18th International Symposium on Zirconium in the Nuclear Industry

Transcription

1 Temperature and Neutron Flux Dependence of In-reactor Creep for Cold-worked Zr-2.5Nb 18th International Symposium on Zirconium in the Nuclear Industry R. DeAbreu, G. Bickel, A. Buyers, S. Donohue, K. Dunn, M. Griffiths, and L. Walters 2016 May -1-

2 Introduction The Zr-2.5Nb pressure tube is a key component in the CANDU 1 reactor. Empirical data has been obtained from a large in-reactor experiment performed to characterize pressure tube deformation over a wide range of operating conditions. 1 CANDU is a registered trademark of Atomic Energy of Canada Limited. -2-

3 The Zr-2.5Nb Pressure Tube The Zr-2.5Nb pressure tube resides in the CANDU reactor core and it is the pressure boundary surrounding the fuel The pressure tube is 6.3 m long, 104 mm ID and 4.2 mm wall thickness -3-

4 Creep Capsule Tests in NRU Reactor to Assess Pressure Tube Deformation Pressurized Zr-2.5Nb capsules Similar manufacturing route to pressure tubes Cold work: 12 and 27% Kearn s basal texture parameters f R = , f T = Radial grain thickness: µm Temperatures: 280, 320, and 340 C Neutron fluxes (E >1 MeV): ~10 15 to ~10 17 n m -2 s -1 Hoop stresses: 0 to 200 MPa -4-

5 Specimen Module Creep capsules are placed in heating modules. Each module has: Controlled heating 12 specimen holes 3 thermocouples 3 flux monitor Fe wires Up to 12 Zr-2.5Nb microstructure evolution monitor bars -5-

6 Instrumented Irradiation Test Rig SHIELD PLUG 466 (142.0 m) Module 1 HEATER ZONE 1 36 OUT-OF-FUEL CAPSULES Module 2 HEATER ZONE 2 Module 3 HEATER ZONE 3 HELIUM PURGE F/N ROD COOLANT FLOW HANGER TUBE TOP of FUEL (141.0 m) 12 CAPSULES PER ZONE HEATER WINDINGS CENTERING SPACERS OUTER PROTECTIVE CAN Module 5 Module 6 HEATER ZONE 4 HEATER ZONE 5 HEATER ZONE 6 Creep insert capabilities Φ fast : ~10 15 to n m -2 s -1 T: 250 to 360 C OXYGEN GETTER BOTTOM of FUEL (139.5 m) Passive gas-gap cooling NOSE CONE -6-

7 NRU Mk-4 Fast Neutron (FN) Rod Mk-4 FN Rod NRU data to be compared with data from CANDU pressure tubes and data from creep capsules irradiated in Osiris -7-

8 Effect of Neutron Flux 280 C, 125 MPa, 27% CW Secondary Creep Primary Creep -8-

9 Effect of Cold Work and Temperature on Secondary Diametral Creep 125 MPa, 12% and 27% CW -9-

10 What is the effect of irradiation on creep? What can we learn from a comparison with out-reactor tests? -10-

11 Unirradiated, Pre-irradiated, and Irradiation Out-reactor axial secondary creep rate is ~0, indicative of isotropic behaviour for a biaxial stress Pre-irradiated out-reactor test shows lower diametral creep rate and suppression of primary creep. Indicates hardening effect of irradiation 280 C, 125 MPa, 27% CW In-reactor creep is high and anisotropic compared to out-reactor creep -11-

12 Thermal creep before and after irradiation to a low dose Published on Oct 7, 2014 Movies illustrating dislocation motion with in-situ straining before and after ion irradiation. Material is 304 stainless steel held in-situ at 400 C. Irradiation was with 1 MeV Kr ions to dose of 3x10 13 ions/cm 2 about 0.2 dpa M. Briceno, J. Fenske, M. Dadfarnia, P. Sofronis and I.M. Robertson, Effect of Ion Irradiation produced Defects on the Mobility of Dislocations in 304 Stainless Steel, J. Nucl. Mater. 409 (2011)

13 Diametral Strain Rate as a Function of Fast Neutron Flux (E >1 MeV) in an NRU Pressure Tube Diametral/transverse steady-state strain rates vary depending on local fast neutron flux Creep suppression zone for a specific range of fluxes related to the hardening effect of irradiation and locking of dislocations Trasverse Strain Strain Strain / 10 / 10-4 Rate -4 / h E E E E E Unfuelled Zone Fuelled Zone Flux << 1 x n m -2 s -1 Flux > n m -2 s -1 OUTLET 305 C Creep Suppression Zone 1 x n m -2 s -1 < Flux < 1 x n m -2 s INLET C E E+24 2E+24 1E+254E E+256E+24 2E E+25 8E+24 3E+25 1E E E+25 4E+251.4E E+25 5E Fluence / 10/ n.m 25-2 n.m -2 Elevation / m Creep is lower in out-of-core region relative to in core. -13-

14 Experimental and Gauging Data Fast Neutron (E >1 MeV) Fluence Dependence Diametral strain At the CANDU, minimum MPa of the creep suppression zone there is no Trillium 2, capsule M18, 125 MPa detectable irradiation NRU D28 damage from XRD or TEM, but there is a measurable increase in hardness Candu Equivalent Fluence (n/m 2 x ) Strain compared at 280 C and MPa Non-linearity in fluence apparent over a range of fluxes Creep is complex Data at ~280 C NRU creep capsules Flux = 0.4 Data 1.52 at ~300 x Cn.m -2.s -1 CANDU PT NRU PT Flux 2.3 = x x x n m n.m -2-2 s.s -1-1 OSIRIS creep capsules Flux = 1.75 x n.m -2.s

15 Dislocation Densities vs. Fast Fluence c-type a-type dislocation density is fluence (dose) dependent and reaches saturation at a fluence > of 25 about x n.mx n m

16 Fast Neutron (E >1 MeV) Flux Dependence of Secondary Creep Rate Strain rate /s E E E E E E-11 NRU loop assembly CANDU in-service tubes OSIRIS capsule M18 Rates compared at 285 C and MPa at h At a given point in time, traditional models are nearly linear with flux 4.0E E E+00 NRU capsules Model 0 5E+17 1E E+18 2E+18 Non-linearity apparent over a large range of fluxes CANDU Equivalent Flux (n m -2 s -1 ) Model Christodoulou et al., ASTM STP 1295, 1996, p

17 What could be causing the non-linearity as a function of flux? Mutual recombination effects -17-

18 Mutual Recombination for a High Vacancy Migration Energy Experimental data indicates that vacancy migration energies in Zr could be either 1.3 ev (intrinsic) or 0.7 ev (extrinsic). G.M. Hood, in: Solute-Defect Interaction, Theory and Experiment, Eds. S. Saimot, G.R. Purdy and G.V. Kidson (Pergamon Press, Toronto, 1986) p. 83. This plot shows the atom flux to dislocations as a function of dose rate at 280 C for the intrinsic and extrinsic migration energies. This plot shows the atom flux to dislocations as a function of temperature for three flux conditions and intrinsic vacancy migration energy, 1.3 ev. -18-

19 What else could be causing the non-linearity? Microstructure evolution -19-

20 Postulated Diametral Creep Model at h The final creep rate as a function of neutron flux is non-linear Creep by mass-transport is increased with neutron flux Climb of edge components is increased with neutron flux thus enhancing their glide Thermal creep by glide of screw components is suppressed by irradiation Strain Rate / s Thermal C&G Creep suppression due 0.30 Mass Transport to climb of screw Total 0.25 components of dislocations Trend over a large range of fast neutron fluxes 0 1E+17 2E+17 Neutron Flux / n.m -2.s -1 Effect of a-type dislocation loops Vacancy c-type loops as modifiers of reduce the diametral mass transport strain rate and barriers to dislocation glide -20-

21 Summary - Diametral Strain Rate as a Function of Fast Neutron Flux Similar non-linear flux dependence at higher temperature Increasing rate with increasing temperature at all flux levels -21-

22 Conclusions Irradiation creep has a non-linear dependence on dose and dose rate (neutron fluence and neutron flux). At low fluxes the creep behaviour is complex: Irradiation suppresses creep by dislocation glide Irradiation also enhances creep by enabling dislocation glide by climb or by simple mass transport, or both The evolving a-type loop structure affects creep by further inhibiting dislocation glide and/or by affecting the mass transport At high fluxes (>10 18 n m -2 s -1 ), non-linearity in flux can occur because of increased mutual recombination of point defects. At high fluences, non-linearity in fluence occurs because of microstructure evolution (e.g. c-loops). -22-

23 Thank you. Questions? -23-