Description

At each stage of construction of a repository for radioactive waste, there is a need to predict the geological conditions for new areas of the facility, based on observations from areas that have already been excavated. The Fractured Rock Extrapolation, Suitability Criteria and Inflow Prediction (FRESCIP) Task is aimed to develop and test alternative modeling concepts/methodologies such as discrete fracture network (DFN) and channel network models (CNM), with a particular emphasis on conditional simulation based on the types of data that can realistically be expected at successive stages of repository construction.

FRESCIP takes advantage of in-situ data that were obtained as part of the Demonstration Area experiment in the ONKALO facility below the island of Olkiluoto, on the Baltic coast of Finland. This exercise was carried out by Posiva Oy as a test of their methodology for applying rock-suitability criteria in the construction and operation of a spent-nuclear-fuel repository at the same site. This facility is situated in crystalline rock, predominantly migmatitic gneiss.

Experimental Data

Two types of data will be used in FRESCIP:

• Synthetic data based on a DFN statistical model of the Olkiluoto site, consistent with the state of information at the time of the Demonstration Area experiment.
• Actual site data obtained from site characterization prior to and during the Demonstration Area experiment, including fracture frequencies, fracture trace maps, hydrologic packer-test and flow-logging results from pilot holes, and groundwater inflows to the demonstration tunnels and deposition hole.

The use of synthetic data along with actual site data will allow a study of cases with fewer measurement uncertainties, as well as options for exploring larger spatial scales. This will expand the possibilities for assessment of the significance of discrepancies between model predictions and observations.

The actual site data are provided by Posiva exclusively for use within this FRESCIP task.

Approach

The task is divided into six main stages or steps including a benchmarking step:

Step 0: Benchmarking based on synthetic data (with substeps corresponding to each of the next four steps which will use the actual site data).

Step 1: Predictions of fracture geometry and hydraulic properties in the actual pilot holes drilled prior to the demonstration tunnels.

Step 2: Predictions of fracture geometry in the demonstration tunnels.

Step 3: Predictions of fracture geometry and hydraulic properties in pilot holes drilled prior to deposition holes.

Step 4: Predictions of fracture geometry and inflows in the deposition holes.

In each step, there will be an opportunity to compare predictions with the actual observations from the Demonstration Area. These steps will be followed by a more open-ended step:

Step 5: Applications and reporting

The scope of this final step will be determined by the time and interests of the modeling teams. Possibilities include, for example, predictions of post-closure flows to deposition holes, transport resistance for pathways associated with the deposition holes, and how well the uncertainty is constrained by the progressive stages of data obtained during repository construction. It is expected that different teams may take different directions in the final step.

Participating Groups

• Sweden: Uppsala University/Swedish Radiation Safety Authority (SSM)
• Canada: Canadian Nuclear Safety Commission (CNSC, engagement expected later in the phase)
• China: Chinese Academy of Sciences (CAS), Beijing Research Institute of Uranium Geology (BRIUG)
• Korea: DynaFrax/Korea Radioactive Waste Agency (KORAD), Korean Atomic Energy Institute (KAERI)
• Taiwan: Taiwan Power Company (TaiPower)
• USA: Department Of Energy (Los Alamos National Laboratory)

Further Information

For further information, please contact the task leader, Joel Geier.

References

1. Ask D., 2011. Semi-integration of overcoring stress data and review of rock stress data at the Olkiluoto site. Posiva Working Report 2011-16, Posiva Oy.
2. Fox A., Forchhammer K., Pettersson A., La Pointe P. & Lim D-H., 2011. Geological Discrete-Fracture Network Model for the Olkiluoto Site, Finland, (Version 2.0). Posiva Report 2012-27, Posiva Oy.
3. Häkkinen, T., Merjama, S., and Mönkkönen, H., 2014. ONKALO Rock Mechanics Model (RMM) Version 2.3. Posiva Working Report 2014-33
4. Hartley, L., Appleyard, P., Baxter, S., Mosley, K., Williams, T., and Fox, A., 2017. Demonstration Area Discrete Fracture Network Modelling at Olkiluoto, Posiva Working Report 2017-31.
5. Hartley, L., Baxter, S., and Williams, T. 2016. Geomechanical Coupled Flow in Fractures during Temperate and Glacial Conditions. Posiva Working Report 2016-08.
6. Mattila, J., Suikkanen, J., and Read, R. (editors), 2018. Rock Mechanics of Olkiluoto. Posiva Report 2021-18.
7. Posiva 2011. Olkiluoto Site Description 2011, Posiva Report 2011-02.
8. Tammisto, E. and Palmén, J., 2011. Database for Hydraulically Conductive Fractures – Update 2010. Posiva Working Report 2011-12, Posiva Oy.