Predicting Oxidation and Deuterium Ingress for Zr-2.5Nb CANDU Pressure Tubes

Bahurmuz, A.A.; Muir, I.J.; Urbanic, VF

doi:10.1520/jai12342

Cited by 9 publications

(6 citation statements)

References 7 publications

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“…The barrier oxide structure is product of the substrate microstructure and a stochastic growth-rupture mechanism, where H pickup is dependent on the accumulation of many successive growth-61 rupture events. This stochastic mechanism of accumulated small step changes, rather than a gradual change in kinetics, is consistent with observed increasing variability in H pickup with exposure time for alloys that have otherwise well-controlled composition and microstructure [2].…”

Section: Introductionsupporting

confidence: 80%

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Using EIS/PEDRA to Describe Barrier Oxide Films on Irradiated Zirconium Alloys

Maguire¹

2014

MRS Proc.

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Electrochemical Impedance Spectroscopy (EIS) and the Parallel Electrical Dielectric Response Analysis (PEDRA) application were used to describe the inner barrier oxide films on irradiated zirconium alloys. This is achieved with minimal surface preparation and without disturbing the outer porous oxide. These two distinguishable inner and outer oxide layers result from a growthfracture oxidation mechanism. Key to success of the EIS technique in describing the barrier oxide layer are: 1) the model and procedure used to fit EIS spectra, 2) the validation of the fit, and 3) converting circuit parameters (R, C and n) into physical attributes of the barrier oxide.The barrier oxide is defined as the inner-dense layer adjacent to the metal-oxide interface. The integrity of barrier oxide is thought to effect both oxidation (i.e. access of water to the interface), and hydrogen pickup (i.e. failure hydrogen to escape away from the interface). Using EIS and the PEDRA application, the barrier oxide is described in terms of multiple independent dielectric responses to yield a unique 'micro-macro' picture of the barrier oxide that can be used to explain observed H pickup behavior.

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Section: Introductionsupporting

confidence: 80%

“…Instead the percent pickup is the total available H less the amount that escapes back into the water environment: %H pickup = (H total -H escape) / (H total) (2) For oxidation to continue water must diffuse into the barrier oxide to near the metal-oxide interface. It does this via oxide grain boundaries and connected ribbon porosity.…”

Section: Introductionmentioning

confidence: 99%

Using EIS/PEDRA to Describe Barrier Oxide Films on Irradiated Zirconium Alloys

Maguire¹

2014

MRS Proc.

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“…In addition, the measured data are reasonably bounded by model predictions and fall below the target limits described in Table 1 [13].…”

Section: Corrosion and Hydrogen Ingressmentioning

confidence: 71%

“…For this reason it is important to have predictive models of deuterium ingress for fitness-for-service assessments for operating pressure tubes and for the development of new reactor designs. A predictive model for assessing the longterm oxidation of, and deuterium ingress into, the body of the pressure tubes has been developed from in-reactor tests of samples which had been pre-oxidized to obtain oxide thickness values representative of long-term behavior [13]. Deuterium ingress is modeled based on a fraction (2-10%) of the corrosion-freed deuterium entering the metal.…”

Section: Corrosion and Hydrogen Ingressmentioning

confidence: 99%

In-reactor performance of pressure tubes in CANDU reactors

Rodgers

Coleman

Griffiths

et al. 2008

Journal of Nuclear Materials

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“…In many cases there are synergistic relationships between the variables making it difficult to determine the relative importance of any one variable in terms of its influence on pressure-tube corrosion and deuterium ingress behaviour from reactor data alone. Well-designed experiments are needed to understand the mechanisms of corrosion and deuterium ingress in order to reduce ingress in pressure tube, and to develop predictive models for fitness-for-service assessments for operating pressure tubes [36].…”

Section: In-reactor Performance Of Pressure Tubes In Candu Reactors -mentioning

confidence: 99%

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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Predicting Oxidation and Deuterium Ingress for Zr-2.5Nb CANDU Pressure Tubes

Cited by 9 publications

References 7 publications

Using EIS/PEDRA to Describe Barrier Oxide Films on Irradiated Zirconium Alloys

Using EIS/PEDRA to Describe Barrier Oxide Films on Irradiated Zirconium Alloys

In-reactor performance of pressure tubes in CANDU reactors

Performance of Pressure Tubes in Candu Reactors

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