Effect of Alloying Elements, Cold Work, and Hydrogen on the Irradiation Growth Behavior of Zirconium Alloy Variants

Transcription

1 Effect of Alloying Elements, Cold Work, and Hydrogen on the Irradiation Growth Behavior of Zirconium Alloy Variants

2 Acknowledgments Work performed under auspices of NFIR Program ( ) Coauthors: Yagnik, Suresh (EPRI, USA) Adamson, Ronald (Zircology Plus, USA) Kobylyansky, Gennady (RIAR, Russian Federation) Chen, J-H (INER, Taiwan) Gilbon, Didier (CEA, France) Ishimoto, Shinji (GNF-Japan) Fukuda, Takuji (NFI, Japan) Hallstadius, Lars (WES, Sweden) Obukhov, Alexander (RIAR, Russian Federation) Mahmood, S-T (Independent, USA) Posthumously: Andrei Novoselov (RIAR), Craig Eucken (ATI, USA), and Seigfried Ostrovsky (RIAR) 2

3 Presentation Outline Objective and Approach Materials: Program and Contributed Program, including pre-hydrided and pre-irradiated Contributed by four NFIR member organizations (coauthors) Experimental Results IIG vs dose data on the materials listed above; Effects, particularly, of [H] and Fe; Influence of texture and volume change; Effects of O and S; PIE beyond IIG data, particular TEM <c> loop density Key Conclusions 3

4 Stress-free Irradiation Induced Growth (IIG) Objective: IIG of Zr-alloys is affected by a complex interplay of: Composition (addition of Fe, Nb, Sn, and hydrogen); Fabrication (cold work, texture); Irradiation conditions (T irr, fluence) Impurities (e.g., S, O) Approach: Irradiation of several alloy variants in BOR-60 MTR T irr : 320 ± 10 C (applicable to PWRs and BWRs) Maximum fluence (~ 1.7) x m -2 (E > 1 MeV) 37 dpa 57 dpa for certain pre-irradiated specimens 4

5 Material Variants Program (1): A-Series Nominal composition: Grain-size, Texture Parameters, and actual composition in the paper 5

6 Material Variants Program (2) Pre-hydrided Four selected variants (H-Series): Zr-2, Zr-4, M5-like, and Zirlo-like Uniformly pre-hydrided to 116, 335, and 718 ppm Unhydrided (as-fabricated) ~ 10 ppm Uniformity in rolling direction ensured Pre-irradiated Zry-2 and NSF RXA Cold worked 2, 10, and 20% Beta-quenched Compared to Zry-2, NSF has Lower Sn and Cr; Higher Fe; and 1% Nb Similar to E635 Previously reported data up to ~ 23 dpa on these variants Kobylyansky et. al, 15 th ASTM Zr-Symposium Dose extend to ~57 dpa in this work 6

7 Material Variants Contributed Several variants: F-Series: High Sn, high O, RXA Zr-4 Low-tin Zr-4 RXA and SRA X-Series: High Fe Ziron VB Alloy V-Series: HiFi Alloy NDA Alloy W-Series Zirlo RXA and SRA Alloy A Beta-quenched Zr-2 Composition, Final heat treatment, and IIG data in full paper 7

8 Experimental: IIG Specimens and Irradiation Rig Specimens Geometry: Mostly flat rectangular: 35 x 6.5 x 0.8 mm Some curvilinear (cutouts from cladding tubes) All pre-filmed to ~ 1 micron Irradiation Rig (IR): Sodium environment In all 644 new Program & Contributed specimens irradiated in BOR-60 and IIG measured Plus 24 pre-irradiated ones (Zr-2 and NSF) 8

9 Irradiation Matrix Irradiation in 5 stages (8 MC micro-cycles) Damage ranged from ~ 4 to ~37 dpa, depending on position of canisters in the IR 9

10 IIG Measurements: LDT based precision length change Stationary specimen scanned along its width, using Linear Displacement Transducers (LDT) Length change of ~ 10 μm in long direction at the lowest level of dpa; Accuracy of measurement ± 2 mm 10

11 Results (1): Effect of H on IIG No effect at low fluence < 5 x m -2 ); At higher fluence, acceleration in IIG for [H] > 100 ppm Relative acceleration is highest for A10 In all pre-unhydrided specimens, some hydrides must be remaining in the specimens at T irr [H] content above TSS In unhydride specimens all hydrogen must be in solution Some hydrogen (20-50 ppm) was picked up during prefilming 11

12 Results (2): Program Specimens IIG Notable Trends IIG strains at the highest fluence ~ 16 x m -2 (or ~ 33 dpa) have been ranked (Table 9 in the paper): Adding Nb to Zr-alloys lowers IIG; Zr with Sn has the highest growth rate of all RXA, SRA or cold worked materials examined Fe addition tends to lower the growth strain, especially at 1000 ppm and above. (Next 2 slides) Differences among materials become more pronounced beginning at ~ 6 x m -2 (or ~ 12 dpa) breakaway growth For Zr-1Nb-0.05Fe alloy, adding S and O seem to increases IIG rate (3 rd slide next) Beneficial effect of S on creep has been noted by other investigators 12

13 Results (3): Program Specimens IIG Effect of Fe Higher the Fe; lower the IIG Strain, consistently: For Zr-1% Sn (A5, A6, A7, and A8) the blue diamonds For Zr-1% Nb (A9, A10, A11, and A12) the pink squares For Zr-1% Sn-1% Nb (A18, A19, A20, and A21) the orange triangles 13

14 Results (4): Effect of Fe (cont d) with increasing dpa Program and Contributed Zr- 2 variants compared Higher the dpa; higher the IIG (as expected) At two highest doses, increasing Fe decreases IIG But an opposite effect is seen at two lowest doses 14

15 Results (5): Program Specimens IIG Effect of O and S Comparing (A10 and A17) and (A13 and A35) S increases IIG Comparing (A17 and A35) higher the O; lower the growth 15

16 Results (7): Influence of Texture and Volume change Orthogonal specimens from Zr-4 spacer-strip material; Measured Kearns basal pole parameter values do not follow strict 1-3f = 0 relationship Net volume change is close to zero in pre-breakaway dose range Less so at high doses 16

17 Results (8): Pre-irradiated Specimens achieved the highest dpa Kobylyansky Data Extended: Ref Zr-2 growth data found to be consistent Effect of cold work: 70% CW data added 17

18 Results (9): IIG of RX and CW Materials tend to converge at high dose Examples from Program Specimens and Contributed Specimens IIG for RX is lower than CW with fluence At high dose (~ 33 dpa) they tend to converge 18

19 Post-irradiation examinations beyond IIG measurements PIE of Selected Specimens: Density No significant change even up to high dose levels Micro-hardness Large increased from 0 to 33 dpa; Then relatively less so from 33 to 54 dpa Hydrogen evaluation after thermal-cycling SPP characterization for Ref Zr-2 Unhydrided and 718 ppm [H] Ref Zr-2 compared after: Thermal-cycling: Heating to 320 C, hold for 2h, followed by cooling to room temp Simulating BOR-60 start-ups and shutdown No effect on hydride-morphology nor specimen length 19

20 Dislocation Loop Characterization (TEM) Appearance of <c> loops coincides with breakaway growth whether it s the cause or the effect is uncertain General trend: higher the dose (or, fluence); higher the <c> loop density (Next slide) As the loops get larger with dose, quantification of <c> loop density needs to be clarified In this work, we used Random Sectioning Method ƩL/V Method 20

21 Random Sectioning Method 21

22 (ƩL)/V Method 22

23 Key Conclusions (1) With increasing fluence (or exposure) which also increases average <c> dislocation loop density the IIG increases in all materials examined The effect of alloying elements is as follows: The addition of Nb to alloys slows down the IIG; The addition of Fe also slows down IIG in binary (Zr-Sn, Zr-Nb), tertiary (Zr-Sn-Nb) Program alloys and also Contributed alloys The addition of Sn exhibited the highest growth, irrespective to the type of heat treatment (RXA, SRA or CW) The beta-quenched Zr-alloys exhibited the lowest IIG values (practically no growth), up to the maximum dose ~ 57 is observed for beta-quenched Zr alloys For several alloy variants, an accelerated growth occurs at a neutron fluence of (7-10) m -2 (E > 1 MeV) or ~11-17 dpa 23

24 Key Conclusions (2) For re-crystallized M5-like, Zirlo-like, reference Zircalory-2 and spacer strip Zircaloy-4 materials with different [H], including the initial impurity hydrogen, varying the [H] content from ~116 to ~718 ppm was had a minor effect on IIG rates up to the highest neutron fluence achieved However, compared to unhydrided materials (where [H] is well below TSS at T irr ), the pre-hydrided materials had a significantly higher growth rate with increasing dose For pre-hydrided samples, the accelerated growth stage occurs at a slightly lower fluence as compared to samples with no additional H. The effect of texture on growth corresponds basically to Є ~(1-3f); however, at high neutron fluence, this quantitative correlation is less precise 24

25 Together Shaping the Future of Electricity 25