www.inl.gov3rd Advanced Graphite Creep Capsule (AGC-3) IrradiationProceedings of the 2013 14th International Nuclear Graphite Specialists MeetingINGSM-14

September 16 – 18, 2013, Seattle, Wa. USA

Agenda• Graphite irradiation overview• Advanced Test Reactor (ATR)

irradiation locations and details • Graphite specimens• Capsule and test train design• Control and monitoring systems• AGC-3 Experiment – Design – Irradiation

• Summary

ATR Core During Reactor Operation

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Graphite Irradiation Experiments

Graphite material property database

• Irradiation creep

• Thermal changes

• Mechanical changes

• Physical changes

High dose tensile irradiation creep studies needed for pebble bed design

Database for previous nuclear graphite grades

900 ºC

1200 ºC

AGC - 2600 ºC

1500 ºC

AGC - 1

AGC - 4

AGC - 6

Dose (dpa)

1 3 4.5 6

HTV-1 HTV-2

AGC - 3

AGC - 5

• Historic nuclear grade graphites are no longer available due to loss of feedstock

• ATR experiments to be irradiated: – 600, 900 and 1200ºC– Up to 4 or 7 dpa (5.5 and

9.6 × 1021 n/cm2 for E > 0.1 MeV)

• AGC-1 was irradiated from September 2009 to January 2011

• AGC-2 was irradiated from April 2011 to May 2012

• AGC-3 will be irradiated from November 2012 to March 2014

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• AGC-1 and AGC-2 were irradiated in the South Flux Trap position

• AGC-3 is being irradiated in the East Flux Trap of the ATR

• Use of ATR Flux Trap– Maximizes number of graphite

specimens, stacks/channels, loads, and combinations

– Flux rate minimizes irradiation time to meet NGNP program schedule

• Test trains rotated to minimize flux gradient across diameter

• Most of ATR core height (44” of 48”) used to maximize specimen numbers and provide spectrum of fast fluence damage levels

AGC Experiment Locations

I-1 I-2I-3

I-4

I-5

I-6

I-7

I-8

I-9I-10I-12 I-11I-13

I-14

I-15

I-16

I-17

I-18

I-19I-20

OS-1 OS-2

OS-3 OS-4 OS-5 OS-6 OS-7

OS-8 OS-9 OS-10 OS-11 OS-12

OS-13 OS-14 OS-15 OS-16 OS-17

OS-18 OS-19 OS-20 OS-21 OS-22

ON-1 ON-2

ON-3 ON-4 ON-5 ON-6 ON-7

ON-8 ON-9 ON-10 ON-11 ON-12

B1

B2

B3

B4B5

B6

B7

B8

B9

B10

B11

B12

I21

I22I23

I24

Fuel Elements

South Flux Trap Location for AGC-1 & 2

North

H Positions

I Positions

Small B Position

Control Drum

ATR Core Cross Section

East Flux Trap Location for AGC-3

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• Some large and small specimens – Large – Ø ½” (12.3 mm) × 1” (25.4 mm) tall– Small – Ø ½” (12.3 mm) × ¼” (6.4 mm) tall

• New ‘intermediate’ size specimen container– Ø ½” (12.3 mm) × ½” (12.7 mm) tall

• 6 Perimeter Stacks– 18 large size specimens above core center– 18 large and 3 small size specimens below core center

• Center Stack – 152 small and 9 intermediate size specimens

• Flux wires in spacers between graphite specimens

Core Centerline

Full Size Unloaded Specimens

Compressive Load Push RodUnloaded Small

SpecimensLoaded Large Specimens

AGC-3 Graphite Specimens

Flux Monitor

Spacer

Small Specimen

Large Specimen

AGC-2 Specimen Stack5

AGC-3 Irradiation Requirements• 900ºC design temperature• Fast neutron damage up to 3 to 4 dpa• Compressive loads on specimens

– 2 stacks with 2 ksi (14 MPa) compressive load

– 2 stacks with 2.5 ksi (17 MPa) compressive load

– 2 stacks with 3 ksi (21 MPa) compressive load

• Loaded and unloaded companion specimens

• Lift specimens during reactor outages to verify specimen load condition

• Grab samples of temperature control gas to monitor for oxidation of specimens

AGC Being Inserted into the ATR

AGC Experiment

ATR Top Head

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AGC Capsule Design Features• 6 specimen stacks around capsule

perimeter with compressive load on upper half of stack

• 7th specimen stack in center without compressive load

• Graphite holder to contain graphite specimen stacks and thermocouples (TCs)

• 12 TC locations with positions located throughout core height

• Insulating gas jacket to attain desired temperature

• Radiation heat shield to limit radiation heat transfer

AGC Capsule Cross Section

ThermocouplesSpecimen Holder

Graphite Specimens

Heat Shield/Gas Jacket Area

Temperature Control Gas Line

Lower Bellows Gas Line

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Temperature Control• Utilize neutron capture and

gamma heating of specimens as heat source

• Manipulate temperature by adjusting ratio of conducting and insulating gases in insulating gas gap

• AGC irradiations use He and Ar to maximize control band for temperature control

• All AGC experiments utilize same temperature control system

• Distributed control system used for control and data collection

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• Pneumatic rams provide compressive load on specimens in six peripheral stacks located above the ATR core centerline – no load on specimens below core centerline

• Load cells between pneumatic rams and push bars to monitor specimen load• Push bars translate and transmit compressive load to push rods located in smaller

circle directly over specimen stacks– Stainless steel push rods transition to graphite in higher temperature areas of experiment

• Gas bellows below core to lift top specimens during outages to verify load conditions– Position indicators attached to push bars to verify specimen movement during outages

• Compressive loads imposed on diametrically opposite specimen stack pairs to avoid eccentrically loading the graphite holder

AGC Test Train

Push RodPneumatic Ram Gas BellowsLoad CellPosition IndicatorsPush Bar Graphite

Specimens

Compressive Load System

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AGC-2 Design Changes/Improvements

TC Pair Locations in AGC-2

TC Locations

• TC12 moved to same elevation as TC9 to provide temperature gradient across the whole experiment

• Replaced stainless steel with aluminum in some internal components to reduce weight– Load cell adapter, plates, push bars and

sleeves• Tungsten ‘gamma heaters’ added to

top and bottom of center channel• Zirconia gamma heaters added to the

bottom of peripheral channels• Removed spacers in specimen stacks

to increase number of specimens– 36 large and 14 to 18 small specimens in

peripheral stacks (vs. 29 and 14)– 170 (vs. 172) small specimens in center

stack due to tungsten heaters 10

• East Flux Trap vs. South Flux Trap – 15% lower nominal power– 20% power variation versus 10% for AGC-1

and AGC-2• Increased specimen creep from higher

design temperature (900ºC)– Slightly smaller diameter specimens – Additional stroke in pneumatic cylinders– Additional room at core center for creep in

specimens and housing• Elevated mean wall temperature in

pressure boundary from higher temperature• Five zones versus single vertical

temperature control zone– Significantly enhanced temperature control – Significantly improved axial temperature

distribution• Different gamma ‘heaters’

– Molybdenum vs. tungsten and zirconia

AGC-3 Design Challenges and Changes

AGC Capsule Cross Section

Thermocouples

Specimen Holder

Graphite Specimens

Heat Shield/Gas Jacket Area

Temperature Control Gas Line

Lower Bellows Gas Line

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Lower Gas Bellows installed on test train

Outer shell with gas bellows installed inside

Gas Bellows before installation in outer shell• Design initiated – April 2011• Final design reviews – March 2012• Test train inserted in ATR – August 2012• Start of irradiation – November 2012– Moisture level during start-up– Excellent temperature control– Extremely flat axial temperature profile– Compressive load control system leakage

– Helium shortage– Loads reduced on stacks 2 and 5 to

replace/supplement stacks 1 and 4• End of first irradiation cycle – January

2013– Accumulated 51 EFPDs– Peak fast neutron damage – 1.0 dpa

• Removed for short high power operating cycle – January 2013

• Re-insertion in ATR – July 2013• Irradiation complete – March 2014

AGC-3 Schedule and Status

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Temperatures During Irradiation

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Compressive Loads During Irradiation

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AGC-3 Experiment• Multiple design improvements and lessons

learned from AGC-1 and AGC-2 incorporated

• New design challenges from increased temperature and new irradiation position

• Irradiation started in November 2012– Significant improvement in temperature

control and axial temperature profile– Compressive load control system leakage– Accumulated 51 EFPDs– Peak fast neutron damage level – 1.0 dpa

• Removed in January 2013 with re-insertion completed in July 2013

• Irradiation complete in March 2014

AGC Experiment Installed in ATR

Summary

AGC Test Train

ATR Core

ATR Fuel

ATR Flux Trap Top Head Penetration

ATR Vessel

AGC Connections to Control Systems

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Michael Davenport Idaho National LaboratoryMichael.Davenport@inl.gov (208) 526-6214

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