In:
Safety of Nuclear Waste Disposal, Copernicus GmbH, Vol. 1 ( 2021-11-10), p. 173-174
Abstract:
Abstract. The disposal of heat-generating nuclear waste in deep geological formations is an internationally
accepted concept. Several repository systems are under discussion in Germany, whereby claystone, salt
or crystalline rock could act as the host rock. In this contribution we focus on repository systems where the
Containment Providing Rock Zone (CRZ) ensures safe enclosure of the waste and thus the geologic barrier is
essential. Even though the various rock types considered differ substantially in their mechanical, hydraulic, thermal
and chemical behavior, they must all meet the same safety requirements as defined by the German Federal
Ministry for the Environment, Nature Conservation and Nuclear Safety (BMU) in 2020. As part of these
safety requirements, it must be shown that the integrity of the CRZ is guaranteed for the verification period, i.e.
the retention of the properties essential for the containment capacities must be demonstrated over 1 million years.
Therefore, the formation of new pathways must be avoided and temperature development must not significantly
impair the barrier effect. The anticipated stresses and fluid pressures should not exceed the dilatancy strength
and the fluid pressure capacity, respectively. In order to assess the compliance of these requirements, numerical
modelling is an essential and powerful tool. Even though great progress has been made regarding the efficiency of computational
methods, multiphysical modelling on different length scales over long time periods is still a challenging task. Moreover, since readily
available solutions do not exist, adapted methods have to be developed and evaluated, in order to verify concepts and numerical
implementations. The BGR gained experience in the field of thermal, hydraulic, mechanical (THM) numerical analysis of the integrity of the CRZ in salt rock
and clay stone joined research projects on German disposal options. For crystalline rocks, first concepts are currently being developed
within the CHRISTA II project. Compared to clay stone and salt rock, special features have to be taken into account: First of all, crystalline
rock is characterized by fractures and other discontinuities. Thus, it cannot be assumed that an undisturbed
area of sufficient size can be found for the entire nuclear waste. Consequently, several smaller CRZs must be
defined, each providing undisturbed rock. Numerical analysis must deal with smaller CRZs and mechanical and
hydraulic boundary conditions that are influenced by fractures. In addition, the processes in the individual CRZs
may influence each other (e.g. Temperature distribution). Preliminary modelling approaches and results of numerical THM analyses,
considering an upscaled fracture network, are presented.
Type of Medium:
Online Resource
ISSN:
2749-4802
DOI:
10.5194/sand-1-173-2021
DOI:
10.5194/sand-1-173-2021-supplement
Language:
English
Publisher:
Copernicus GmbH
Publication Date:
2021
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