The dose rate and temperature measurement programme OBSERVE as a method of monitoring the condition of casks during extended interim storage is key part of the research programme of BGZ.

The distribution of dose rates and temperature across the cask surface is influenced by the arrangement and characteristics of the radioactive contents and cask components. Measurements are routinely carried out prior to the placement of casks in storage. The aim is to verify compliance with the relevant dose rate and temperature limits for storage in the corresponding storage facility. These measurements are performed at designated representative measuring points on the cask surface, in order to obtain reliable information about the mean or maximum values.

In contrast to this, the OBSERVE programme, initiated by BGZ, is designed to measure the dose rate and temperature over the entire surface of selected casks. In the first stage of the project, sensitivity studies were carried out to check the extent to which dose rate and temperature measurements are suitable for drawing conclusions about the condition of cask components and the inventory. The sensitivity analyses have demonstrated that, to a certain extent, both changes in the fuel and shielding arrangement can be detected by close-meshed dose rate measurements on the cask surface. It can therefore already be stated that the OBSERVE measurement programme is a suitable addition to existing ageing management measures and is able to assess the cask’s condition by means of measurement.

During the second project phase, a measuring device will be developed capturing values at the entire cask surface automatically in accordance with ALARA principles. For this purpose, the results of the sensitivity analyses will be utilized to ascertain the requirements for the measurement programme and the measuring device. This includes the definition of a suitable measurement location within the storage facility and the consideration of background radiation effects.

In order to evaluate the measurement results, a comparison will be made with the pre-calculation values. These pre-calculations must consider the actual inventory at the time of measurement as well as the cask configuration. The results of the comparison and the respective distribution are used to conclude about the actual shielding and heat dissipation properties. Assuming the measured values are within the expected range, this confirms that no unexpected changes have occurred. In this way, the measurement programme makes an active contribution to ageing management. Furthermore, safety-related assessments of the long-term behaviour of the cask components and the inventory can be used as direct input for safety analysis of future approvals.

How to cite: Klingen, J. H., Schneider-Eickhoff, R., Böning, Dr. N., and Becker, Dr. J.: OBSERVE – A comprehensive dose rate and temperature measurement programme for long-term interim storage, Third interdisciplinary research symposium on the safety of nuclear disposal practices, Berlin, Germany, 17–19 Sep 2025, safeND2025-5, https://doi.org/10.5194/safend2025-5, 2025.

The transition to a more sustainable energy system remains one of the major challenges of the 21st century. While much of the scientific and public discourse focuses on future technologies, the responsible management of the fossil and nuclear legacy is equally crucial. Using nuclear energy over several decades in Germany has resulted in a substantial accumulation of high-level radioactive waste, which poses significant technical, regulatory, and societal challenges in its management.

At the moment, this high-level radioactive waste is stored in decentralized interim storage facilities. Originally, those were licensed for 40 years, based on assumptions that the site for a deep geological repository would be found by 2030. However, recent assessments indicate that the site selection may extend into the second half of the 21st century, requiring an extension of interim storage durations well beyond the original licensing terms. This development necessitates new permits including a comprehensive Environmental Impact Assessment (EIA) as mandated by German and European regulations to assess and mitigate environmental impacts as well as to ensure transparent decision-making processes and effective public participation.

This research examines specific challenges which have to be dealt with in EIAs for extended interim storage in Germany as of today. Key challenges include scientific uncertainties resulting from gaps of knowledge regarding the storage cask’s ageing behavior, an increased risk of extreme weather events due to climate change, and evolving security threats, such as potential terrorist and military attacks. Additionally, the extended storage duration can have profound implications for affected communities, raising concerns about public participation, environmental justice, and psychological stress among local populations.

An international case study analysis is conducted to derive if and how the identified key challenges are addressed in other licensing processes for interim storage facilities. Thereby, recommendations for improving the German EIA process are meant to be obtained. Preliminary findings suggest that the current German practice of EIA in nuclear waste management may require adjustments to adequately address uncertainties, emerging risks and societal challenges. Strengthening the EIA within the licensing process could enhance both the technical robustness and societal legitimacy of extended interim storage.

The study aims to contribute to an effective and adaptive approach to the safe management of high-level radioactive waste in Germany. Given the complexity of radioactive waste management, profound and forward-looking EIA processes are essential to ensure environmental protection, public safety, and long-term sustainability in nuclear waste governance.

How to cite: Neugebauer, J.: Challenges for Environmental Impact Assessment in the Context of Extended Interim Storage of High-Level Radioactive Waste in Germany, Third interdisciplinary research symposium on the safety of nuclear disposal practices, Berlin, Germany, 17–19 Sep 2025, safeND2025-80, https://doi.org/10.5194/safend2025-80, 2025.

With regard to delays in finding and preparing final repositories, e.g. in Germany, the prolongated interim dry storage phase for spent fuel may exceed several decades. Therefore, further evidence for the integrity of spent nuclear fuel for longer storage periods needs to be gathered. The integrity, and thus the state of degradation in connection with e.g. hydride embrittlement of cladding tubes, needs to be evaluated for these prolongated storage periods. Adequate experimental data with dry storage related test conditions are rare. Instead, modelling is the only approach to predict the long-term storage behaviour of spent nuclear fuel during dry storage. However, the codes and tools for these modelling activities need to be based on realistic parameters and correlations, which only can be gained and improved experimentally. In this context, the worldwide first long-term large-scale bundle experiment LICAS-01 was conducted in the framework of the SPIZWURZ project with conditions very similar to dry storage conditions, as e.g. a very slow cooling phase.

Using the LICAS facility at the Karlsruhe Institute of Technology, a bundle of 21 fuel rod simulators with a length of 2.5 m was heated up to about 400°C and then cooled down uniformly in order to simulate the slow cooling process that is characteristic for the dry storage phase. Three cladding tube materials (Zircaloy-4, optimized ZIRLO™, DX D4), each with two different hydrogen contents (100 and 300 wt.ppm) and two different inner pressures (106 and 146 bar) were used and subjected to a cooling transient of 250 days. Post-test measurements were conducted non-destructively and destructively, concerning the post-test creep behaviour, the hydrogen diffusion behaviour in the cladding tubes and the hydride reorientation process. Mutually and after the analysis, a blind and open benchmark simulation showed the usability of different fuel rod performance codes with regard to the hydrogen related aspects and the cladding creep behaviour. The cladding creep and the reorientation of hydrides showed a different behaviour between Zircaloy-4and DX-D4 compared to optimized ZIRLO™. The latter was hardly affected by a reorientation of hydrides, which was not predicted by computer codes in a corresponding blind benchmark exercise. These results show that further data is crucial to improve and to extend the database used for modelling purposes.

This paper presents the LICAS-01 bundle experiment and its results, focussing on the cladding creep and the behaviour of hydrogen in Zr-based cladding tubes.

How to cite: Weick, S., Grosse, M., Kolesnik, M., Roessger, C., Steinbrueck, M., and Stuckert, J.: Results of the world's first long-term large-scale dry storage bundle experiment with fuel rod simulators, Third interdisciplinary research symposium on the safety of nuclear disposal practices, Berlin, Germany, 17–19 Sep 2025, safeND2025-86, https://doi.org/10.5194/safend2025-86, 2025.

In 2022, Germany will have a total of about 1,750 transport and storage casks with high-level radioactive waste, spent fuel and vitrified waste. The search for a repository for high-level radioactive waste is separate from storage. However, storage licences will expire before a repository is available. The aim of this research project was to investigate possible interactions between extended storage and final disposal [1], [2].

The research project 'KombiLyse' [2] was carried out by GRS gGmbH. GRS investigated ageing effects and damage mechanisms on the waste, including the transport and storage casks. This included international test and investigation programmes on material and component behaviour. The analyses did not give any indication of inadmissible temperature-related effects during dry storage. The effect of ionising radiation during storage was also found to be low. According to the results of the study, no systematic failure of cladding tubes, casings or barriers is expected during extended storage of up to 100 years.

Hypothetical scenarios were analysed, leading to hypothetical measures that could counteract the degradation of cladding tubes, enclosures or barriers. For example, if undesirable radiation-related effects were to occur, they could be mitigated by early removal to a buffer storage facility at a site where conditioning into the final waste form would be possible.

The study used reference disposal concepts to assess the impact of the hypothetical measures. These included the former German concept for rock salt, the Swiss concept for claystone and the Swedish concept for crystalline rock. The temperature, composition and availability of a fluid are important factors influencing corrosion and radionuclide mobility in a repository. Estimated containment times for radionuclides in canisters are still in the range of several thousand to hundreds of thousands of years (based on in-situ experiments, which show significantly lower corrosion rates than laboratory tests), considering hypothetical measures.

In Germany, waste acceptance criteria for high-level radioactive waste are still to be developed, which have a strong influence on conditioning and repackaging measures. A key finding is the highly significant influence of the future repository site and concept on the preceding disposal measures. Once a specific repository site, concept and waste acceptance criteria have been derived, it is recommended that hypothetical measures for extended storage and their interrelationships with disposal be reassessed. This would allow re-analysis of whether measures for extended storage could become realistic in relation to disposal and, if so, what the consequences for final disposal might be. At present, the study has not identified any hypothetical measures that appear to be necessary.

[1] G. Bracke, C. Borkel, F.-N. Sentuc, O. Bartos, F. Rowold, J. Krüger, K. Hummelsheim, M. Tzivaki, J. Nicol, Analysis of Safety-relevant Aspects regarding Dry Interim Storage and Final Disposal of High-Level Radioactive Waste: Evaluation of Hypothetical Measure and Their Implications, in: International Conference on the Management of Spent Fuel from Nuclear Power Reactors: Meeting the Moment (SFM24), Wien, International Atomic Energy Agency (IAEA), 10. - 14. Juni 2024.

[2] O. Bartos, K. Hummelsheim, J. Krüger, J. Nicol, F. Rowold, F.-N. Sentuc, M. Tzivaki, Vorhaben 4719F10701 (KombiLyse), Abschlussbericht, 2024.

How to cite: Bracke, G., Borkel, C., Maerten, L., and Kandemir, T.: Interim Storage and Final Disposal: Overview on hypothetical measures from a Study on Interrelationships, Third interdisciplinary research symposium on the safety of nuclear disposal practices, Berlin, Germany, 17–19 Sep 2025, safeND2025-141, https://doi.org/10.5194/safend2025-141, 2025.