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Issues Related to Long-term Dry Storage of UsedNuclear Fuel
Nuclear Waste Technical Review BoardMeetingLas Vegas NV, 11 June 2009
John KesslerManager, Used Fuel and HLWManagement Program
Outline
" Dry cask storage system functions" Dry Cask Storage Characterization Project (DCSC)
review
* Potential long-term degradation mechanisms
* EPRI plans for future work
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Functions of a Dry Cask Storage System thatMust be Maintained
* NUREG-1536 (NRC, 1997) identifies the functionsimportant to safety that the dry cask systems mustmaintain:- thermal performance
- radiological protection
- confinement- sub-criticality- retrievability
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Dry Cask Storage Characterization (DCSC)Project Review
" Four-year effort (1999-2002)
" Impetus: end of the initial 20-year licenses (2006)
" Investigation of Castor V/21 cask at INL
- In dry storage for 15 years
- Represented the lead (spent) fuel in dry storage in the U.S.
" Co-funded by NRC-Research, EPRI, DOE-RW, DOE-EM
" Documented in EPRI reports:
- Interim report 1000157 (2000)
- Interim report 1003010 (2001)
- Final report 1002882 (2002)
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DCSC Project Tasks
" Reopen Castor V/21 at INL- Cask cavity gas analysis- External dose rate measurements- Visual inspection of assemblies and cask internals
- Remove rods from assembly in Castor at INL
" Rod testing at ANL- Profilometry at ANL-West
- Rod puncturing for fission gas release at ANL-West- Destructive exams of Zircaloy at ANL-East
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Castor V/21 on TransporterHeaded to ot Shop
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DCSC Profilometry: No Evidence of CreepDuring Storage
The nominal as-fabricated cladding outer diameter is 10.72 mm.
EE.
E
CUc,)
1 0.75
1 0.70
10.65
10.60
0 500 1000 1500 2000 2500 3000 3500 4000
Location (mm, from rod bottom)
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DCSC: Morphology of Hydrides MostlyCircumferential -----------
Mid plane 0.5m above mid planeElECTRIC POWER
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Main Conclusions from the Four-Year DCSCEffort
" No cask functional degradation observed
" Assemblies still look the same- No sticking; no significant bowing upon removal
- No visual signs of degradation (color, oxide, damage)
" No leaks during storage
" No significant additional fission gas release to rodinternals
" No significant hydride reorientation
, Zero to minuscule creep during storage" "Creep life" remains
• Result: basis for license extensions out to --60 years
" Most severe conditions are during first 20 years© eELECTRIC POWER
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Examples ofAddress
Issues the DSCS Program did not
" High burnup used fuel" Long-term concrete degradatione Effect of marine environments (examined in EPRI
1011820, September 2005)report
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Review of Potential Degradation MechanismsOutline (from EPRI report 1003416, December 2002)
III II - ,. .Mechanism Claddingj~%.~.
Initial ExtendedI • Initial ExtendedNormalOxidation N Nfgr Y NCreep, Y NDCCG N NH2 reorientation Y NDHC N NSCC maybeH2 embrittlement NH2 migration Y N%4_ __
Annealing Y NCrud Spallation maybe NOff-Normal __ _
Oxidation due to air Y Yingress UCreep Y DEAnnealing Y DEAccident-impactFracture DE DEOxidation DE DEImpact Breach DE DECrud spallation DE DEAccident-fire ____
Stress rupture YAnnealing Y YH2 reorientation YDHC = Delayed Hydrogen CrackingDCCG = Diffusion Controlled Cavitation GrowthFgr = fission gas releaseSCC = Stress Corrosion Cracking
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Temperature-related Dry Storage SystemDegradation Mechanisms
'7NEI
* Fuel cladding creep caused by increased claddingductility and increased stress- Due to higher temperatures causing higher pressures inside the
cladding
" Hydride reorientation in the spent
" Corrosion* Degradation of neutron shielding
* Concrete dry-out and cracking
fuel cladding
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Changes as the System gets Cooler
" Mostly good things
-Reduced metal creep rates
- Reduced corrosion rates
-Reduced gamma and neutron radiation
" Potential negatives (mostly related to cladding)
-Additional hydride precipitation
Decreased ductility
* Potentially more susceptible to breakageduring storage and transportation
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Reduced Degradation with Time does not MeanDegradation Stops
* Corrosion (in oxidizing environments)
" Helium buildup inside fuel rods
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Aging Management Options
* "Initial" activities- Additional analyses to extend progress of degradation
mechanisms- Enhanced monitoring and
" "Eventually"
- Canning- Repackaging
- Over-packaging
• When is "eventually"?
inspection
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Potential Sequence of Events for Extended DryStorage (from EPRI report TR-1 08757, 1998, assumes 100-yr storage)
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Potential Sequence of Events for Extended DryStorage After an Accident Event
no effect
Continue DryStorage
fuel damaged cask OK
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Potential EPRI Work on Very Long-term Used[7 Fuel Storage and Transportation Issues
" Workshop (Fall 2009)* "Paper" analyses
• Experimental (with others?)* Licensing issues* Operational issues
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Together...Shaping the Future of Electricity
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