overview of spent fuel sf ssafety and security · generic regulatory analysis • spent fuel pool...
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Overview of Spent FuelS f SSafety and Security
Dr. Jennifer UhleOffice of Nuclear Reactor Regulation
National Academy of Sciences Meetingy gJanuary 29, 2015
Status of Spent Fuel Pools
• Widespread adoption of dry storage as pool storage limits are approachedstorage limits are approached
– High-density pool storage broadly deployed
– Pool storage nearing capacity at many sites
– Fuel transfer to dry storage at rate to manageFuel transfer to dry storage at rate to manage inventory
NRC planning for long term storage at sites– NRC planning for long-term storage at sites
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Safety Perspectives
• SFPs and dry casks both provide adequate y p qprotection
• Overall risk to safety from spent fuel is low• Overall risk to safety from spent fuel is low
• Strict requirements are in place for safe storage of spent fuel
• NRC maintains oversight of spent fuel storageNRC maintains oversight of spent fuel storage through routine inspections
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Spent Fuel Pool Risk
Expedited Transfer Analysis
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Plant & Scenario Specific
Spent Fuel Pool D f i D thDefense-in-Depth
• SFPs are robust structures with reinforced• SFPs are robust structures, with reinforced concrete walls and floors 3 to 6 feet thick
• Leak-tight stainless steel liner plates, typically ¼ inch thick, line the walls and floors of SFPs
• Safe pool storage of spent fuel achieved by maintaining water inventory and geometryg y g y
• Special features to protect against cask drops
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Enhancements to Safety d S itand Security
• Following the terrorist attacks of 9/11:g– Implemented 10 CFR 50.54(hh)(2), “Loss of Large
Areas Due to Fires or Explosions”
– New security requirements in 10 CFR 73
• Following the accident at Fukushima Dai-ichi:Following the accident at Fukushima Dai ichi:– Implementing Order EA-12-049, “Mitigation
Strategies for Beyond Design Basis Events”g y g
– Implementing Order EA-12-051, “Reliable Spent Fuel Pool Level Instrumentation”
– Seismic and flooding reevaluations being conducted6
Overview of 2004 NAS R tReport
• NRC found the 2004 NAS study on spent fuel• NRC found the 2004 NAS study on spent fuel safety and security to provide useful insights
• NRC agreed with majority of the recommendations
• Follow-up activities have been completed
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NRC Actions in Response t 2004 NAS R tto 2004 NAS Report
• Upgrade security requirements for protection of spent fuel from theft
• Independent review of spent fuel security• Additional analysis of loss of SFP coolant• Implement prompt actions to reduce theImplement prompt actions to reduce the
consequences of spent fuel pool accidents• Update 10 CFR 72 to include results ofUpdate 10 CFR 72 to include results of
vulnerability assessments• Improve sharing of vulnerability findingsImprove sharing of vulnerability findings
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Conclusion
• Spent fuel storage (wet and dry) is safe and p g ( y)secure
• Enhancements have been made to spent fuel• Enhancements have been made to spent fuel safety and security
• Continued safe and secure storage of spent fuel is assured through regulatory oversight
• NRC looks forward to the Academy’s insights on spent fuel safety and securityp y y
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Spent Fuel SafetyStudies and Analyses
Steven JonesDivision of Safety Systems
Office of Nuclear Reactor Regulation
National Academy of Sciences MeetingNational Academy of Sciences MeetingJanuary 29, 2015
Agenda
• History of SFP AnalysesHistory of SFP Analyses• Recent Spent Fuel Pool Study (NUREG-
2161)2161)• Recent Expedited Transfer Analysis p y
(COMSECY-13-0030)• Risks associated with expedited transfer• Risks associated with expedited transfer• Conclusion
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History of Regulatory ActivitiesComprehensive Site
Level 3 PRA Study(~2018)
NUREG 2161 S t
Action Plan Activities to Increase SFP Cooling Reliability (mid 90s) NUREG-2161 Spent
Fuel Pool Study (2013)Reliability (mid-90s)
Transition to High-Density SFP Racking(starting in late 70s) National Academy of Sciences
Study (2004)
(starting in late 70s)
Post-Fukushima Activities
(2011 – 2016)NUREG-1738 Studyfor Decommissioning
Early SFP Consequence Studies (e.g., NUREG/CR-0649) and High Density ( 0 0 6)
Post-9/11 Security Activities
(1999 – 2001)
NUREG-1353 Resolution of
0649) and High-Density Racking Review Criteria Development (late 70s) COMSECY-13-0030
Expedited Transfer
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Activities(2001 – 2009)Generic Issue 82, “Beyond Design
Basis Accidents in Spent Fuel Pools” (late-80s)
Analysis (2013)
Past SFP Studies
Cask /NUREG-1353*C k /
NUREG-1738**
Annual frequency of SFP fuel uncovery as reported in previous SFP risk studies
Seismic
Cask / Heavy Load Drop
S i i
Cask / Heavy Load DropSeismic
Other
Seismic
Other
* Total frequency of fuel uncovery 2.0 E-06/yr, based on PWR best estimate results. Results for BWRs higher.
** Total frequency of fuel uncovery 2.3 E-06/yr based on Livermore seismic hazard curves
• Very strong seismic events found to be the dominant contributor to fuel uncovery; low frequency did not support regulatory action
• Conservative evaluation of accident progression and consequencesInformation sed in e pedited f el transfer anal sis to s pplement
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• Information used in expedited fuel transfer analysis to supplement results described in NUREG-2161
Overview of SFPS (NUREG-2161)
• Uses state-of-the-art tools to evaluate accident progression after a large earthquake g g
• BWR4 Mark I was used as reference plant• Two conditions considered:
– Representative of the current situation for the reference plant (i.e., high-density loading and a relatively full SFP)
– Representative of expedited movement of older fuel to a dry cask storage facility (i.e., low-density loading)
• Study updates publicly available consequence• Study updates publicly available consequence estimates for spent fuel pool accidents
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NUREG-2161 Results
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Overview
(COMSECY-13-0030)
(NUREG-2161)
(NUREG-2161)
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Regulatory Analysis Process
• Safety Goal Screening Evaluation– Based on the Commission Safety Goal Policy y y
Statement– Used the Quantitative Health Objectives (QHOs) to
evaluate achievement of the safety goalsevaluate achievement of the safety goals• Cost/Benefit Analysis
Intended to identify maximum potential benefit– Intended to identify maximum potential benefit– Analyzes costs and benefits for representative pool
design groupsg g• Sensitivity Studies
– Evaluates key factors to illustrate their effect on the final result
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Expedited Transfer Dry Cask Loading EstimatesLoading Estimates
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Source: Technical Report 1021049, “Impacts Associated with Transfer of Spent Nuclear Fuel from Spent Fuel Storage Pools to Dry Storage After Five Years of Cooling,” EPRI, November 2010.
Assumptions to Maximize B fitBenefit
• Release fraction and mitigation effectiveness assumptions provide conservative estimate of potential benefitprovide conservative estimate of potential benefit
• Regulatory Baseline – Maintain the Existing Spent Fuel Storage Requirementsg q– High cesium release fractions (SFPS value of ~40% for elevated
pools and past study value of 75% for other groups in base case)– Ineffective mitigation (most accidents result in release)Ineffective mitigation (most accidents result in release)
• Expedited Transfer Alternative - Low-density Spent Fuel Pool Storage– Low cesium release fractions (SFPS value of 3% for all groups in
base case)– Effective mitigation (most accidents result in no release)
• Sensitivity to evaluate effect of successful mitigation
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Risks Associated withExpedited TransferExpedited Transfer
• Risk of spent fuel storage:– Dominated by high decay heat assemblies (SFP)– Cask loading affects frequency of cask drop events
D i f f l ff– Density of fuel storage affects event consequences
• Actions to improve safety:– Mitigation strategies/equipment– Dispersed fuel storage
Ri k d d it ifi f t• Risks depend on site-specific features:– Seismicity of site
SFP d i d ti
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– SFP design and operation– Reliability of mitigating features
Safety Perspectives
• Pools provide adequate protection and defense-in-depth• Overall estimated frequency of damage to stored fuel is lowq y g
– Base case release frequencies for existing pools are on the order of a few times in a million years
– These frequencies exclude effective deployment of mitigationThese frequencies exclude effective deployment of mitigation capability and generally exclude consideration of air cooling
– No early fatalities and 1.5x10-8 latent cancer fatality risk
Spent Fuel Pool Maintains Defense in Depth• Spent Fuel Pool Maintains Defense-in-Depth– Defense-in-depth consists of layers of protection with reliability of
each layer commensurate with the frequency of challenges– SFP designed to prevent coolant inventory loss under accident
conditions, which results in a low frequency of coolant inventory loss– Safety improvements have been made such as dispersal of spent
fuel, coolant makeup, and spray capabilities
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COMSECY-13-0030 (2013)
• Staff Evaluation and Recommendation for Japan Lessons-Learned Tier 3 Issue on Expedited Transfer of Spent Fuel
• Concluded that expedited transfer would provide only a minor or limited safety benefit, and that its
t d i l t ti t ld t bexpected implementation costs would not be warranted.
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SECY-14-0136 (2014)
• Response to Commission Direction on Spent Fuel Pool Limited Term Operational Vulnerabilities
• Refers to the allowable period of time for plicensee’s to achieve a dispersed (e.g. 1 x 4) spent fuel configuration in the SFP following discharge from the reactor core.
• Concludes that current requirements for SFP qmitigation measures are sufficient to ensure adequate protection of public health and safety, as well as common defense and security.
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Conclusion
• Health risks from SFP accidents are less than 1% of the Quantitative Health ObjectivesQuantitative Health Objectives
• Regulatory analysis of expedited transfer of spent fuel to g y y p pdry cask storage showed that the costs outweigh the expected benefits
• Commission has concluded that no further regulatory action is needed on this issue
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Backup Slides:Backup Slides:Expedited Transfer of Spent Fuel
Generic Regulatory Analysis• Spent Fuel Pool Study (Appendix D) and Tier 3 Regulatory
Analysis consider initiating events beyond the event in SFPS:th k– more severe earthquake
– cask drop– loss of power/loss of coolant inventory events
• Tier 3 Regulatory Analysis covers all SFP designs used with operating reactors in the U.S.
PWRs and BWRs with Mark III containments (spent fuel stored– PWRs and BWRs with Mark III containments (spent fuel stored in at-grade pool separate from reactor building)
– new reactors (AP-1000)
• Assessment of security events handled separately– regulatory changes implemented (e.g., 10 CFR 50.54(hh))– effect of security changes reflected in regulatory baselineeffect of security changes reflected in regulatory baseline
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Safety Goal Screening Results
• Limited safety benefit based on comparison with QHOswith QHOs– No risk of fatalities due to nature of release
Potential benefit is a very small fraction (0 76%)– Potential benefit is a very small fraction (0.76%) of latent cancer goal
– Cancer risk relatively insensitive to magnitude of– Cancer risk relatively insensitive to magnitude of release due to slow accident progression and effective protective actions (SFPS)p ( )
• Sufficient margin to QHOs that regulatory analysis guidelines call for no cost-benefitanalysis guidelines call for no cost benefit analysis
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Attributes Considered in a C t B fit A l iCost-Benefit Analysis
Principal AttributesPrincipal Attributes
Public Health (Routine) Public Health (Accident)
Occupational Health (Routine)
Occupational Health (Accident)
Industry Operation Offsite Property
Industry Implementation Onsite Property
NRC ImplementationNRC Implementation
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Cost-Benefit Analysis• Evaluated one alternative - Expedited Transfer
– Transfer fuel with more than 5 years decay to dry casks Store remaining fuel in low density configuration in existing racks– Store remaining fuel in low-density configuration in existing racks
• Established SFP Groups– Four groups evaluated representing operating and new plants– Groups representing shutdown/decommissioning reactors not
evaluated due to low risk
• Major Assumptions (Regulatory Analysis Table 2)Major Assumptions (Regulatory Analysis Table 2)– Initiating SFP Event Frequencies and Accident Progression– Economic modeling (e.g., definition of representative plants, future
spent fuel discharge projections etc )spent fuel discharge projections, etc.)– Timing (e.g., dry cask storage loading, occupational dose, etc.)
• Established a base case• Performed sensitivity studies
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Base Case Analysis
• Staff considers base case appropriate for decision whether to pursue additional research to refine assumptions
• Base case includes appropriately conservative assumptions, but not bounding values, for the following:
Initiating Events (USGS 2008 information for Peach Bottom seismic– Initiating Events (USGS 2008 information for Peach Bottom seismic hazard, and NUREG-1738 and NUREG-1353 for other initiators)
– Seismic liner fragilities (based on results of SFPS and past studies)C i i t i f h (b d SFP it t– Cesium inventories for each group (based on SFP capacity, reactor power, and fuel burnup for reactors in group)
– Plume dispersion (uses MAACS2 and Peach Bottom Meteorology)– Population density and economic activity (used data for Surry)– Industry implementation costs (EPRI information modified for
representative site)
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Base Case Analysis (Con’t)• Uncertainty regarding spent fuel pool conditions (i.e., pool
water level, fuel distribution, and location of liner tears)• Conservative assumption to bound effects
– Generally make bounding assumption of inadequate heat removal if fuel is uncovered for base case
– Results in dominant initiating events progressing to release without mitigation
– Conservative because SFPS and other studies indicate substantialConservative because SFPS and other studies indicate substantial potential for air cooling when pool is drained or decay heat is low
– Exception for Mark I and II BWRs• SFPS reduces uncertainty for specific scenario evaluatedSFPS reduces uncertainty for specific scenario evaluated • Used SFPS information of 8% inadequate cooling for SFPS quake scenario
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Cost-Benefit Analysis Results
• Base case costs outweigh benefits B fit b d $2000/ ithi 50 il– Benefits based on $2000/person-rem within 50 miles
– Changes in discount rate do not change result
• Sensitivity Analyses ($4000/person-rem and analysis y y ($ p ybeyond 50 miles) produce marginal benefits– Base case costs outweigh benefits for Groups 1 & 2
– Base case benefits marginally outweigh costs for Groups 3 & 4
• The staff considers the base case an appropriately conservative analysis for use as the primary basis for theconservative analysis for use as the primary basis for the staff’s recommendation.
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Effect of Burnup on Decay Heat
Source: Technical Report 1025206 “Impacts Associated with
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Source: Technical Report 1025206, Impacts Associated with Transfer of Spent Nuclear Fuel from Spent Fuel Storage Pools to Dry Storage After Five Years of Cooling, Rev. 1” EPRI, 2012.
Implementation of Lessons Learned from the FukushimaLearned from the Fukushima
Dai-ichi Accident
Eric BowmanJapan Lessons-Learned DivisionJapan Lessons Learned Division
Office of Nuclear Reactor Regulation
N ti l A d f S i M tiNational Academy of Sciences MeetingJanuary 29, 2015
NRC Order EA-12-049Issued March 12 2012
Licensees or construction permit holders shall
Issued March 12, 2012
Licensees or construction permit holders shall develop, implement, and maintain guidance and strategies to maintain or restore coreand strategies to maintain or restore core cooling, containment and spent fuel pool cooling capabilities following a beyond-cooling capabilities following a beyonddesign-basis external event.
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Mitigation Strategies for Spent Fuel PoolsSpent Fuel Pools
• Makeup with a portable injection source• Makeup with a portable injection source– Rate to exceed boil off for design basis heat load
H d k– Hoses on deck– Connection to SFP cooling piping– Vent pathway
• Spray capability (200 gpm/unit to pool)
3
Rulemaking
• Rulemaking in process makes NRC Order EA-12-049 generically applicableEA 12 049 generically applicable
• Proposed requirements for Severe Accident Management Guidance (SAMG):Management Guidance (SAMG):– Post-Fukushima addition of SFP Candidate High
Level Actions in the SAMG Technical BasisLevel Actions in the SAMG Technical Basis Report (EPRI Report 1025295)
• SFP Makeup• SFP Spray• Ventilation
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NRC Order EA-12-051SFP InstrumentationSFP Instrumentation
• Major purpose is to inform decision-makers– Instrument level range encompasses key decision
pointsL l d t i ti i i i d i li it d– Level determination minimizes drain on limited resources
• Supports prompt identification of these pool• Supports prompt identification of these pool conditions:– Level adequate for operation of forced coolingLevel adequate for operation of forced cooling– Level threatening access – inadequate shielding– Level at or below top of stored fuel
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Level at or below top of stored fuel
NAS Phase 1 Report on Lessons Learned from F k shimaLearned from Fukushima
• Recommendation 5.1A– Attention to availability, reliability, redundancy,
and diversity of plant systems and equipment is y p y q pspecifically needed for Instrumentation for monitoring critical thermodynamic parameters in
t t i t d t f l lreactors, containments, and spent fuel pools.
6
SFP Instrumentation St t iStrategies
• Contingencies for reading instrumentsContingencies for reading instruments– Using portable instruments (e.g., multimeters)– Connect to terminal boards (at containment penetrations) ( p )
for instrument sensors
• Instructions for loss of control power• Instructions for operation prior to obtaining readings
7
Conclusion
• Continued storage of fuel in spent fuel pools is safesafe
• NRC is moving forward to implement safety fenhancements based on lessons learned from
the accident at Fukushima Dai-ichi
• NRC continues to evaluate additional lessons learned for applicability to spent fuel and will t k i t ti iftake appropriate action if necessary
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Backup Slide:Backup Slide:Mitigation Strategiesfor Spent Fuel Pools
Example Implementation
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Spent Nuclear Fuel Securityp y
Sandra WastlerDivision of Security PolicyDivision of Security Policy
Office of Nuclear Security and Incident Response
N ti l A d f S i M tiNational Academy of Sciences MeetingJanuary 29, 2015
Agenda
• Operating Reactor Spent Nuclear Fuel Security Ope a g eac o Spe uc ea ue Secu y
• Decommissioning Reactor Spent Nuclear Fuel SecuritySecurity
• Dry-Cask Storage Spent Nuclear Fuel Security
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Nuclear Power Plant Security ZonesZones
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Operating Reactor Spent Nuclear Fuel (SNF) Security ( ) y
• Title 10 of the Code of Federal Regulations Part 73, Section 73 55 titled “Requirements for Physical Protection of73.55 titled, Requirements for Physical Protection of Licensed Activities in Nuclear Power Reactors Against Radiological Sabotage” and the NRC security orders apply
• Licensees required to provide high assurance that activities involving special nuclear material are not inimical to the common defense and security and do not constitute an unreasonable risk to the public health and safety
• Protective strategy is to ensure that the capabilities to detect, assess, interdict, and neutralize threats up to and including the DBT of radiological sabotage as stated in 10 CFR 73 1
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the DBT of radiological sabotage as stated in 10 CFR 73.1 are maintained at all times
Decommissioning Reactor SNF SecuritySNF Security
• Licensee notifies the NRC of permanently p yceased operations in accordance with 10 CFR 50.82(a)(1)(i) and has certified permanent removal of fuel from thepermanent removal of fuel from the reactor vessel under 50.82(a)(1)(ii)
f C f• Title 10 of the Code of Federal Regulations Part 73, Section 73.55 and the NRC security orders still apply
• Protective strategy still applies to spent fuel
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Dry-Cask Storage SNF Security • Construction of a licensed ISFSI under
10 CFR Part 50 General License or an application for a Specific License subjectapplication for a Specific License subject to 10 CFR 73.51
S f S S C f• Submission of an ISFSI security plan to the NRC for approval
• NRC conducts inspection activities verifying licensee can demonstrate adequate effectiveness in implementing the physical security programphysical security program
• Protective Strategy for an ISFSI is to provide for detection, t d i ti f d t ff it
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assessment and communication for an adequate offsite response by a local law enforcement agency (LLEA)
Conclusion
• No specific threat to these facilities, only general credible threatcredible threat
• High level of assurance that a security related event will not impact operating reactors, decommissioning reactors, or dry cask storage
• NRC continues to evaluate security/threat environment and will take appropriate actions as necessary
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High Burnup Fuel
Paul CliffordDivision of Safety SystemsDivision of Safety Systems
Office of Nuclear Reactor Regulation
N ti l A d f S i M tiNational Academy of Sciences MeetingJanuary 29, 2015
Increased Fuel Utilization
• Longer reload cycles, power uprates, and more efficient fuel management (prompted by advancements in computational g (p p y pmethods) have resulted in increased discharge burnup– License fuel exposure limits have not changed in decades.
46
50
Wd/
MTU
Burnup Limits:60 62 GWd/MTU rod average
38
42
ssem
bly
Dis
char
ge B
U (G
W 60-62 GWd/MTU rod average70-74 GWd/MTU peak pellet
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Ave
rage
As
2
301990 1991 1992 1993 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003 2004 2005 2006 2007 2008
Year
PWR Fuel Trends, Source: EPRI
Challenges of High Duty Fuel• Challenges of high burnup and extended in-reactor service:
– Progressive changes in fuel pellet microstructure and g g pproperties
– Higher decay heat loadsHi h fi i l d d i l– Higher fission gas release and rod internal pressures
– Progressive changes in fuel cladding microstructure and properties• Cladding corrosion and hydrogen uptake• Cladding corrosion and hydrogen uptake
– Dimensional changes in fuel rod and assembly components due to irradiation-induced growth, creep, and corrosion
• Spacer spring relaxation• BWR channel distortion
NRC regulations and standards acknowledge and account
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• NRC regulations and standards acknowledge and account for these effects
Evolving Pellet Characteristics
• Pellet cracking due to thermal stresses.
• Accumulation of fission products.
• Decrease in fuel thermal conductivity.
• Growth of porous rim structure and fuel-clad bonding.
Porous Rim →
Bonding Layer →Bonding Layer →
Cladding →
4Source: NUREG/CR-6967
Evolving Cladding CharacteristicsCharacteristics
• Irradiation damage (point defects and dislocation loops) i i ld t th d d d tilitincreases yield strength and decreases ductility
• Irradiation-induced free growth and irradiation-assisted creep alter as-fabricated dimensionscreep alter as-fabricated dimensions
• Water side corrosion results in a progressive ZrO2 layer and hydrogen uptake in the base metal
5
Zirconium Hydrides
• The impact of absorbed hydrogen on cladding properties depends onon cladding properties depends on concentration, distribution, and orientation of zirconium hydride l t l t
Source: NUREG/CR-6967
platelets
• Hydrogen uptake depends on many parameters including y g y galloy composition, time-at-temperature, water chemistry, fluence, and proximity to dissimilar metals
• Hydride distribution and orientation is influenced by many parameters including texture, heat treatment, and cladding t
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stress
Recent Changes to Regulatory FrameworkRegulatory Framework
• Cladding hydrogen decreases the time-at-temperature to nil ductility during postulated loss-of-coolant accidents
• Hydrides decrease cladding ductility and the ability of the cladding to withstand pellet thermal expansion during
ti i t d ti l dover power anticipated operational occurrences and accidents
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Evolving Fuel Designs• In order to achieve higher duty core reloads, core designers
have implemented assembly design and fuel management h hchanges, such as:– New fuel lattice designs (e.g. part-length rods, rod pitch,
larger pellet, thinner cladding)larger pellet, thinner cladding)– Integral fuel burnable absorbers (IFBAs)– Annular fuel pellets– Fuel pellet additives– Radial and axial enrichment and poison zoning– Advanced cladding and assembly materials– Improved grid spacers and midspan mixing vanes
Improved analytical methods
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– Improved analytical methods– Low leakage core loading patterns
Conclusion
• To address high duty phenomena, NRC has introduced burnup dependent and hydrogen dependent regulatoryburnup-dependent and hydrogen-dependent regulatory criteria and guidance– Regulatory framework ensures continued safe operation
with high burnup fuel• Nuclear industry has evolved fuel designs and fuel
management to meet the challenges of high dutymanagement to meet the challenges of high duty– Fuel reliability continues to improved
• As commercial nuclear power plants seek higher fuel duty, regulatory requirements and standards will be continuously scrutinized to ensure the health and safety of the public
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of the public
Licensing Considerations for Dry Storage and Transportation of
High Burnup Spent FuelDr. Aladar Csontos
Division of Spent Fuel ManagementDivision of Spent Fuel ManagementOffice of Nuclear Materials Safety and Safeguards
N ti l A d f S i M tiNational Academy of Sciences MeetingJanuary 29, 2015
Dry Storage System Design ReviewDesign Review
• Normal and Off-Normal Conditions• Accident Conditions and Natural Phenomena
– Tornado winds/tornado missiles – Earthquakes– Floods and tsunamis – Fires and explosions– Floods and tsunamis – Fires and explosions
• Technical Reviews:– Structural: Confinement maintained under all conditions – Criticality: Fuel subcritical under all conditions– Shielding: Meets off-site radiation dose rate requirements– Thermal: Cladding protected under normal conditionsThermal: Cladding protected under normal conditions– Retrievability: By normal means– Materials:
P ti i t l d i l ti
2
• Properties appropriately assumed in evaluations• Aging effects managed during renewed storage period
Transportation Package Design ReviewDesign Review
• Same technical discipline reviews as for storage:– Ensure that package meets external dose rate limits– Ensure fuel remains subcritical
E t i t i i t i d– Ensure containment is maintained
• Normal & accident conditions differ from storage:– Normal transport:
• Vibration • Small drops and impactsH t d ld• Heat and cold
– Postulated Accidents:30ft d i ldi f P t
3
• 30ft drop on unyielding surface • Puncture• Fire • Water immersion
Potential Material Degradation MechanismsMechanisms
• Known potential degradation p gmechanisms
Stress Corrosion Cracking– Stress Corrosion Cracking– Concrete degradation– High burnup (HBU) fuel
• Currently unknown potentialCurrently unknown potential degradation mechanismsLearning aging management program
4
• Learning aging management program
Storage Aging Management ConsiderationsConsiderations
• HBU fuel cladding behaviorg– Hydride reorientation − Vibration response– Drying − Cladding stress– Temperature predictions − Source Term
• Canister degradation (confinement/structural):– Chloride Induced Stress Corrosion Cracking– Localized & general corrosion − Loss of ductility
• Concrete degradation (shielding/structural):– Cracking − Spalling and scaling
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– Loss of strength/bond − Distortion
Dry Storage HBU FuelGuidance and ResearchGuidance and Research
• HBU Fuel Monitoring Aging Management Program f SRP f St R l (NUREG 1927R1)from SRP for Storage Renewals (NUREG-1927R1)
• ISG-24: Use of a Demo Program as Confirmation of Integrity for Continued Storage of HBU Beyond 20YIntegrity for Continued Storage of HBU Beyond 20Y
• Monitoring DOE Cask Demonstration Surveillance Programg
• NRC HBU Regulatory Issue Summary 2015• Ongoing confirmatory research activities:g g y
– Temperature modeling– Cladding stress in spent fuel during extended storage
Vib ti t ti ORNL
6
– Vibration testing program – ORNL
Waste Confidence – Continued Storage RuleStorage Rule
• Addresses environmental impact of continuing to p gstore spent nuclear fuel after the end of licensed life for reactor operations until final disposition in a geological repository
• Analyzed three time frames: short term up to 60 * l t t 160 * d i d fi ityears*, long term up to 160 years*, and indefinite
storageGeneric environmental impact statement includes• Generic environmental impact statement includes assumption of repackaging every 100 years
*after end of reactor life7
Conclusion
• HBU is safe for storage and transportation
• 10 CFR Part 71 & 72 assures safe storage and transportation of10 CFR Part 71 & 72 assures safe storage and transportation of spent nuclear fuel to include HBU through a multi-disciplinary technical review (confinement is key)
• NRC confirmatory research indicates reasonable expectation that cladding won’t significantly degrade in inert environments during storage of HBF for 20 and likely up to 60 years of storageg y p y g
• DOE HBU Demo Surveillance Program to confirm cladding performance of HBU beyond 20 years
• NRC RIS to identify paths to ensure integrity of HBU cladding during normal conditions of transport when test data is unavailable
• NRC continues to conduct research activities to confirm integrity of
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• NRC continues to conduct research activities to confirm integrity of HBU cladding during normal conditions of transport
Backup Slides:Backup Slides:High Burnup Spent Fuel
Temperature Modeling
• What are realistic maximum temperatures?1. Cladding creep2. Hydride reorientation3. Cladding stress
• What are realistic lower temperatures?1. Cladding DBTT
• How does temperature evolve with time?1. Low temperature Creep2. Delayed Hydride Cracking
2
Cladding Stress in Spent Fuel During Extended Dry StorageDuring Extended Dry Storage
• GOAL: Is sufficient cladding stress present to drive the potential for low temperature creep (LTC) and delayed hydride cracking (DHC) failures
• TASK: NRC has performed an analytic study to determine if sufficient of cladding stress exists in
t l f l (SNF) f 300 i d fspent nuclear fuel (SNF) for a 300 year period of dry storage to drive either LTC or DHC
• This work is part of the ongoing research effort for Extended Storage and Transportation (EST)
3
Vibration Testing Objective
• Investigate a number of important attributes of the high burnup, fuel/cladding system including:– Determining if the presence of fuel increases the flexural
rigidity (bending stiffness) of the fuel rod by comparing the moment/curvature relationship from the test to themoment/curvature relationship from the test to the theoretical results for cladding only. (storage and transport accident)Determining if the presence of fuel increases the failure– Determining if the presence of fuel increases the failure strain of the cladding by comparing the failure strain from the bending tests to the failure strain from tension tests. (storage and transport accident)(storage and transport accident)
– Determining the number of cycles to failure for high burnupfuel rods at a range of elastic strain levels. (normal
4
transportation)
Future Vibration Work
• Finalize NUREG/CR report, documenting the results of the Phase 1 testing program (early 2015)the Phase 1 testing program (early 2015)
• Finish NRC vibration testing at ORNL on HBF Zry-4 with fuel segments after hydride reorientation - Does itwith fuel segments after hydride reorientation Does it replicate fatigue results with circumferential hydrides?
• Determine Effect of Integrated loadg
• Integrate DOE replication on other HBF cladding types
• Interact with Sandia, DOE, Railroad Association toInteract with Sandia, DOE, Railroad Association to determine if vibration is an issue for normal transportation
5
Conclusion of NRC Presentation
• Spent fuel storage (wet and dry) is safe and secure
Presentation
• NRC continues to evaluate enhancements to safe storage of spent fuel
• NRC maintains strong oversight of spent fuel storage
• We look forward to receiving the Academy’s insights onWe look forward to receiving the Academy s insights on spent fuel safety and security
• For any questions, please contact: Kevin Witt, NRC Liaison to NAS Phone: 301-415-2145 Email: [email protected]