Full-scale Engineered Barriers Expmnt. (FEBEX-DP)

Participants of the final FEBEX-DP Meeting (Madrid, May 2017)

FEBEX-DP Overview Video

History

The FEBEX experiment consists of an in-situ full-scale engineered barrier system (EBS) test for the disposal of high level waste (HLW). It is performed under natural conditions in crystalline rock in which the canisters are placed horizontally in drifts and are surrounded by a clay barrier constructed of highly compacted bentonite blocks. It was initiated and led by Enresa in 1995 and has been one of the research subjects in three subsequent European projects. In 2008, a consortium consisting of SKB, Ciemat, Posiva, and Nagra (and since 2013 KAERI) undertook the continuation of the experiment under the project name FEBEXe.

Construction of FEBEX - 1994

Heating started in 1997 and since then a constant temperature of 100°C has been maintained in the remaining heater, while the bentonite buffer has been slowly hydrating in a natural way. A total of 632 sensors in the bentonite barrier, the rock mass, the heaters and the service zone record temperature, water saturation, humidity, total pressure, displacement, and water pressure. A partial dismantling and sampling of the EBS was carried out during 2002.

At the end of the heating phase, the hydration pattern is relatively symmetric, with no major differences along the axis. Although the host rock is characterized by heterogeneities with zones of higher permeability, the resaturation process is driven by the suction of the bentonite rather than by the availability of water in the rock, especially in the early phase. After 18 years, the water content in the buffer close to the heater still continues to increase slowly. The hydraulic pore pressures in the buffer and the geosphere have practically stabilized. The total pressure in general continues to increase in most points into the buffer, where in some parts pressures of over 6 MPa are registered.

The long monitoring phase and the partial dismantling in 2002 indicate that the EBS has largely performed as expected. Furthermore, the major processes and couplings affecting the buffer saturation during the initial thermal period identified prior to the start of the experiment have been confirmed (Lanyon & Gaus, 2013).

FEBEX-DP

For the dismantling of the second heater, the project FEBEX-DP was initiated and will last until the end of 2016. Additional partners were invited to join the FEBEX-DP project with ANDRA, BGR, Obayashi, RWM, SURAO, US-DOE/LBNL following this invitation.

1. Febex tunnel in Grimsel.

2. Drilling of small pilot boreholes.

3. Planning and drilling of larger boreholes

4. Overcoring of plug/bentonite interface

5. Removal of overcore

6. Dismantling first stage of Plug

7. Planning of further boreholes

8. Dismantling second stage of Plug

9. Planned Removal of dummy heater

10. Removal of dummy heater

10a. Main heater exposed, ready for extraction

10b. Removal trolley arrives

10c. Removal trolley positioned, pulley attached

10d. Extraction of heater

10e. Trolley removes heater

11. Planned removal during dismantling

12. Fully dismantled tunnel

The objectives of the FEBEX-DP are:

• Characterization of the key physical properties (e.g., density, water content) of the barrier and their distribution and comparison with results from the partial dismantling and model predictions
• Characterization of corrosion and microbiological processes on heater, instruments and coupons resulting from evolving redox conditions and saturation states, including gas analysis 
• Characterization of mineralogical interactions at material interfaces (e.g., cement-bentonite or iron-bentonite, rock-bentonite) by macro- and micro level studies 
• Assessment of sensor performance 
• Further increasing understanding of the thermo-hydro-mechanical (THM) and thermo-hydro-chemical (THC) processes through integration of monitoring and dismantling results

The dismantling activities started in late 2014 and were completed during the summer of 2015. An extensive laboratory programme on the over 1300 samples is being undertaken.

References

Lanyon G.W., Gaus I. (Ed.) (2013): Main outcomes and review of the FEBEX In Situ Test (GTS) and Mock-Up after 15 years of operation. Nagra Arbeitsbericht. NTB 15-04. Nagra, Wettingen.

Section 36 during excavation (May 2015)

Full Scale Engineered Barriers Experiment - Dismantling Project (FEBEX-DP)