The Effects of Microstructure and Operating Conditions on Irradiation Creep of Zr-2.5Nb Pressure Tubing

Walters, Lori; Bickel, G. A.; Griffiths, M.

doi:10.1520/stp154320120158

Cited by 11 publications

(25 citation statements)

References 12 publications

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“…The basal plane normals are predominant in the transverse direction of Zr-2.5Nb pressure tube. The effect of the textures on growth strains for 2 types of tubes referred to as fuel sheathing (FS) and micro-pressure tube (MPT) is given in Figure 6 by using the strain data provided in Table 3 in Walters et al [25]. Similar growth strain is observed in the axial direction for both FS and MPT material due to very few basal plane normals in that direction.…”

Section: Effect Of Texturementioning

confidence: 92%

“…The 2 most prominent mechanisms are stress-induced preferential absorption of point defects at dislocations and climb followed by glide of dislocation [27]. The application of a diffusional mass transport model based on interstitial/vacancy diffusion towards grain boundary sinks appears to be a strong support on the effect of grain size/ shape [25].…”

Section: Figurementioning

confidence: 99%

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Irradiation Effects on ZR-2.5NB in Power Reactors

Song

2016

CNL Nuclear Review

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Zirconium alloys are widely used as structural materials in nuclear applications because of their attractive properties such as a low absorption cross-section for thermal neutrons, excellent corrosion resistance in water, and good mechanical properties at reactor operating temperatures. Zr-2.5Nb is one of the most commonly used zirconium alloys and has been used for pressure tube materials in CANDU (Canada Deuterium Uranium) and RBMK (Reaktor Bolshoy Moshchnosti Kanalnyy, “High Power Channel-type Reactor”) reactors for over 40 years. In a recent report from the Electric Power Research Institute, Zr-2.5Nb was identified as one of the candidate materials for use in normal structural applications in light-water reactors owing to its increased resistance to irradiation-induced degradation as compared with currently used materials. Historically, the largest program of in-reactor tests on zirconium alloys was performed by Atomic Energy of Canada Limited. Over many years of in-reactor testing and CANDU operating experience with Zr-2.5Nb, extensive research has been conducted on the irradiation effects on its microstructures, mechanical properties, deformation behaviours, fracture toughness, delayed hydride cracking, and corrosion. Most of the results on Zr-2.5Nb obtained from CANDU experience could be used to predict the material performance under light water reactors. This paper reviews the irradiation effects on Zr-2.5Nb in power reactors (including heavy-water and light-water reactors) and summarizes the current state of knowledge.

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Section: Effect Of Texturementioning

confidence: 92%

Section: Figurementioning

confidence: 99%

Irradiation Effects on ZR-2.5NB in Power Reactors

Song

2016

CNL Nuclear Review

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“…The neutron irradiation creates interstitials and vacancies that migrate to sinks such as dislocations, grain boundaries, and in some cases cavities (neutral sinks). Qualitative agreement for the diametral strain dependence on aspect ratio and that calculated with the rate theory expressions has been demonstrated [26]. Since manufacturing practices control the microstructure to some extent, understanding how the texture and grain shape affect deformation may lead to the development of a pressure tube with optimum deformation performance.…”

Section: Deformationmentioning

confidence: 66%

“…Consequently, as texture strongly controls axial strain [25], the HM-and H-series tubes behave very similarly with respect to elongation (Figure 10). In contrast, the diametral strain rate of the HM-series tubes is significantly higher than the H-series tubes ( Figure 11) [26]. In Figure 11, the measured diametral strain at the same axial location and under the same operating conditions is compared.…”

Section: Deformationmentioning

confidence: 95%

“…As a result of the manufacturing differences, the HM-series tube population differed from the H-series tube population by having grains with shorter transverse widths but similar radial thickness. The relative diametral strain is plotted as a function of the mean grain aspect ratio, radial/transverse, in Figure 12 [26]. The aspect ratio (or transverse grain width) has a strong correlation with diametral strain when all other potential variables are held constant.…”

Section: Deformationmentioning

confidence: 99%

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Performance of Pressure Tubes in Candu Reactors

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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