On the Nature of the Breakaway Corrosion Phenomenon during Zr and Zr Alloy Oxide Growth 19 th International Symposium on Zirconium in the Nuclear Industry Brendan Ensor a , Arthur Motta b , J. Partezana c , Ashley Lucente a , John Seidensticker a , and Zhonghou Cai d a Naval Nuclear Laboratory, b The Pennsylvania State University, c Westinghouse Electric Co., d Argonne National Laboratory The Naval Nuclear Laboratory is operated for the U.S. Department of Energy by Fluor Marine Propulsion, LLC, a wholly owned subsidiary of Fluor Corporation
Zirconium Alloy Corrosion • Development of Zircaloys in the 1950s addressed the unstable oxide growth that was observed in pure Zr • Small amount of alloying Crystal Bar Zr elements solve the problem 10 days, 360 ° C • Why? • Unstable Oxide Growth • Accident scenarios (LOCA) Zircaloy-4 • Neutron Irradiation Induced 70 days, 360 ° C • Poor alloy performance 2
What is Unstable Oxide Growth? Unstable oxide growth is defined as having any or more of the following characteristics: A Stable Oxide No Oxide Unstable Oxide A) White, spalling oxide B) Acceleration of corrosion rate away from linear post-transition rates B C) Uneven oxide growth at the metal-oxide interface that significantly deviates from a generally planar appearance with only minor short-order differences D) Formation of nodules or other local regions of advanced oxide growth C Oxide D Nodule B) T. Kido, K. Kanasugi, M. Sugano and K. Komatsu, "PWR Zircaloy cladding corrosion behavior: quantitative analyses," Journal of Nuclear Materials, vol. 248, pp. 281-287, 1997; C) A. T. Motta, M. J. G. da Silva, A. Yilmazbayhan, R. J. Comstock, Z. Cai and B. Lai, "Microstructural characterization of oxides formed on model Zr alloys using synchrotron radiation," Journal of ASTM International, vol. 5, no. 3, pp. 1-20, 2008.; D) T. R. Allen, R. J. M. Konings and A. T. Motta, "Corrosion of Zirconium Alloys," in 3 Comprehensive Nuclear Materials , vol. 5, R. J. M. Konings, Ed., Oxford, UK, Elsevier, 2012, pp. 49-68.
What is Breakaway Corrosion? • Sudden change in the oxidation kinetics leading to rapid corrosion of the metal • Loss of oxide protectiveness without the ability to recover • Recognized by white color of the oxide (as opposed to a black protective oxide) - Corrosion of Crystal Bar Zr of various temperatures Hillner, Edward, "Corrosion of Zirconium- Base Alloys —An Overview,“ Zirconium in the Nuclear Industry, ASTM STP 633, A. L. Lowe, Jr. and G. W. Parry, Eds., American Society for Testing and Materials, 1977, pp. 211-235. 4 4
What is Breakaway Corrosion? • Not predictable/repeatable • As opposed to commercial zirconium alloys which corrode in a regular fashion b) Alloy 42 - Crystal Bar Zr 120 42-9 42-10 a) Weight gain (mg/dm2) 100 42-11 Alloy 41 - Sponge Zr 42-10 42-12 42-13 80 120 42-14 42-15 60 Weight gain (mg/dm2) 42-16 100 Archive 41-9 41-9 41-10 40 80 41-11 41-12 20 41-13 60 41-14 41-15 41-10 0 40 41-16 Archive 0 20 40 60 80 100 20 Exposure time (d) 0 c) Alloy 43 - Zircaloy-4 0 20 40 60 80 100 140 Exposure time (d) 43-9 120 43-10 Weight gain (mg/dm2) 43-11 100 43-12 43-13 43-10 43-14 80 43-15 43-16 60 Plots from INERI (International Nuclear Energy Archive Research Initiative ) final report 40 43-15 20 5 0 0 100 200 300 400 500 Exposure time (days) 5
Causes of Unstable Oxide Growth • First let’s examine “breakaway corrosion” • Zr metal undergoes breakaway, most zirconium alloys do not • What about the alloying elements corrects uneven oxide growth? • Difference is only a few tenths of a percent in alloying element • How do alloying elements stabilize oxide growth? • Is there some baseline alloying element content that allows for even oxide growth (a minimum amount that promotes stable oxide growth) Heterogeneous distribution of alloying elements causes differential oxide growth, leading to accumulation of stresses and eventually breakaway corrosion (unstable growth) Accumulation Unstable Hypotheses of stresses at Oxide Alloying Uneven oxide put forth the oxide- Growth: Elements growth here metal Breakaway interface Corrosion 6
Elemental Effects on the Stability of Zirconium Oxide Growth - Alloy Fabrication Alloy Fabrication Name Nominal Composition • Alloys were prepared by arc-melting ZC1 Zr (crystal bar)* 300 g buttons • β -solution treated at 1050 ° C for 30 min ZS1 Zr (sponge)* in a vacuum furnace FC1 Zr-0.1Fe-0.05Cr • Hot-rolled after pre-heating for between FC2 Zr-0.05Fe-0.025Cr 580 - 720 ° C for 10 min • FC3 Zr-0.05Fe-0.05Cr Cold-rolled three times to a final thickness FE1 Zr-0.2Fe • Between each rolling step, sheets were CR1 Zr-0.1Cr intermediate-annealed at a temperature SN1 Zr-0.2Sn between 580-720 ° C • SN2 Zr-0.4Sn Final anneal to recrystallize the samples (800 ° C for 30min) SN3 Zr-0.1Sn • Surface treatment (pickling) was done Luvak Inc. Chemical Analysis (wt %) in 45H 2 O:45HNO 3 :10HF • Sheets were cut into ~1” x 1” coupons, Sample H O Fe Cr Crystal Bar 0.0014 0.011 0.0061 <.0005 with a thickness of ~30 mils. • Sponge 0.0050 0.058 0.0200 0.013 Piece was sent for elemental analysis 7
Characterization • Corrosion Testing • 600 ° C in air for 40 hours • 360 ° C water in autoclave for 70 days • SEM • FIB/SEM • EBSD • Raman Spectroscopy • Synchrotron X-ray fluorescence 8
Elemental Effects on the Stability of Zirconium Oxide Growth - First tests were done in a furnace with 600 ° C oxygen, 40 hrs Additional Model Zr alloys and alloys provided by Westinghouse were tested Alloy Composition ↑ Sn KR12 Zr-0.4Sn KR14 Zr-1.2Sn Fe/Cr Stabilized Oxide Growth KR21 Zr-0.2Nb KR22 Zr-0.4Nb KR41 Zr-1.0Nb KR42 Zr-1.5Nb 60 KR43 Zr-2.5Nb Xbar 1.0Fe 1.0Fe 0.6Fe 0.6Fe 0.6Fe 0.5Mo Xbar 0.4Sn 1.2Sn 0.2Nb 0.4Nb 1.0Nb 1.5Nb 2.5Nb 0.3Cr 0.5Cr 0.3Mo 1.0Cr Alloy Composition Oxide Thickness (µm) 40 N101 Zr-1.0Fe ↑ Nb ↑ Sn N102 Zr-1.0Fe-0.5Cr Fe/Cr/Mo Stabilized Oxide Growth N201 Zr-0.6Fe 20 N202 Zr-0.6Fe-0.3Cr N203 Zr-0.6Fe-0.3Mo N302 Zr-0.5Mo-1.0Cr 0 ZC1-3 N101 N102 N201 N202 N203 N302 ZC1-7 KR12 KR14 KR21 KR22 KR41 KR42 KR43 9
Elemental Effects on the Stability of Zirconium Oxide Growth - First tests were done in a furnace with 600 ° C oxygen, 40 hrs Additional Model Zr alloys and alloys provided by Westinghouse were tested Alloy Composition ↑ Sn KR12 Zr-0.4Sn KR14 Zr-1.2Sn Fe/Cr Stabilized Oxide Growth KR21 Zr-0.2Nb KR22 Zr-0.4Nb KR41 Zr-1.0Nb KR42 Zr-1.5Nb Oxide Thickness as a function of Sn or Nb Content KR43 Zr-2.5Nb 50 Alloy Composition 40 Oxide Thickness (µm) N101 Zr-1.0Fe 30 N102 Zr-1.0Fe-0.5Cr Sn (Model Zr) N201 Zr-0.6Fe 20 Sn (Westinghouse) N202 Zr-0.6Fe-0.3Cr Nb 10 N203 Zr-0.6Fe-0.3Mo 0 N302 Zr-0.5Mo-1.0Cr 0 0.5 1 1.5 2 2.5 Sn or Nb Content (Weight %) 10
Elemental Effects on the Stability of Zirconium Oxide Growth- Furnace T ested Samples (SEM) SN1 SN3 (Zr-0.2Sn) (Zr-0.1Sn) SN2 50 µm SN2 (Zr-0.4Sn) (Zr-0.4Sn) 11
Elemental Effects on the Stability of Zirconium Oxide Growth- Furnace T ested Samples (SEM) SN1 SN3 (Zr-0.2Sn) (Zr-0.1Sn) Increasing the Sn content increases the amount of oxide grown on the alloys in 40 hours. Areas of advanced oxide growth begin to appear, consistent with different metal grains. Suspected to be the different levels of Sn in each metal grain 12
Elemental Effects on the Stability of Zirconium Oxide Growth-Autoclave Tested Samples • To better replicate corrosion conditions, model Zr alloys were corroded in autoclave with 360 ° C water for up to 70 days, with periodic removals for weight gain 3 samples experienced 35 breakaway, 2 more showed 30 signs of unstable oxide growth (b)&(c) Weight Gain (mg/dm 2 ) 25 (a) 20 15 10 Zr-Sn Alloys, Zircaloy-4, Zr-Fe-Cr Alloys, Zr-Fe Alloy, Zr-Cr Alloy, Sponge Zr, 5 Crystal Bar Zr (Multiple samples of each) (a) 0 0 10 20 30 40 50 60 70 (b)&(c) Time (days) 13
Elemental Effects on the Stability of Zirconium Oxide Growth-Autoclave Tested Samples • Interesting note: Less alloying elements generally led to less weight gain… • …although also tended to have breakaway corrosion 40 Minimum 30 Weight Gain (mg/dm 2 ) amount of ■ 1 day alloying ♦ 3 days elements ● 10 days 20 ▲ 20 days needed for stable ⃰ 40 days ▬ 70 days growth? 10 0 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 Alloying Element Content (Weight %) 14
Elemental Effects on the Stability of Zirconium Oxide Growth - Autoclave Tested Samples (SEM) ZC1 (Crystal Bar Zr) CR1 (Zr-0.1Cr) 10 days, 360 ° C FC1 (Zr-0.1Fe-0.05Cr) 20 days, 360 ° C, 0.9 µm 20 days, 360 ° C, 1.2 µm FC2 (Zr-0.05Fe-0.025Cr) FC3 (Zr-0.05Fe-0.05Cr) SN1 (Zr-0.2Sn) 20 days, 360 ° C, 1.3 µm 20 days, 360 ° C, 1.3 µm 3 days, 360 ° C SN3 (Zr-0.1Sn) ZS1 (Sponge Zr) 20 days, 360 ° C, 1.0 µm 70 days, 360 ° C, 1.4 µm EBSD ZS1 (Sponge Zr) SN1 (Zr-0.2Sn) 10 days, 360 ° C, 0.8 µm 3 days, 360 ° C Grain-to-grain Differential Growth 15
Recommend
More recommend
