Assessing Engineered Systems in Geologic Repositories: WIPPGeologic Repositories: WIPP

Presented at the Performance Assessment C it f P ti W k hCommunity of Practice Workshop

Salt Lake City UtahJuly 13-14, 2009

Frank Hansen, PhD. Sandia National LaboratoriesSandia National Laboratories

Albuquerque New Mexico

Sandia is a multiprogram laboratory operated by Sandia Corporation, a Lockheed Martin Company,for the United States Department of Energy’s National Nuclear Security Administration

under contract DE-AC04-94AL85000.

WIPP: A Solution of a National ProblemWIPP: A Solution of a National ProblemWIPP: A Solution of a National ProblemWIPP: A Solution of a National Problem

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Waste Isolation Pilot PlantChronology 1975-2009

1975

1979

20002000

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WIPP Underground LayoutWIPP Underground LayoutWIPP Underground LayoutWIPP Underground Layout

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Bedded Salt Was Chosen for the Siting of the gUS Defense Nuclear Wastes

• Salt can be mined easily • Salt has a relatively high thermal conductivity

Wid hi di t ib ti ( t ti l it )• Wide geographic distribution (many potential sites)• Salt is plastic *• Salt is essentially impermeable *• Salt is essentially impermeable • Fractures in salt are self healing *• Salt has existed underground for millions of years *g y

* Attributes of Natural Barrier

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Assessing Engineered BarriersAssessing Engineered Barriers

EPA defines barriers as “any material or structure that yprevents or substantially delays movement of water or radionuclides toward the accessible environment”

1. Salt – the Most Important Barrier2. Shaft Sealing System3 P l Cl S t3. Panel Closure System4. Magnesium Oxide Engineered Barrier5. Materials Interaction

Discussion will reverse the order

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Waste Package Performance

• HLW waste package material• Materials Interface Interaction Tests• Simulated RH and CH TRU corrosion/durability• BAMBUS II• Potash Basin Experience (1930’s)

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WIPP Disposal Room EvolutionWIPP Disposal Room EvolutionWIPP Disposal Room EvolutionWIPP Disposal Room Evolution

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WIPP Room Evolution at Time=0 yearsWIPP Room Evolution at Time=0 years

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WIPP Room Evolution at Time=12 yearsWIPP Room Evolution at Time=12 years

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WIPP Room Evolution at 1000 yearsWIPP Room Evolution at 1000 years

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Waste Package InteractionsWaste Package Interactions

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MgO Engineered BarrierMgO Engineered Barrier

• MgO will act as an engineered barrier in the WIPP by decreasing actinide g g y gsolubilities.

• Control PCO2 and pH within favorable ranges.

• Only engineered barrier recognized by EPA.

• Ongoing lab studies imply MgO will effectively remove H O and CO• Ongoing lab studies imply MgO will effectively remove H2O and CO2.

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Option D Panel Closure SystemOption D Panel Closure System

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Proposed Panel Closure SystemProposed Panel Closure System

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Shaft Seal System Design GuidanceShaft Seal System Design Guidance

• Limit hazardous constituents reaching regulatory g g yboundaries

• Restrict groundwater flow through the sealing system• Use materials possessing mechanical and chemical

compatibility• Protect against structural failure of system components• Protect against structural failure of system components• Limit subsidence and prevent accidental entry• Utilize available construction methods and materials

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Shaft Sealing SystemShaft Sealing SystemN e a r - s u r fa c e U n i ts

S e a l in g S y s t e m C o m p o n e n t s

1 . E a r t h e n f i l l0

1 7 m

D e p t h

D e w e y L a k eR e d b e d s

2 . C o n c r e t e p l u g

3 . E a r t h e n f i l l

1 6 2 m

R u s t le rF o r m a t io n

4 . R u s t l e r c o m p a c t e d c l a y c o l u m n

5 . C o n c r e t e p l u g

6 . A s p h a l t c o l u m n

7 . U p p e r c o n c r e t e - a s p h a l t w a t e r s t o p

2 5 6 m

S l d

8 . U p p e r S a l a d o c o m p a c t e d c l a y c o l u m n

9 . M i d d l e c o n c r e t e - a s p h a l t w a t e r s t o p

S a la d oF o r m a t io n

1 0 . C o m p a c t e d s a l t c o l u m n

1 1 . L o w e r c o n c r e t e - a s p h a l t w a t e r s t o p

1 2 . L o w e r S a l a d o c o m p a c t e d c l a y c o l u m n

1 3 . S h a f t s t a t i o n m o n o l i t h6 5 5 mT R I- 6 1 2 1 - 3 2 0 - 4

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Shaft Seal System ConclusionsShaft Seal System Conclusions

• The WIPP shaft seal system effectively limits fluid flow• The WIPP shaft seal system effectively limits fluid flow within the seal system.

• The salt column becomes an effective barrier to gas and gbrine migration by 100 years after closure.

• Long-term flow rates within the seal system are limited.

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Natural Barrier It’s the saltNatural Barrier – It’s the salt

Salt formations are used for disposal at WIPP. Germany has several disposal facilities for toxic and

radioactive waste in salt:• Herfe Neurode• Herfe-Neurode• Morsleben• Asse

Salt is an attractive disposal medium. Additional heat from the disposed waste can accelerate encapsulationfrom the disposed waste can accelerate encapsulation. Salt provides a viable disposal option for heat-generating nuclear material, such as fission products res lting from rec cling f el rodsresulting from recycling fuel rods

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Salt Behavior is well UnderstoodSalt Behavior is well Understood

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Disturbed Rock Zone around a Disposal pRoom

0 year 1 year 17 years Undisturbed Zone:

270 IJ ⋅≤

0 year 1 year 17 years Undisturbed Zone:

270 IJ ⋅≤ 12 27.0 IJ ⋅≤ 12 27.0 IJ ⋅≤

50 years248 years10 000 years 50 years248 years10 000 years 50 years248 years10,000 years 50 years248 years10,000 years

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Thermomechanical Response of SaltThermomechanical Response of Salt

• Thermal activation will increase creep of the salt• Thermal activation will increase creep of the salt• Plastic creep deformation would enhance room closure

and encapsulationp• WIPP’s original mission included defense HLW and

spent fuel• Thus, there is a considerable amount of information on

heat-generating waste in a salt repository

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Temperature Effect on Salt DeformationTemperature Effect on Salt Deformation0.35

All tests performed at a deviatoric axial stress of 10 MPa

0.25

0.30 200 C

100 C

70 C

0 15

0.20

l Cre

ep S

trai

n

70 C

20 C

0.10

0.15

Axi

al

0.00

0.05

0 10 20 30 40 50 60 70 80 90 100

Time, days

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Major Tests in the WIPPMajor Tests in the WIPP

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Axisymmetric Test with InsulationAxisymmetric Test with Insulation

Room H

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18 W/m2 Thermomechanical Test18 W/m2 Thermomechanical Test

•“A” Rooms

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Measured vs Predicted Room ClosureMeasured vs. Predicted Room Closure

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Summary It’s the saltSummary – It’s the salt

• The concept of disposal of heat generating nuclearThe concept of disposal of heat generating nuclear waste in salt has been considered viable for many years

• Thermal acceleration of plastic creep deformation can positively affect encapsulation

• A significant number of full-scale field demonstrations of heater tests in salt have been completedheater tests in salt have been completed

• Salt remains an attractive medium for disposal of nuclear waste

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ReCapReCap

• Several barriers engineered for WIPPSeveral barriers engineered for WIPP • No performance credit for waste package• MgO engineered barrier (assurance)g g ( )• Panel closure performance implication• Shaft seal system• It’s the salt

Next: Salt thermal studies indicate balance of local and far field heat provides considerable volume forfar field heat provides considerable volume for disposal of large volumes of other possible inventories (GTCC).

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