Glacial erosion of the bentonite buffer

Matti Liukkonen, Markus Olin

Research output: Chapter in Book/Report/Conference proceedingConference article in proceedingsScientificpeer-review

Abstract

According to the KBS-3 concept. the bentonite buffer is an essential part of a safe nuclear waste repository in the granitic bedrock, Glacial erosion of the bentonite buffer may occur due to potential intrusion of low-saline groundwater during the highly variable flow conditions following a glaciation period. The stability of the bentonite buffer is influenced by divalent cations, particularly pore-water calcium, present both in the bentonite pore water and in soluble minerals. As long as calcium containing minerals are present in the bentonite, calcium loss into fresh groundwater coming into contact with the bentonite can be replenished by the dissolution of these minerals. When a mineral is depleted near to the water flow interface, the gel may form a sol, which can be carried away by the groundwater flow. This exposes new gel to the water flow, and a steady state mass loss rate of the bentonite may be attained.
The main focus of this modeling study is on the changes in composition of the cation exchangers before and, especially, after a glacial period. The bentonite composition will change, to at least some degree, prior to the glacial period. The system will therefore reach a state of equilibrium during the different groundwater periods prior to the glacial period. From the point of view of preserving the beneficial characteristics (density and Na- content) of the bentonite buffer, it is essential to estimate whether the Na -bentonite will ultimately transform into mixed Ca/Na -bentonite.
The simulation results show that the colloid formation capacity remains low, even during the intrusion of glacial melt waters, since the cation exchanger changes from sodium to calcium one.
In this PetraSim simulation, a 1-D model of the composition of the cation exchangers was applied using the Gaines-Thomas model. The RESTART module was applied to simulating the long-term effects of groundwater and glacial melt water on repository conditions.
Original languageEnglish
Title of host publicationProceedings of the TOUGH Symposium 2009
Subtitle of host publicationSeptember 14—16, 2009
Place of PublicationBerkeley
Pages478-485
Publication statusPublished - 2009
MoE publication typeA4 Article in a conference publication
EventTOUGH Symposium 2009 - Berkeley, United States
Duration: 14 Sep 200916 Sep 2009

Conference

ConferenceTOUGH Symposium 2009
CountryUnited States
CityBerkeley
Period14/09/0916/09/09

Keywords

  • THC
  • bentonite
  • modelling

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    Liukkonen, M., & Olin, M. (2009). Glacial erosion of the bentonite buffer. In Proceedings of the TOUGH Symposium 2009: September 14—16, 2009 (pp. 478-485). https://drive.google.com/open?id=0By-1oCLrzv_JS2M1SmI1R3NxTk0