Lessons Learned from Large-Scale Experiments at the Asse Mine Germany

1. Lessons Learned from Large-Scale Experiments at the Asse Mine Germany Tilmann Rothfuchs Gesellschaft für Anlagen- und Reaktorsicherheit (GRS) mbHBraunschweig/Germany W. Bollingerfehr DBE TECHNOLOGY GmbHPeine/Germany W. BechtholdForschungszentrum KarlsrugeGermany T. Rothfuchs, W. Bollingerfehr; W. Bechthold: Lessons learned at Asse

2. Structure of Presentation • Introduction: German Concept on HLW Disposal • Overview of Large-Scale Experiments/Tests at Asse Mine/Germany • Detailed Results of Asse Experiments • Conclusions T. Rothfuchs, W. Bollingerfehr; W. Bechthold: Lessons learned at Asse

3. Introduction • In Germany two types of heat generating high-level radioactive waste (HLW) have to be disposed in an underground repository:(a) steel canisters containing vitrified fission products remaining from spent fuel reprocessing (b) Pollux steel casks containing non- reprocessed Spent Fuel assemblies • About 30 years ago, salt formations have been selected to host a repository for all kinds of radioactive waste T. Rothfuchs, W. Bollingerfehr; W. Bechthold: Lessons learned at Asse

4. Introduction Continued • The "Gorleben" salt dome has been investigated since 1979 • In 1998, the German government expressed certain doubts with respect to the suitability of salt as host rock in general and of the Gorleben site in particular • All exploration activities were halted by the end of 2000 • A moratorium was imposed for three to ten years • New formation-independent site selection criteria have been developed in order to identify alternative sites with favourable geological settings • URL research has been started 30 years ago in the Asse mine T. Rothfuchs, W. Bollingerfehr; W. Bechthold: Lessons learned at Asse

5. Salt Deposits in Northern Germany Gorleben Hamburg Asse Hanover T. Rothfuchs, W. Bollingerfehr; W. Bechthold: Lessons learned at Asse

6. Asse salt mine • Shaft sinking 1906 -1908 • Salt mining 1908 – 1964 • Testing of radioactive waste disposal 1967 – 1978 • Underground research laboratory 1978 - • Backfilling and closure1994 - 2012 T. Rothfuchs, W. Bollingerfehr; W. Bechthold: Lessons learned at Asse

7. Underground HLW Testing at the Asse Mine T. Rothfuchs, W. Bollingerfehr; W. Bechthold: Lessons learned at Asse

8. Thermal Simulation of Drift Emplacement (TSDE) T. Rothfuchs, W. Bollingerfehr; W. Bechthold: Lessons learned at Asse

9. TSDE Objectives • to improve the understanding of backfill consolidation behaviour in a repository in rock salt • to increase the data base on important phenomena and processes in the repository • to develop further the computer codes and material models required for long-term safety analyses T. Rothfuchs, W. Bollingerfehr; W. Bechthold: Lessons learned at Asse

10. TSDE: Comparison of Measured and Predicted Data(2D-Modelling in 1990) Temperature Drift Convergence T. Rothfuchs, W. Bollingerfehr; W. Bechthold: Lessons learned at Asse

11. Objective of TSDE Post-Test InvestigationsDetermination of the status of crushed salt backfill, host rock and instruments at termination of the experiment including in detail: • Determination of remaining porosity and permeability in the compacted crushed salt backfill • Investigation of the Excavation Disturbed Zone around the test drifts • Post-test inspection and recalibration of measuring instruments • Collection of data for improvement of computer models to predict and assess host rock and backfill behaviour in the TSDE experiment and in a HLW repository • Post-test investigation of corrosion specimens T. Rothfuchs, W. Bollingerfehr; W. Bechthold: Lessons learned at Asse

12. Post Test Investigations in the TSDE Test Field Uncovering of the TSDE Test Field Using a Front Loader T. Rothfuchs, W. Bollingerfehr; W. Bechthold: Lessons learned at Asse

13. Post Test Investigations in the TSDE Test Field Core Drilling Machine at Cross Section I1 T. Rothfuchs, W. Bollingerfehr; W. Bechthold: Lessons learned at Asse

14. Post Test Investigations in the TSDE Test Field Core K4 T. Rothfuchs, W. Bollingerfehr; W. Bechthold: Lessons learned at Asse

15. Post Test Investigations in the TSDE Test Field Backfill Settling Measuring Device at D1-1 T. Rothfuchs, W. Bollingerfehr; W. Bechthold: Lessons learned at Asse

16. Post Test Investigations in the TSDE Test Field Convergence Measuring Rod at CS B+1 T. Rothfuchs, W. Bollingerfehr; W. Bechthold: Lessons learned at Asse

17. TSDE: Comparison of Measured and Predicted Data(Improved 3D-Modelling in 2003) Temperature Drift Convergence T. Rothfuchs, W. Bollingerfehr; W. Bechthold: Lessons learned at Asse

18. Overview of Codes and Constitutive Models Used in TSDE T. Rothfuchs, W. Bollingerfehr; W. Bechthold: Lessons learned at Asse

19. Investigation of EDZ in the TSDE test Field • All permeability values determined from the four measurements were in the order of 10-22 m2. This value represents a completely healed EDZ • Modelling of EDZ generation was fine, but modelling of healing failed (Olivella, 2003) T. Rothfuchs, W. Bollingerfehr; W. Bechthold: Lessons learned at Asse

20. Corrosion Investigations • Materials considered: Ti99.8-Pd, Hastelloy C4 and C22, Cr-Ni steels 1.4306 and 1.4833 • 280 specimens distributed in the test field on container surfaces and in the backfill T. Rothfuchs, W. Bollingerfehr; W. Bechthold: Lessons learned at Asse

21. Corrosion Investigations Results • confirm that the alloy Ti99.8-Pd and the unalloyed/low-alloyed steels have a high resistance to general and pitting corrosion. Therefore, they are very promising materials for the manufacturing long-lived containers for the disposal of HLW/spent fuel in rock salt. • show that materials Hastelloy C4 and C22, cast iron and the Cr-Ni steels 1.4306 and 1.4833 exhibited a good corrosion resistance to general and local corrosion under the conditions of the TSDE experiment. However, it is well known from previous investigations that under some severe conditions (e.g., low pH, very high Cl-content of the brine, presence of strong oxidants), these materials suffer from pitting corrosion and/or intergranular corrosion. T. Rothfuchs, W. Bollingerfehr; W. Bechthold: Lessons learned at Asse

22. The DEBORA Project • Backfill behaviour in disposal boreholes, especially in borehole sealsbetween the canister stack and the disposal drift T. Rothfuchs, W. Bollingerfehr; W. Bechthold: Lessons learned at Asse

23. Results of DEBORA 2Material models confirmed by good agreement of measurements and predictions Porosity development in the backfilled borehole of DEBORA 2 Temperature development in the backfilled borehole of DEBORA 2 T. Rothfuchs, W. Bollingerfehr; W. Bechthold: Lessons learned at Asse

24. Results of DEBORA 2 • Porosity/permeability relation obtained from DEBORA confirms older laboratory results of various investigators (Müller-Lyda et a.,1999) T. Rothfuchs, W. Bollingerfehr; W. Bechthold: Lessons learned at Asse

25. The HAW project: Transient emplacement of 30 highly radioactive radiation sources (Cs-137+ Sr-90) in the Asse mine • Planned to be performed in the 8ties and 9ties of the last century • Project stopped in 1992 • Two heater test operated over 5 years • Development and testing of a transport and emplacement system for HLW canisters T. Rothfuchs, W. Bollingerfehr; W. Bechthold: Lessons learned at Asse

26. Arrangement of Test Boreholes in the Test Field at the 800-m Level in the Asse mine T. Rothfuchs, W. Bollingerfehr; W. Bechthold: Lessons learned at Asse

27. Development and Testing of a Transport and Emplacement System for High-Level Radioactive Waste Canisters • Emplacement of radioactive canisters never realized • System, however, successfully tested without radioactive material • System approved by the responsible mining authority • Extremely valuable experiences for the operation of a HLW repository in salt formations T. Rothfuchs, W. Bollingerfehr; W. Bechthold: Lessons learned at Asse

28. Conclusions • The three large-scale experiments performed in the Asse mine yielded most important data for the validation of material and computer models needed to assess the coupled thermo-hydro-mechanical long-term behaviour of rock salt and crushed salt backfill in a repository in geological salt formations • 2D-Modelling was found inadequate to simulate complex experiment geometries. If end-effects are to simulated adequately, as in the TSDE experiment, full 3D-modelling is required • Post-test investigations of host rock, backfill and recalibration of measuring instruments were extremely useful for the confirmation of applied models and measuring techniques • A complete transport and emplacement system was developed and successfully tested in the framework of the HWA-project. Although such a system will certainly be designed differently on basis of advanced technologies in about 20 to 30 years when a repository will be taken into operation, the exercises at Asse mine demonstrated the principle availability of the techniques for the safe handling of HLW canisters T. Rothfuchs, W. Bollingerfehr; W. Bechthold: Lessons learned at Asse

29. Acknowledgements BAMBUS II Project Committee on August 31, 2000 The work was co-funded by the national governments and authoritiesand by the European Commission. The authors would like to thank for this support. Special thanks also to all project partners (ANDRA, BGR, DBE, DOE-CBFO, ECN, ENRESA, FZK, G.3S, GSF, IfG, NRG, UPC) for their continuous support and the fruitful discussions in the many project meetings. T. Rothfuchs, W. Bollingerfehr; W. Bechthold: Lessons learned at Asse