Current research findings regarding repository temperature limit

Jochen Ahlswede speaking at the BASE temperature limit workshop Source: BASE

The temperatures of containers with high-level radioactive waste constitute a relevant safety aspect of both the repository site search as well as the design and construction of a repository. The relevant actors in the site selection procedure presented their approach and the existing research findings on the topic at an event entitled "Temperature limit as a requirement in the site selection procedure" organised by the Federal Office for the Safety of Nuclear Waste Management (BASE). The term "temperature limit" (Site Selection Act (Stand AG) Section 27 para. 4) refers to the maximum permissible temperature on the outer surface of the waste containers in a repository for high-level radioactive waste.

Around 30 participants at the Berlin office of BASE and up to 80 online participants took part in the discussion and posed questions to BASE, BGE mbH and the invited scientists.
In addition to scientists from various institutions, representatives of the Federal Ministry for the Environment, Nature Conservation and Nuclear Safety (BMUV), the federal states and municipalities, the National Citizens’ Oversight Committee and interested members of the public also took part in the event.

Effects of temperature development in a repository - technical debate, legal requirements and interpretation

The question of potential effects of the temperature development in a repository on the safety of the site formed the background of the event. There is no uniform international approach to this question. In Germany, the relevant expert debate has been going on for years, too. This is why the legislator provided for a precautionary temperature limit of 100 °C for the final disposal of high-level radioactive waste, as long as no newer research findings are available that confirm the safety of higher temperatures.

During the workshop, experts from the research projects commissioned by BASE and BGE mbH presented review studies and findings from experiments on the permeability of clay rock and rock salt at different temperatures. The topics of discussion ranged from details on the set-up of experiments to higher-level procedural issues. BASE also provided its interpretation of the law (Section 27 (4) StandAG). BGE mbH outlined the potential role of the temperature aspect in current and upcoming investigations.

Existing studies show that, in terms of safety, higher temperatures can have both advantages and disadvantages. BGE mbH has not yet completed its research on the topic either. In principle, all proposals made by BGE mbH as the implementer must be scientifically proven, and it must be ensured that the methodology used does not place any area at an obvious disadvantage. The open wording of section 27(4) allows for such a procedure. Once BGE mbH proposes siting regions at the end of Phase I of the site selection procedure, and submits corresponding safety analyses for these regions, BASE will also examine the temperature question in the scope of its technical review. This means that if BGE mbH wishes to deviate from the legally prescribed precautionary temperature, this procedure must be justified in a scientifically sound manner, and stand up to the technical scrutiny of the supervisory authority.

The documentation of the event can be found on the repository search information platform.