Host rocks

HOST ROCKS

As the historical analysis shows, today’s repository concepts have developed relatively specifically in the direction of the disposal of nuclear waste in the continental crust (see chapter 5.1). From the very beginning, mainly salt rocks but also montmorillonites, such as clay minerals and clays, were regarded as particularly interesting host rocks due to their very low permeability and high sorption capacity. The search for siting areas for high-level waste focused particularly on these two types of rock. However, the options had to be extended relatively quickly to other host rocks because some countries did not have such formations in their subsoil. Especially the choice of crystalline rocks of the Baltic Shield by the two Nordic states using nuclear power (Sweden, Finland) is due to this circumstance. However, the Nordic programs in particular were forced to massively reinforce the artificial barriers (copper canisters) at the expense of geological isolation in order to counter the groundwater inflows through the fissured and permeable crystalline rock. Japan, too, resorted to the rocks found in the subsoil of the circum pacific fire belt: crystalline rocks and pelagic or hemipelagic sediments.190

There are also other exotics among the host rocks: volcanic tuffs, which were intended for example primarily for Yucca Mountain, Nevada191—the site of the US repository program that has been abandoned in the meantime (see section 7.8)—and which raise fundamental questions of suitability because of their permeability. Equally problematic are the generally relatively thin layers of anhydrite, which appear as rocks accompanying rock salt deposits. They were an early specialty of the Swiss disposal programs.192 Other rocks selected in the course of the site search were, for example, basalts in the US Hanford Program lying below the quaternary cover193 or alpine marls of Wellenberg in Switzerland.194

Historically, “exotic” host rocks often occurred in the immediate vicinity of nuclear facilities or mines such as the iron ore mine of Schacht Konrad near Salzgitter in Germany195 or the uranium mine “Beta” in the pegmatites of El Cabril in Spain.196 Regardless of the fact that only limited experience is available in the implementation of geological repositories, salt and clay rocks or crystalline rocks are usually considered to be particularly suitable host rock formations.

190 NEA 2016, Japan’s Siting Process for the Geological Disposal of High-Level Radioactive Waste, Nuclear Energy Agency / OECD, viewed 1 August 2019, pp. 15, https://www.meti.go.jp/shingikai/enecho/denryoku_gas/genshiryoku/ chiso_shobun/pdf/018_s01_00.pdf 191 Walker, S. 2009, The Road to Yucca Mountain, University of California Press 192 Buser, M. 2017b, Short‐term und Long‐term Governance als Spannungsfeld bei der Entsorgung chemo‐toxischer Abfälle (Short-term and long-term governance as a field of tension in the disposal of chemotoxic waste), Vergleichende Fallstudie zu Entsorgungsprojekten in der Schweiz und Frankreich: DMS St‐Ursanne und das Bergwerk Felsenau (beide Schweiz) und Stocamine (Frankreich), ITAS‐ENTRIA‐Arbeitsbericht 2017‐02, viewed 1 August 2019, http://www.itas.kit.edu/pub/v/2017/buse17a.pdf 193 Milnes 1985, pp. 154-155. 194 Mosar, J. 2010, Beurteilung der Tektonik im Standortgebiet Wellenberg (Kt. NW/OW) hinsichtlich eines Tiefenlagers für schwach- und mittelradioaktive Abfälle (Assessment of tectonics in the Wellenberg siting area (NW/OW) with regard to a deep geological repository for low- and intermediate-level radioactive waste), Sachplan geologische Tiefenlager, z. Hd. Baudirektion Nidwalden, pp. 4-6, viewed 1 August 2019, https://www.nw.ch/_docn/30814/gutachten_tektonik_prof._mosar.pdf 195 Physikalisch-Technische-Bundesanstalt Braunschweig 2012, Schachtanlage Konrad (Shaft Konrad), viewed 1 August 2019, https://epic.awi.de/id/eprint/37594/1/schacht-konrad.pdf 196 Hernando-Fernández, J. L., Hernando Luna, R. 2002, Descubrimiento, explotación y tratamiento de los minerales radioactivos de Sierra Albarrana, El Cabril, Córdoba (Discovery, exploitation and treatment of the radioactive minerals of Sierra Albarrana), viewed 1 August 2019, https://helvia.uco.es/xmlui/bitstream/handle/10396/6947/braco143_2002_1.pdf?sequence=1&isAllowed=y