Corrosion Behavior Of Zircaloy-4 Research Articles

Effects of Hydrogenation on the Corrosion Behavior of Zircaloy-4.

Hydrogen plays an important role in the corrosion of zirconium alloys, and the degree of influence highly depends on the alloy composition and conditions. In this work, the effects of hydrogenation on the corrosion behavior of Zircaloy-4 in water containing 3.5 ppm Li + 1000 ppm B at 360 °C/18.6 MPa were investigated. The results revealed that hydrogenation can shorten the corrosion transition time and increase the corrosion rates of Zircaloy-4. The higher corrosion rates can be ascribed to the larger stress in the oxide film of hydrogenated samples, which can accelerate the evolution of the microstructure of the oxide film. In addition, we also found that hydrogenation has little effect on the t-ZrO2 content in the oxide film and there is no direct correspondence between the t-ZrO2 content and the corrosion resistance of the Zircaloy-4.

Corrosion of Zircaloy-4, Zr-1Nb and FeCrAl alloys in deaerated water at 330 °C and 14 MPa: Superior corrosion resistance and corrosion mechanism of FeCrAl alloy by experiments and molecular dynamics simulations

After the Fukushima explosion, the research and development of accident tolerant fuel (ATF) cladding has become a hot spot in the nuclear field. In this work, corrosion behavior of Zircaloy-4, Zr-1Nb and FeCrAl alloys was investigated in deaerated water at 330 °C and 14 MPa. All alloys were found to lose weight. In Li/B water, the corrosion resistance followed an order of FeCrAl > Zr-1Nb > Zircaloy-4. Local corrosion occurred on the Zircaloy-4 surface and developed towards the interior of the matrix, leading to selective oxidation. A certain thickness of oxide layer was formed on the surface of Zr-1Nb, but the distribution was uneven. Significant oxide exfoliation made Zr-1Nb display complex defects. The oxide film of FeCrAl alloy had a double-spinel structure. Low surface adsorption energy and weak interaction between Fe and O atoms is responsible for superior corrosion resistance of FeCrAl alloy.

Determination of the initial oxidation behavior of Zircaloy-4 by in-situ TEM

The corrosion behavior of Zircaloy-4 (Zry-4), specifically by oxidation, is a problem of great importance as this material is critical for current nuclear reactor cladding. The early formation behavior and structure of the oxide layer during oxidation was studied using in-situ TEM techniques that allowed for Zry-4 to be monitored during corrosion. These environmental exposure experiments were coupled with precession electron diffraction to identify and quantify the phases present in the samples before and after the oxidation. Following short-term, high temperature oxidation, the dominant phase was revealed to be monoclinic ZrO2 in a columnar structure. These samples oxidized in-situ contained structures that correlated well with bulk Zry-4 subjected to autoclave treatment, which were used for comparison and validation of this technique. By using in-situ TEM the effect of microstructure features, such as grain boundaries, on oxidation behavior of an alloy can be studied. The technique presented herein holds the potential to be applied any alloy system to study these effects.

Corrosion behavior of Zircaloy-4 in aqueous solution of methanol at 320ºC under gamma-irradiation

Corrosion behavior of Zircaloy-4 in aqueous solution of methanol at 320ºC under gamma-irradiation

On the corrosion behavior of zircaloy-4 in spent fuel pools under accidental conditions

After zircaloy cladding tubes have been subjected to irradiation in the reactor core, they are stored temporarily in spent fuel pools. In case of an accident, the integrity of the pool may be affected and the composition of the coolant may change drastically. This was the case in Fukushima Daiichi in March 2011. Successive incidents have led to an increase in the pH of the coolant and to chloride contamination. Moreover, water radiolysis may occur owing to the remnant radioactivity of the spent fuel. In this study, we propose to evaluate the corrosion behavior of oxidized Zr-4 (in autoclave at 288°C for 32days) in function of the pH and the presence of chloride and radical forms. The generation of radicals is achieved by the sonolysis of the solution. It appears that the increase in pH and the presence of radicals lead to an increase in current densities. However, the current densities remain quite low (depending on the conditions, between 1 and 10μAcm−2). The critical parameter is the presence of chloride ions. The chloride ions widely decrease the passive range of the oxidized samples (the pitting potential is measured around +0.6V (vs. SCE)). Moreover, if the oxide layer is scratched or damaged (which is likely under accidental conditions), the pitting potential of the oxidized sample reaches the pitting potential of the non-oxidized sample (around +0.16V (vs. SCE)), leaving a shorter stable passive range for the Zr-4 cladding tubes.

Effect of surface nanocrystallization on the corrosion behavior of Zircaloy-4

The contrastive corrosion experiments between surface nanocrystallined Zircaloy-4 and coarse-grained Zircaloy-4 under the condition of 673 K/10.3 MPa in pure water are carried out, and the microstructure of oxide films has been studied. The results indicate that the growth rate of oxide films formed on the nanocrystalline Zircaloy-4 is lower than that of oxide films formed on the coarse-grained Zircaloy-4. Simultaneously, the oxide/metal interface of the former is more regular and glossy than that of the latter. For nanocrystalline Zircaloy-4, the low oxygen diffusion rate through the oxide/metal interface can hinder the reaction of oxygen ion with metal ion. Furthermore, more tetragonal ZrO2 are observed in the oxide films, which can delay the martensite phase transition from tetragonal to monoclinic phase in oxide films.

Effect of copper ions implantation on corrosion behavior of zircaloy-4 in 1 M H 2SO 4

In order to study the effect of copper ion implantation on the aqueous corrosion behavior, samples of zircaloy-4 were implanted with copper ions with fluences ranging from 1 × 10 16 to 1 × 10 17 ions/cm 2, using a metal vapor vacuum arc source (MEVVA) operated at an extraction voltage of 40 kV. The valence states and depth distributions of elements in the surface layer of the samples were analyzed by X-ray photoelectron spectroscopy (XPS) and Auger electron spectroscopy (AES), respectively. Glancing angle X-ray diffraction (GAXRD) was employed to examine the phase transformation due to the copper ion implantation. The potentiodynamic polarization technique was employed to evaluate the aqueous corrosion resistance of implanted zircaloy-4 in a 1 M H 2SO 4 solution. It was found that a significant improvement was achieved in the aqueous corrosion resistance of zircaloy-4 implanted with copper ions when the fluence is smaller than 5 × 10 16 ions/cm 2. The corrosion resistance of implanted samples declined with increasing the fluence. Finally, the mechanism of the corrosion behavior of copper-implanted zircaloy-4 was discussed.

Role of chromium ion implantation on the corrosion behavior of zircaloy-4 in 0.5M H2SO4

In order to study the effect of chromium ion implantation on corrosion behavior, samples of zircaloy-4 were implanted with chromium ions with fluence ranging from 1×1016 to 1×1017 ions/cm2, using a metal vapor vacuum arc source operated at an extraction voltage of 40 kV. The valence states and depth distribution of elements in the surface of the samples were analyzed by X-ray photoelectron spectroscopy and auger electron spectroscopy, respectively. Transmission electron microscopy was used to examine microstructure of the chromium-implanted samples. The potentiodynamic polarization technique was employed to evaluate the aqueous corrosion resistance of the zircaloy-4 samples in a 0.5 M H2SO4 solution. It was found that a significant improvement was achieved in the aqueous corrosion resistance of zircaloy-4 compared with that of as-received zircaloy-4 when the fluence is smaller than 5×1016 ions/cm2. The mechanism of the corrosion behavior of chromium-implanted zircaloy-4 was discussed.

Studies on the aqueous corrosion behavior and microstructure of zircaloy4 which has been subjected to high-dose Ar ion bombardment

In order to investigate the ion bombardment effect on the corrosion behavior of zircaloy4, the specimen surfaces were bombarded by Ar ion using an accelerator at an energy of 150 keV with a dose range from 3×10 15 to 1×10 17 ions/cm 2 at liquid nitrogen temperature. Post-bombardment corrosion tests were conducted to rank the corrosion resistance of the resulting specimens by potentiodynamic polarization curve measurements in a 0.5 M H 2SO 4 water solution at room temperature. The vacancy profile induced by Ar ions bombardment was calculated using Monte Carlo simulation program SRIM 96, and measured by means of the slow positron annihilation spectroscopy (SPAS). The surface microstructures were examined using glancing angle X-ray diffraction (GAXRD). The potentiodynamic tests showed that with the bombardment dose increasing, the passive current density, closely related to the surface corrosion resistance, decreased firstly and increased subsequently. The mechanism of the corrosion behavior transformation was due to the amorphous phase formation firstly and the amorphous phase destruction and the polycrystalline structure formation in the bombarded surface subsequently.

Role of chromium ion implantation on the corrosion behavior of zircaloy-4 in 0.5 M H 2SO 4

In order to study the effect of chromium ion implantation on corrosion behavior, samples of zircaloy-4 were implanted with chromium ions with fluence ranging from 1×10 16 to 1×10 17 ions/cm 2, using a metal vapor vacuum arc source operated at an extraction voltage of 40 kV. The valence states and depth distribution of elements in the surface of the samples were analyzed by X-ray photoelectron spectroscopy and auger electron spectroscopy, respectively. Transmission electron microscopy was used to examine microstructure of the chromium-implanted samples. The potentiodynamic polarization technique was employed to evaluate the aqueous corrosion resistance of the zircaloy-4 samples in a 0.5 M H 2SO 4 solution. It was found that a significant improvement was achieved in the aqueous corrosion resistance of zircaloy-4 compared with that of as-received zircaloy-4 when the fluence is smaller than 5×10 16 ions/cm 2. The mechanism of the corrosion behavior of chromium-implanted zircaloy-4 was discussed.

Electrochemical behavior of niobium-implanted zircaloy-4 induced by heat treatment

The effect of niobium ion implantation on the corrosion behavior of zircaloy-4 was studied by using a MEVVA source at 40 keV energy with a fluence range from 1 × 10 16 to 2 × 10 17 ions/cm 2. Subsequent to ion implantation, three-sweep potentiodynamic polarization curves were measured in a 1 N H 2SO 4 solution and scanning electron microscopy analyses were performed to study the surface morphology of the samples after polarization tests. It was interesting that a significant improvement was achieved in the aqueous corrosion resistance of zircaloy-4 compared with that of un-implanted zircaloy-4. The most remarkable phenomenon was that ion implantation with a fluence of 5 × 10 16 ions/cm 2 showed the optimal improvement of the electrochemical property among the implanted samples. In addition to X-ray photoemission spectroscopy analysis, heat treatment and the following polarization measurement were also carried out to investigate the possible mechanism of the improvement of the corrosion resistance.

Reaction of Zircaloy-4 with tellurium under different oxygen potentials

Corrosion behavior of Zircaloy-4 has been studied under different oxygen potentials and tellurium vapor pressures. The oxygen potential was controlled by buffer over the range of −600 to −430 kJ/mol. Under the condition of oxygen potential of less than −500 kJ/mol with coexisting tellurium vapor, duplex corrosion layers were formed on the surface of Zircaloy-4 specimens, which consisted of zirconium telluride and zirconium oxide. The thickness of corrosion layer was increased with tellurium vapor pressure. For the oxygen potential over −430 kJ/mol, only zirconium oxide was observed on the specimen surface regardless of coexistence of tellurium vapor.

Studies on the corrosion behavior of yttrium-implanted zircaloy-4

In order to study the effects of yttrium ion implantation on the aqueous corrosion behavior of zircaloy-4, specimens were implanted with yttrium ions using a MEVVA source at an energy of 40 keV, with a dose range from 1 × 1016 to 1 × 1017 ions/cm2 at about 150°C. Transmission electron microscopy (TEM) was used to obtain the structural character of the yttrium-implanted zircaloy-4. The valence of the yttrium ions in the surface layer was analyzed by X-ray photoemission spectroscopy (XPS). Three-sweep potentiodynamic polarization measurement was employed to evaluate the aqueous corrosion behavior of zircaloy-4 in a 1 N H2SO4 solution. It was found that a significant improvement was achieved in the aqueous corrosion resistance of zircaloy-4 compared with that of the as-received zircaloy-4. The mechanism of the corrosion resistance improvement of the yttrium-implanted zircaloy-4 is probably due to the addition of the yttrium oxide dispersoid into the zirconium matrix.

The Effect of Niobium Additions on the Corrosion Behavior of Zircaloy-4

Alloying additions of 0.5 and 1.0 wt% niobium, respectively, have been added to Zircaloy-4 in an attempt to improve its high-temperature corrosion resistance. Ingots of these modified alloys were fabricated to a 0.76-mm-thick sheet via a processing sequence compatible with commercial tubing production and were given one of four different final anneals. Subsequent testing indicated that the niobium additions had little or no effect on corrosion resistance in 360°C water. In 427°C steam, however, the 0.5%-niobium addition provided increased resistance to spalling, while the 1.0%-niobium addition decreased both cumulative weight gains and post-transition corrosion rates. The weight gains exhibited by the 0.5%-niobium alloy were relatively insensitive to final heat treatment, whereas the 1.0%-niobium alloy suffered a degradation in properties as the extent of the final anneal increased. These trends in corrosion performance were subsequently correlated with the second-phase particle size distributions present in the alloys, the best performance being obtained when the mean particle diameter was <400 to 500 Å. It was concluded that both niobium additions improved the corrosion performance of Zircaloy-4 at elevated temperatures, but that the best performance was obtained at the 1.0-wt%-niobium level.

Zirconium Alloy Corrosion In High-Temperature Halide Solutions

Abstract The corrosion behavior of Zircaloy-4 has been studied in 680 F halide solutions adjusted to pH 10.5 with LiOH or NH4OH. No accelerated corrosion was observed after 56 days' exposure to 0.01 M solutions of LiCI, Lil, NH4Cl or NH4l, with or without Fe3O4 suspensions in the solutions. Severe attack occurred in Fe3O4-free 0.01 M LiF and NH4F solutions. Although large quantities of Fe3O4 in suspension decreased attack by decreasing the fluoride concentration of the solution, thin surface deposits of Fe3O4 on the Zircaloy-4 surface did not appear to increase or retard attack in the 0.01 M fluoride solutions. No unusual corrosion occurred in 0.001 M LiF or 0.0001 M NH4F solutions.