Carbon-14 and Iodine-129 Migration in Cement (CIM) - Experiment concept

Design

  • A large diameter borehole (Ø 388 mm) backfilled with OPC mortar is being used as a proxy for cementitious material used as backfill and/or support material in L/ILW or TRU waste repositories.

  • In the centre of the mortar backfill, a small diameter (Ø 56 mm) borehole was drilled in November 2019 and equipped with a multi-packer system for the circulation of the test cocktail. Figure 1 shows the schematic setup in a sub-vertical borehole. The cocktail will be based on cement water and be prepared with the ions listed in Table 1.

  • The circulation interval will be connected to surface equipment, allowing for continuous monitoring of the fluid composition by online sensors and sampling. The monitoring will focus on activities of the injected radionuclides, chemistry, and microbiology.

  • Three monitoring boreholes drilled at relatively short distance (ca 15 cm) from the circulation borehole will allow to monitor the progress of the weakest sorbing compounds in the rock.

  • Based on the results from the experiment monitoring and discussions between the partners, the in-situ experiment will be overcored to allow for the analysis of diffusion profiles in the mortar and/or in the rock.

 

Table 1: Isotopes (radioactive and stable) foreseen for the circulation in the CIM experiment.

Isotope Species
C-14 Formate HCOO-
I-129 Iodide I-
H-3 HTO
Cl-36 Cl-
Cs-134 Cs+
Ba-133 Ba2+

 

HPF backfilled borehole

Four vertical or slightly inclined boreholes resulting from the overcoring of the HPF experiment at GTS have been backfilled with OPC mortar in 2004 (Figure 2).

One of these boreholes is being used as circulation borehole for the CIM experiment. The borehole and the depth of the circulation interval was selected in order to position the latter in an area of dense matrix with no distinct water conducting features. The selection was based on available geological logs from the HPF project. Three monitoring boreholes were drilled at short distance (ca 15 cm) from the source borehole.

Fig1 Setup of the circulation CIM

Figure 1: Setup of the circulation in a sub-vertical borehole

Fig 2 Schematic 3D view of the planned CIM borehole

Figure 2:          Schematic 3D view of the HPF and planned CIM borehole relative to the AU-126 shear zone and AU tunnel at the GTS

The GTS underground facilities are also available to interested 3rd parties for underground testing and research. The GTS offers cost-effective access to a fully developed, well characterised underground research facility with round the year logistical support - please contact Dr. Ingo Blechschmidt, Head of the Grimsel Test Site, for further details.