Colloid Formation and Migration (CFM)

The LIT was emplaced during 2014 successfully on May 12th 2014. It consists of a solid bentonite (FEBEX and Zn-Montmorillionite) source with radionuclide tracers added in glass vials. The bentonite source was placed into the MI shear zone, which is a known water-conducting zone.

Monitoring of the bentonite colloid formation and the subsequent transport of radionuclides was performed in three dedicated monitoring boreholes and in the existing tunnel outflows such as Pinkel. The hydraulic flow field around the bentonite source was controlled by the continuous outflow at Pinkel.

The emplaced effective swelling pressure of the bentonite is expected to reach approximately 1.05 MPa. The bentonite was built-in as bentonite rings around a mandril. The tracer cocktail contains strongly sorbing tracers (²⁴¹Am, ²⁴²Pu, ¹³⁷Cs) and weakly sorbing tracers (⁹⁹Tc, ⁴⁵Ca, ⁷⁵Se, ²³⁷Np, ²³³U).

The packer system used for the bentonite source was custom-made to allow a later overcoring and therefore disconnection of the packer 3 from the packer 1 and 2. The bentonite source being emplaced between packer 1 and 2.

Final preparation of the bentonite rings and assemblage of the bentonite source

Schematic representation of a bentonite ring interface

Bentonite source emplacement procedure

3D images showing CFM LIT study with CFM 06.002 host of the LIT

CFM site-preparation was finalised for the hot migration experiment (CFM RUN 12-02RN) and the first “hot” experiment started in the frame of the CFM project on 29th of February 2012. The tracer cocktail was delivered on 29th in the afternoon and injection started at 8pm at the same day. For the proceeding day and night, shifts were organised to develop a comprehensive data set from the tracer injection test. For a description on the input parameters of the injection please see below.

Sven, Tom, Thorsten, Karam – final inspection before the CFM Tracer Test started

Ready for sampling

Careful dismantling of CFM tracer tank

Lead-shielded tracer tank

Final destination of the lead-shielded tank in the injection cabinet

Preparation of auto sampler

and start of the CFM tracer injection…

.. before closing the injection cabinet doors.

GTS Phase VI - CFM Project : Radionuclide – Colloid/Conservative Tracer Test _Run CFM 12-02RN

Colloid Formation and Migration Experiment

Field Tracer Testing 2009 onwards

During 2009 and 2010 a series of tracer migration tests using conservative, bentonite colloid and homologues (trivalent & tetravalent) have been performed in the shear zone between borehole interval  CFM06.002i2 and the Pinkel surface packer.

Source interval CFM 06.002i2

The borehole interval used as the tracer source is located in CFM 06.002 and centred on a brittle fracture in the MI shear zone. Hydraulic tests show a transmissivity of about 10-6 m2/s compared to a large-scale shear zone transmissivity of ~5 x 10-7 m2/s.  The concentration in the interval is controlled by a recirculation loop to the injection cabinet containing a pump, fluorometer, pH, EC and turbidity sensors.  The loop has a volume (including the borehole interval) of 1litre plus the volume of the tracer tank. All lines are made of PEEK to minimise sorption.

Recovery at the Pinkel

Tracer recovery is via the Pinkel surface packer located on a flowing point on the brittle fracture horizon within the MI shear zone.  The surface packer is connected to the tracer extraction cabinet containing sampling lines, fluorometer, pH, EC and turbidity sensors via PEEK lines. An autosampler is used to perform routine background sampling and unattended sampling during testing.

	Conservative tracer test 52 ml/min extraction from Pinkel 78.8% Uranine recovery at end of test
	Homologue/colloid tracer test 48 ml/min extraction from Pinkel 84% Uranine recovery at end of test Colloid recovery 52-67% Th (IV) 32 +/- 10% Hf(IV) 30 +/- 5% Tb(III)  7 +/- 5% Eu(III) 14 +/- 3%
	Conservative tracer test 10 ml/min extraction from Pinkel 90.1% Uranine recovery 95.2% Iodide recovery
	Homologue/colloid tracer test 10 ml/min extraction from Pinkel 20.5% Uranine recovery Colloid recovery varied according to technique. Possibility of mobilisation of additional colloids Th (IV) 14 +/- 2% Hf(IV)  6 +/- 2% Tb(III) 46 +/- 6% Eu(III) 43 +/- 10%
	Conservative tracer test (LiI & Uranine) at 25 ml/min extraction to test recovery at higher rates following 10-03. Uranine recovery 91.9% Li recovery 97.6% I recovery 93.1%
Drilling and completion of near-field monitoring boreholes Feb-July 2011 Packer systems designed for subsequent resin injection and overcoring.
	Homologue tracer test Repeat of test 10-03 using better control of tracer pH and additional conservative tracer (Amino-G). Monitoring boreholes instrumented but not sampled during test.

Drilling and completion of monitoring boreholes CFM 11.001, CFM 11.002 & CFM 11.003
After emplacement of the bentonite source in CFM 06.002 it is planned to monitor the near field geochemical conditions by sampling the fluid from the shear zone close to the source. To accomplish this 3 new boreholes have been drilled during 2011. The boreholes need to be within the planned overcore so that they can be used for resin injection to stabilise the shear zone and source prior to excavation. Highly accurate drilling was required to ensure that the new boreholes did not intersect CFM 06.002 or depart from the overcore volume.  The planned distance between the boreholes was 40mm and the survey showed that deviations from the planned trajectory were less than 10mm and that all boreholes were contained within the planned overcore volume.

Specially designed monitoring packer systems have been installed that can be used for resin injection and sampling and can be overcored.  Interval and sampling line volumes have been minimised to facilitate low flow rate sampling close to the source. All material in the interval and lines is PEEK or coated with PEEK to minimise sorption.  The systems are engineered to allow resin injection at the end of the test prior to overcoring.

Colloid Formation and Migration Experiment