EPRI Extended Storage Collaboration ProjectDecember 7-8, 2010Charlotte, North Carolina
Preliminary DOE Gap Analyses and R&D Needs
Team Members
Pacific Northwest National Laboratory: Brady Hanson
Sandia National Laboratories: Christine Stockman
Oak Ridge National Laboratory: John Wagner
Idaho National Laboratories: Sandra Birk, Abdelhalim Alsaed
Savannah River National Laboratory: Natraj Iyer
Lawrence Livermore National Laboratory: Bill Halsey
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Policy Issues Consequences
Policy The Administration’s decision to cancel Yucca Mountain means that the nation will need to store used fuel for the foreseeable future (>120 yrs).
Issues Licenses for long term dry storage of used fuel are issued for 20 years, with possible renewals up to 60 yrs. A new rule-making will allow the initial license for 40 years with one possible 40-year extension. Questions regarding
– retrieval and transport of used fuel after long term storage– storage and transportation of high burnup fuel (>45 GWD/MTU)
Consequences Technical bases need to be developed to justify licensing;
– used fuel storage beyond 60 to 80 years– retrievability and transportation of used fuel after long-term storage– transportation of high burnup fuel
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UFD Storage Work PackagesHow do we address these consequences?
R&D Opportunities– Data gap analysis– Plan to address gaps– Development of technical basis
Security– Regulatory assessment– Identify areas peculiar to long-term storage– Evaluate vulnerability analysis methodology
improvements
Conceptual Evaluations– Develop process for development of
technical basis– Evaluate several scenarios for decision
makers
TransportationUFD Storage Implementation Plan Goals• 1 yr: Project Implementation Plan Framework• 5 yr: Project Implementation Plan & Development of Technical Basis• 10 yr: Field operating project
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Assumptions
At some point, DOE will be responsible for very long term storage (VLTS) of used fuel
Active monitoring and aging management plans to mitigate issues if they arise Followed by ultimate disposition- awaiting Blue Ribbon Commission
recommendations– Geologic repository
• 8 generic scenarios being investigated by the Used Fuel Disposition Campaign– Reprocessing facility
Retrievability (integrity) of used fuel after VLTS must be maintained– Defense in depth suggests desire to maintain clad integrity and fuel source term
• Especially important for repository scenarios with advective flow– Maintain ability to tailor fuel content under reprocessing scenarios
Potential for multiple movements of used fuel– From orphaned sites?– Centralized storage?– Ultimate disposition
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If Geologic Disposal is Recommended
The DOE needs may be more “conservative” than current practice– Meet fuel retrievability as defined in ISG-2, Rev. 1– May desire minimization of cladding breaches (including pinhole
leaks and hairline cracks) and not just “protected…against degradation that leads to gross rupture” (ISG-1, Rev. 2)
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• Develop the technical bases to demonstrate VLTS for a period of up to 300 years.
• Low and high burnup fuel• Develop technical bases for fuel retrievability and transport after long term storage.• Develop the technical basis for transport of high burnup fuel.
• Compare DOE gap analyses with those of NRC and NWTRB• Obtain industry input• Solicit data and information• Reevaluate and prioritize gaps and needs
R&D Opportunities Objectives
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Tasks
Identify major storage system components
Define functional requirements Identify mechanisms affecting VLTS Identify gaps Prioritize testing needs Conduct tests/analyses Initiate modeling and simulation
work Develop monitoring capability
INL Dry Cask Storage Characterization (DCSC) Project
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Storage System Components
I. FuelI. PelletII. Fuel/CladIII. Assembly
II. CaskI. BasketII. InternalsIII. CanisterIV. Overpack
III. ISFSII. PadII. RebarIII. Physical Protection
IV. Monitoring SystemsI. Remote inspectionII. In-package sensorsIII. Security
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Storage Functional Requirements
Regulatory Requirements:– 10CFR72
• Allows for storage up to 120 years (60 yrs in-pool and 60 yrs dry storage)
• Used fuel cladding must be protected against degradation that leads to gross failure
• Must maintain confinement of intact and damaged used fuel• Must be retrievable
– NUREG-1536 requires maintenance of;• Protection against environmental conditions• Thermal performance• Radiological performance• Confinement• Sub-criticality• Retrievability
Minimize cladding breaches
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Identify mechanisms effecting VLTS
A Features, Events, and Processes (FEPS) methodology combined with an extensive literature review is used to identify degradation mechanisms
Systems analyzed:
Fuel/clad system Fuel assemblyHardware Baskets Neutron Poisons/Shields Container Over pack Pad Monitoring, security, institutional control
Topics investigated for each system:
Goes back to Functional Requirements:ThermalRadiationConfinementCriticalityRetrievability/Transportation
FY10 focus on commercial LWR used fuels under normal operating conditions
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Current Technical Bases
Industry Experience: Technical issues addressed from past R&D program; [EPRI/DOE/NRC Dry Cask Storage Characterization (DCSC) Project at INL]
– No cask functional degradation observed after 15 years– Assemblies look the same
• No sticking; no significant bowing upon removal• No visual signs of degradation
– No leaks during storage– No significant additional fission gas release to rod internals – No significant hydride reorientation– No creep during storage– “Creep life” remains– Most severe conditions during first 20 years???
Challenge:Demonstrate similar behavior for up to300 years
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Technical Bases Required
Industry Experience: What hasn’t been addressed?
– Effect of marine environment• Cannot rule out corrosion and stress corrosion cracking
– Advanced cladding materials and assembly designs• Bulk of publicly available data is on Zry-2 and Zry-4
– MOX fuel– Long-term concrete degradation– High burnup fuel (>45GWD/MTU)
• Hydride reorientation• Hydride embrittlement• Creep• Plenum gas pressure• Corrosion
Challenge:Demonstrate material degradation behavior for high burnup used fuel over a long storage period.
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Criteria for Ranking
Are there multiple Systems, Structures, and Components (SSCs) Important to Safety (ITS) to fulfill the function?
Is it a primary SSC ITS? What is the likelihood of occurrence? What are the potential consequences?
– Would it occur under geologic disposal conditions anyway? Can it be readily mitigated?
– Assume repackaging or repairs are possible
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General Needs- Temperature Profiles (High)
Since most mechanisms are temperature dependent, accurate (i.e., not conservative or peak) temperature profiles (axial and radial) of fuel and cask materials must be modeled and validated– Need detailed temperature history
• During wet storage for X years• During drying• Over very-long-term storage periods (i.e., up to 300 years)
Industry input– Temperature profiles and associated assumptions– Typical loading patterns to date– Future loading (how long will oldest fuel be in pool?)
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General Needs- Drying Issues (High)
Since many degradation mechanisms are dependent on or accelerated by the presence of water, need to model and measure how much water remains in a cask after drying.– Develop dryness criteria and methods for achieving and verifying
compliance– Determine how much water remains in a cask after drying
• Chemisorbed, physisorbed, free, trapped– Understand the influence of fuel condition on drying and verifying
dryness– Determine need for mitigation
Industry input– Experience, Lessons Learned– Participation in ASTM Standard update
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General Needs- Fuel Retrieval (High)
Investigation of retrieval methods and potential impacts on ITS SSCs– Wet (back in pool)
• Lower temperature• “Quench”• Breached fuel
– Dry Transfer System• Examine fuels from one or more ISFSIs• Near-term need to address orphan fuel problem
Industry input– Experience, Lessons Learned– Details on dry transfer systems
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General Needs- Monitoring Systems (High/Medium)
Monitoring and Sensor systems (to minimize need to open package frequently)– Internal
• Temperature• Pressure• H2O • Xe, Kr• O2 • Dimensions (creep, bowing, etc.)
– External• Dose• Welds (or develop welding techniques that are less susceptible to SCC)
– Security Industry input
– Package designs/how instrumentation could be accommodated
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Reexamine INL DCSC (Medium/High)
Additional 10+ years Obtain data on low burnup fuels
and cask components– Don’t have baseline data
Instrument casks Obtain information for
development of the Test & Evaluation Facility for high burnup fuels
INL Dry Cask Storage Characterization (DCSC) Project
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General Needs- Subcriticality (Medium)
Demonstrate subcriticality for transportation and retrieval operations– Burnup Credit
• Radiochemical assay data for isotopic concentration validation• Critical benchmark experiments for credited isotopes• Fuel depletion characteristics
– Moderator Exclusion
Industry input– Code validation data– Needs?
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FY10 Initial Findings: Fuel
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StressorDegradation Mechanism
Influenced by VLTS or Higher
Burnup
Additional Data Needed
Importance of R&D
Thermal and Mechanical
Fuel Fragmentation Yes Yes Low
Restructuring/ Swelling Yes Yes Low
Radiation None
Chemical
Attack of fission products on cladding
Yes Yes Low
Fuel oxidation Yes Yes Low Example of Pellet Cracking and Flow Path for ATM-106 rod NBD-107 (taken from Guenther et al. 1988, Figure E.1.g)
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FY10 Initial Findings: Cladding
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StressorDegradation Mechanism
Influenced by VLTS or Higher
Burnup
Additional Data Needed
Importance of R&D
Thermal
Annealing of Radiation Effects
No Yes Medium
Metal Fatigue caused by temperature Fluctuations
Yes Yes Low
Phase change TBD TBD TBD
Radiation Embrittlement Yes Yes TBD
Chemical
Emissivity changes from Zn or oxidation
TBD TBD TBD
H2 effects: Embrittlement, Delayed Hydride Cracking
Yes Yes High
Oxidation Yes Yes Medium
Wet Corrosion: Waterlogged Rods, Radiolysis, General, Pitting, SCC, Crevice, Galvanic, Fission Products
No Yes TBD
Mechanical Creep Yes Yes Medium
Inner clad oxidation from CSNF Abstraction Model
Radial hydrides from Kubo et al., 2010 LWR Fuel Performance Mtg.
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FY10 Initial Findings: Grid Spacers, Fuel Baskets
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Stressor Degradation Mechanism
Influenced by VLTS or Higher Burnup
Additional Data Needed
Importance of R&D
Thermal and Mechanical Creep Yes No N/A
Metal fatigue caused by temperature fluctuations
Yes Yes Low
Chemical Wet corrosion No Yes Low
Stressor Degradation Mechanism
Influenced by VLTS or Higher Burnup
Additional Data Needed
Importance of R&D
Thermal and Mechanical Creep Yes Yes Low
Metal fatigue caused by temperature fluctuations
Yes Yes Low
Chemical Wet corrosion No Yes Low
Grid Spacers
Fuel Baskets
Top weld crack in fuel basket from 15-yr demo at INL
Upper grid spacer and differing fuel rod growth from INL test
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FY10 Initial Findings: Neutron Poisons and Shields
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Stressor Degradation Mechanism
Influenced by VLTS or Higher Burnup
Additional Data Needed
Importance of R&D
Thermal and Mechanical Embrittlement and cracking
Yes Yes Low
Metal fatigue caused by temperature fluctuations
Yes No N/A
Creep Yes No N/A
Radiation Poison burnup Yes Yes Low
Embrittlement and Cracking
Yes Yes Low
Chemical Wet corrosion(Blistering)
No Yes Low
Stressor Degradation Mechanism Influenced by VLTS or /Higher Burnup
Additional Data Needed
Importance of R&D
Thermal and Mechanical Embrittlement, cracking, shrinkage, and decomposition
Yes Yes Low
Radiation Poison burnup Yes Yes Low
Embrittlement and Cracking
Yes Yes Low
Chemical Wet corrosion No Yes Low
Neutron Shields
Neutron Poisons
Example of BORAL blisteringfrom EPRI
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FY10 Initial Findings: Container
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Stressor Degradation Mechanism Influenced by VLTS or Higher
Burnup
Additional Data Needed
Importance of R&D
Thermal and Mechanical
Embrittlement of elastomer O-rings
Yes Yes Low
Temperature Fluctuations Relax Seals and Bolts
Yes Yes Medium
Radiation Embrittlement of Elastomer O-rings
Yes Yes Low
Chemical Humid Oxidation Yes Yes High
Marine Environment Yes Yes High
Wet Corrosion: General, Pitting, SCC, Crevice, Galvanic
Yes Yes High
Cask bottom cover plate bolt corrosion observed in 15-yr demo at INL
White coloring on metal gasket from remainingwater after 5 yr storage. Aida et al., IAEA 2010
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FY10 Initial Findings: Overpack
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Stressor Degradation Mechanism Influenced by VLTS or Higher Burnup
Additional Data Needed
Importance of R&D
Thermal
Dry Out Yes Yes Low
Fatigue Yes Yes Low
Freeze Thaw Yes Yes Low
Radiation
Aggregate Growth Yes Yes Low
Decomposition of Water Yes Yes Low
Chemical
Aggregate Reaction Yes Yes Low
Calcium leaching Yes Yes Low
Chemical Attack Yes Yes Low
Corrosion of Embedded Steel
Yes Yes Low
Mechanical
Blocked Air Flow Yes No N/A
Creep Yes No N/A
Shrinkage No No N/A
Examples of concrete degradation at INL ISFSI
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Preliminary List of High and Medium Priority R&D Needs (Normal Conditions)
System Issue Importance of R&D
Cladding
Annealing of Radiation Effects Medium
Oxidation MediumH2 effects: Embrittlement, Delayed Hydride Cracking
High
Creep Medium
Container (Welds, Bolts, Metal Seals)
Humid Oxidation HighMarine Environment High
Wet Corrosion: General, Pitting, SCC, Crevice,
GalvanicHigh
Temperature Fluctuations Relax Metal Seals and Bolts Medium
Monitoring SystemsDevelop New Performance
Confirmation Monitoring Systems
Medium
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Accident Conditions & Data Needs
Which SSCs are important to analyze? Which mechanisms?
If systems are monitored, then corrective actions can be taken to mitigate any accidents– Have to assure that dose and release criteria are met
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ESCP Input & Assistance
Provide better quality pictures of DCSS and ISFSIs Provide release of pictures Participate in the fuel survey led by SRNL
– Availability of fuel, provide history, wet or dry, cask handling, schedule, cost Provide data on newer cladding (M5, ZIRLO, etc.) and assembly designs (e.g.,
partial length rods)
“Waste”– Is any utility willing to take sectioned pieces of fuel rods, remaining fuel rods, etc. after
testing back?
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FY11 Work Plan & Pathforward
Objectives: Complete gap analyses (by February 2011)
Accident conditions Transportation
Develop Experimental and Modeling Plan DOE workshop February 2011
Prioritize data needs (by end of March 2011) Input from EPRI ESCP committee Compare with NRC and NWTRB gap analyses Input from international collaborators
Develop testing and modeling needs for TEF Issue M1 Milestone Report (June 2011) Initiate testing and modeling to fill gaps