WP 5.1:Constitutive model

Workpackage number

WP5.1

Start date or starting event:

Month 6

Activity type

Constitutive model – RTD

Participant id

1

2

3

4

5

6

7

8

9

10

12

Person-months per participant:

2

1

1.2

7

8

16

11

8

12

18

5

Objectives

This workpackage aims to develop numerical tools allowing simulation at time and repository scale. These numerical tools are essential to address the following relevant questions:

  • What is the expected evolution of the clay around a disposal system for heat-emitting waste during the thermal period ?
  • What are the main uncertainties about the EDZ+TDZ evolution and how can these uncertainties be dealt with ?
  • What the ultimate thermal limits of the clay could be in the context of the long term performance of the repository system

Description of work

Task 1: THM coupling

Within the task "THM coupling", Thermo-Hydro-Mechanical constitutive models will be futher advanced and  numerical codes will be developed and improve. The achievement of this task will be principally based on Work Package 2 and complemented with the test results performed in WP3.1 (calibration and determination of parameters).

The major developments will consist of:

  • Constitutive modelling of the clay rocks, in a continuum framework to incorporate heat changes and transfers, moisture transfer, mechanical stress – strain evolution (including the development, evolution of microcracks and  the viscous – creep effects), and their interaction, especially in relation with thermal effects
  • Utilisation of local 2nd gradient models in order to provide objective descriptions of the behaviour in the post-localization regime. In particular, it will be possible to objectively describe the shear band thickness, which governs the interaction with other emerging or existing shear bands and with the water transfer properties.
  • Extension of THM coupling in an unsaturated set to the 2nd gradient model.
  • Modelling of the transition from the onset of strain localization up to rupture (fracturing), with related effects on permeability and coupled effects.
  • Development of remeshing techniques in the related numerical codes when necessary.

The codes used by the different modelling teams are:

EPFL will use a Thermo-Hydro-Mechanical (saturated/unsaturated) model developed at LMS-EPFL

ENPC will use the q-Stock THM coupled finite element code

ULG and UJF will use  the Lagamine code

GRS and CIMNE will use CODE_BRIGHT

EURIDICE and NRG will use FLAC code

NAGRA intends to use the THM-code Mherlin (continuum model) and an extension of the Connectflow, which can handle self-sealing processes along discrete fractures (final code evaluation is part of this task)

ITASCA will use PFC3D code

Task 2: Sealing processes

Modelling of sealing processes under thermal load based on PFC3D (discontinuum) code will be performed by ITASCA. The work will consist in:

  • Improve the current numerical models in order to reproduce the short and long term behaviours of each clay rock.
  • Model the fracturing and the sealing process at ambient temperature and study the impact of temperature on their evolution.
  • Assess the effect of discrete fractures and fracture connectivity on the effective axial hydraulic properties of the DZ.

Task 3: Chemical processes

SCK•CEN will perform some static thermodynamic calculations to have an idea on the combined effect of temperature and pore water chemistry on the mineralogy and to help evaluating the results of WP3-2.

CIMNE will perform  the coupled THMC analysis, using CODE_BRIGHT, to examine the possible role of geochemical variables on the development and evolution of the DZ. Attention will be especially paid to osmotic flow, salt dissolution and precipitation and thermal effects. The code will be applied to the PRACLAY large scale heater test to simulate the chemical evolution (oxidation during excavation and different heating /cooling phases) around the test.

Deliverables

D.10: Report on the constitutive models development

Milestones and expected result

Modelling tools allowing simulation at time and repository scale will be the result of this workpackage. This constitutes a milestone for workpackage 5.2

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

Modelling tools allowing simulation at time and repository scale ...............................................Month 36