WP 3.2:Mineralogic changes / Input for THMC

Workpackage number

WP3.2

Start date or starting event:

Month 3

Activity type

Mineralogic changes / Input for THMC – RTD

Participant id

3

 

 

 

 

 

 

Person-months per participant:

3.5

 

 

 

 

 

 

Objectives

This workpackage aims to determine the possible thermally induced modifications of clays mineralogy which is a dominant factor influencing the key properties of the clays and THM behaviour. The investigation in this sub-workpakage provide thus key elements to answer the following questions: Specific attention will be given to the possibility of the creation of irreversible changes.

  • Under which thermal condition can the favourable clay properties be modified ?
  • Under which conditions do the changes in clay properties become irreversible ?

A ultimate temperature limit in terms of geochemical properties can be assessed through these analysis. The impact of these modification of the geochemical properties on the hydromechanical behaviour of the clays can be qualitatively assessed. 

Description of work

The thermo-hydro-chemical phenomena will influence the hydro-mechanical behaviour of the clay.  It is known that the THC will influence the mineralogy (clay and non-clay minerals), which can affect the swelling behaviour, the permeability and the cohesion.  Consequently, the mineralogical changes within the THMC experiments will be analysed.

First of all, due to the higher temperatures used, mineralogical changes of the clay particles might occur.  It is well known that illitization starts at about 80°C.  This can be quite important with respect to the sealing potential of the clays, as illitization will lower the swelling capacity.  However, this process is mostly not fast and thus effects might be very limited within these set-ups.  Therefore, some laboratory tests at higher temperatures (in order to speed up the process) will be performed.  These tests are mainly meant to have an idea on possible extreme effects and to focus later analyses.

In order to check the effects of a broader range of thermal loadings on clay mineralogy, a few tests at higher temperatures will be performed. This will give some indications on the temperature at which important, irreversible processes take place that might hamper the performance of the repository system. However taking into account the long thermal period (up to 2000 years) considered in a real repository, the possible long term effects cannot be investigated through the laboratory tests. 

Secondly, the combined effect of increased temperature and oxidising or alkaline plume conditions during the permeability tests, might result in an increased precipitation of non-clay minerals (e.g. carbonates and sulphates). Therefore, all samples available after the permeability tests with permeameter cell (thus with different pore water chemistry conditions) will be subjected to mineralogical analyses.  Detailed petrographical analyses will be performed.  By means of SEM-EDX and thin section analyses, neoformed precipitates will be searched for and analysed.  The obtained petrographical results might be qualitatively linked to the hydromechanical observations.

The SMARAGD project (contractnumber 028403 – Intra European fellowships - EURATOM) foresees experiments to study the changes in clay mineralogy as a result of temperature increase. 
It is clear that the results will be made available for the TIMODAZ partners and will be included in the conclusions made. Within this proposal the combined effect of temperature increase and oxidising or alkaline plume conditions will be evaluated (these are not considered in the SMARAGD project).  This combined effect can result in neoformed precipitates that might speed up the sealing process and can have effects on the geomechanical properties of the samples. Therefore, all samples available after the permeability tests with permeameter cell (thus with different pore water chemistry conditions) will be subjected to mineralogical analyses.  Detailed petrographical analyses will be performed.  By means of SEM-EDX and thin section analyses, neoformed precipitates will be searched for and analysed.  The obtained petrographical results might be qualitatively linked to the hydromechanical observations.

Deliverables

D.6 Report on thermally induced modifications of clays

Milestones and expected result

The result of this workpackage is the determination of the thermally induced modifications of clays. This constitutes a milestone for task 3 of WP5.1

Protocol and objectives of the tests performed  as input for the first end-users group review ……….Month 5

Prior approval by the GB of the enduser review reports to proceed with the next related tests - Months 8,26,44

Thermally induced modifications of clays ............................................................................................Month 30