rempe - possible reactor safety enhancements from sample examination

8/2/2019 Rempe - Possible Reactor Safety Enhancements from Sample Examination

1/16

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


2/16

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


3/16

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


4/16


5/16

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


6/16

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.


7/16

OECD TMI-2 VIP Provided Insights Regarding

Relocating Melt /Structure Interactions

TMI-2

Photo and Videos Courtesy DOE and NRC


8/16

OECD TMI-2 VIP Provided Data for Model

Assessment

TMI-2

Photo and Videos Courtesy DOE and NRC


9/16

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


10/16

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


11/16

Combined Insights from Examinations, Analyses, andPlant Data Essential for Improving Simulation Tools

TMI-2


12/16

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


13/16

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


14/16

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


15/16

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


16/16

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

rempe - possible reactor safety enhancements from sample examination

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