Abstract. Since 2019, transdisciplinary research on the scientifically challenging and often controversially debated topic of nuclear waste management on a larger scale has been carried out for the first time in Germany within the co-operative project “TRANSENS” (http://www.transens.de, last access: 21 October 2021). While various and sometimes diverging definitions and understandings of the term “transdisciplinarity” can be found in the literature (e.g., Klein, 2013), we understand it as a specific type of “problem-orientated” basic research integrating a variety of knowledge bodies, values and expectations coming not only from academia but also from the dialogue with society. We consider transdisciplinarity a reflexive, integrative, methodology-guided scientific principle directed at the solution of a societal problem and related scientific challenges by involving non-specialists and actors from practise. Obviously, the safety of nuclear waste management and particularly of waste disposal is an important concern of stakeholders. For specialists, the Safety Case is an established and well-developed instrument supporting safety-informed decisions in a stepwise disposal programme (OECD/NEA, 2013). The idea of Sicherheitsuntersuchungen (safety evaluations) informing decisions in the German siting process is based on the Safety Case concept. However, different stakeholders and interested persons have different notions and views about safety and different values behind these notions (Röhlig and Eckhardt, 2017). The idea behind the TRANSENS Working Package SAFE is to elicit such views and, if possible, to derive conclusions on optimisation potential for the Safety Case. Specifics and potential challenges of this research and ways to address them include: While transdisciplinary research in many cases involves directly affected individuals and groups, TRANSENS is an application-orientated basic research project which does not aim at interfering with the site selection procedure in Germany. Therefore, our research partners from civil society include permanent groups of interested individuals – but not of stakeholders – recruited in a well-defined process. Transdisciplinary research often starts by performing “co-design”, i.e. by jointly formulating the research question(s), but project “funding logic” requires problem definitions already in the application phase of a project. We attempt to overcome this by working in “theme corridors”, which define overarching research questions but leave leeway for later adjustment within these corridors. Being a complex concept, the Safety Case as such might not be well amenable to non-specialists. We address the problem by (i) taking a stepwise approach starting with a preparatory focus group format involving individuals with “Safety Case experience”; (ii) aiming at continuous involvement of one of the permanent groups mentioned above, allowing focussed and in-depth discussions; (iii) being flexible concerning additional transdisciplinary formats and partnerships. The SAFE Working Package team has successfully completed the focus group format under pandemic conditions and is currently preparing the next steps. Preliminary findings include those related to the tool “Safety Case”, to the feasibility of the focus group format in a transdisciplinary context, to observations concerning social interactions within the focus group, and to the way forward. The SAFE team sees opportunities particularly in discussing aspiration and philosophy of safety demonstration, in reflecting potential disciplinary biases influencing both production and criticism of the Safety Case, and for developing new concepts for the interplay between civil society and experts on this complex and elaborated analytical tools in various transdisciplinary formats.