MICROSTRUCTURE CHARACTERIZATION OF ZIRLO STRUCTURAL COMPONENTS IRRADIATED TO HIGH BURNUP

Transcription

1 MICROSTRUCTURE CHARACTERIZATION OF ZIRLO STRUCTURAL COMPONENTS IRRADIATED TO HIGH BURNUP J.M. García-Infanta 1, M. Aulló 1, D. Schrire 2, F. Culebras 3 A. M. Garde 4 1 ENUSA Industrias Avanzadas C/ Santiago Rusiñol Madrid (Spain). jmgi@enusa.es 2 Vattenfall Nuclear Fuel AB SE Stockholm (Sweden) 3 Asociación Nuclear Ascó-Vandellós II Edificio Sede L Hospitalet de l Infant 4389 Tarragona (Spain) 4 Westinghouse Electric Company Columbia, SC (USA) 17 th International Symposium on Zirconium in the Nuclear Industry. 3-7 th of February 213, Hyderabad, India

2 OUTLINE OF THE PRESENTATION 1.- Introduction 2.- Experimental scope 3.- Results and discussion - Oxide thickness - Hydriding - Guide tube bulge joints - Grid growth 4.- Conclusions 22

3 INTRODUCTION Objective: Microstructure characterization of ZIRLO samples extracted from the skeleton of assemblies irradiated to usual end-of-life exposures and high burnups. Fuel assembly characteristics and operational information Assembly Id NPP Design Structure material Irradiation Cycles Burnup (GWd/tU) A Ringhals 2 15x15 ZIRLO 4 / annual 54 B Vandellós II 17x17 RFA ZIRLO 3 / eighteen months 52 LTA Vandellós II 17x17 RFA ZIRLO 4 / eighteen months 68 3

4 EXPERIMENTAL SCOPE: ASSEMBLY A Top nozzle Guide tube-top nozzle joint sectioning L1 Top grid T1 T2 Grid 6 Grid 6 IFM 3 Guide tube-top nozzle joint Section T1 3 mm Grid 5 Guide tube IFM 2 Grid 4 IFM 1 Guide tube-grid joint Section T2 Grid 2 Grid 3 Grid 2 Bottom grid P-grid Bottom nozzle Samples from: grid 2, guide tube (between IFM3 and Grid 6), grid 6, guide tube-grid 6 bulge joint and guide tube top nozzle insert bulge joint. Examinations: - Oxide layer thickness (optical microscopy) - Hydrogen content (SEM and hot vacuum extraction) - Metallography for hydrides distribution 4

5 EXPERIMENTAL SCOPE: ASSEMBLY B AND LTA 2.54 mm Top nozzle Top grid Grid 7 Vane extraction Grid 6 Grid 5 Grid 4 Grid 3 Outer strap detail Samples: outer strap grid vanes from grids 5, 6 y 7 (LTA) and grid 7 (assembly B) Grid 2 Examinations: Bottom grid P-grid Bottom nozzle - Oxide layer thickness (optical microscopy) - Hydrogen content (hot vacuum extraction) - Metallography for hydrides distribution - Grid growth (on-site LVDT system) 5

6 EXPARIMENTAL SCOPE: TEMPERATURE AND NEUTRON FLUX Top nozzle Fuel column Neutron flux Temperature Tout Top grid Grid 7 Grid 6 Grid 5 Grid 4 Grid 3 Grid 2 Bottom grid P-grid Bottom nozzle Tin 6

7 One-sided oxide thickness (mm) RESULTS AND DISCUSSION: OXIDE THICKNESS ASSEMBLY A AND B Previous data guide thimble Previous data strap Previous data welds/haz A Guide thimble end piece A Guide thimble at grid 6 A Bulge at grid 6. Guide thimble A Grid 6 outer strap A Grid 2 outer strap A Grid 6 inner strap A Grid 6 dimple A Grid 6 spring A Grid 6 welds/hazs B Grid 7 outer strap vane Elevation (mm) - Consistency with previous experience at equivalent exposures - Maximum values at upper ZIRLO grid elevation: Guide tube 2 mm; Grid strap 3mm; grid HAZ/welds 5 mm - No significant differences between grid strap and cold deformed shapes (dimple/springs) - Guide tube top nozzle bulge joint 1 mm, out of the fuel column. No crevice or galvanic corrosion effects 7

8 One-sided oxide thickness (mm) RESULTS AND DISCUSSION: OXIDE THICKNESS LTA GRID VANES 6 5 Previous data 17x17 ZIRLO grid strap A B LTA grid 6 grid 7 4 grid 5 grid Elevation (mm) - Maximum values at grid 6 elevation 5 mm; - Comparison with Assembly B upper ZIRLO grid (grid 7) oxide thickness 5% higher. Acceleration of oxidation during the 4th LTA cycle. 8

9 One-sided oxide thickness (mm) RESULTS AND DISCUSSION: OXIDE THICKNESS LTA GRID VANES Previous data 17x17 ZIRLO grid strap A B LTA grid 5 grid 6 grid 7 grid 7 5% Elevation (mm) - Maximum values at grid 6 elevation 5 mm; - Comparison with Assembly B upper ZIRLO grid (grid 7) oxide thickness 5% higher. Acceleration of oxidation during the 4th LTA cycle. 9

10 [H] (ppm) RESULTS AND DISCUSSION: HYDROGEN CONCENTRATION IN GUIDE TUBE Previous data 17x17 ZIRLO guide tube Assembly A grid End joint Elevation (mm) - Consistency with previous experience at equivalent exposures at grid 6 elevation. - Maximum value at grid 6 is 6 ppm. - Guide tube top nozzle bulge joint is 2 ppm, out of the fuel column 1

11 [H] (ppm) RESULTS AND DISCUSSION: HYDROGEN CONCENTRATION IN GRID STRAP 1 8 Previous data 17x17 ZIRLO grid strap Assembly A outer strap Assembly B outer strap vanes LTA outer strap vanes LTA grid 7 6 LTA grid 6 B grid 7 4 LTA grid 5 A grid 6 2 A grid Elevation (mm) - Assembly A and B consistent with previous experience at equivalent exposures at upper ZIRLO grid elevation - LTA maximum [H] value is 9 ppm at upper ZIRLO grid elevation. - Comparing LTA with assembly B at upper ZIRLO grid, [H] is 8% higher. Acceleration of H pick-up during the 4th LTA cycle. 11

12 [H] (ppm) RESULTS AND DISCUSSION: HYDROGEN CONCENTRATION IN GRID STRAP Previous data 17x17 ZIRLO grid strap Assembly A outer strap Assembly B outer strap vanes LTA outer strap vanes A grid 2 LTA grid 5 LTA grid 6 B grid 7 LTA grid 7 8% A grid Elevation (mm) - Assembly A and B consistent with previous experience at equivalent exposures at upper ZIRLO grid elevation - LTA maximum [H] value is 9 ppm at upper ZIRLO grid elevation. - Comparing LTA with assembly B at upper ZIRLO grid, [H] is 8% higher. Acceleration of H pick-up during the 4th LTA cycle. 12

13 HPF (%) RESULTS AND DISCUSSION: HYDROGEN PICK-UP FRACTION HPF ZIRLO database High Burnup Assembly (US plant) Assembly A Assembly B LTA LTA grid 6 LTA grid 7 A grid 7 15 LTA grid 5 B grid Temperature (ºF) - Assembly A and B consistent with previous experience at equivalent exposures at upper ZIRLO grid elevation - LTA HPF values are above the previous experience at grid 6 and 7. - LTA show higher HPF than assembly B at upper ZIRLO grid. Acceleration of H pick-up during the 4th LTA cycle. 13

14 RESULTS AND DISCUSSION: HYDRIDE DISTRIBUTION IN ASSEMBLY A Guide tube above grid 6 cross (C) and longitudinal (L) sections [H] ~ 6 ppm Top nozzle Grid 2 and Grid 6 cross sections Grid 6 [H] ~ 4 ppm Grid 2 [H] ~ 15 ppm C-section L-section Top grid Grid 6 IFM 3 Grid 5 IFM 2 Grid 4 IFM 1 Grid 3 Grid 2 Bottom grid P-grid Bottom nozzle Plane of view 14

15 RESULTS AND DISCUSSION: HYDRIDES DISTRIBUTION IN ASSEMBLY B AND LTA GRID STRAP VANES LTA Assembly B Top nozzle 2 mm 918 ppm 2 mm 57 ppm Top grid Grid 7 Grid 6 Grid 5 2 mm 713 ppm Grid 4 Grid 3 Plane of view Grid 2 2 mm 414 ppm Bottom grid P-grid Bottom nozzle 15

16 Avg. 1-sided oxide thickness (mm) Avg. 1-sided oxide thickness (mm) 27º 9º 9º Avg. 1-sided oxide thickness (mm) 27º Avg. 1-sided oxide thickness (mm) RESULTS AND DISCUSSION: GUIDE TUBE BULGE JOINTS. OXIDE THICKNESS a) 315º º T2 45º º 18º 135º Radial position (º) Guide tube to top nozzle insert bulge joint oxide thickness ~1 mm Guide tube-top nozzle joint sectioning T1 T2 L1 Section T1 b) 225º 315º º 18º c) T º 135º Radial position (º) Section T2 3 4 L Axial position (º) Guide tube to grid 6 bulge joint d) Sleeve (outer tube) 5 Guide tube Axial position (º) 16

17 RESULTS AND DISCUSSION: GUIDE TUBE - TOP NOZZLE BULGE JOINT HYDRIDES DISTRIBUTION [H]<2 ppm. Low in comparison with the guide tube at grid 6 elevation. Reason, it is located above the fuel column. - Some radial and 45º oriented hydrides in the plastically deformed areas - Normal hydrides distribution in the non plastically deformed areas 17

18 Grid growth (%) RESULTS AND DISCUSSION: GRID GROWTH CONTRIBUTIONS.8 = irr + [H] + creep.7 LTA grid LTA grid 5 LTA grid 6 irr ~.1% [H] ~.3% creep ~.3%? [H] (ppm) More research is necessary to know exact mechanisms grid growth 18

19 CONCLUSIONS Oxide thickness, hydrogen concentration and hydrogen pick up fraction depend on the axial elevation of the piece as an effect of the coolant temperature rise. Results from LTA show an acceleration of the oxidation reaction and hydrogen pickup, and it is attributed excessive microstructure degradation due high burnup. Good performance of guide tube bulge joints. No galvanic or crevice corrosion observed. Estimation of the different contributors to grid growth reveals that corrosion of the grid straps has a major effect at highest elevations. 19

20 THANK YOU VERY MUCH FOR YOUR ATENTION QUESTIONS? 2