Oxide Surface Peeling of Advanced

Transcription

1 Oxide Surface Peeling of Advanced Zirconium Alloy Cladding Oxides after High Burnup Irradiation A.M.Garde, G.Pan, A.J.Mueller & L.Hallstadius Westinghouse Electric Company Platform Presentation at the 17 th ASTM International Symposium on Zirconium i in the Nuclear Industry, Hyderabad, d India, February 2013 Optimized ZIRLO, AXIOMTM and ZIRLO are trademarks or registered trademarks of Westinghouse Electric Company LLC in the United States and may be registered in other countries throughout the world. All rights reserved. Unauthorized use is strictly tl prohibited. Other names may be trademarks of their respective owners. 1

2 Introduction Poolside Post-Irradiation Visual Examination of Fuel Rods Encountered Non-Uniform Appearance of Waterside Oxide -High Corrosion Resistance Alloys with thin oxide -Surface cracks, Crocodile skin, De-lamination patches High Burnup Rods Examined in Hot Cell (Oxide layer characterization, Measurement of Hydrogen level in metal, Hydride distribution in metal, cladding mechanical tests for specimens with and without nonuniformity features) Objective: To Evaluate the Impact of Surface non-uniformities on Nuclear Fuel Rod Performance Results of Oxide Surface Peeling (OSP) Evaluation presented in this paper p 2

3 Evaluated Materials High Corrosion Resistance Zirconium Alloys (AXIOM alloys, Optimized ZIRLO and Duplex) Burnups up to 72 GWd/MTU Irradiation in five different PWRs Waterside Oxide thickness range 12 to 69 microns Poolside and Hot-Cell Examinations Visual Appearance non-uniformity & Oxide Surface Peeling (OSP) recognized due to Improved Resolution of Poolside Examination Photographic Equipment Careful re-examination of past results indicated possible presence of OSP missed due to equipment limitations 3

4 Poolside OSP (AXIOM X5, 55 GWd/MTU, PWR A): Association with Crud Deposition? Maximum OSP at ~3m rod elevation 4

5 Westinghouse Non-Proprietary Class 3 Poolside OSP (Optimized ZIRLO, 60 GWd/MTU, PWR E) 5

6 Westinghouse Non-Proprietary Class 3 Other forms of surface appearance non-uniformityy Fine Surface cracking g Optimized ZIRLO, 65 GWd/MTU, PWR E, Pellet/Pellet Interface Crocodile C dil Ski Skin AXIOM,70GWd/MTU,PWR E 6

7 Hot Cell OSP (72 GWd/MTU, PWR E): Metallography Layered Structure of Oxide, OSP delaminates layer/layers AXIOM Optimized ZIRLO 7

8 Hot Cell OSP: Hydride Distribution No Hydride Localization under the Peeled Oxide Region AXIOM Optimized ZIRLO 72 GWd/MTU, PWR E 8

9 Hot Cell OSP (Optimized ZIRLO & AXIOM, 72 GWd/MTU, PWR E): Axial Tensile Test OSP does not Reduce Irradiated Ductility 1000 Optimized ZIRLO 1000 AXIOM tress [MPa] St tress [MPa] St OptZ_RT_1.5m OptZ_RT_3m OptZ_RT_3m OptZ_HT_1.5m OptZ_HT_3m OptZ_HT_3m Strain [%] AXIOM_RT_3m AXIOM_RT_3m AXIOM_RT_3m AXIOM_HT_3m AXIOM_HT_3m AXIOM_ HT_ 3m Strain [%] 9

10 Quantitative Analysis of Hydrides in Clad Microstructure t (Optimized i ZIRLO, 72 GWd/MTU) Relative Hydride area fraction similar under Peeled and non-peeled oxide The fraction of Hydride showing radial orientation are similar in peeled and non-peeled regions OSP has no Impact on Preferential Hydride Localization or enhanced radial orientation ti of Hydrides OSP does not enhance Hydride Induced Embrittlement of the Cladding 10

11 Comparison of Oxide Spalling & Oxide Surface Peeling Oxide Spalling OSP Alloy Corrosion Resistance Low High TtlWt Total Waterside >60 microns <45 microns Oxide Thickness Hydride Localization Yes No under Damaged Oxide Clad Ductility Significant None Degradation Impact on Wear Resistance Locally Possible Could be Significant 11

12 Mechanism of OSP Tensile Stress on Thin Oxide Layer is Necessary Circumferential Oriented Defects/Cracks Associated with Corrosion Rate Transitions. Function of residence time between corrosion rate transitions? Number of Oxide Sublayers depends on Alloy Corrosion Resistance Radial Cracks after development of Tensile Stress (Possible causes Pellet Swelling, Hydride Precipitation, Pellet Chips, Oxide Thickness, Coolant Nucleate Boiling etc.) Peeling of some oxide sublayer/sublayers when radial cracks meet the circumferential cracks 12

13 Impact of OSP on Nuclear Fuel Performance No impact on Cladding Embrittlement No impact on Cladding Corrosion Resistance Improvement of design margin against wear (Debris Fretting and Grid-to-rod-fretting, GTRF) need to be addressed by other fuel design features Alloy Development Focus on Corrosion Resistance alone may not be sufficient for overall optimum fuel performance 13

14 Conclusions Surface de-lamination of thin oxides on Corrosion Resistant Zirconium alloys is observed and is termed as OSP High Corrosion Resistance Zirconium alloys are susceptible to OSP Oxide Surface Peeling is Different from Oxide Spallation experienced in the past for low corrosion resistance alloys OSP does not lead to Hydride Localization & Embrittlement OSP may impact design margin against wear (both due to Debris and GTRF). Other fuel design modifications may be needed with the new high corrosion resistance cladding alloys. 14

15 Questions? 15