EURADWASTE 04: Sixth European Commission Conference on Management and Disposal of Radioactive Waste 29 March – 1 April 2004, Luxembourg T. Rothfuchs, W

T. Rothfuchs, W. Bollingerfehr; W. Bechthold: Lessons learned at Asse

EURADWASTE ’04: Sixth European Commission Conference on Management and Disposal of Radioactive Waste29 March – 1 April 2004, Luxembourg

Lessons Learned from Large-Scale Experiments at the Asse Mine

GermanyTilmann Rothfuchs

Gesellschaft für Anlagen- und Reaktorsicherheit (GRS) mbHBraunschweig/Germany

W. BollingerfehrDBE TECHNOLOGY GmbH

Peine/Germany

W. BechtholdForschungszentrum Karlsruge

Germany



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



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

disposal drift

HLW disposalboreholes

salt backfill

waste canister



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



Salt Deposits in Northern Germany

Gorleben

Asse

Hamburg

Hanover



Asse salt mine Shaft sinking 1906 -1908 Salt mining 1908 – 1964 Testing of radioactive waste disposal 1967 – 1978

Underground research laboratory 1978 - Backfilling and closure

1994 - 2012



Underground HLW Testing at the Asse Mine

Test/Experiment Period

Temperature Test 1-3 1967 - 1976

Temperature Test 4 1978 - 1979

Temperature Test 5 1982-1983

Temperature Test 6 1985

Brine Migration Test 1983 - 1985

Test Disposal of Highly Radioactive Radiation Sources (abandoned) 1988 – 1993

DEBORA-Project (Development of Seals for HLW disposal boreholes)

1991 – 1995 (Phase I)1996 – 1999 (Phase II)

Thermal Simulation of Drift Emplacement (TSDE)

Post Test Analysis of the TSDE experiment

1990 – 2000

2000 - 2004



Thermal Simulation of Drift Emplacement (TSDE)



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



TSDE: Comparison of Measured and Predicted Data(2D-Modelling in 1990)

Temperature

Drift Convergence



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

Objective of TSDE Post-Test Investigations

Determination of the status of crushed salt backfill, host rock and instruments at termination of the experiment including in detail:



Uncovering of the TSDE Test Field Using a Front Loader

Post Test Investigations in the TSDE Test Field



Core Drilling Machine at Cross Section I1




Core K4




Backfill Settling Measuring Device at D1-1





Convergence Measuring Rod at CS B+1



TSDE: Comparison of Measured and Predicted Data(Improved 3D-Modelling in 2003)

01.01.1990 01.01.1992 01.01.1994 01.01.1996 01.01.1998 01.01.200030

60

90

120

150

180

210

Exp. Calc. Sec. A-A Heater surface B-B Pillar wall B-B Roof A-A 1.2 m below drift A-A 5.0 m below drift

Tem

per

atu

re

[ °C

]

Time

Temperature

Drift Convergence

01.01.1990 01.01.1992 01.01.1994 01.01.1996 01.01.1998 01.01.20000,0

0,1

0,2

0,3

0,4

0,5

0,6

0,7

ExperimentPhase II: 3D

DBE

Co

nv

erg

en

ce

[

m ]

Time



Overview of Codes and Constitutive Models Used in TSDE

Institution Code Const. Model Remarks

BGR DJIFE (3D) Heemann (2003) full 3D

DBE FLAC3D Hein (1991) full 3D

NRG MARC Hein (1991) full 3D

UPC Code_Bright Olivella-Gens full 3D

FZKFAST-BEST

ADINA, MAUS Hein (1991)3D Temperature2D Stress-Strain

G.3S ANTHYC G.3S3D Temperature2D Stress-Strain

IfG FLAC2D IfG 2D



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)



Corrosion Investigations

280 specimens distributed in the test field on container surfaces and in the backfill

Materials considered: Ti99.8-Pd, Hastelloy C4 and C22, Cr-Ni steels 1.4306 and 1.4833



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.

Corrosion Investigations Results



The DEBORA Project Backfill behaviour in disposal

boreholes, especially in borehole sealsbetween the canister stack and the disposal drift

Salt Concrete Seal

Crushed Salt

- 13975

- 14225

r=1.1 m

Gas InjectionPipe

DRIFT FLOOR (without paving)

Gas Collection Volume(Alumina Beads)

Heater Elements1 and 2

- 13475

- 7975

- 7475

- 6475

- 11225

- 10225

- 7225

600

1000

1600

- 3925

- 75

Heater BoreholeTest Borehole

Heater Elements3 and 4

- 0

- 13705

+ 470

+ 1380

Gas Injection Volume



Results of DEBORA 2Material models confirmed by good agreement of measurements and predictions

0,0

20,0

40,0

60,0

80,0

100,0

120,0

140,0

160,0

22. Sep 97

31. Dez 97

10. Apr 98

19. Jul 98

27. Okt 98

4. Feb 99

15. Mai 99

23. Aug 99

Tem

pe

ratu

re /

°C

Calc. Hein's Param., 10.1 mCalc. Hein's Param., 12.1 mCalc. Hein's Param., 14.1 mCalc. GRS Param., 10.1 mCalc. GRS Param., 12.1 mCalc. GRS Param., 14.1 mMeasurement 10.1 mMeasurement 12.1 mMeasurement 14.1 m

Temperature development in the backfilled borehole of DEBORA 2

Porosity development in the backfilled borehole of DEBORA 2

0,00

0,05

0,10

0,15

0,20

0,25

0,30

0,35

0,40

22 Sep 97

31 Dez 97

10 Apr 98

19 Jul 98

27 Okt 98

4 Feb 99

15 Mai 99

23 Aug 99

Po

ros

ity

/ -

Calc. Hein's Param., 10.1 mCalc. Hein's Param., 12.1 mCalc. Hein's Param., 14.1 mCalc. GRS Param., 10.1 mCalc. GRS Param., 12.1 mCalc. GRS Param., 14.1 mMeasurement 10.1 mMeasurement 12.1 mMeasurement 14.1 m



Results of DEBORA 2

Porosity/permeability relation obtained from DEBORA

confirms older laboratory results of various investigators(Müller-Lyda et a.,1999)

DEBORA 8 mm

k = 1.12 . 10-8 5.25

DEBORA 30 mm

k = 6.7 . 10-112.64

1,E-18

1,E-17

1,E-16

1,E-15

1,E-14

1,E-13

1,E-12

1,E-11

1,E-10

0,01 0,1 1porosity [-]

Per

mea

bili

ty K

[m

2 ]DEBORA 8 mm

DEBORA 30 mm

TSDE In-Situ Test Value

TSDE Post Test Data I

TDSE Post Test Data II

TDSE backfill

k = 8 . 10-11 2.5



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



Arrangement of Test Boreholes in the Test Field at the 800-m Level in the Asse mine



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



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



Acknowledgements

The work was co-funded by the national governments and authorities and 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.

BAMBUS II Project Committee on August 31, 2000

Documents

EURADWASTE 04: Sixth European Commission Conference on Management and Disposal of Radioactive Waste 29 March – 1 April 2004, Luxembourg T. Rothfuchs, W