Results from the HCPB pebbleResults from the HCPB pebble--bed bed assembly irradiationassembly irradiation

L. Magielsen, J.H. Fokkens, J.B.J. Hegeman,

M.S. Stijkel, J.G. van der Laan

a NRG Petten, the Netherlands

Ceramic Breeder workshop 127, 1 December 2005

OutlineOutline

Objectives of the Pebble Bed Assembly irradiationIrradiation characteristics and designIn-pile performance of the capsuleModel developmentsOutlook

ObjectivesObjectives

Study the thermo-mechanical behaviour under neutron irradiation of a section of the solid breeder blanketAchieve DEMO representative levels of temperature and defined thermal-mechanical loads

45 m

m8

45 m

m8

9

Ceramic pebbles: Li4SiO4 : ~ 0.5 mmor Li2TiO3/Li2ZrO3 : ~ 1 mm

Beryllium pebbles: large : ~ 2 mm small : ~ 0.15 mm

BERYLLIUM BINARY PEBBLE-BED

CERAMIC PEBBLE-BED

BERYLLIUM BINARY PEBBLE-BED

Strategy for blanket developmentStrategy for blanket development

Out-of-pileComponent

Tests

Out-of-pileComponent

Tests

Basic Material

Tests

Basic Material

Tests

In-pileSubmodules

Tests

In-pileSubmodules

Tests

Beryllium (ref. & irrad.)Ceramic (ref. & irrad.)Eurofer (ref. & irrad.)

Helica (ref.)Helicatta (ref.)

PBA irradiatiom

TBM design & test blanket moduleTBM design & test blanket moduleD

EM

O b

lank

et d

esig

nan

d de

velo

pmen

tD

EM

O b

lank

et d

esig

nan

d de

velo

pmen

t

Strategy for HCPB Strategy for HCPB pebblepebble--bed irradiationbed irradiation

Basic Materials

tests

ModellingPebble bed

Design pebble bed assembly

In pile performance pebble bed assembly

Improved model

irradiation effects

PIE Pebble bed

deformation, gas gap formation

HCPB – TBM design

Validation of gas gap

formationOut of pile

performance pebble bed assembly

Model improvements by out-of-pile

results

PBA module

thermocouple

Aluminium filler

Aluminium filler

Beryllium bed

dosimeter

heat barrier EuroferFloating plate Eurofer

Beryllium bed

ceramic bedBellow inconel 718

Containment Eurofer

Purge gas tubes

Containment 316L

Pebble bed assembliesPebble bed assemblies

Filling procedure and module assemblyFilling procedure and module assembly

Filling in a number of stepsPre compactionX-ray inspections to check for the plate positions

Filling procedureFilling procedure

After inspection of assembled test-element:Stepped pre-compaction, 1, 2, 3 MPa plus 24 hrs at 350°CLast inspections prior and after sealing.

Purge line splitter

pebbles well aligned with plate

large pebble: low density near wall

Pre-compaction procedure (1)

0

50

100

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450

0 5 10 15 20 25 30 35

Time [ s ]

Tem

pera

ture

[ °C

]

0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

Pres

sure

[ M

Pa ]

temperaturepressure

Target temperaturesTarget temperatures

Li2TiO3

T= 850 oC

Li4SiO4

T= 650 oC

Li2TiO3

T= 850 oC

Li4SiO4

T= 850 oC

Test element #1 and # 4 same material at different temperatureTest element # 2 and # 3 different in grain size and creep behaviour All first containments are continuously purged with He + 1000 ppm H2 and optionally with Ne/He + 1000 ppm H2 for extra T control

MaterialsMaterials

Test element 1 2 3 4Material Li4SiO4 Li2TiO3 Li2TiO3 Li4SiO4Supplier FZK CEA CEA FZKNRG code NRG 100 NRG 113 NRG 105 NRG 1006 Li enrichmentLithium burn upPebble dimensions mm 0.25-0.63 0.8-1.2 0.8-1.2 0.25-0.63Quantity of breeder material g 24.94 32.28 32.62 25.17Quantity of Beryllium g 91.54 92.7 92.95 92.95Beryllium supplierBeryllium pebble size mmPurge gas 1st containment 2nd containmentGas flow 1st containment ml/min 2nd containment ml/minPressure 1st containment bar 2nd containment barMax. temperature breeder oC < 725 < 900 < 950 < 910Temp. Floating plates oC < 450 < 580 < 600 < 585Temp. Eurofer 1st containment oC < 200 < 285 < 300 < 290Temp. Beryllium beds oC < 420 < 540 < 550 < 540

20-12033

0.9-1.1He + 0.1 vol. % H2

Mixture He/ Ne100

7.5% (natural)plm. 3%

NGK

InIn--pile resultspile results12th cycle ended Nov.2005, with accumulated 300 Full Power Days (~ 7200 hours)Accumulate in 12 cycles, or 7200 hours:

Approx. 2 dpa in Eurofer8 1022 at T productionTotal lithium burn ups 2 to 3 %

Cycle Exp. Orientation Incore position Material filler elementNeutroradiograph -- -- --

03-04 Z H4 AlNeutroradiograph -- -- --

03-06 Z H4 Stainless steel03-07 N H6 Al03-08 Z H6 Al03-09 N H6 Al03-10 Z H6 Al03-11 N H6 Al03-12 Z H6 Al

Neutroradiograph -- -- --04-03 N H6 Water rich04-04 N H6 Al04-08 Z H4 Al04-09 N H4 Al

Neutroradiograph -- -- --

InIn--pile resultspile results

Tritium production: (n,Tritium production: (n,αα) nuclear heating) nuclear heating

0 5 10 15 20 250

0.2

0.4

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Time [days]

IC1

sign

al [

mC

i/min

]

IC1 signal IC1

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IC1

sign

al [

mC

i/min

]

IC1

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sign

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mC

i/min

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IC1 signal IC1

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Time [days]

IC1

sign

al [

mC

i/min

]

IC1 signal IC1

InIn--pile resultspile results

Before start of in-pile operation, after first cycle and after 8 cycles a radiograph was takenTE-#3 gives best image for evaluation, parallax for other quite significantNo evidence for large gaps found yet; to be detailed with the post-irradiation neutrography

Conclusion from the inConclusion from the in--pile behaviourpile behaviour

PBA irradiation has been completed after 12 irradiation cycles (300 FPD)Power density slightly lower than expected, reducing temperaturecontrol margins; use of Neon in primary containment reference purge gas (He-Ne+0.1%H2)The neutron flux gradient is significant, but allows reconstruction of radial temperature profilesThermocouple tubes interfere with the heat transport, giving underestimate readings for the breeder bed and overestimate readings for the lower floating platesIn addition the thermal contact between the Eurofer test-element and Al filler is enhanced by the thermal flux, and neon addition to primary purge No evidence for gaps from intermediate neutrography

Modelling of pebble bedsModelling of pebble beds

0 1 2 3axial strain (%)

0

2

4

6

unia

xial

stre

ss (M

Pa)

first pressure increase:important for pressurebuild-up at BOL

thermal creep: important for compensation of swelling

first pressure decrease:important for gap formaqtion

1σ ε1

Engineering modelFitting experimental data from oedometric tests

Modelling of the PBAModelling of the PBA

Model improvements with the in-pile operation experienceIncluded the thermal barrier for pre compaction calculation to achieve lower compaction in the upper beryllium bedIncluding the a gas gap between eurofer and lower Al fillerStart up calculation of first irradiation cycle with all power steps to simulate the actual start-up to allow the proper creep compactionCooldown of PBA irradiation at shut down of reactor

InstrumentationInstrumentation

Radial distribution Thermo-couples axial distribution

Temperatures during the first startTemperatures during the first start--upup

Beryllium pebble beds

Upper Beryllium bed, high Upper Beryllium bed, close to breeder

Upper Beryllium bed , close to breeder Lower Beryllium bed, bottom

Ceramic pebble bed

Temperatures during the first startTemperatures during the first start--upup

Ceramic bed, close to centre

ceramic bed, outside radius

Temperatures during the first startTemperatures during the first start--upup

Upper plate, ΔT=30 oC

Lower plate, ΔT=90 oC

Eurofer floating plates

Change of thermal conductivity in berylliumChange of thermal conductivity in beryllium

Due to compaction of the beryllium beds which results in higher contact area between the pebble beds the effective thermal conductivity increases

Creep compaction in the breeder bedsCreep compaction in the breeder beds

Mean stresses in the Pebble Bed AssemblyMean stresses in the Pebble Bed Assembly

Cool down after neutron irradiation Cool down after neutron irradiation

Cool down after 24 hrs of in-pile operation at 45 MWInstantaneous shut-down of the powerAllow for a cool down period of 250 s

Conclusions from the thermoConclusions from the thermo--mechanical mechanical modelmodel

All calculated temperatures for the Be beds are 50oC lower than in-pile measurementsFor Breeder bed calculated tempertures are well comparable to in-pile dataCalculated floating plate temperatures differ more for the lower floating plate, due to heat transport Even after 48 hours the beds did not reach the final compaction state

After cooling gas gaps predicted between the floating plates and the pebble beds

Possible PIE of PBAPossible PIE of PBA

For the validation of the model resultsGas-gap detection by infiltration methods in the 2nd containmentGas-gap (eurofer floating plates and pebble beds) detection by pebble-bed infiltrationPebble bed deformation to estimate compactionPebble deformation (if possible number of contacts and contact area’s etc.)

For the verification of the HCPB conceptPebble fragmentation, porosity, tritium release for ceramic and beryllium pebblesResidual strength of the materialsEurofer-breeder and Eurofer-beryllium interactionsTritium/hydrogen interactions with eurofer

Validation of the instrumentation usedSPND’s, thermocouples, Ionisation chambers

Possible PIE of PBAPossible PIE of PBA

Infiltration of the 2nd containmentPartially infiltration of the PBA pebble beds

Bed deformations

Gas gaps

interfaces

Pebble characteristics

impregnated Separate pebbles

Eurofer with T and H2

RemarksRemarks

PBA combine a number of inherent HCPB performance issues:pebble-bed filling, vibration, packing densitythermal behaviour of pebble-bedsmechanical behaviour of pebble-beds (2-D/3-D)bed-solid interfaces; possibility of gap formationmodelling capabilities (e.g. SCATOLA benchmark)reference gas purge in all pebble-beds & tritium permeation compatibility of ceramic and beryllium with Eurofer-97, and tube clads (vz. TBM instrumentation)Eurofer-97 in a structural function during irradiation, in hydrogen rich environmentBeryllium pebbles in TBM relevant temperature and dose range

OutlookOutlook

Dismantling 2nd containmentsStart cutting and evaluate gas gapsResin impregnationDetailed P.I.E.Neutron dosimetryCutting scheme to be determined along with additional P.I.E. on Be and Eur-97 and interfaces