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8/2/2019 Rempe - Possible Reactor Safety Enhancements from Sample Examination
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Possible Reactor Safety
Enhancements from SampleExamination and Evaluationat Fukushima Daiichi
J. Rempe (INL), M. Farmer (ANL), M. Corradini (UW),L. Ott (ORNL), R. Gauntt and D. Powers (SNL), and
M. Plys (FAI)
International Experts Meeting on Reactor and Spent
Fuel Safety in the Light of the Accident at the
Fukushima Daiichi Nuclear Power PlantIAEA Headquarters
Vienna, Austria
March 2012
Photo Courtesy TEPCO
8/2/2019 Rempe - Possible Reactor Safety Enhancements from Sample Examination
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Fukushima Daiichi Whats Known
Multiple large seismic andflooding events
Extended loss of power Operators/staff faced adverse
conditions
Degraded instrumentation
Multiple-unit event damage
Several building explosions Some reactor fuel damaged
Most (if not all) fuel in unit 4storage pool intact
Fukushima
3/11 14:469.0
3/11 15:086.7
3/11 15:157.9
3/11 15:257.7
3/12 3:596.3
3/12 4:466.2
3/15/ 22:316
3/23 7:125.7
4/7 23:327.1
4/11 17:166.6
Photos and Graphics Courtesy TEPCO
8/2/2019 Rempe - Possible Reactor Safety Enhancements from Sample Examination
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Fukushima Daiichi Much Unknown
Amount of water addition
Cooling system operation
Component failures
Fuel damage extent
Seawater addition effects
Final core material location
Fukushima
Post-accident examinations andevaluations needed
Core
RPV
CV
SFP
S/C
Photos Courtesy GE and TEPCO
8/2/2019 Rempe - Possible Reactor Safety Enhancements from Sample Examination
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8/2/2019 Rempe - Possible Reactor Safety Enhancements from Sample Examination
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Plant Instrumentation Information Difficult to Obtain,Incomplete, Inaccurate, and Difficult to Synthesize
TMI-2
TMI-2Control Room
Some plant instrumentation data inaccurate
Daiichi Unit 1Control Room
Photos Courtesy GPU, and NHK, and TEPCO
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TMI-2 Core Degradation
Observed Three Years Later
TMI-2
for the first time, (we recognized that) five feet of the core was gone.That's when we really saw that the core had been severelydamaged.
Robert Long, former GPU vice president, regardingFirst Look Examinations on July 21, 1982
Photo and Videos Courtesy GPU and PBS
Core melting not known until 1986.
8/2/2019 Rempe - Possible Reactor Safety Enhancements from Sample Examination
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OECD TMI-2 VIP Provided Insights Regarding
Relocating Melt /Structure Interactions
TMI-2
Photo and Videos Courtesy DOE and NRC
8/2/2019 Rempe - Possible Reactor Safety Enhancements from Sample Examination
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OECD TMI-2 VIP Provided Data for Model
Assessment
TMI-2
Photo and Videos Courtesy DOE and NRC
8/2/2019 Rempe - Possible Reactor Safety Enhancements from Sample Examination
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TMI-2 VIP Data emphasized need to
improve PWR Vessel Failure Models
0
5
10
15
20
Pressure(
MPa)
0 2 4 6 8 10 12 14 16 18
Time after scram (h)
Blockvalve
closed
Majorrelocation
TMI-2 reactor coolant system pressureEstimated timeof global
vessel failure
0.00
0.5E3
2.0E3
2.5E3
Pressure
(psi)
1.5E3
1.0E3
TMI-2
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TMI-2
Subsequent Tests with UO2-ZrO2 Confirmed
Postulated Crack and Gap Cooling Mechanisms
Thermally-induced cracks and furrows observed in relocated debris (in-vesseland ex-vessel conditions)
Intermittent contact between relocated debris and test plate (in-vessel
conditions.
SSWICS Test FacilityFARO Test Facility
Photos Courtesy Nuclear Engineering and Design and ANL
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Combined Insights from Examinations, Analyses, andPlant Data Essential for Improving Simulation Tools
TMI-2
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PWR-specific tests:
Large scale tests (LOFT, TMI-2)
Debris beds (MP)
Fission product release series
(PHEBUS)
Most tests focus on in-coredegradation (notably CORA andQUENCH)
In-pile with irradiated fuel rods(LOFT, TMI, PBF, FLHT, PHEBUS)
Out-of-pile tests(CORA and QUENCH)
BWR-specific tests:
Most tests focus on in-coredegradation (DF-4, CORA)
One in-pile test (DF-4)
No tests with irradiated fuel
Out-of-pile tests (CORA and XR)
XR focus is on lower 1 m of core(including core plate)
BWR fuel assembly degradation More than 40 PWR-specific tests as opposed to 9 BWR-specific tests
No BWR full- assembly tests opposed to some full length/full assembly PWR tests
Fukushima Offers Unique Opportunity
to Improve Severe Accident Models
Fukushima
Core
RPV
CV
SFP
S/C
Reactorbuilding
Pedestal
Mark I liner
Salt water on reactor fuel, cladding, and structural materials No data
Salt water and concrete within spent fuel storage pool No data
Interactions with BWR support structures (core plate), lowerhead penetrations, vessel, and vessel skirt PWR-specific TMI-2 evaluations and tests in 1/10th scale facility
No data to account for BWR-specific features,such as 185 control blade drive mechanisms andmassive structures outside RPV lower head.
Mark I liner/melt interactions No full-scale data with prototypic materials
Core-concrete interactions MACE large-scale prototypic data available
No full-scale data with prototypic materials
Photo Courtesy: GE
Photo Courtesy GE
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TMI-2 Post-Accident Examination
Experience Offers Planning Insights
Effort Evolved with Knowledge Initial small GEND
(GPU/EPRI/NRC/DOE) effort tocooperate on development of sampleextraction effort, reactor recovery, andaccident research
Expanded as knowledge aboutrelocation increased
Proposed Program
A priorieffort needed to assure appropriate focus
Plant instrumentation data
Operator interview information
Smaller-scale separate effects tests with well-defined conditions Refinement of severe accident models based on separate effects data,
Post-accident inspections and sample extraction related to in-vessel phenomena, vesselfailure phenomena, and ex-vessel/containment phenomena
Photo Courtesy GPU
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Well-Organized Efficient International
Program Advantageous
Key knowledge for program definition
Simulations to estimate of core material endstate location(separate effects needed a priori to reduce uncertainties)
Video examinations
Sample type and number definition
Based on expert opinion of possible benefit in reducinguncertainty in predicting accident progression
Sample extraction effort
Ensuring appropriate methods available and tested a priori
Sample analysis effort
Ensuring appropriate methods available to obtain requireddata available a priori
Analysis effort
JAPAN: SAMPSON EU:ICARE2, ATHLET/CD and SVECHA package
US: MELCOR and MAAP
Separate effects tests
Materials interactions
Proposed Program
Program closely coupled to D&D effortsShielded canister for
sample retrievalEDM lower head
cutting electrodes
Photos Courtesy MPR and DOE
Subsurfacedebris sampling
device
Surface debrissampling device
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Outer Oxide(Fe3O4)
Inner Oxide
(FeCr2O4)
Stainless
Steel
Initial Author Ideas on Information
Possible From Daiichi
BWR-specific melt progression and vessel failure: End state (mass, composition, distribution, morphology) and peak temperatures of
undamaged, damaged, and relocated core materials
Evidence of interactions between fuel, cladding, fuel channel, control, andinstrumentation materials
Evidence of stratification within once-molten materials
Physical characteristics affecting debris coolability (particulate, cracks, gaps)
Peak temperatures and deformation of the lower head, lower head structures, andpenetrations
Size and location of any vessel failures
Impact of saltwater (structural corrosion, chemical interaction with core materials,fission product retention)
Ex-vessel phenomena (if vessel failure observed): End state, peak temperature, and location of ex-vessel debris
Physical characteristics affecting debris coolability (particulate, cracks, gaps)
Evidence of debris-water interactions
Evidence of physical interactions and heat transfer between ex-vessel debris and
structures below the RPV Evidence of damage to drywell structures and penetrations
Ablation of concrete and structures by ex-vessel debris
Fission product behavior: Evidence of in-vessel non-volatile releases from deposits on RPV internal structures
Evidence of ex-vessel fission product release from aerosol deposits in containment
Evidence of interactions between in-vessel and ex-vessel sources from aerosol
deposits
Evidence for the roles of structural material and concrete material aerosols
Proposed Program
Backscatteredelectronsimage
Photos Courtesy GPU, DOE, NRC and Sandia
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Fukushima Daiichi Offers Unique Opportunity toImprove Severe Accident Simulation Capabilities
Final insights may not be obtained formany years
Full understanding requirescombination of:
Plant instrumentation data
Operator interview information
Separate effects tests with well-definedconditions
Validation of models with test data A priorisevere accident simulation to guide
inspections, and
Post-accident inspections, AND
Updated simulations with enhanced severeaccident tools.
Internationally-funded effort needed toreap safety benefits from Fukushimapost-accident evaluations!!
Summary
Photos Courtesy: TEPCO