the initial retention, partial shallow water redistribution, and stability of particulate form(s) of this radioactive analogue. These results have relevance for appropriate management and remediation strategies for the adjacent legacy site as well as for similar sites across the globe.

Vadose Zone Transport of Tritium and Nitrate under Ponded Water Conditions

Vadose zone transport of tritium and nitrate can be important considerations at radioactive waste sites, landfills, or areas with industrial impacts. These contaminants are of particular concern because they typically have a relatively higher mobility in the subsurface compared to other compounds. Here, we describe a semiarid site with tritium and nitrate contamination involving a manmade ponded water source above a thick unsaturated zone at Los Alamos National Laboratory in New Mexico, USA. This study demonstrates the value of vadose zone flow and transport modeling for the development of field investigation plans (i.e., identifying optimal borehole locations and depths for contaminant characterization), and how a combination of modeling with isotope and geochemical measurements can provide insight into how tritium and nitrate transport in the vadose zone in semiarid environments. Modeling results suggest that at this location, tritium transport is well predicted by classical multiphase theory. Our work expands the demonstrated usefulness of a standard tritium conceptual model to sites with ponded surface conditions and agrees with previous results where a standard model was able to explain the evolution of a tritium plume at an arid waste disposal site. In addition, depth-based analyses of δ18O and δ2H of pore waters helped confirm the extent of pond infiltration into the vadose zone, and the δ15N of nitrate showed that the contaminant release history of the site was different than originally assumed.

Characteristics of hydraulic conductivity in mountain block systems and its effects on mountain block recharge: Insights from field investigation and numerical modeling

The process wherein groundwater flowing from mountain bedrock into lowland and adjacent alluvial aquifers, known as mountain-block recharge (MBR), is found across various climatic and geological settings. An understanding of the potential groundwater flow paths in mountain block systems is necessary for comprehending MBR spatial distribution. However, poorly characterized mountain block hydraulic properties, and especially a lack of direct measurements of hydraulic conductivity (K) at depths > 200 m, limit the characterization and quantifications of the MBR processes. In this study, we analyze hydraulic data set, namely 555 in-situ K measurements at various depths from two borehole sections extending from mountain block to mountain front in a potential disposal site for high-level radioactive waste. The K dataset was categorized into two groups: one for bedrock and another for fault zones, which was further classified into fault core K, damage zone K, and general fault zone K. Using a permeability conceptual model and multiple scenarios numerical modelling, this study examined the potential flow paths of MBR processes, mainly focusing on the characteristics of K in bedrocks and the hydraulic role of fault zones in mountain block systems. The distribution of Bedrock K supports the assumption of decreased trend with depth. A logarithmic fit through Bedrock K and depth pairs resulted in Log(K) = −1.62*Log(z) − 6.52, with low predictive power. This study illustrated the localized effects and spatially variable roles of fault zones in MBR within this particular hydrogeological configuration in Beishan, China. Our results provide insights into the MBR process in crystalline mountain block systems. Additionally, the hydraulic conductivity presented here provides data on the subsurface properties of mountain block systems in a crystalline area, and further facilitates the characterization and quantification of mountain-block recharge.

Development of mini column experiments (MCE) by coupling microliter flow HPLC with ICP-MS for the analysis of metal retention under conditions close to nature

The development and implementation of mini column experiments (MCE) can be of great importance to improve existing analytical methods such as highly standardised but unrealistic batch laboratory experiments or lengthy long-term diffusion experiments to study metal sorption/desorption properties. One envisaged application would be to test the retention of repository-relevant metals in claystone, which is a promising candidate for the host rock of a final repository site for high-level radioactive waste (HLW). The used MCE setup is derived from classical high performance liquid chromatography (HPLC). On this basis, coupling of MCE to ICP-MS (inductively coupled plasma mass spectrometry) detection was realised. This online separation enables the dynamic monitoring of metal sorption and desorption experiments on clay minerals (kaolinite), natural clay (Opalinus Clay) and mixtures with quartz sand in background solutions close to nature, and without the common use of metal complexing ligands, other reaction partners or buffers for the analysed metal ions. The optimised method allows the analysis of the retention of various contaminants in real groundwater solutions and compact clay samples in a reasonable amount of time and a small amount of sample. In addition, the coupling to the unspecific mass detector of ICP-MS enables the study of different radionuclides and homologues rather than the limited UV detection of a common HPLC.

Rare earth elements and yttrium as tracers of waste/rock-groundwater interactions

Increasing concentrations of Rare Earth Elements (REE) plus yttrium (REY) are entering the environment due to human activities. The similar chemical behaviour across the whole REY, i.e. the lanthanide series (lanthanum to lutetium) and yttrium, allows their use as tracers, fingerprinting rock-forming processes and fluid-rock interactions in earth science systems. However, their use in fingerprinting waste and particularly low-level radioactive waste has not received much attention, despite the direct use of REE in the nuclear industry and the traditional use of REE as proxies to understand the environmental mobility of the actinide series (actinium to lawrencium). The highly instrumented low-level radioactive waste site at Little Forest (Australia) allows a detailed REY study, investigating interactions with local strata, neighbouring waste forms and shallow groundwater flows. Groundwater samples and solids from cored materials were recovered from 2007 to 2012 from the study site and regional baseline sites in the same geological materials. The REY in water samples were analysed by automated chelation pre-concentration (SeaFast, ESI) followed by ICP-MS determination, while solid samples were analysed using Neutron Activation Analysis (NAA) and X-ray fluorescence scanning (ITRAX). Solid rocks showed no REY departed from typical Upper Crust compositions in either Little Forest or regional background sites. Shallow groundwater from ~4–5 m, at or slightly below waste trench levels, showed water-waste interaction as a marked enrichment, relative to shale-normalised patterns, in samarium, europium and gadolinium, with depleted yttrium. Leachate samples from the neighbouring urban landfill show different REY normalised patterns. REY distribution changes with depth through increased interaction with shales and sandstones. Variations in pH and redox conditions lead to widespread precipitation of Fe-hydroxides, which scavenge REY with differential uptake by precipitating solids, resulting in increases in Y and higher Y/Ho ratio in the groundwater along the flow path. Our study revealed that the Little Forest low-level radioactive waste has a REY fingerprint different to that of groundwater in surrounding land uses. REY can be used to fingerprint diverse waste sources, assess the mobility of lanthanides inferring the mobility of selected actinides, and to trace the fate of REY during groundwater recharge. The approach presented can refine source allocation and trace pollutant mobility in current and legacy urban, mixed and radioactive waste sites around the world.

Co-transport of bentonite colloid and U(VI) in particulate granite column: role of colloid concentration, ionic strength, pH and flow rate

Abstract China is considering Beishan granitic formation (Gansu Province, China) as the site for high-level radioactive waste (HLW) repositories. Thus, it is crucial to understand the transport behavior of radionuclide in Beishan granitic media under disposal conditions. In this context, the co-transport of U(VI) (as the representative of radionuclides) and bentonite colloid (BC, from erosion of compacted bentonite) in particulate Beishan granite was studied as a function of important in-situ factors, such as BC concentration, ionic strength, pH and flow rate. We found that the increase of BC concentration (BC = 240–480 mg/L) did not affect the transport of individual BC, whereas it significantly facilitated the transport of U(VI). The increase of ionic strength (I = 0.001–0.01 M NaCl) or decrease of pH (pH = 7.50–5.40) obviously inhibited the BC transport, where these inhibiting effects were relatively slight for the transport of U(VI). The increase of flow rate significantly facilitated both the transport of BC and U(VI). Finally, a two-site kinetic attachment/detachment model was applied to describe the breakthrough curves of individual and co-transport of BC. The experimental and modeling results of this study have a significant implication on the safety assessment of HLW repositories built in granitic formation.

An Exploratory PPGIS for the Nuclear Waste Repository Siting Procedure in Germany – a Transdisciplinary Approach to Enable Meaningful Participation?

Germany's debate on nuclear energy is characterized by a potential for conflict. With the Repository Site Selection Act, a new strategy was adopted for a participatory search process for the best possible repository site for high-level radioactive waste in Germany. To gain insights into how a Public Participatory GIS application (PPGIS) can contribute to this strategy, a transdisciplinary approach was adopted. By involving a citizen group to take part in the research process, we co-designed and addressed three research questions regarding the role of the PPGIS, its usability and ability to enable dialogue. Key findings include the need for guidance on how to interpret the data provided. Although the potential of a PPGIS to support dialogue is recognized, the need for content moderation emerged as a significant challenge. The transdisciplinary approach was useful in capturing multiple viewpoints and providing new insights into how a PPGIS should be designed to maximize its usefulness.

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

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.

Public opinion in the site selection process: survey methodologies

Abstract. The aim of the site selection process (StandAV) is to find the repository site for high-level radioactive waste with the best possible safety. Transparency and public involvement contribute to ensuring that the outcome of the site selection process is “supported by a broad consensus in society and can thus also be tolerated by those affected” (StandAG § 5 para. 1). In order for the public to be suitably informed and involved, BASE (Federal Office for the Safety of Nuclear Waste Management), in particular, as the body responsible for public participation, must base its work on the knowledge, attitudes and needs of the German population. In order to gain the respective knowledge, the company aproxima Gesellschaft für Markt- und Sozialforschung Weimar mbH was commissioned to conduct a repetitive representative survey (research project EWident). The study briefly deals with nuclear energy in general, but mainly focuses on questions related to the topic of final disposal (knowledge of the topic and especially the StandAV, interest in information and involvement, relevance of particular questions in the process, etc.). The first survey took place in summer 2020. A special focus was placed on the younger generation (14- to 29-year-olds). The results can be viewed on the BASE website (Götte and Ludewig, 2020). They show that the level of knowledge about and interest in StandAV are still rather feeble; at the same time, it is clear that questions of safety are a central driver for accepting a possible site in one's own region. A second survey is planned for autumn 2021. A comparably broadly drawn survey has not been carried out in recent years. However, the fact that the topic of final disposal is becoming increasingly important is shown by thematically related surveys that ask about attitudes towards nuclear energy or examine particular aspects of StandAV in more detail. Within the framework of the TRANSENS research association (Transdisciplinary Research on the Management of High-Level Radioactive Waste in Germany), for example, trust and confidence in the context of the site selection process were surveyed. The 60 min workshop is aimed at interested parties and researchers who would like to contribute their own experiences with related surveys. In the workshop we provide three incentives. aproxima introduces the methods and key results of EWident's first survey. BASE gives an insight into the practical use of these results. Roman Seidl of Leibniz University Hannover reports the results of the TRANSENS survey. Subsequently, we would like to discuss the following questions, among others, with the participants in the workshop. What is remarkable about the results? Do they differ from other StandAV surveys and experiences, and if so, how? How can this be explained? What further research needs can be identified? With what approaches could they be met?