Investigations into the "maximum physically possible temperatures" pursuant to Section 27 StandAG with regard to the limit temperature at the outer surface of waste containers

The §27(4) of the Act on the Search for and Selection of a Site for a Disposal Facility for High-Level Radioactive Waste (Site Selection Act - StandAG 2017) sets a draft temperature limit of 100°C on the outer surface of the containers with highly radioactive waste in a disposal facility. This draft limit shall be applied in preliminary safety analyses if the "maximum physically possible temperatures" in the respective host rocks have not yet been determined due to pending research work. This study looked at thermohydraulic, mechanical, chemical and biological processes as well as at issues related to retrievability and recovery, and wether limiting temperatures can be deduced for disposal facilities in the host rocks rock salt, claystone and crystalline rock. Based on FEP databases, several temperature-dependent processes have been identified and assessed for possible impacts to derive temperature limits from different components. The interactions of these processes must be considered to determine a temperature limit on the outer surface of the containers. Limiting temperatures to 200 °C could be feasible but a limiting temperature depends strongly on safety concept and design of the disposal facility. No temperature limits could be deduced from issues of retrieval and recovery. Technical solutions for retrieval and design options for recovery seem to be viable up to 200 °C with different penalties. Technical solutions and design options for containers still must be developed and checked for their practicability. Temperature limits on the outer surface of the containers should be derived for a specific safety concept for design of the disposal facility and the respective host rock. Any general temperature limits could hinder the site selection process due to the restricted possibilities of optimization of the disposal facility.