The Praclay Heater Test

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The Praclay Heater Test

• F. Bernier (ESV EURIDICE GIE)
• E. Weetjens and X. Sillen (SCK.CEN)
• URF HADES Conference
• Mol, 27-29 January 2004

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The EBS architecture for disposal of cat. C waste
has been reviewed

• Three alternatives are considered
• Supercontainer (SC)
• Borehole
• Sleeve
• Choices has to be kept as flexible as possible to
  get the possibility to reorient parts of the
  design towards another alternative at minimal
  cost

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Consequences on thePRACLAY experiment

• Experience as initially planned specific to one
  detailed design will not be possible
• PRACLAY has to be
• Addressed to the three alternatives
• Enlarged to characterisation, verification,
  confirmation and demonstration

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The PRACLAY testspreliminary design
Heated part 30m
1m
10m
2 m

• Heater Test
• THM/C at large scale

• H. Plug Test
• Disposal gallery cut-off
• Installation
• Performance

• Backfill Test
• Fabrication
• Installation
• Performance
• ESDRED - EC

Crossing Test - EDZ - no starting chamber
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Main objectives of the heater test

• Configuration similar to a real repository
• Combined effect of the EDZ and the TDZ
• Effect of the thermal load on the stability of
  the lining (retrievability)
• Verification and confirmation of our knowledge of
  the THM/C behaviour of Boom Clay
• Demonstration that the thermal load does not
  affect the performance of the Boom Clay layer

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The test has some limitation

• Short heating period (10 years) compared with a
  real repository
• Different boundary conditons
• Different heat source
• No radioactive source
• ..
• The aim of the test is to reproduce in a
  conservative way the most critical state and
  phenomena that could occur in the host rock

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Why a large scale heater?

• Boom Clay is considered as the main barrier
• Confidence building
• Confirmation that BC behaves as predicted
• Milestone for the disposal strategy
• The thermal load is the most severe transient
  that the repository system will undergo on a
  large spatial scale and in a relatively short
  period of time
• Results will not be affected with local
  heterogeneities

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Case study showing the large scale impact of the
thermal load(Picard Giraud 1995)
200 m
Initial thermal flux 1W/m³
10 m
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Experience from small-scale heater tests

• CACTUS, CERBERUS, BACCHUS, ATLAS
• The THM behaviour is quite consistent
• ? T ? ? p, ?
• dissipation of p and ? but ? in a smaller
  proportion
• ? permeability and water content
• ? density
• consolidation

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The large scale heater test will be
representative for all the designs
3D - Borehole design
2D SC and sleeve design
2 canisters per 5 m (201 W/m)
200 m
100 m
T in function of the distance from the source?
1 m
20 m
20 m
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For X gt 2m the influence of the design on T is
very limited
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Optimisation of the heat source

• Accurate time-dependant heat output of HLW
• will increase excessively the period of the test
• The objective is to heat a large volume of clay
  within a period of 10 years to be representative
  in terms of maximal temperature and thermal
  gradient

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Constant flux (290W/m ___ ) or Constant
temperature (90C - - -)?
T016C
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30 m is considered for the length of the heat
source
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Isotherms around the heaterare representative in
the central part
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The heater test will be accompanied with

• A characterisation programme of each part of the
  system
• Modelling
• Instrumentation
• from the connecting gallery
• radially to the PRACLAY gallery
• temperature, displacements, pore water and total
  pressure, fracturation, water sampling (chemical
  analysis)

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Planing

• General design 2004
• Characterisation programme 2005
• Construction of the PRACLAY gallery and
  installation of tests 2006
• Start of the heat phase 2007
• Preliminary conclusions 2012
• Start of the cooling phase 2017

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Conclusions

• The large scale thermal behaviour is a remaining
  key issue
• Most severe impact that the repository will
  undergo
• The whole thickness of Boom Clay will be affected
• Milestone for the disposal strategy
• Confidence building
• Open to international cooperation
• Design not yet fixed