1. 1 INGSM 14, Seattle 2013 - NOT PROTECTIVELY MARKED BEG/FORM/COMM/026A REV 007 Graphite Core Inspection, Measurement of Brick Stress M Brown – EDF-E E Kingston and X Ficquet - Veqter Ltd J Whittington – JFNL Ltd

2. 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 2 INGSM 14, Seattle 2013 - NOT PROTECTIVELY MARKED BEG/FORM/COMM/026A REV 007

3. Stresses within AGR graphite bricks 3 INGSM 14, Seattle 2013 - NOT PROTECTIVELY MARKED BEG/FORM/COMM/026A REV 007 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

4. Benefits of performing local stress measurements 4 INGSM 14, Seattle 2013 - NOT PROTECTIVELY MARKED BEG/FORM/COMM/026A REV 007 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

5. The Deep Hole Drilling Method (Veqter Ltd) 5 INGSM 14, Seattle 2013 - NOT PROTECTIVELY MARKED BEG/FORM/COMM/026A REV 007 Ø Ø0Ø0 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 2 3 56 4 7 8 Air Probe diameter measurements

6. Application of the DHD method to graphite 6 INGSM 14, Seattle 2013 - NOT PROTECTIVELY MARKED BEG/FORM/COMM/026A REV 007 Test drilling on Gilsocarbon and PG25 Guhring solid carbide straight flute – best hole

7. Application of the DHD method to graphite 7 INGSM 14, Seattle 2013 - NOT PROTECTIVELY MARKED BEG/FORM/COMM/026A REV 007 4-point bend tests using Gilsocarbon and PG25 filter graphite Comparison with stresses calculated from strain gauge values

8. Phase 1 Laboratory based tool (Veqter/JFNL) 8 INGSM 14, Seattle 2013 - NOT PROTECTIVELY MARKED BEG/FORM/COMM/026A REV 007 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

9. Phase 1 Laboratory based tool (Veqter/JFNL) 9 INGSM 14, Seattle 2013 - NOT PROTECTIVELY MARKED BEG/FORM/COMM/026A REV 007 Ø243mm Maximum drilled depth of 90mm Weight ≈ 12kg

10. Phase 1 Laboratory based tool (Veqter/JFNL) 10 INGSM 14, Seattle 2013 - NOT PROTECTIVELY MARKED BEG/FORM/COMM/026A REV 007 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

11. Summary of results – step 1 11 INGSM 14, Seattle 2013 - NOT PROTECTIVELY MARKED BEG/FORM/COMM/026A REV 007 Before and after trepanning – diameter measurements for each angle Diameter measurements between 10.004 and 10.028mm Angle 2 Angle 3 (Simple cylinder brick)

12. Summary of results – step 2 12 INGSM 14, Seattle 2013 - NOT PROTECTIVELY MARKED BEG/FORM/COMM/026A REV 007 Calculate difference in measured diameter for each of the 8 angles Differences in measured diameter between -6 to 18 microns

13. Summary of results – step 3 13 INGSM 14, Seattle 2013 - NOT PROTECTIVELY MARKED BEG/FORM/COMM/026A REV 007 Calculate stresses based on reference hole deformation and using P28 Young’s modulus Comparisons with predicted stress based on strain gauge measurements

14. Summary of results – stress reversed 14 INGSM 14, Seattle 2013 - NOT PROTECTIVELY MARKED BEG/FORM/COMM/026A REV 007 Tensile stress at bore – comparison with predicted stress calculated using strain gauge readings

15. Summary of results – as machined cylinder 15 INGSM 14, Seattle 2013 - NOT PROTECTIVELY MARKED BEG/FORM/COMM/026A REV 007 Simple machined cylinder small tensile stress at bore – no external applied stress

16. Conclusions 16 INGSM 14, Seattle 2013 - NOT PROTECTIVELY MARKED BEG/FORM/COMM/026A REV 007 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.