Graphite Core Inspection, Measurement of Brick Stress

1 INGSM 14, Seattle 2013 - NOT PROTECTIVELY MARKED BEG/FORM/COMM/026A REV 007

Graphite Core Inspection, Measurement of Brick StressM Brown – EDF-E

E Kingston and X Ficquet - Veqter Ltd

J Whittington – JFNL Ltd

Contents

• Stresses within AGR graphite bricks• Benefits of performing local stress measurement• The Deep Hole Drilling method• Application of the DHD method to graphite• Phase 1 Laboratory based tool• Summary of results• Conclusions


Stresses within AGR graphite bricks


Tensile forces at Bore(early in life)

Compressive forces at Bore (later in life)

• Internal stresses created by differential shrinkage across brick wall – as a result of irradiation gradient

Benefits of performing local stress measurements


• A measurement method i.e. independent of models (if the core is extracted and DYM measured)

• Could provide a new reduced uncertainty datum line (starting condition)

• Validation route for FEA models

• Measurement of stress state of brick – potential to assess brick to brick variability

• Possible to infer stress value at keyways

• Potential to improve predictions of the onset and rate of keyway root cracking

The Deep Hole Drilling Method (Veqter Ltd)


Ø

Ø0

Cross-section through simple component

Weld

Bushes

Stage 1 – Attach reference bushes

Stage 4 – EDM coaxial core

Stage 5 – Re-measure reference hole

Stage 3 – Measure reference hole

Stage 2 – Gundrill

reference hole

1

23

56 47

8

Air Probe diameter measurements

Application of the DHD method to graphite


4.90

4.95

5.00

5.05

5.10

5.15

5.20

0 5 10 15 20 25 30 35 40 45 50

Diam

eter

, mm

Depth, mm

Angle1-0° Angle2-90°

Angle3-0°

TEST XDrill : 5mm Guhring 05513 single flute DHD m/cMaterial : Gilsocarbon GraphiteDrilled at 500rpm, 7mm/min. Through air coolant, Vacuum to draw in the dust

4.90

4.95

5.00

5.05

5.10

5.15

5.20

0 10 20 30 40 50 60

Dia

met

er, m

m

Depth, mm

Angle1-0° Angle2-22.5°




TEST 8Drill : 5mm Guhring 05513 single flute DHD m/cMaterial : PG25 GraphiteDrilled at 2300rpm, 87.6mm/min. Through air coolant, Vacuum to draw in the dust

• Test drilling on Gilsocarbon and PG25• Guhring solid carbide straight flute – best hole

Application of the DHD method to graphite


-0.0020

-0.0015

-0.0010

-0.0005

0.0000

0.0005

0.0010

0.0015

0.0020

0 5 10 15 20 25

Norm

alise

d Dist

ortio

ns

Depth, mm

Angle1 Angle2 Angle3

Angle4 Angle5 Angle6

Angle7 Angle8

-5.00

-4.00

-3.00

-2.00

-1.00

0.00

1.00

2.00

3.00

4.00

5.00

0 5 10 15 20 25

Appl

ied

Stre

ss, M

Pa

Depth, mm

Longitudinal Transverse Shear

Four point bend test - Gilsocarbon GraphiteApplied strain = 285 microstrains (strain gauge)Applied Stress = 3.42MPa (using E=12GPa approx.)

5% error in E Drilling Direction

• 4-point bend tests using Gilsocarbon and PG25 filter graphite

• Comparison with stresses calculated from strain gauge values

Phase 1 Laboratory based tool (Veqter/JFNL)


• Designed to fit in envelope of 243mm diameter

• 3 functions, Pilot hole / Air Probe / Relief cutter

• 90mm cutter depth, 10mm Ø pilot hole

• Clamping mechanism to hold tool within brick

• Internal calibration gauges within tool



Ø243mmMaximum drilled depth of 90mmWeight ≈ 12kg



• Two types of test bricks

- Split and glued

- Split and actuated via a scissor mechanism

• Simple cylinders and real AGR bricks

• Sensitivity tests – temperature, pressure, channel air flow

• Bricks strain gauged – inside and outside

Summary of results – step 1


• Before and after trepanning – diameter measurements for each angle

• Diameter measurements between 10.004 and 10.028mm

Angle 2 Angle 3

(Simple cylinder brick)



• Calculate difference in measured diameter for each of the 8 angles

• Differences in measured diameter between -6 to 18 microns



• Calculate stresses based on reference hole deformation and using P28 Young’s modulus

• Comparisons with predicted stress based on strain gauge measurements

Summary of results – stress reversed


• Tensile stress at bore – comparison with predicted stress calculated using strain gauge readings

Summary of results – as machined cylinder


• Simple machined cylinder small tensile stress at bore – no external applied stress

Conclusions


• The Deep Hole Drilling method has been successfully developed with respect to measurements in virgin graphite.

• Further work on the evaluation of the technique in representative porous material is required.

• Sensitivity of the measurement to temperature, pressure and channel flow has been evaluated.

• Measurements on a variety of pre-stressed bricks has demonstrated accuracy to better than 1MPa (comparison with strain gauge - scaled FEA models).

• Resolution of the technique in Virgin AGR bricks has been shown to be better than 0.5MPa.

Graphite Core Inspection, Measurement of Brick Stress

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