The PRACLAY experiment

1
The PRACLAY experiment

• Exchange meeting n1
• EIG PRACLAY - SCKCEN - ONDRAF/NIRAS
• 18/01/01

2
The objectives of the PRACLAY experiment have
been revised

• Revision of the objectives (April 2000)
• Report Methodical and detailed description of
  the PRACLAY Experiment
• Revision of the design
• longitudinal design (plugs, central tube, ...)
• hydration system
• thermal load
• instrumentation
• proposal of additional experiments

3
The PRACLAY experiment

• in-situ verification and confirmation of the
  present status of scientific and conceptual
  knowledge
• better understanding of
• the disposal system
• the interactions between its different components.

4
Differences exist with the real disposal concept

• Geometry
• Influence of the boundary conditions
• Thermal load
• Hydration process
• Instrumentation
• The PRACLAY experiment will not reflect exactly
  the real concept but will give the tools to
  understand it with a good confidence level

5
Instrumentation is installed to observe the
behaviour of the different components

• Instrumentation has to be optimised so that as
  much meaningful information as possible can be
  collected from each sensor
• Instrumentation has to be redundant to guarantee
  that a sufficient fraction will resist at long
  term
• External devices (instruments, samples, ...) may
  never alter the demonstration character of the
  PRACLAY experiment.

6
Confirm and improve our knowledge of the
reference concept

• Comparison between
• Prediction based on our interpretation of the
  reality (models)
• What we can measure
• Agreementgt a certain prediction level is
  reachedgt confirmation of our knowledge
• Differencegt some aspects are misunderstoodgt
  improvements are required

7
The desired output is (1)

• Observation of the behaviour of the whole
  disposal system
• interactions with the main gallery
• plugs
• central tube (possibility of retrievability)
• Characterisation of the disturbed zone (EDZ and
  TDZ) and its evolution in time
• verification of the hypothesis considered in the
  performance assessment

8
The desired output is (2)

• Verify the hydration process through the backfill
  material
• useful information for the work sequence of the
  final repository
• Study of the THM phenomena occurring inside the
  backfill material and the possible Geochemical
  coupling
• heat and water transport process
• swelling capacity of the backfill

9
The desired output is (3)

• The study of the Geo-Chemistry phenomena
• Microbial characterisation
• Saline fronts
• concentration of chloride
• problems of pitting corrosion
• Alkaline plume
• decrease of the swelling properties
• hardening by precipitation of calcium carbonate
• Oxydation of Boom clay
• Thermal degradation

10
Additional experiment proposals

• Corrosion - Bruno Kursten
• Migration - Pierre De Cannière

11
Localised corrosion of candidate overpack
materials on a 11 scale

• Ring shaped elements
• around the central tube - isolated electrically
• makes part of the central tube (welding)
• Contact with bentonite - Mock-up 1000mg/L Cl-
• Characterisation of the chemical composition of
  the backfill pore-water (anion content, pH,
  temp., oxygen content, )
• Determination of the corrosion potential Ecorr
  under realistic conditions

12
Migration experiment (1)

• Radial piezometers outside the middle of the
  PRACLAY experiment
• Aim
• general characterization of the transport
  properties of the backfill at large scale and
  under in situ conditions
• models validation
• detection of preferential water paths in the
  backfill.

13
Migration experiment (2)

• Migration experiment on backfill and Boom Clay
  samples after a thermal loading (in lab)
• In situ migration experiments in Boom Clay after
  dismantling of the PRACLAY experiment

14
Current choices forthe PRACLAY experiment

• Thermal load 240 W/m
• 100 C after 5 years of heating
• 30 C after 1 year of cooling
• Lining designed to resist to the mechanical and
  the thermal load
• Backfill material the same as form OPHELIE
• Swelling pressure limit to 2 MPa
• Radial hydration from outer

15
The longitudinal design of the PRACLAY experiment