MICROSTRUCTURAL EVOLUTION OF Q12 ALLOY IRRADIATED IN PWR AND COMPARISON WITH OTHER Zr BASE ALLOYS

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1 MICROSTRUCTURAL EVOLUTION OF Q12 ALLOY IRRADIATED IN PWR AND COMPARISON WITH OTHER Zr BASE ALLOYS Authors: S. Doriot, B. Verhaeghe, A. Soniak, P. Bossis, D. Gilbon, V. Chabretou, J. P. Mardon, M. Ton-That, A. Ambard. CEA Sylvie Doriot 18 th INTERNATIONAL SYMPOSIUM ON «ZIRCONIUM IN THE NUCLEAR INDUSTRY», MAY 15-19, 2016, HILTON HEAD S.C. US

2 AIM OF THE STUDY Q12 a quaternary alloy developped by AREVA NP for structural components Sn Fe Cr 1 Nb M5 < 100 ppm Zr1Nb0.3Sn0.1Fe Zr1Nb0.3Sn0.2Fe Q RXA Zy-4 [11] % Q12 is compared to M5 and to 2 other quaternary alloys: If we disregard Sn content, the chemical composition of these alloys differs mainly by their iron content in the range of 350 to 2000 ppm. 1 Cr is an impurity element in M5 and in the three quaternary alloys 9 DÉCEMBRE 2013 Microstructural evolution of Q12. Doriot et al. MAY 2016 PAGE 2

3 AIM OF THE STUDY In quaternary alloys Fe and Sn are added to enhance creep strength and tensile properties of Fuel Assemblies (F.A.). Shishov V.N. ASTM STP 1529, 2012, pp Iron rejected out of the precipitates during irradiation is supposed to promote the <c>-component loop nucleation responsible for growth 2 phenomenon in Zy-4 alloys. D. Gilbon et al. ASTM STP 1245,1994, pp What about Fe influence for Quaternary alloys? 2 growth and creep are responsible for dimensional changes in F.A. Microstructural evolution of Q12. Doriot et al. MAY 2016 PAGE 3

4 Normalized free growth Normailzed free growth AIM OF THE STUDY M5 Zy Fluence (10 25 n/m²) 1,2 Q12 Zr-1Nb0.3Sn-0.1Fe Zr-1Nb-0.3Sn-0.2Fe M5 1,0 0,8 0,6 0,4 0,2 0, Fluence n/m²) Zy-4 Fe 2000 ppm Q12 Fe 1000 ppm M5 Fe 350 ppm 100nm 200nm 200nm It seems that iron content is not the only element governing the growth behavior. The aim of this study was to assess the evolution of the Zr(Fe,Nb) 2 Laves phases in correlation with the <c>-component loop linear density versus fluence and with the growth behavior. 9 DÉCEMBRE 2013 Microstructural evolution of Q12. Doriot et al. MAY 2016 PAGE 4

5 OUTLINE I.- Materials of the study and irradiation conditions II.- Experimental results - Radiation - enhanced needle-like particles - Zr(Fe,Nb) 2 particle changes versus fast neutron fluence - Basal irradiation-induced <c>-component loops III.- Conclusion Microstructural evolution of Q12. Doriot et al. MAY 2016 PAGE 5

6 I.- MATERIALS OF THE STUDY AND IRRADIATION CONDITIONS

7 I.1.- MATERIALS OF THE STUDY MICROSTRUCTURE OF PRECIPITATION BEFORE IRRADIATION Q12 contains a homogeneous highly refined dispersion of bnb phase precipitates and a coarser precipitation of Zr(Fe,Nb) 2 Laves Phases Q12 Zr1Nb0.3Sn0.1Fe: 1000 ppm Fe similar to Q12. Zr1Nb0.3Sn0.2Fe: 2000 ppm Fe similar to Q12, with more Laves phases and some (Zr,Nb) 4 Fe 2 FCC particles. 1 mm M5 M5 350 ppm Fe homogeneous highly refined dispersion of bnb. All the materials are in a fully recrystallized state. Microstructural evolution of Q12. Doriot et al. MAY 2016 PAGE 7

8 x% I.1.- MATERIALS OF THE STUDY MICROANALYSES ON THE SECOND PHASE PARTICLES IN Q12 The microanalysis results on several precipitates in the non-irradiated Q12 alloy are plotted on this graph (atomic percentage of iron, chromium, tin and niobium versus zirconium) Q12 90 % Nb K % Fe K 60 %Cr K % Sn L Zr % Before irradiation : two populations of SPPs can be observed 1) contains only Zr and Nb and corresponds to bnb, 2) contains Zr, Fe, Nb and Cr and corresponds to Laves phase: Nb/Fe~2 Microstructural evolution of Q12. Doriot et al. MAY 2016 PAGE 8

9 I.1.- MATERIALS OF THE STUDY MORPHOLOGICAL ASPECT OF THE LAVES PHASES COMPARED TO bnb Q12 The Laves phases are larger than the bnb precipitates (about 150 nm in diameter instead of 30 nm for bnb). Stacking faults can be noticed in Laves Phases as it is classically observed on theses SPPs Microstructural evolution of Q12. Doriot et al. MAY 2016 PAGE 9

10 I.2.- IRRADIATION CONDITIONS All the samples were irradiated in PWR conditions The quaternary alloy samples for Transmission Electronic Microscopy microstructural observations were sections of cladding tubes irradiated in a French power plant: fluence level up to about 13x10 25 n/m 2 (E>1 MeV) Fluence, n/m 2 (E>1MeV) Number of 18 month PWR cycles Dose dpa Zr1Nb0.3Sn0.2Fe ~10 Zr1Nb0.3Sn0.1Fe ~10 Q ~10 Q ~20 Free-growth test tubes of M5 and of the quaternary alloys were launched in a European power plant in order to determine irradiation free growth behavior: fluence level up to about 18x10 25 n/m 2 (E>1 MeV) Microstructural evolution of Q12. Doriot et al. MAY 2016 PAGE 10

11 II.- EXPERIMENTAL RESULTS

12 II.1.- RADIATION - ENHANCED NEEDLE-LIKE PARTICLES MICROGRAPHS 100 nm Zr1Nb0.3Sn0.2Fe Zr1Nb0.3Sn0.1Fe Q12 M5 ~7x10 25 n/m 2 ~7x10 25 n/m 2 ~7x10 25 n/m 2 ~7x10 25 n/m 2 This precipitation modifies the matrix niobium content S. Doriot et al., ASTM STP 1543, 2015, pp No noticeable difference in the size distribution and in the density of the radiation-enhanced particles between the different materials and irradiation conditions Q12 M5 ~13x10 25 n/m 2 ~13x10 25 n/m 2 Microstructural evolution of Q12. Doriot et al. MAY 2016 PAGE 12

13 II.1.- RADIATION - ENHANCED NEEDLE-LIKE PARTICLES EVOLUTION OF THE LENGTH AND THE WIDTH VERSUS FAST FLUENCE No significant difference between the quaternary alloys and M5 despite the difference in iron content. M5 : S. Doriot et al., ASTM STP 1543, 2015, pp Microstructural evolution of Q12. Doriot et al. MAY 2016 PAGE 13

14 II.1.- RADIATION - ENHANCED NEEDLE-LIKE PARTICLES EVOLUTION OF NUMBER DENSITY VERSUS FAST FLUENCE number density m ,5 4 3,5 3 2,5 2 1,5 1 0,5 0 M5 Q12 Zr1Nb0.3Sn0.2Fe fluence n/m 2 The number density of «needle-like» particles remains constant all along the irradiation and close to 1.5x10 22 m -3 for M5 and for the quaternary alloys. There is no impact of iron content in the range of 350 to 2000 ppm. M5 : S. Doriot et al., ASTM STP 1543, 2015, pp Microstructural evolution of Q12. Doriot et al. MAY 2016 PAGE 14

15 II.2.- Zr(Fe,Nb) 2 PARTICLE CHANGES VERSUS FAST NEUTRON FLUENCE MICROSTRUCTURAL CHANGES Q12 After a fluence of about 7x10 25 n/m 2, part of the particles can still be indexed as hexagonal Zr(Fe,Nb) 2 Laves phase. 100 nm 7x10 25 n/m nm 7x10 25 n/m 2 After a fluence of about 13x10 25 n/m 2, no possible indexation as hexagonal Zr(Fe,Nb) 2 Laves phase. Former Laves phases appear as micro-crystallized and highly faulted particles in the three quaternary alloys and in M5 Microstructural evolution of Q12. Doriot et al. MAY 2016 PAGE 15

16 X % X % X % X % II.2.- Zr(Fe,Nb) 2 PARTICLE CHANGES VERSUS FAST NEUTRON FLUENCE MICRO-CHEMICAL CHANGES Zr % % Nb % Fe % Cr % Sn Zr % % Nb % Fe % Cr % Sn % Nb % Fe % Cr % Sn After a fluence of about 7x10 25 n/m 2, two populations remain in the three quaternary alloys but the Laves phases contain only a low percentage of iron % Nb % Fe % Cr % Sn Zr % Zr % After a fluence of 13x10 25 n/m 2 (Q12 ), only one population still exists, with only Zr and Nb. Microstructural evolution of Q12. Doriot et al. MAY 2016 PAGE 16

17 Nb/Zr Cr/Zr, Fe/Zr Homogeneous profile in the core of the Laves phase with a very low content of Fe (Nb/Fe~10) and the same content of Cr than before irradiation II.2.- Zr(Fe,Nb) 2 PARTICLE CHANGES VERSUS FAST NEUTRON FLUENCE CONCENTRATION PROFILE AFTER A FLUENCE OF ~7x10 25 n/m 2 0,7 0,6 0,5 0,4 0,3 0,2 0,1 0,0 Nb/Zr Fe/Zr Cr/Zr Zr1Nb0.3Sn0.Fe periphery core nm a) 0,1 0,08 0,06 0,04 0,02 No Fe nor Cr at the periphery and a higher Nb content The core probably produces the hexagonal diffraction diagram seen just before. The periphery is probably transformed into CC bnb particles as said in the literature (Shishov V.N ASTM STP 1529, 2012, pp ) Microstructural evolution of Q12. Doriot et al. MAY 2016 PAGE 17

18 II.2.- Zr(Fe,Nb) 2 PARTICLE CHANGES VERSUS FAST NEUTRON FLUENCE LAVES PHASES AND <c>-component LOOPS In the quaternary alloys, the correlation between the Laves phases and the <c>-component loops is expressed by a higher density of <c>-component loops at the vicinity of the Laves phases. bnb bnb 100 nm In M5, no correlation between Laves phases and <c>-component loops Zr(Fe,Nb) 2 Zr(Fe,Nb) 2 Zr1Nb0.3Sn0.1Fe ~7x10 25 n/m 2 Zr(Fe,Nb) 2 1. c) bnb Zr1Nb0.3Sn0.2Fe ~7x10 25 n/m 2 Zr(Fe,Nb) 2 Zr(Fe,Nb) 2 Zr(Fe,Nb) 2 bnb 100 nm bnb Zr(Fe,Nb) 2 M5 14x10 25 n/m 2 Q12 ~7x10 25 n/m 2 Q12 ~13x10 25 n/m 2 Microstructural evolution of Q12. Doriot et al. MAY 2016 PAGE 18

19 II.3.- BASAL IRRADIATION-INDUCED <C>-COMPONENT LOOPS MICROGRAPHS AFTER A FLUENCE OF ~7x10 25 n/m 2 Zr1Nb0.3Sn0.1Fe Zr1Nb0.3Sn0.2Fe Q12 Q12 2 cycles 200 nm Particularly limited in numbers and can be seen only at the vicinity of Laves phases Evenly spread in the material M5 200 nm 200 nm Correlated to Laves phases but can be observed at few 100 nm from the precipitates. <c>-component loops seem less numerous in the quaternary alloys than in M5 for the same fluence level (~7x10 25 n/m 2 ) Microstructural evolution of Q12. Doriot et al. MAY 2016 PAGE 19

20 II.3.- BASAL IRRADIATION-INDUCED <C>-COMPONENT LOOPS MICROGRAPHS AFTER A FLUENCE OF ~13x10 25 n/m 2 Q12 M5 200 nm 200 nm This tendency is confirmed here at higher fluence ~13x10 25 n/m 2 <c> component loops correlated to Laves phases in Q12 and evenly dispersed in M5. Microstructural evolution of Q12. Doriot et al. MAY 2016 PAGE 20

21 II.3.- BASAL IRRADIATION-INDUCED <C>-COMPONENT LOOPS <C>-COMPONENT LOOP DENSITY VERSUS FLUENCE linear density m/m M5 RXA Zy-4 Zr1Nb0.3Sn0.2Fe Zr1Nb0.3Sn0.1Fe Q fluence n/m 2 For RXA Zy-4 alloys irradiated in PWR conditions (at~320 C) a fluence level of about 10x10 25 n/m 2 appeared to correspond already to the growth breakaway regime (S. Doriot et al., ASTM STP 1467, pp ). For this fluence the <c>-component loop linear density was measured as high as 10x10 13 m/m 3 (S. Doriot et al., ASTM STP 1543, pp ). <c>-component loop linear density is much lower than 5x10 13 m/m 3 for M5 cladding tubes for a very high dose in PWRs. The curve slope for <c>-component loops versus fluence of Q12 alloy is similar to that of M5. This is consistent with the similar free growth behavior of the two alloys. Microstructural evolution of Q12. Doriot et al. MAY 2016 PAGE 21

22 CONCLUSION - The influence of iron on the <c>-component loops and on the growth behavior seems more complex than expected. - This influence is expressed locally by a higher density of <c>-component loops at the vicinity of the Laves phases. - But globally the total iron content seems to have little influence on the <c>-component loop linear density in the alloys studied here, in the range 0.2 % to 350 ppm. - This is consistent with a similar free growth behavior of M5 and of the quaternary alloys and with no growth breakaway on M5 and on quaternary fuel rod elongations in the usual fuel assembly fluence irradiation range, despite their different iron content (S. Doriot et al., ASTM STP 1467, pp , V. Chabretou et al., ASTM STP 1529). Microstructural evolution of Q12. Doriot et al. MAY 2016 PAGE 22

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