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Graphite Core Inspection, Measurement of Brick Stress

Graphite Core Inspection, Measurement of Brick Stress. M 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

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Graphite Core Inspection, Measurement of Brick Stress

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

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

  3. Stresses within AGR graphite bricks • Internal stresses created by differential shrinkage across brick wall – as a result of irradiation gradient Tensile forces at Bore (early in life) Compressive forces at Bore (later in life) 3 INGSM 14, Seattle 2013 - NOT PROTECTIVELY MARKED BEG/FORM/COMM/026A REV 007

  4. 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 4 INGSM 14, Seattle 2013 - NOT PROTECTIVELY MARKED BEG/FORM/COMM/026A REV 007

  5. The Deep Hole Drilling Method (Veqter Ltd) Cross-section through simple component Stage 1 – Attach reference bushes Stage 2 – Gundrill reference hole Stage 3 – Measure reference hole 6 5 4 7 3 Weld 2 8 Bushes 1 Stage 4 – EDM coaxial core Stage 5 – Re-measure reference hole Ø0 Ø Air Probe diameter measurements 5 INGSM 14, Seattle 2013 - NOT PROTECTIVELY MARKED BEG/FORM/COMM/026A REV 007

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

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

  8. 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 8 INGSM 14, Seattle 2013 - NOT PROTECTIVELY MARKED BEG/FORM/COMM/026A REV 007

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

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

  11. 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) 11 INGSM 14, Seattle 2013 - NOT PROTECTIVELY MARKED BEG/FORM/COMM/026A REV 007

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

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

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

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

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

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