Preliminary design of a disposal facility for high-level radioactive waste in claystone, crystalline rock, and rock salt

Introduction

The Federal Company for Radioactive Waste Disposal (BGE) is responsible for the search and selection of a site with the best-possible safety for the disposal of high-level radioactive waste (HLW) in Germany. The federal Repository Site Selection Act, (Standortauswahlgesetz – StandAG) [1] regulates the Site Selection Procedure. It requires the site selection to be participatory, transparent, learning, and self-questioning based on scientific expertise. In the current Step 2 of Phase I, representative preliminary safety analyses (rvSU) are carried out for the sub-areas identified in Step 1 [2] in order to determine potential regions for surface exploration (Phase II). In accordance with section 6 (4) EndlSiUntV [3], the rvSU comprise preliminary designs of the geologic disposal facility (GDF) for the three considered host rocks: claystone, crystalline rock, and rock salt. The areal footprint of a GDF is an important result of the design work that influences the judgement of suitability of areas for disposal.

GDF design and areal footprint

The type and amount of radioactive waste and the way in which it shall be emplaced are among the important basic elements for the development of a GDF design. One of the key aspects of the design is the underground layout, which is central for the evaluation of areal requirements. The main parts of the layout are the arrangement of disposal and access galleries, an infrastructure area, the cross-sections, and the diameters of the galleries including rock support and pillar widths. The required pillar widths can vary over depth and are one of the most sensitive factors for the areal footprint of the GDF. Consequently, rock mechanical calculations have been carried out to determine the aforementioned parameters. Based on this, thermal simulations were used to determine the maximum thermal loading of the canisters respecting predefined maximum temperatures on the surface of the canister. 

Figure 1: Schematic representation of a repository mine in crystalline rock with close-ups of sealings and galleries.

An example for the repository layout for crystalline rock is depicted in Fig. 1. It is primarily based on the KBS-3-concept of Posiva [4] and consists of two parallel access galleries, which are connected at regular intervals by crosscuts. The disposal galleries branch off perpendicularly from the access galleries. In the disposal galleries, the HLW-canisters are each placed in vertical boreholes, which are filled with bentonite blocks. The backfill material used for the disposal galleries and sealing structures consists of bentonite and concrete. The area required for the GDF is made up of an area for infrastructure, the disposal area, and the area in between.

References

[1] “Standortauswahlgesetz vom 5. Mai 2017 (BGBl. I S. 1074), das zuletzt durch Artikel 8 des Gesetzes vom 22. März 2023 (BGBl. 2023 I Nr. 88) geändert worden ist“, 2023.
[2] BGE, “Zwischenbericht Teilgebiete gemäß § 13 StandAG”, 2020.
[3] “Endlagersicherheitsuntersuchungsverordnung vom 06. Oktober 2020 (BGBl. I S. 2094, 2103)“, 2020.
[4] Posiva Oy (2023): Safety Case for the Operating Licence Application (SC-OLA). Hg. v. Posiva Oy (Website). Available online at: https://cms.posiva.fi/, checked on 26.09.2023.