Delayed hydrogen embrittlement in Zr-2.5 wt % Nb

Simpson, C.J.; Ells, C.E.

doi:10.1016/0022-3115(74)90174-3

“…DHC is a stable crack-growth mechanism that has led to failures in Zr-2.5Nb fuel cladding [16], pressure tubes [17], and possibly in Zircaloy fuel cladding [18][19][20]. The conventional view is that the DHC process consists of several steps [16,17,21,22]:…”

Section: Dhc Mechanismmentioning

confidence: 99%

Performance of Pressure Tubes in Candu Reactors

DouglasRodgers

¹

,

MalcolmGriffiths

²

,

GrantBickel

³

et al. 2016

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The pressure tubes in CANDU reactors typically operate for times up to about 30 years prior to refurbishment. The in-reactor performance of Zr-2.5Nb pressure tubes has been evaluated by sampling and periodic inspection. This paper describes the behavior and discusses the factors controlling the behaviour of these components. The Zr–2.5Nb pressure tubes are nominally extruded at 815 °C, cold worked nominally 27%, and stress relieved at 400 °C for 24 hours, resulting in a structure consisting of elongated grains of hexagonal close-packed alpha-Zr, partially surrounded by a thin network of filaments of body-centred-cubic beta-Zr. These beta-Zr filaments are meta-stable and contain about 20% Nb after extrusion. The stress-relief treatment results in partial decomposition of the beta-Zr filaments with the formation of hexagonal close-packed alpha-phase particles that are low in Nb, surrounded by a Nb-enriched beta-Zr matrix. The material properties of pressure tubes are determined by variations in alpha-phase texture, alpha-phase grain structure, network dislocation density, beta-phase decomposition, and impurity concentration that are a function of manufacturing variables. The pressure tubes operate at temperatures between 250 °C and 310 °C with coolant pressures up to about 11 MPa in fast neutron fluxes up to 4 × 1017 n·m−2·s−1 (E > 1 MeV) and the properties are modified by these conditions. The properties of the pressure tubes in an operating reactor are therefore a function of both manufacturing and operating condition variables. The ultimate tensile strength, fracture toughness, and delayed hydride-cracking properties (velocity (V) and threshold stress intensity factor (KIH)) change with irradiation, but all reach a nearly limiting value at a fluence of less than 1025 n·m−2 (E > 1 MeV). At this point the ultimate tensile strength is raised about 200 MPa, toughness is reduced by about 50%, V increases by about a factor of 6, while KIH is only slightly reduced. The role of microstructure and trace elements in these behaviours is described. Pressure tubes exhibit elongation, diametral expansion, and sag. The deformation behaviour is a function of operating conditions and the material properties that vary from tube-to-tube and as a function of axial location. Semi-empirical predictive models have been developed to describe the deformation response of average tubes as a function of operating conditions. The effect of material variability on corrosion behaviour is less well defined compared with other properties but there are instances where tube orientation and ingot source can be identified as factors that have an effect on hydrogen pick-up.

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“…With each step of strain corresponding stresses surrounding each atom is calculated and the configurations are dumped at each change in timestep. The script below is modified from LAMMPS software to provide us the required output 2 all custom 1000 zr.dump id type x y z dump_modify 2 every 1000 pair_coeff * * meamf ZrN NULL ZrN ZrN ZrN #minimization parameters fix 1 all nve/limit 0.1 minimize 1.0e-30 1.0e-30 100000 1000000 unfix 1 undump 2 velocity all create 600.0 4928459 rot yes dist gaussian fix 1 all nvt temp 600.0 600.0 100.0 compute 1 hydrogen msd compute 2 zr msd thermo 1000 thermo_style custom step etotal ke temp pe press vol c_1 [1] c_1 [2] c_1 [3] c_1 [4] c_2 [1] c_2 [2] c_2 [3] c_2 [4] …”

Section: Methodsmentioning

confidence: 99%

“…As it is well known, hydride precipitates play an important role in the hydrogen embrittlement of various zirconium alloys, and a great number of studies [1][2][3][4][5][6][7][8][9][10] Hydride reorientation [4] and cracking under hoop stress in zircaloy tubes is the major problem in the nuclear industry. The occurrence of hydride reorientation under stress usually involves the preferential precipitation of hydride along circumferential direction of zirconium tube.…”

mentioning

confidence: 99%

Molecular Dynamics Study of Zirconium and Zirconium Hydride

Siripurapu

¹

,

Szpunar

²

,

Szpunar

³

2013

Proceedings of the 8th Pacific Rim International Congress on Advanced Materials and Processing

0

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Molecular dynamics (MD) simulations were used in order to investigate structure and mechanical properties of zirconium and zirconium hydride. Calculation of temperature dependent failure of zirconium, diffusion of hydrogen in zirconium, properties of interfaces in zirconium and zirconium hydride and effect of hydrogen on crack nucleation and propagation were in good agreement with available experimental data. These are the first computer simulations where large-scale atomic/molecular massively parallel simulator (LAMMPS) code was used with the Embedded Atom Method (EAM) and Modified Embedded Atom Method (MEAM) to study structure and mechanical properties of zirconium hydrogen system (Zr-H) and zirconium hydride (ZrH2).Verification of methods was done in order to establish the best potential for zirconium and zirconium hydride. EAM and MEAM potentials successfully predicted lattice parameters, mechanical properties and variation of lattice parameters with temperature for α-Zr. MEAM potential was used to predict correctly the face centered structure for ZrH2 and also its mechanical properties.Temperature dependent stress-strain curves were calculated in order to predict yielding point for α-Zr. Results indicate early yielding and failure with increase of temperature in zirconium on application of tensile and compressive strains. Anisotropic stress variation with temperature in α-Zr was calculated.Hydrogen ingress through diffusion of hydrogen in zirconium is a mechanism responsible for formation of hydrides. Temperature-dependent hydrogen diffusion and activation energy for diffusion was calculated and the agreement with experiments was satisfactory. Anisotropy of diffusion of hydrogen is observed for Zr crystal. Hydrogen diffusion was also modeled under tensile and compressive strain and a possible formation of hydrides in the direction perpendicular to applied strain was observed.The effect of strain on orientation of hydride was investigated. Hydride {111} oriented crystal Bonds surrounding atoms and stress concentration analysis were performed using OVITO and VMD software respectively. Weaker bonds and higher stress concentrations are observed in the presence of hydrogen in zirconium. The presented results clearly demonstrate that MD simulation can be used to predict structure and processes that are important for understanding failure in Zr based nuclear materials.iv PREFACE Sections of this thesis have been submitted as a multi-authored paper in refereed conference papers. The research, data analyses and manuscript preparation were carried out by me and the co-authors contributed in editing the manuscripts for submission to refereed conference papers.

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“…These hydrides precipitate at both intergranular boundaries and within the grains causing deleterious impact on the mechanical properties of the zirconium [8]. Research studies [1][2][3] have shown that intergranular hydrides could play more important role in hydride-induced rupture compared with intra-granular hydrides, because cracking is more likely to take place in intergranular hydrides [1].…”

Section: Interfacial Cracking Of Hydride In Zirconiummentioning

confidence: 99%

Molecular Dynamics Study of Zirconium and Zirconium Hydride

Siripurapu¹,

Szpunar²,

Szpunar³

2013

Pricm

0

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Molecular dynamics (MD) simulations were used in order to investigate structure and mechanical properties of zirconium and zirconium hydride. Calculation of temperature dependent failure of zirconium, diffusion of hydrogen in zirconium, properties of interfaces in zirconium and zirconium hydride and effect of hydrogen on crack nucleation and propagation were in good agreement with available experimental data. These are the first computer simulations where large-scale atomic/molecular massively parallel simulator (LAMMPS) code was used with the Embedded Atom Method (EAM) and Modified Embedded Atom Method (MEAM) to study structure and mechanical properties of zirconium hydrogen system (Zr-H) and zirconium hydride (ZrH2).Verification of methods was done in order to establish the best potential for zirconium and zirconium hydride. EAM and MEAM potentials successfully predicted lattice parameters, mechanical properties and variation of lattice parameters with temperature for α-Zr. MEAM potential was used to predict correctly the face centered structure for ZrH2 and also its mechanical properties.Temperature dependent stress-strain curves were calculated in order to predict yielding point for α-Zr. Results indicate early yielding and failure with increase of temperature in zirconium on application of tensile and compressive strains. Anisotropic stress variation with temperature in α-Zr was calculated.Hydrogen ingress through diffusion of hydrogen in zirconium is a mechanism responsible for formation of hydrides. Temperature-dependent hydrogen diffusion and activation energy for diffusion was calculated and the agreement with experiments was satisfactory. Anisotropy of diffusion of hydrogen is observed for Zr crystal. Hydrogen diffusion was also modeled under tensile and compressive strain and a possible formation of hydrides in the direction perpendicular to applied strain was observed.The effect of strain on orientation of hydride was investigated. Hydride {111} oriented crystal Bonds surrounding atoms and stress concentration analysis were performed using OVITO and VMD software respectively. Weaker bonds and higher stress concentrations are observed in the presence of hydrogen in zirconium. The presented results clearly demonstrate that MD simulation can be used to predict structure and processes that are important for understanding failure in Zr based nuclear materials.iv PREFACE Sections of this thesis have been submitted as a multi-authored paper in refereed conference papers. The research, data analyses and manuscript preparation were carried out by me and the co-authors contributed in editing the manuscripts for submission to refereed conference papers.

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Delayed hydrogen embrittlement in Zr-2.5 wt % Nb

Cited by 99 publications

References 8 publications

Performance of Pressure Tubes in Candu Reactors

Performance of Pressure Tubes in Candu Reactors

Molecular Dynamics Study of Zirconium and Zirconium Hydride

Molecular Dynamics Study of Zirconium and Zirconium Hydride

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