The oxidation characteristics for Zircaloy-4 and Zirlo in the temperature range of 700-1200°C under steam supply condition were investigated by using a modified thermo-gravimetric analyzer.The specimens were oxid...The oxidation characteristics for Zircaloy-4 and Zirlo in the temperature range of 700-1200°C under steam supply condition were investigated by using a modified thermo-gravimetric analyzer.The specimens were oxidized for 3600 s at each temperature and then quenched in a furnace.The oxidation rate constants were measured from the weight gains to evaluate the oxidation behavior in Zircaloy-4 and Zirlo.The weight gain rates of Zirlo were lower than those of Zircaloy-4,leading to the low rate constants.The different oxidation behaviors between both cladding materials were considered to be due to the difference in their chemical compositions.展开更多
The mechanical properties and microstructural evolution of zircaloy-4 subjected to cumulative strains of 1.48,2.96,4.44 and 5.91 through multiaxial forging（MAF） at cryogenic temperature（77 K） were investigated.The...The mechanical properties and microstructural evolution of zircaloy-4 subjected to cumulative strains of 1.48,2.96,4.44 and 5.91 through multiaxial forging（MAF） at cryogenic temperature（77 K） were investigated.The mechanical properties of the MAF treated alloy were measured through universal tensile testing and Vickers hardness testing equipment.The zircaloy-4 deformed up to a cumulative strain of 5.91 showed improvement in both ultimate tensile strength and hardness from 474 MPa to 717 MPa and from HV 190 to HV 238,respectively,as compared with the as-received alloy.However,there was a noticeable decrement in ductility（from 18%to 3.5%） due to the low strain hardening ability of deformed zircaloy-4.The improvement in strength and hardness of the deformed alloy is attributed to the grain size effect and higher dislocation density generated during multiaxial forging.The microstructural evolutions of deformed samples were characterized by optical microscopy and transmission electron microscopy（TEM）.The evolved microstructure at a cumulative strain of 5.91 obtained after MAF up to 12 cycles depicted the formation of ultrafine grains with an average size of 150-250 nm.展开更多
To investigate the degradation of corrosion resistance of Zircaloy-4 in LiOHaqueous solution, SIMS (secondary ion mass spectrometry) analysis was performed to examine theprofiles of Li^+, K^+, and OH^- in oxide layers...To investigate the degradation of corrosion resistance of Zircaloy-4 in LiOHaqueous solution, SIMS (secondary ion mass spectrometry) analysis was performed to examine theprofiles of Li^+, K^+, and OH^- in oxide layers formed in the same concentration (0.1 mol/L) LiOHand KOH solutions. Even though the oxide layers have an equal thickness, the pene-tration depth ofK^+ is shallower than that of Li^+, and the penetration depth of OH^- corroded in KOH solution isalso shal-ower than that corroded in LiOH solution. It shows that the diffusion of OH^- into oxidelayer is accompanied by the corresponding cation. The difference of degradation effect of LiOH andKOH solutions on the corrosion resistance of Zircaloy-4 was discussed.展开更多
The effect of surface state on the nodular corrosion resistance of Zircaloy-4 alloy was investigated in super- heated steam at 500 ℃/10.3 MPa by autoclave tests. The microstructures of oxide films on the corroded spe...The effect of surface state on the nodular corrosion resistance of Zircaloy-4 alloy was investigated in super- heated steam at 500 ℃/10.3 MPa by autoclave tests. The microstructures of oxide films on the corroded specimens were observed by TEM and SEM. The results indicate that surface strained layer delays the appearance of nodular spots on the specimen surfaces and improves the nodular corrosion resistance. The columnar grains orientation of the oxide films formed on the specimens with surface strained layer was more consistent than that on the specimens without surface strained layer when a comparison was made on the same orientation of the grain surfaces. Such a kind of oxide micro- structure formed on the specimens with surface strained layer can hinder the diffusion of oxygen ions along the grain boundaries and delay the growth of oxide films, therefore retard the formation process of nodular spots. This indicates that the microstructure of the initial oxide films has an important influence on the subsequent growth of the oxide films.展开更多
Corrosion re sistance of Zircaloy-4 alloy tube in superheated steam at 673 K/10.3 MPa is anisotropic.A part of the surface undergoes uniform corrosion while the other suffers nodular corrosion.Narrow and wide nodules ...Corrosion re sistance of Zircaloy-4 alloy tube in superheated steam at 673 K/10.3 MPa is anisotropic.A part of the surface undergoes uniform corrosion while the other suffers nodular corrosion.Narrow and wide nodules are observed after an exposure period of 3 and 30 days,respectively.A new matrix transformation method is established in order to study the formation mechanism of nodules in the cross-section(CS) of Zircaloy-4 alloy tube using the EBSD technique,while the CS perpendicular to axial direction(AD).The results reveal that the microtexture is a key factor behind the two types of corrosion.Furthermore,the oxide layers grow anisotropically over the corroded surface.A thick oxide layer forms over the nodular corrosion region on the grains with c-axis oriented in the range of 40° around tangential direction(TD),whereas a thin oxide layer over the uniform corrosion region is detected on the grains with c-axis oriented in the range of 68° around TD.In short,the anisotropic growth of oxide layer was caused by the change of microtexture of the Zr-4 alloy tube,and this anisotropic growth of oxide layer contributed to the nodules formation.展开更多
The microstructures of the oxide layers formed on near （0001） plane of Zircaloy-4 were investigated by autoclave tests at 360 ℃ in lithiated aqueous solution. Oxygen-rich regions with hcp structure were observed at...The microstructures of the oxide layers formed on near （0001） plane of Zircaloy-4 were investigated by autoclave tests at 360 ℃ in lithiated aqueous solution. Oxygen-rich regions with hcp structure were observed at the undulating O/M interface, and the inner surface morphology of the oxide layers formed on （0001） was only concave- convex. Monoclinic, tetragonal and cubic phases and a kind of zirconium sub-oxide with bcc structure were detected in the oxide layer near the metal matrix. This zirconium sub-oxide layer had a coherent relationship with a-Zr matrix, and the growth direction of the zirconium sub-oxide layer was nearly parallel to the [0001] direction of a-Zr regardless of the orientation of metal matrix. The orientations scattering of columnar grains formed on near （0001） plane differ from that formed on near （1010） plane.展开更多
The microstructural evolution of zircaloy-4 was studied, including the amorphization and recrystallization of Zr（Fe, Cr）2 precipitates, and the density of dislocations under in situ Ne ion irradiation and post annea...The microstructural evolution of zircaloy-4 was studied, including the amorphization and recrystallization of Zr（Fe, Cr）2 precipitates, and the density of dislocations under in situ Ne ion irradiation and post annealing. The results show that irradiation at a relatively high temperature and dose induces the formation of nanocrystals in pre-amorphized Zr（Fe, Cr）2 precipitates. The recrystallized nanocrystals also have the structure of hcp-Zr（Fe, Cr）2. The formation of the nanocrystals is thought to be the consequence of competition between atomistic disordering and the recrystallization of precipitates under ion irradiation. The free energy of the nanocrystal is lower than that of the amorphous state, which is another reason for the recrystallization of the precipitates. With increased annealing temperature, the density of the nanocrystals is increased. The dislocation density sharply decreases with the increase in the annealing temperature, and its size increases.展开更多
Zircaloy 4 was implanted with nitrogen at 120 keV with various ion doses between 1×10 13 and 1×10 14 ions/m 2. Fretting wear tests were performed at various cycles and loads under water immersion condition b...Zircaloy 4 was implanted with nitrogen at 120 keV with various ion doses between 1×10 13 and 1×10 14 ions/m 2. Fretting wear tests were performed at various cycles and loads under water immersion condition by the fretting simulator, The implanted surfaces were analyzed by Auger electron spectroscopy (AES) and transmission electron microscope (TEM). Micro hardness tester measured surface hardness. It is shown that nitrogen implantation produced Zirconium nitride oxide and high density dislocations in implanted layer, surface hardness was enhanced from HK280 for unimplanted specimen to HK1 800 for a total ion dose of 1×10 14 ions/m 2. The nitrogen ion implantation treatment provided significant improvements in the resistance of fretting damage.展开更多
Fatigue lifetime curves of Zircaloy-4 at different temperatures were measured, and the fatigued dislocation configurations were investigated using transmission electron microscopy. Ii was found that prismatic slip is ...Fatigue lifetime curves of Zircaloy-4 at different temperatures were measured, and the fatigued dislocation configurations were investigated using transmission electron microscopy. Ii was found that prismatic slip is the primary deformation mode. for Zircaloy-4fatigued at RT prismatic plus Pyramidal slip at 400℃,and prismatic plus (0001) basic slip at 600℃. The corresponding dislocation configurations are parallel dislocation lines al RT, elongated cells at 400℃ and two sets of mutually Perpendicular dislocation bands at 600℃.respectively. The relationship among. fatigue deformation mode, dislocation configuration and lifetime is discussed.展开更多
To simulate irradiation damage, argon ion was implanted in the Zircaloy-4 with the fluence ranging from 1 × 10^16 to 1 × 10^17 cm^-2, using accelerating implanter at an extraction voltage of 190 kV and liqui...To simulate irradiation damage, argon ion was implanted in the Zircaloy-4 with the fluence ranging from 1 × 10^16 to 1 × 10^17 cm^-2, using accelerating implanter at an extraction voltage of 190 kV and liquid nitrogen temperature. Then the influence of argon ion implantation on the aqueous corrosion behavior of Zircaloy-4 was studied. The valence states of elements in the surface layer of the samples were analyzed using X-ray photoelectron spectroscopy （XPS）. Transmission electron microscopy （TEM） was used to examine the microstructure of the argon-implanted samples. The potentiodynamic polarization technique was employed to evaluate the aqueous corrosion resistance of implanted Zircaloy-4 in 1 mol/L HzSO4 solution. It is found that there appear bubbles on the surface of the samples when the argon fluence is 1 × 10^16 cm^-2. The microstructure of argon-implanted samples changes from amorphous to partial amorphous, then to polycrystalline, and again to amorphous. The corrosion resistance of implanted samples linearly declines with the increase of fluence approximately, which is attributed to the linear increase of the irradiation damage.展开更多
In order to investigate the ion irradiation effect on the corrosion behavior and microstructure of Zircaloy-4, the Zircaloy-4 film were prepared by electron beam deposition on the Zircaloy-4 specimen surface and irra...In order to investigate the ion irradiation effect on the corrosion behavior and microstructure of Zircaloy-4, the Zircaloy-4 film were prepared by electron beam deposition on the Zircaloy-4 specimen surface and irradiated by Kr ions using an accelerator at an energy of 300 keV with the dose from 1×1015 to 3×1016ions/cm2. The post-irradiation corrosion tests were conducted to rank the corrosion resistance of the resulting specimens by potentiodynamic polarization curve measurements in a 0.5 mol/L H2SO4 water so- lution at room temperature. Transmission electron microscopy (TEM) was employed to examine the microstructural change in the surface. The potentiodynamic tests show that with the irradiation dose increasing, the passive current density, closely related to the surface corrosion resistance, decreases firstly and increases subsequently. The mechanism of the corrosion behavior transformation is due to the amorphous phase formation firstly and the amorphous phase destruction and the polycrystalline structure formation in the irradiated surface subsequently.展开更多
The zircaloy-4 is an alloy of zirconium, which has a very weak thermal neutron absorption, satisfactory mechanical properties and good corrosion resistance at high temperature. For these reasons, zircaloy-4 is used as...The zircaloy-4 is an alloy of zirconium, which has a very weak thermal neutron absorption, satisfactory mechanical properties and good corrosion resistance at high temperature. For these reasons, zircaloy-4 is used as a material of cladding fuel rod of nuclear reactors. In this environment, it is submitted to different severe conditions of temperature and pressure. The objective of this work is to study the oxidation kinetics of zircaloy-4 in air by the X-ray diffraction technique. The experiments were realized in a “HTK1200” furnace installed as a sample holder in the diffractometer at different temperatures;25°C, 350°C, 500°C, 830°C and 1000°C. The results show that the monoclinic and the tetragonal phases are formed at 350°C temperature. The volume fraction of these phases increased with the temperature until 1000°C where the α phase disappears completely. For simulating the case of loss-of-coolant-accident (LOCA), we have done x-ray diffraction of Zry-4 samples water quenched at 1050°C with different ageing times at this temperature. At 10 seconds and more, there is an important evolution of monoclinic and tetragonal zirconias, which leads to the degradation of zircaloy-4 properties.展开更多
In the present work, the expansion coefficient due to hydrogen incorporation was measured for the axial direction of a Zircaloy-4 cooling channel, similar to that installed in the Atucha I PHWR, Argentina, trying to s...In the present work, the expansion coefficient due to hydrogen incorporation was measured for the axial direction of a Zircaloy-4 cooling channel, similar to that installed in the Atucha I PHWR, Argentina, trying to simulate the nuclear power reactor operating conditions. As a first step, the solubility curve of hydrogen in Zircloy-4 was determined by two techniques: differential scanning calorimetry and differential dilatometry. The comparison with classical literature curves showed a good agreement with them, although the calorimetric technique proved to be more accurate for these determinations. Dilatometry was able to detect the end of hydride dissolution from concentrations around 60 wppm-H up to 650 wppm-H, where the eutectoid reaction: α + δ→α + β takes place (at 550oC). We assume that this ability is a good indicator of the aptitude of the technique to measure dimensional changes in the given hydrogen concentration range. Then, the expansion of Zircaloy-4 homogeneously hydrided samples was measured at 300oC, the typical operating temperature of a nuclear power reactor, obtaining a relative expansion of 2.21 * 10-4% per wppm-H. Considering the relative expansion observed for Zircaloy-4 at room temperature due to hydriding, starting from a hydrogen free sample, the total relative expansion rate is calculated to be 5.21 * 10-4% per wppm-H.展开更多
The welding joints of Zircaloy 4 plates obtained by diffusion welding at 800°C under pressure in vacuum were cracked during autoclave tests at 400°C superheated steam after exposure longer than 150 days. T...The welding joints of Zircaloy 4 plates obtained by diffusion welding at 800°C under pressure in vacuum were cracked during autoclave tests at 400°C superheated steam after exposure longer than 150 days. The section of specimens was examined by optical microscopy and the composition at the tips of cracking was analyzed by electron microprobe. The result shows that the combination of oxidation and hydriding induced cracking is responsible for this failure of the welding joints.展开更多
基金supported by the Korea Science & Engineering Foundation through the BAERI Program(GrantNo.M20508110003)
文摘The oxidation characteristics for Zircaloy-4 and Zirlo in the temperature range of 700-1200°C under steam supply condition were investigated by using a modified thermo-gravimetric analyzer.The specimens were oxidized for 3600 s at each temperature and then quenched in a furnace.The oxidation rate constants were measured from the weight gains to evaluate the oxidation behavior in Zircaloy-4 and Zirlo.The weight gain rates of Zirlo were lower than those of Zircaloy-4,leading to the low rate constants.The different oxidation behaviors between both cladding materials were considered to be due to the difference in their chemical compositions.
基金BRNS,Bombay for their financial grant to this work through grant No.BRN-577-MMD
文摘The mechanical properties and microstructural evolution of zircaloy-4 subjected to cumulative strains of 1.48,2.96,4.44 and 5.91 through multiaxial forging（MAF） at cryogenic temperature（77 K） were investigated.The mechanical properties of the MAF treated alloy were measured through universal tensile testing and Vickers hardness testing equipment.The zircaloy-4 deformed up to a cumulative strain of 5.91 showed improvement in both ultimate tensile strength and hardness from 474 MPa to 717 MPa and from HV 190 to HV 238,respectively,as compared with the as-received alloy.However,there was a noticeable decrement in ductility（from 18%to 3.5%） due to the low strain hardening ability of deformed zircaloy-4.The improvement in strength and hardness of the deformed alloy is attributed to the grain size effect and higher dislocation density generated during multiaxial forging.The microstructural evolutions of deformed samples were characterized by optical microscopy and transmission electron microscopy（TEM）.The evolved microstructure at a cumulative strain of 5.91 obtained after MAF up to 12 cycles depicted the formation of ultrafine grains with an average size of 150-250 nm.
基金This work was financially supported by the National Natural Science Foundation of China (Nos. 50301009 and 50171039)the Education Development Foundation of Shanghai (No. 03AK24)
文摘To investigate the degradation of corrosion resistance of Zircaloy-4 in LiOHaqueous solution, SIMS (secondary ion mass spectrometry) analysis was performed to examine theprofiles of Li^+, K^+, and OH^- in oxide layers formed in the same concentration (0.1 mol/L) LiOHand KOH solutions. Even though the oxide layers have an equal thickness, the pene-tration depth ofK^+ is shallower than that of Li^+, and the penetration depth of OH^- corroded in KOH solution isalso shal-ower than that corroded in LiOH solution. It shows that the diffusion of OH^- into oxidelayer is accompanied by the corresponding cation. The difference of degradation effect of LiOH andKOH solutions on the corrosion resistance of Zircaloy-4 was discussed.
基金financially supported by the National Natural Science Foundation of China (No. 51171102)
文摘The effect of surface state on the nodular corrosion resistance of Zircaloy-4 alloy was investigated in super- heated steam at 500 ℃/10.3 MPa by autoclave tests. The microstructures of oxide films on the corroded specimens were observed by TEM and SEM. The results indicate that surface strained layer delays the appearance of nodular spots on the specimen surfaces and improves the nodular corrosion resistance. The columnar grains orientation of the oxide films formed on the specimens with surface strained layer was more consistent than that on the specimens without surface strained layer when a comparison was made on the same orientation of the grain surfaces. Such a kind of oxide micro- structure formed on the specimens with surface strained layer can hinder the diffusion of oxygen ions along the grain boundaries and delay the growth of oxide films, therefore retard the formation process of nodular spots. This indicates that the microstructure of the initial oxide films has an important influence on the subsequent growth of the oxide films.
文摘Corrosion re sistance of Zircaloy-4 alloy tube in superheated steam at 673 K/10.3 MPa is anisotropic.A part of the surface undergoes uniform corrosion while the other suffers nodular corrosion.Narrow and wide nodules are observed after an exposure period of 3 and 30 days,respectively.A new matrix transformation method is established in order to study the formation mechanism of nodules in the cross-section(CS) of Zircaloy-4 alloy tube using the EBSD technique,while the CS perpendicular to axial direction(AD).The results reveal that the microtexture is a key factor behind the two types of corrosion.Furthermore,the oxide layers grow anisotropically over the corroded surface.A thick oxide layer forms over the nodular corrosion region on the grains with c-axis oriented in the range of 40° around tangential direction(TD),whereas a thin oxide layer over the uniform corrosion region is detected on the grains with c-axis oriented in the range of 68° around TD.In short,the anisotropic growth of oxide layer was caused by the change of microtexture of the Zr-4 alloy tube,and this anisotropic growth of oxide layer contributed to the nodules formation.
基金financially supported by the National Natural Science Foundation of China (Nos. 51171102 and 51271104)
文摘The microstructures of the oxide layers formed on near （0001） plane of Zircaloy-4 were investigated by autoclave tests at 360 ℃ in lithiated aqueous solution. Oxygen-rich regions with hcp structure were observed at the undulating O/M interface, and the inner surface morphology of the oxide layers formed on （0001） was only concave- convex. Monoclinic, tetragonal and cubic phases and a kind of zirconium sub-oxide with bcc structure were detected in the oxide layer near the metal matrix. This zirconium sub-oxide layer had a coherent relationship with a-Zr matrix, and the growth direction of the zirconium sub-oxide layer was nearly parallel to the [0001] direction of a-Zr regardless of the orientation of metal matrix. The orientations scattering of columnar grains formed on near （0001） plane differ from that formed on near （1010） plane.
基金Project supported by the Key Laboratory of Neutron Physics of China Academy of Engineering Physics(Grant No.2012AB02)the Fundamental Research Funds for the Central Universities of China(Grant No.ZYGX2012YB017)the Major Program of the National Natural Science Foundation of China(Grant No.91126001)
文摘The microstructural evolution of zircaloy-4 was studied, including the amorphization and recrystallization of Zr（Fe, Cr）2 precipitates, and the density of dislocations under in situ Ne ion irradiation and post annealing. The results show that irradiation at a relatively high temperature and dose induces the formation of nanocrystals in pre-amorphized Zr（Fe, Cr）2 precipitates. The recrystallized nanocrystals also have the structure of hcp-Zr（Fe, Cr）2. The formation of the nanocrystals is thought to be the consequence of competition between atomistic disordering and the recrystallization of precipitates under ion irradiation. The free energy of the nanocrystal is lower than that of the amorphous state, which is another reason for the recrystallization of the precipitates. With increased annealing temperature, the density of the nanocrystals is increased. The dislocation density sharply decreases with the increase in the annealing temperature, and its size increases.
文摘Zircaloy 4 was implanted with nitrogen at 120 keV with various ion doses between 1×10 13 and 1×10 14 ions/m 2. Fretting wear tests were performed at various cycles and loads under water immersion condition by the fretting simulator, The implanted surfaces were analyzed by Auger electron spectroscopy (AES) and transmission electron microscope (TEM). Micro hardness tester measured surface hardness. It is shown that nitrogen implantation produced Zirconium nitride oxide and high density dislocations in implanted layer, surface hardness was enhanced from HK280 for unimplanted specimen to HK1 800 for a total ion dose of 1×10 14 ions/m 2. The nitrogen ion implantation treatment provided significant improvements in the resistance of fretting damage.
文摘Fatigue lifetime curves of Zircaloy-4 at different temperatures were measured, and the fatigued dislocation configurations were investigated using transmission electron microscopy. Ii was found that prismatic slip is the primary deformation mode. for Zircaloy-4fatigued at RT prismatic plus Pyramidal slip at 400℃,and prismatic plus (0001) basic slip at 600℃. The corresponding dislocation configurations are parallel dislocation lines al RT, elongated cells at 400℃ and two sets of mutually Perpendicular dislocation bands at 600℃.respectively. The relationship among. fatigue deformation mode, dislocation configuration and lifetime is discussed.
基金the National Nature Science Foundation of China(No.50501011)the Postdoctoral Research Foundation of China(No.2005037079)
文摘To simulate irradiation damage, argon ion was implanted in the Zircaloy-4 with the fluence ranging from 1 × 10^16 to 1 × 10^17 cm^-2, using accelerating implanter at an extraction voltage of 190 kV and liquid nitrogen temperature. Then the influence of argon ion implantation on the aqueous corrosion behavior of Zircaloy-4 was studied. The valence states of elements in the surface layer of the samples were analyzed using X-ray photoelectron spectroscopy （XPS）. Transmission electron microscopy （TEM） was used to examine the microstructure of the argon-implanted samples. The potentiodynamic polarization technique was employed to evaluate the aqueous corrosion resistance of implanted Zircaloy-4 in 1 mol/L HzSO4 solution. It is found that there appear bubbles on the surface of the samples when the argon fluence is 1 × 10^16 cm^-2. The microstructure of argon-implanted samples changes from amorphous to partial amorphous, then to polycrystalline, and again to amorphous. The corrosion resistance of implanted samples linearly declines with the increase of fluence approximately, which is attributed to the linear increase of the irradiation damage.
文摘In order to investigate the ion irradiation effect on the corrosion behavior and microstructure of Zircaloy-4, the Zircaloy-4 film were prepared by electron beam deposition on the Zircaloy-4 specimen surface and irradiated by Kr ions using an accelerator at an energy of 300 keV with the dose from 1×1015 to 3×1016ions/cm2. The post-irradiation corrosion tests were conducted to rank the corrosion resistance of the resulting specimens by potentiodynamic polarization curve measurements in a 0.5 mol/L H2SO4 water so- lution at room temperature. Transmission electron microscopy (TEM) was employed to examine the microstructural change in the surface. The potentiodynamic tests show that with the irradiation dose increasing, the passive current density, closely related to the surface corrosion resistance, decreases firstly and increases subsequently. The mechanism of the corrosion behavior transformation is due to the amorphous phase formation firstly and the amorphous phase destruction and the polycrystalline structure formation in the irradiated surface subsequently.
文摘The zircaloy-4 is an alloy of zirconium, which has a very weak thermal neutron absorption, satisfactory mechanical properties and good corrosion resistance at high temperature. For these reasons, zircaloy-4 is used as a material of cladding fuel rod of nuclear reactors. In this environment, it is submitted to different severe conditions of temperature and pressure. The objective of this work is to study the oxidation kinetics of zircaloy-4 in air by the X-ray diffraction technique. The experiments were realized in a “HTK1200” furnace installed as a sample holder in the diffractometer at different temperatures;25°C, 350°C, 500°C, 830°C and 1000°C. The results show that the monoclinic and the tetragonal phases are formed at 350°C temperature. The volume fraction of these phases increased with the temperature until 1000°C where the α phase disappears completely. For simulating the case of loss-of-coolant-accident (LOCA), we have done x-ray diffraction of Zry-4 samples water quenched at 1050°C with different ageing times at this temperature. At 10 seconds and more, there is an important evolution of monoclinic and tetragonal zirconias, which leads to the degradation of zircaloy-4 properties.
文摘In the present work, the expansion coefficient due to hydrogen incorporation was measured for the axial direction of a Zircaloy-4 cooling channel, similar to that installed in the Atucha I PHWR, Argentina, trying to simulate the nuclear power reactor operating conditions. As a first step, the solubility curve of hydrogen in Zircloy-4 was determined by two techniques: differential scanning calorimetry and differential dilatometry. The comparison with classical literature curves showed a good agreement with them, although the calorimetric technique proved to be more accurate for these determinations. Dilatometry was able to detect the end of hydride dissolution from concentrations around 60 wppm-H up to 650 wppm-H, where the eutectoid reaction: α + δ→α + β takes place (at 550oC). We assume that this ability is a good indicator of the aptitude of the technique to measure dimensional changes in the given hydrogen concentration range. Then, the expansion of Zircaloy-4 homogeneously hydrided samples was measured at 300oC, the typical operating temperature of a nuclear power reactor, obtaining a relative expansion of 2.21 * 10-4% per wppm-H. Considering the relative expansion observed for Zircaloy-4 at room temperature due to hydriding, starting from a hydrogen free sample, the total relative expansion rate is calculated to be 5.21 * 10-4% per wppm-H.
文摘The welding joints of Zircaloy 4 plates obtained by diffusion welding at 800°C under pressure in vacuum were cracked during autoclave tests at 400°C superheated steam after exposure longer than 150 days. The section of specimens was examined by optical microscopy and the composition at the tips of cracking was analyzed by electron microprobe. The result shows that the combination of oxidation and hydriding induced cracking is responsible for this failure of the welding joints.
