Call - Effects of subrosion on the barrier function of the ...

Call
Effects of subrosion on the barrier function of the effective
containment zone and the overburden of a potential
repository site for high-level radioactive waste
BGE-Forschungsauftragsnummer STAFuE-21-11-Klei

As per 07/12/2021

          Geschäftszeichen: SG01203/24/1-2021#1 – Objekt-ID: 886041 – Revision: 00

Call
Effects of subrosion on the barrier effect of the effective containment zone and
the overburden of a potential repository site for high-level radioactive waste

1         Cause and subject
On September 21, 2016, the Bundesgesellschaft für Endlagerung mbH (BGE) was
founded in the business division of the Federal Ministry for the Environment, Nature Con­
servation and Nuclear Safety based on the act on the reorganization of the organizational
structure in the area of final disposal from June 2016.
As of April 24, 2017, the task of the Federal Government was transferred to the BGE in
accordance with Section 9a (3) Sentence 1 of the Atomic Energy Act (AtG). Pursuant to
Section 3 of the Act on the Search and Selection of a Site for a Repository for High-Level
Radioactive Waste (Site Selection Act of May 5, 2017 (BGBl. I p. 1074)), last amended
by Article 247 of the Ordinance of June 19, 2020 ((BGBl. I p. 1328) StandAG), the BGE
is the project sponsor for the site selection procedure.
On September 5, 2017, the start of the site selection process took place in Berlin. At the
beginning, a "white map" of Germany was assumed. The BGE started with the exclusion
of regions according to the legally defined exclusion criteria, minimum requirements and
by implementation of the geoscientific consideration criteria. On September 28, 2020,
the first step of Phase I was completed with the publication of the “Sub-areas Interim
Report”. At this time, 90 areas with an area of approx. 240,874 km² have been desig­
nated as sub-areas according to Section 13 StandAG.
In Step 2 of Phase I, the BGE implements the comparative analysis based on existing
data, in accordance with the legally defined geoscientific and planning-scientific consid­
eration criteria, as well as the representative preliminary safety investigations. The BGE
then proposes siting regions for surface exploration to the Federal Office for the Safety
of Nuclear Waste Disposal (BASE). Phase I has been completed with the decision of the
German Bundestag and the Bundesrat on which siting regions will undergo surface ex­
ploration.
When assessing the safe confinement of radionuclides in a repository system ("the re­
pository system provides the safe containment of radioactive waste through the interac­
tion of the various components, [...]" StandAG) for high-level radioactive waste, it must
be ensured that the effective containment zone retains its barrier function over the period
of 1 million years. Processes that can negatively affect barrier properties (e.g. rock per­
meability, thickness, extension of the effective containment zone) include subrosion pro­
cesses which can lead for example to damage of the effective containment zone as well
as the overburden.
Subrosion (also known as karstification) is the underground leaching of easily soluble
rocks by contact to low mineralized groundwater. As a result, subrosion can create path­
ways for fluids to the subsurface and lead to the collapse of solution cavities.
In order to analyze the existence as well as the possible effects of subrosion on the
safety of a repository system, morphologically visible structures on the earth's surface
such as sinkholes, karst troughs, uvalas or poljen (Martin & Eiblmaier 2001; Pfeffer 2003;
Grotzinger & Jordan 2017) as well as fossil collapse structures, which are often no longer

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Call
Effects of subrosion on the barrier effect of the effective containment zone and
the overburden of a potential repository site for high-level radioactive waste

morphologically recognizable, must be taken into account. The structures created by
subrosion are manifold. Sinkholes for example are divided into six main types based on
their formation process (Waltham et al. 2005).
In Central Europe, subrosion mainly affects chlorides (mostly rock salt), sulphates (gyp­
sum or anhydrite) and carbonates (limestone, dolomite). Subrosion processes can be
caused by meteoric groundwater (epigenous karst) and diffusely ascending deep
groundwater (hypogenic karst), whereby the latter can also affect greater depths
(Jeannin et al. 2015). So-called mixed-water karst, on the other hand, only occurs in
costal regions where salt water is mixed with fresh water (meteoric groundwater)
(Jeannin et al. 2015).
During the assessment of repository projects in Northern Switzerland, rock formations of
the Malm and Muschelkalk were identified as potentially karst bearing formations. Here,
the Malm was exposed to epigenous and mixed water karstification and the Muschelkalk
to hypogene and locally to epigenous karstification (Jeannin et al. 2015). One scenario
for a deep repository project in the Opalinus Clay in Northern Switzerland takes into
account the possibility of cavities in the Muschelkalk which could affect the Opalinus Clay
as a host rock. In general, soluble layers or intercalations in the barrier rock (e.g. inter­
calations of carbonate layers in the clay rock) can also reduce the barrier function (Stück
et al. 2020).
Rock salt as a potential host rock is subdivided into flat-bedded and steep salt deposits.
Subrosion processes on flat-bedded salts can occur both at the top and at the base of
salt formations, especially in the salt slope area due to lateral groundwater flow (Prinz &
Strauß 2011). A risk of subrosion can also result from formations that overlie salt deposits
and are affected by subrosion (e.g. Muschelkalk, Gipskeuper, Malm).
Subrosion phenomena in salt domes occur primarily locally in the uppermost part of the
salt structure (Buurman 2010). These processes were considered for example in the
context of the Preliminary Safety Analysis Gorleben (Kock et al. 2012) and the decom­
missioning of the Morsleben repository for radioactive waste (z. B. Balzer 1998). Subro­
sion processes at the top of the salt structure can cause a reduction in the overall thick­
ness of a salt dome (Mrugalla 2014). Hardly soluble minerals remain as cap rock at the
top of the salt structure. In case of intensive subrosion, cavities can develop and col­
lapse, causing the formation of faults and fissures in the overburden (Mrugalla 2014).
Predictions of the future effects of subrosion are difficult due to heterogeneous local con­
ditions and the large number of factors influencing them.

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Call
Effects of subrosion on the barrier effect of the effective containment zone and
the overburden of a potential repository site for high-level radioactive waste

2          Content
With this call, we invite project proposals for two work packages by August 25, 2021, that
address the following aspects with a particular focus on the safety of a repository for
high-level radioactive waste in Germany. Project proposals can be submitted for only
one or both work packages.

2.1        Work package:
This work package focusses on a systematic compilation of areas affected by subrosion
as well as factors and boundary conditions influencing this process.
Tasks:
      1) A regional geological compilation of the stratigraphic units, taking into account in
         particular the tectonic and hydrogeological situation, in which subrosion and
         karstification processes occur. Of special interest are information on the distribu­
         tion, depth, extent and overall influence of solution phenomena on stratigraphic
         units which were identified as sub-areas in the BGE interim report.
      2) Then, a prognosis of the future development for the next one million years of the
         units considered in 1) shall be developed. In particular, how do subrosion pro­
         cesses change with variations in the exogenous and endogenous boundary con­
         ditions, e.g. groundwater inflow or uplift, and how could this affect the barrier
         function of the effective containment zone and the overburden. Subrosion rates
         and their development over time should be qualitatively estimated.
The following questions should be taken into account when answering task 1 and 2:

      •   Which factors or boundary conditions initiate subrosion and karstification pro­
          cesses? At what depth do such processes occur?

      •   How do subrosion or karstification processes affect the barrier function of the
          effective containment zone and the overburden? What are the differences in the
          impacts of such processes on claystone compared to rock salt in flat deposits?

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Call
Effects of subrosion on the barrier effect of the effective containment zone and
the overburden of a potential repository site for high-level radioactive waste

2.2        Work package:
This work package focuses on the effects of subrosion in the context of rock salt in steep
deposit (salt walls, salt domes).
Tasks:
      1) A systematic compilation of observed subrosion rates at salt domes/walls taking
         into account their genesis as well as the tectonical and hydrogeological situation
         based on literature studies.
      2) Based on the results in 1), what are the expected subrosion rates over the next
         one million years, taking into account varying boundary conditions (e.g. climatic
         fluctuations) as well as uncertainties? We encourage the use of geochemical
         model simulations that may be carried out either generically or with reference to
         specific salt domes.

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Call
Effects of subrosion on the barrier effect of the effective containment zone and
the overburden of a potential repository site for high-level radioactive waste

3         References
AtG: Atomgesetz in der Fassung der Bekanntmachung vom 15. Juli 1985 (BGBl. I S.
       1565), das zuletzt durch Artikel 239 der Verordnung vom 19. Juni 2020 (BGBl. I
       S. 1328) geändert worden ist
Balzer, D. (1998): Projekt Morsleben: Geologische Bearbeitung des Hutgesteins.
       Abschlussbericht,   Band     1.   Hannover:    Bundesgesellschaft   für
       Geowissenschaften und Rohstoffe
Buurman, N. (2010): Charakterisierung von Zirkularstrukturen im geologischen
      Untergrund Hamburgs zur Abgrenzung verkarstungsgefährdeter Bereiche.
      Dissertation, Universität Hamburg, Geowissenschaften, S. 279, Hamburg,
Grotzinger, J. & Jordan, T. (2017): Press-Siever Allgemeine Geologie. 7. Aufl., Berlin:
       Springer-Verlag. ISBN 9783662483411. DOI: 10.1007/978-3-662-48342-8
Jeannin, P. Y., Malard, A. & Eichenberger, U. (2015): Grundlagen zur Beurteilung von
       Tiefenlagerprojekten im Hinblick auf Karstphänomene. Expertenbericht.
       Schweizerisches Institut für Speläologie und Karstforschung (SISKA). La Chaux-
       de-Fonds
Kock, I., Eickemeier, R., Frieling, G., Heusermann, S., Knauth, M., Minkley, W., Navarro,
        M., Nipp, H.-K. & Vogel, P. (2012): Integritätsanalyse der geologischen Barriere.
        Bericht zum Arbeitspaket 9.1. Vorläufige Sicherheitsanalyse für den Standort
        Gorleben. Bundesanstalt für Geowissenschaften (BGR), Gesellschaft für
        Anlagen- und Reaktorsicherheit (GRS) mbH, Institut für Gebirgsmechanik GmbH
        (IfG). Köln. ISBN 9783939355625
Martin, C. & Eiblmaier, M. (2001): Lexikon der Geowissenschaften. 4. Band: Nord bis
        Silb. Heidelberg: Spektrum Akademischer Verlag. ISBN 3827404231
Mrugalla, S. (2014): Geowissenschaftliche Langzeitprognose für Norddeutschland -
       ohne Endlagereinfluss (AnSichT). Ergebnisbericht. Hannover: Bundesanstalt für
       Geowissenschaften und Rohstoffe (BGR)
Pfeffer, K.-H. (2003): Karstlandschaften. Nationalatlas Bundesrepublik Deutschland -
        Relief, Boden und Wasser, Bd. 2, S. 94-95
Prinz, H. & Strauß, R. (2011): Ingenieurgeologie. 5. Aufl., Heidelberg: Spektrum
       Akademischer Verlag. ISBN 9783827424723. DOI: 10.1007/978-3-8274-2473-0
Stück, H., Bense, F., Frenzel, B., Henneberg, M., Kneuker, T., Lang, J., Mertineit, M.,
       Noack, V. & Pollok, L. (2020): Ausschlusskriterium "Aktive Störungszonen".
       Abschlussbericht. Hannover/Berlin: Bundesanstalt für Geowissenschaften und
       Rohstoffe (BGR)
Waltham, T., Bell, F. & Culshaw, M. (2005): Sinkholes and subsidence; karst and
      cavernous rocks in engineering and construction. Berlin, Heidelberg, New York:
      Springer. ISBN 3540207252

Geschäftszeichen: SG01203/24/1-2021#1 – Objekt-ID: 886041 – Revision: 00               6

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