In the present work the temperature of terminal solid solubility of hydrogen in the zirconium all... more In the present work the temperature of terminal solid solubility of hydrogen in the zirconium alloy Zr-2.5Nb was measured for material taken from a CANDU type pressure. The measurements were made in a wide concentration range (50-463 wppm) using two techniques, differential scanning calorimetry and differential dilatometry, with the additional purpose of checking the coincidence of the TSS points in both techniques. The work was complemented by microstuctural studies pursuing the (_-Zr) �(_-Zr + _-Zrenr + _-Nb) transformation. This transformation is accelerated if the material remains at temperatures higher than 400 o C, which corresponds to a hydrogen solubility of about 180 wppm. Thus, microstructural studies were made by transmission electron microscopy and energy dispersive
Zirconium-based components in nuclear power plants are embrittled by precipitates of zirconium ... more Zirconium-based components in nuclear power plants are embrittled by precipitates of zirconium hydride, which involves a martensitic-type transformation of the hexagonal -Zr lattice into the face-centered cubic Zr sublattice of the hydride. As a result, the hydride precipitates have a complex and heavily distorted internal structure that manifests as broad peaks in X-ray diffraction experiments. By a detailed analysis of the peak widths measured for different crystal planes we have found that most of this broadening is the result of dislocations. The analysis also showed that -hydride has very anisotropic mechanical elastic properties, in agreement with ab-initio simulations presented in the literature. Provided with this peak-broadening model, we have quantified dislocation densities within -hydrides precipitated in several Zr alloys, by analyzing previously published X-ray diffraction experiments performed at three synchrotron X-ray sources. The specimens investigated correspond to components affected by different hydride embrittling processes, namely: (i) samples from various components, charged in the laboratory with H contents in the 250 wt ppm range, (ii) laboratory-produced hydride blisters in Zr2.5%Nb pressure
RESUMEN En el presente trabajo se busca estimar el crecimiento que experimentan los canales de en... more RESUMEN En el presente trabajo se busca estimar el crecimiento que experimentan los canales de enfriamiento de la central Atucha I (CNA-1) por efecto del hidrógeno. Para ello se ha aplicado la técnica de dilatometría diferencial a muestras de Zircaloy-4 provenientes de un canal de enfriamiento sin irradiar con contenidos de hidrógeno entre 50-750 ppm 1. INTRODUCCION Las vainas de los elementos combustibles y muchos de los componentes estructurales que operan dentro de los reactores nucleares de potencia son fabricados con Zircaloy-4 (Zry-4), aleación de base circonio de referencia para la industria nuclear. Como la mayoría de los metales, las aleaciones de circonio al ser irradiadas con neutrones rápidos (> 0,8 MeV) experimentan crecimiento por irradiación, fenómeno que produce cambios dimensionales macroscópicos en el componente [1]. En términos generales, los procesos que producen cambios dimensionales en los componentes estructurales en operación son el creep, el crecimiento p...
RESUMEN En experiencias recientes, muestras de Zircaloy-4 irradiadas con neutrones provenientes d... more RESUMEN En experiencias recientes, muestras de Zircaloy-4 irradiadas con neutrones provenientes del reactor de la Central Nuclear Atucha I fueron caracterizadas con DRX de alta resolución en el Laboratorio Sincrotrón de Campinas 1 y Microscopia Electrónica Analítica. En los diagramas de DRX de las muestras no irradiadas se observaron 5 de los picos más intensos de la estructura C14 junto con algunos de menor intensidad, mientras que en muestras irradiadas a altos flujos neutrónicos (>10 21 neutrones/cm 2) estos picos no se observaron. Tratamientos térmicos a 400ºC no produjeron cambios significativos respecto de las muestras sin recocer, mientras que tratamientos de 24hs o 72hs a 600ºC mostraron recuperación de la estructura, en otras palabras, la re-precipitación de la fase. Estos resultados indican que la re-precipitación se produce entre los 400 y 600ºC. Las observaciones realizadas utilizando técnicas de Microscopia Electrónica Analítica, a muestras no irradiadas y a muestras...
1) Centro Atómico Ezeiza (CNEA), Buenos Aires, Argentina. (2) Centro Atómico Constituyentes (CNEA... more 1) Centro Atómico Ezeiza (CNEA), Buenos Aires, Argentina. (2) Centro Atómico Constituyentes (CNEA), Buenos Aires, Argentina. The microstructure of Zr alloys has been a subject of study during the last decades due to its influence on the manufacturing of fuel elements sheaths for power reactors. In particular, Zircaloy-4 (%wt Sn 1.45 -1.5, Fe 0.18 -0.24, Cr 0.07 -0.13, O 1400ppm, Zr to balance) is widely used as fuel cladding material, due to its low neutron -capture cross -section, high mechanical strength, high thermal conductivity and good corrosion resistance in water and steam. Of all the alloying elements only tin is in solid solution, and hence relatively uniformly distributed. Iron and chromium are essentially insoluble in Zr at low temperatures (<600º C) and they are, therefore, present almost entirely in the form of second phase particles (SPPs) [1]. There is only one intermetallic compound, Zr (Cr, Fe)2 , which occurs in two structural forms, hexagonal (C14) and cubic (...
The terminal solid solubility of hydrogen in titanium was measured by differential scanning calor... more The terminal solid solubility of hydrogen in titanium was measured by differential scanning calorimetry in the concentration range of 0.3e4.1 at.% which practically corresponds to the whole solubility range of hydrogen in a-Ti. The solvus enthalpy obtained in this range from the overall data set was 22.8 ± 0.5 kJ/molH. However, a more careful analysis of the experimental results shows that the solubility curve has two different behaviors as a function of concentration. In the high concentration range 1.4e4.1 at.% a solvus enthalpy of 29.0 ± 1.5 kJ/molH was obtained representing the a/a þ d equilibrium boundary. In the low concentration range, 0.3 at.% to 1.4 at.%, the slope was noticeably lower with 24.2 ± 1.5 kJ/molH for the solvus enthalpy. This last value should correspond to the [a]/ [a þ g] equilibrium curve. Although it is possible this value might be influenced by the presence of tiny amounts of the now metastable d phaseeas its presence is revealed by Xray diffraction analysis e anyway it is consistent with a a þ d 4 g peritectoid reaction temperature of 168 C obtained from the literature. The eutectoid a þ d 4 b decomposition temperature was determined using samples of high hydrogen contents, ranging from 9 to 11.0 at.%. This temperature was determined to be 319.9 ± 1 C from the analysis of the DSC diagrams. The solubility limit [a]/[a þ d] at this eutectoid reaction was estimated to be 5.44 ± 0.27 at.%. The present results are believe to provide a closer approximation to the solubility values of H in a-Ti as presently reported in the literature.
Acta Crystallographica Section A Foundations of Crystallography, 2011
Pressure tubes are the most important Zr-base components in the core of CANDU nuclear power react... more Pressure tubes are the most important Zr-base components in the core of CANDU nuclear power reactors. The most important mechanisms defining the service life of pressure tubes are: irradiationenhanced coming with deformation, and the delayed hydride cracking. Both processes are determined by a few metallurgical parameters which must be exhaustively controlled: microstructure, dislocation density and texture [1], [2]. Argentina has one CANDU power plant in operation since 1982 (CNE), which is now close to ending its service life. A refurbishment project is underway which will include the replacement of existing fuel channels, composed by Zr-2.5%Nb pressure tubes and Zircaloy2/4 calandria tubes. CNEA is developing a new manufacturing route for Zr-2.5%Nb pressure tubes, using a cold rolling pilger type machine instead of the cold drawing process currently performed in Canada. The new process will be performed at the Planta Piloto de fabricación de aleaciones especiales (PPFAE,CNEA). The extrusion stage produces a strong texture (crystalline preferential orientation) in the material. In this framework, in our laboratory (LMFAE), we calculate the texture factors [3], [4] from x-ray diffraction diagrams obtained from a Bruker D8 FOCUS diffractometer. A qualitative study of the texture was performed using the rocking curve method [5] (figure 1). The collected data was used to build a qualitative direct pole figure. The quantitative study was made through the calculation of Kearns factors (table 1), measuring in the θ/2θ standard way (Bragg-Brentano geometry). The results obtained from the rocking curves were quite satisfactory and they are compatible with the expected texture for the (0002) pole. This pole is essentially oriented in the transverse direction (90%), with small contributions in the radial (8%) and axial directions (2%). The Kearns factors are also in agreement with the these fractions, fulfilling the specified values (0.03≤f axial ≤0.09, 0.27≤f radial ≤0.39, 0.55≤f transversal ≤0.67, and 0.95≤∑f≤1.05 [6]) within a dispersion of ±0.02. Table 1. Average Kearns factors of the Zr-2.5%Nb pressure tube.
Resumen La temperatura de solubilidad terminal del hidrógeno en el circonio y sus aleaciones es u... more Resumen La temperatura de solubilidad terminal del hidrógeno en el circonio y sus aleaciones es un parámetro de interés tecnológico, dado que la precipitación del hidrógeno como hidruro de circonio tiende a fragilizar estos materiales. Dentro de un programa tendiente a determinar el límite de solubilidad del hidrógeno en componentes de aleaciones de circonio de reactores de potencia refrigerados por agua, este trabajo completa las mediciones realizadas hasta el presente en material no irradiado[1] extendiendo estas a todo el rango de solubilidad del hidrógeno en fase α -Zr. Mediante la técnica de calorimetría diferencial de barrido, se construyeron las curvas de solubilidad para Zircaloy-4 en un rango de concentraciones de 40 a 640 ppm en peso de hidrógeno y los resultados se comparan con trabajos previos de otros autores. Palabras clave: Zircaloy, hidrógeno, solubilidad terminal. Abstract The hydrogen terminal solubility temperature in zirconium and its alloys is a parameter of tec...
The axial/tangential expansion coefficient of the Atucha 1 (CNA-1) Zircaloy-4 cooling channels du... more The axial/tangential expansion coefficient of the Atucha 1 (CNA-1) Zircaloy-4 cooling channels due to hydrogen incorporation is determined by differential dilatometry. The evaluation is made in a concentration range from 25 to 720 wppmH. The hydrogen is incorporated as a hydride surface layer through the cathodic charge technique. Using dilatometry, these coefficients are determined by measuring the change in the length due to the hydride precipitation in the bulk after dissolving part of the hydride layer during the heating cycle. The measured expansion coefficient per wppmH at room temperature is 3.00 x10-4 %/wppmH for both, axial and tangential directions. The study was completed with the determination of the temperature of terminal solid solubility in dissolution, TSSd, and in precipitation, TSSp, of the hydrogen in Zircaloy-4 by differential dilatometry and differential scanning calorimetry in order to check the accuracy of the dilatometric technique.
Under reactor operating conditions zirconium components go through transformations which affect t... more Under reactor operating conditions zirconium components go through transformations which affect their original properties. Two phenomena of significant consequencesfor the integrity of the components are hydrogen uptake and radiation damage, since both contribute to the material fragilization. In the case of the Atucha I nuclear power reactor, the cooling channels, Zircaloy-4 tubular structural components about 6 meters long, were designed to withstand the entire lifetime of the reactor. Inside them, fuel elements 5.3 meters long are located. The fuel elements are cooled by a heavy water flow which circulates from the bottom (250 o C) to the top of the reactor (305 o C). The channels are affected by a fast neutron flux (E n >1 Mev), increasing from a nominal value of 1.35 x 10 13 neutrons/cm 2 sec at the bottom to 1.69 x 10 13 neutrons/cm 2 sec at the top, reaching a maximum value of 3.76 x 10 13 neutrons/cm 2 sec at the center of the channels. However, due to the reactor operati...
The different microstructures typically found in nuclear components made of zirconium alloys are ... more The different microstructures typically found in nuclear components made of zirconium alloys are discussed in this paper. These include material in a variety of thermo-mechanical conditions, e. g., cold rolled, stress relieved, recrystallized, welded, biphasic, together with minority second phases belonging to the original material or incorporated due to in-service conditions. The anisotropic crystalline structure of zirconium is exploited in microscopical observations by means of polarizer filters that enhance the contrast between different grains, and greatly aid the identification in most microstructures. Most microstructural variations across a wide range of length-scales, such as those produced by welding processes, can be effectively resolved by traditional optical microscopy (OM). However, some finer microstructures like those found in CANDU1 (CANada Deuterium Uranium) reactor pressure tube material, or some minority second phase particles like the Zr(Fe, Cr)2 precipitates in...
In this work, the dissolution enthalpy, ΔHδ→α, of the δ hydride phase in the αZr matrix in Zircal... more In this work, the dissolution enthalpy, ΔHδ→α, of the δ hydride phase in the αZr matrix in Zircaloy-4 has been determined with a differential scanning calorimeter (DSC) in two different ways: by means of a vant Hoff equation, measuring the terminal solubility temperature in dissolution, TSSd, and by direct measurement of the dissolution heat, Qδ→α, obtaining values of 37 and 39 kJ/mol H. These values are self- consistent and in good agreement with the literature values from the recent revisions made by Zuzek and Dantzer et. al, but reduces considerably the scatter of the literature data, (1,2).
In the present work a method to measure hydrogen concentrations in zirconium-based alloys was dev... more In the present work a method to measure hydrogen concentrations in zirconium-based alloys was developed measuring simultaneously both, the temperature of terminal solid solubility, T TSSd , and the hydride dissolution heat, Q ␦→␣ , using a differential scanning calorimeter (DSC). The hydrogen concentration measured with that technique, [H] Q , and the values obtained with a standard hydrogen gas meter, [H] HGM, shows a linear relation: [H] Q = (1.00 ± 0.03)[H] HGM| + (9.2 ± 8.0) with a correlation factor of 0.99 in the entire solubility interval in the ␣Zr phase, from 15 to 650 wt. ppm-H. The mean enthalpy value determined with two different criteria for T TSSd and Q ␦→␣ measurements is H (Q) ␦→␣ = 39.3 ± 1.5 kJ/mol H. The present method is specially appropriate for alloys where a partition of the overall hydrogen concentration in two phases exists. It is applicable to all hydride forming metals which ideally follows the van't Hoff law.
In this work, the dissolution enthalpy, Delta H delta-->alpha, of the delta hydride phase in t... more In this work, the dissolution enthalpy, Delta H delta-->alpha, of the delta hydride phase in the alphaZr matrix in ZIRCALOY-4 has been determined with a differential scanning calorimeter (DSC) in two different ways: by means of a van't Hoff equation, measuring the terminal solubility temperature in dissolution, TSSd, and by direct measurement of the dissolution heat, Q delta-->alpha, as the area between the base line and the calorimetric curve. The application of the DSC technique to the hydride dissolution heat measurements, a transformation which covers an extended temperature range, is completely original and requires a special treatment of the calorimetric curve. These measurements were done on samples that practically cover the entire solubility range of hydrogen in alphaZr phase (80 to 640 ppm). The values obtained, 36.9 and 39.3 kJ/mol H, respectively, are self-consistent and in good agreement with the values of the more recent revisions, but reduces considerably the scatter of the literature data.
X-ray diffraction diagrams of neutron irradiated Zircaloy-4 were obtained at the Brazilian Synchr... more X-ray diffraction diagrams of neutron irradiated Zircaloy-4 were obtained at the Brazilian Synchrotron Laboratory (LNLS) with the aim to obtain bulk information about the amorphization process in which the Zircaloy-4 second phase particles (SPPs) undergoes due to neutron irradiation. Owing to the low concentration of the SPPs in the alloy (∼ 0.4 V%), no data regarding to the bulk were obtained until now. The synchrotron experiences allowed to detect five of the more intense lines of the phase C14 (SPPs structure) in unirradited Zircaloy-4: b110N θ , b103N θ , b112N θ , b201N θ and b004N θ in the 34°b 2θ b 45°Bragg angle range and others of minor intensity. The diagrams of the samples irradiated at moderate doses (10 20 n/cm 2) show these lines even in the as received samples. In contrast, none of these lines are observed for high fluency samples (∼10 22 neutrons/cm 2), confirming in the bulk what is known by TEM in thin films. In addition, in similar high fluency samples annealed 24 h or 72 h at 600°C the intensity rises just at the 2θ range where the C14 lines were observed, showing a wide peak. That peak is interpreted as a result of the superposition of unresolved diffraction lines corresponding to the Zircaloy SPPs which are in a reconstitution process of crystallization.
In the present work the temperature of terminal solid solubility of hydrogen in the zirconium all... more In the present work the temperature of terminal solid solubility of hydrogen in the zirconium alloy Zr-2.5Nb was measured for material taken from a CANDU type pressure. The measurements were made in a wide concentration range (50-463 wppm) using two techniques, differential scanning calorimetry and differential dilatometry, with the additional purpose of checking the coincidence of the TSS points in both techniques. The work was complemented by microstuctural studies pursuing the (_-Zr) �(_-Zr + _-Zrenr + _-Nb) transformation. This transformation is accelerated if the material remains at temperatures higher than 400 o C, which corresponds to a hydrogen solubility of about 180 wppm. Thus, microstructural studies were made by transmission electron microscopy and energy dispersive
Zirconium-based components in nuclear power plants are embrittled by precipitates of zirconium ... more Zirconium-based components in nuclear power plants are embrittled by precipitates of zirconium hydride, which involves a martensitic-type transformation of the hexagonal -Zr lattice into the face-centered cubic Zr sublattice of the hydride. As a result, the hydride precipitates have a complex and heavily distorted internal structure that manifests as broad peaks in X-ray diffraction experiments. By a detailed analysis of the peak widths measured for different crystal planes we have found that most of this broadening is the result of dislocations. The analysis also showed that -hydride has very anisotropic mechanical elastic properties, in agreement with ab-initio simulations presented in the literature. Provided with this peak-broadening model, we have quantified dislocation densities within -hydrides precipitated in several Zr alloys, by analyzing previously published X-ray diffraction experiments performed at three synchrotron X-ray sources. The specimens investigated correspond to components affected by different hydride embrittling processes, namely: (i) samples from various components, charged in the laboratory with H contents in the 250 wt ppm range, (ii) laboratory-produced hydride blisters in Zr2.5%Nb pressure
RESUMEN En el presente trabajo se busca estimar el crecimiento que experimentan los canales de en... more RESUMEN En el presente trabajo se busca estimar el crecimiento que experimentan los canales de enfriamiento de la central Atucha I (CNA-1) por efecto del hidrógeno. Para ello se ha aplicado la técnica de dilatometría diferencial a muestras de Zircaloy-4 provenientes de un canal de enfriamiento sin irradiar con contenidos de hidrógeno entre 50-750 ppm 1. INTRODUCCION Las vainas de los elementos combustibles y muchos de los componentes estructurales que operan dentro de los reactores nucleares de potencia son fabricados con Zircaloy-4 (Zry-4), aleación de base circonio de referencia para la industria nuclear. Como la mayoría de los metales, las aleaciones de circonio al ser irradiadas con neutrones rápidos (> 0,8 MeV) experimentan crecimiento por irradiación, fenómeno que produce cambios dimensionales macroscópicos en el componente [1]. En términos generales, los procesos que producen cambios dimensionales en los componentes estructurales en operación son el creep, el crecimiento p...
RESUMEN En experiencias recientes, muestras de Zircaloy-4 irradiadas con neutrones provenientes d... more RESUMEN En experiencias recientes, muestras de Zircaloy-4 irradiadas con neutrones provenientes del reactor de la Central Nuclear Atucha I fueron caracterizadas con DRX de alta resolución en el Laboratorio Sincrotrón de Campinas 1 y Microscopia Electrónica Analítica. En los diagramas de DRX de las muestras no irradiadas se observaron 5 de los picos más intensos de la estructura C14 junto con algunos de menor intensidad, mientras que en muestras irradiadas a altos flujos neutrónicos (>10 21 neutrones/cm 2) estos picos no se observaron. Tratamientos térmicos a 400ºC no produjeron cambios significativos respecto de las muestras sin recocer, mientras que tratamientos de 24hs o 72hs a 600ºC mostraron recuperación de la estructura, en otras palabras, la re-precipitación de la fase. Estos resultados indican que la re-precipitación se produce entre los 400 y 600ºC. Las observaciones realizadas utilizando técnicas de Microscopia Electrónica Analítica, a muestras no irradiadas y a muestras...
1) Centro Atómico Ezeiza (CNEA), Buenos Aires, Argentina. (2) Centro Atómico Constituyentes (CNEA... more 1) Centro Atómico Ezeiza (CNEA), Buenos Aires, Argentina. (2) Centro Atómico Constituyentes (CNEA), Buenos Aires, Argentina. The microstructure of Zr alloys has been a subject of study during the last decades due to its influence on the manufacturing of fuel elements sheaths for power reactors. In particular, Zircaloy-4 (%wt Sn 1.45 -1.5, Fe 0.18 -0.24, Cr 0.07 -0.13, O 1400ppm, Zr to balance) is widely used as fuel cladding material, due to its low neutron -capture cross -section, high mechanical strength, high thermal conductivity and good corrosion resistance in water and steam. Of all the alloying elements only tin is in solid solution, and hence relatively uniformly distributed. Iron and chromium are essentially insoluble in Zr at low temperatures (<600º C) and they are, therefore, present almost entirely in the form of second phase particles (SPPs) [1]. There is only one intermetallic compound, Zr (Cr, Fe)2 , which occurs in two structural forms, hexagonal (C14) and cubic (...
The terminal solid solubility of hydrogen in titanium was measured by differential scanning calor... more The terminal solid solubility of hydrogen in titanium was measured by differential scanning calorimetry in the concentration range of 0.3e4.1 at.% which practically corresponds to the whole solubility range of hydrogen in a-Ti. The solvus enthalpy obtained in this range from the overall data set was 22.8 ± 0.5 kJ/molH. However, a more careful analysis of the experimental results shows that the solubility curve has two different behaviors as a function of concentration. In the high concentration range 1.4e4.1 at.% a solvus enthalpy of 29.0 ± 1.5 kJ/molH was obtained representing the a/a þ d equilibrium boundary. In the low concentration range, 0.3 at.% to 1.4 at.%, the slope was noticeably lower with 24.2 ± 1.5 kJ/molH for the solvus enthalpy. This last value should correspond to the [a]/ [a þ g] equilibrium curve. Although it is possible this value might be influenced by the presence of tiny amounts of the now metastable d phaseeas its presence is revealed by Xray diffraction analysis e anyway it is consistent with a a þ d 4 g peritectoid reaction temperature of 168 C obtained from the literature. The eutectoid a þ d 4 b decomposition temperature was determined using samples of high hydrogen contents, ranging from 9 to 11.0 at.%. This temperature was determined to be 319.9 ± 1 C from the analysis of the DSC diagrams. The solubility limit [a]/[a þ d] at this eutectoid reaction was estimated to be 5.44 ± 0.27 at.%. The present results are believe to provide a closer approximation to the solubility values of H in a-Ti as presently reported in the literature.
Acta Crystallographica Section A Foundations of Crystallography, 2011
Pressure tubes are the most important Zr-base components in the core of CANDU nuclear power react... more Pressure tubes are the most important Zr-base components in the core of CANDU nuclear power reactors. The most important mechanisms defining the service life of pressure tubes are: irradiationenhanced coming with deformation, and the delayed hydride cracking. Both processes are determined by a few metallurgical parameters which must be exhaustively controlled: microstructure, dislocation density and texture [1], [2]. Argentina has one CANDU power plant in operation since 1982 (CNE), which is now close to ending its service life. A refurbishment project is underway which will include the replacement of existing fuel channels, composed by Zr-2.5%Nb pressure tubes and Zircaloy2/4 calandria tubes. CNEA is developing a new manufacturing route for Zr-2.5%Nb pressure tubes, using a cold rolling pilger type machine instead of the cold drawing process currently performed in Canada. The new process will be performed at the Planta Piloto de fabricación de aleaciones especiales (PPFAE,CNEA). The extrusion stage produces a strong texture (crystalline preferential orientation) in the material. In this framework, in our laboratory (LMFAE), we calculate the texture factors [3], [4] from x-ray diffraction diagrams obtained from a Bruker D8 FOCUS diffractometer. A qualitative study of the texture was performed using the rocking curve method [5] (figure 1). The collected data was used to build a qualitative direct pole figure. The quantitative study was made through the calculation of Kearns factors (table 1), measuring in the θ/2θ standard way (Bragg-Brentano geometry). The results obtained from the rocking curves were quite satisfactory and they are compatible with the expected texture for the (0002) pole. This pole is essentially oriented in the transverse direction (90%), with small contributions in the radial (8%) and axial directions (2%). The Kearns factors are also in agreement with the these fractions, fulfilling the specified values (0.03≤f axial ≤0.09, 0.27≤f radial ≤0.39, 0.55≤f transversal ≤0.67, and 0.95≤∑f≤1.05 [6]) within a dispersion of ±0.02. Table 1. Average Kearns factors of the Zr-2.5%Nb pressure tube.
Resumen La temperatura de solubilidad terminal del hidrógeno en el circonio y sus aleaciones es u... more Resumen La temperatura de solubilidad terminal del hidrógeno en el circonio y sus aleaciones es un parámetro de interés tecnológico, dado que la precipitación del hidrógeno como hidruro de circonio tiende a fragilizar estos materiales. Dentro de un programa tendiente a determinar el límite de solubilidad del hidrógeno en componentes de aleaciones de circonio de reactores de potencia refrigerados por agua, este trabajo completa las mediciones realizadas hasta el presente en material no irradiado[1] extendiendo estas a todo el rango de solubilidad del hidrógeno en fase α -Zr. Mediante la técnica de calorimetría diferencial de barrido, se construyeron las curvas de solubilidad para Zircaloy-4 en un rango de concentraciones de 40 a 640 ppm en peso de hidrógeno y los resultados se comparan con trabajos previos de otros autores. Palabras clave: Zircaloy, hidrógeno, solubilidad terminal. Abstract The hydrogen terminal solubility temperature in zirconium and its alloys is a parameter of tec...
The axial/tangential expansion coefficient of the Atucha 1 (CNA-1) Zircaloy-4 cooling channels du... more The axial/tangential expansion coefficient of the Atucha 1 (CNA-1) Zircaloy-4 cooling channels due to hydrogen incorporation is determined by differential dilatometry. The evaluation is made in a concentration range from 25 to 720 wppmH. The hydrogen is incorporated as a hydride surface layer through the cathodic charge technique. Using dilatometry, these coefficients are determined by measuring the change in the length due to the hydride precipitation in the bulk after dissolving part of the hydride layer during the heating cycle. The measured expansion coefficient per wppmH at room temperature is 3.00 x10-4 %/wppmH for both, axial and tangential directions. The study was completed with the determination of the temperature of terminal solid solubility in dissolution, TSSd, and in precipitation, TSSp, of the hydrogen in Zircaloy-4 by differential dilatometry and differential scanning calorimetry in order to check the accuracy of the dilatometric technique.
Under reactor operating conditions zirconium components go through transformations which affect t... more Under reactor operating conditions zirconium components go through transformations which affect their original properties. Two phenomena of significant consequencesfor the integrity of the components are hydrogen uptake and radiation damage, since both contribute to the material fragilization. In the case of the Atucha I nuclear power reactor, the cooling channels, Zircaloy-4 tubular structural components about 6 meters long, were designed to withstand the entire lifetime of the reactor. Inside them, fuel elements 5.3 meters long are located. The fuel elements are cooled by a heavy water flow which circulates from the bottom (250 o C) to the top of the reactor (305 o C). The channels are affected by a fast neutron flux (E n >1 Mev), increasing from a nominal value of 1.35 x 10 13 neutrons/cm 2 sec at the bottom to 1.69 x 10 13 neutrons/cm 2 sec at the top, reaching a maximum value of 3.76 x 10 13 neutrons/cm 2 sec at the center of the channels. However, due to the reactor operati...
The different microstructures typically found in nuclear components made of zirconium alloys are ... more The different microstructures typically found in nuclear components made of zirconium alloys are discussed in this paper. These include material in a variety of thermo-mechanical conditions, e. g., cold rolled, stress relieved, recrystallized, welded, biphasic, together with minority second phases belonging to the original material or incorporated due to in-service conditions. The anisotropic crystalline structure of zirconium is exploited in microscopical observations by means of polarizer filters that enhance the contrast between different grains, and greatly aid the identification in most microstructures. Most microstructural variations across a wide range of length-scales, such as those produced by welding processes, can be effectively resolved by traditional optical microscopy (OM). However, some finer microstructures like those found in CANDU1 (CANada Deuterium Uranium) reactor pressure tube material, or some minority second phase particles like the Zr(Fe, Cr)2 precipitates in...
In this work, the dissolution enthalpy, ΔHδ→α, of the δ hydride phase in the αZr matrix in Zircal... more In this work, the dissolution enthalpy, ΔHδ→α, of the δ hydride phase in the αZr matrix in Zircaloy-4 has been determined with a differential scanning calorimeter (DSC) in two different ways: by means of a vant Hoff equation, measuring the terminal solubility temperature in dissolution, TSSd, and by direct measurement of the dissolution heat, Qδ→α, obtaining values of 37 and 39 kJ/mol H. These values are self- consistent and in good agreement with the literature values from the recent revisions made by Zuzek and Dantzer et. al, but reduces considerably the scatter of the literature data, (1,2).
In the present work a method to measure hydrogen concentrations in zirconium-based alloys was dev... more In the present work a method to measure hydrogen concentrations in zirconium-based alloys was developed measuring simultaneously both, the temperature of terminal solid solubility, T TSSd , and the hydride dissolution heat, Q ␦→␣ , using a differential scanning calorimeter (DSC). The hydrogen concentration measured with that technique, [H] Q , and the values obtained with a standard hydrogen gas meter, [H] HGM, shows a linear relation: [H] Q = (1.00 ± 0.03)[H] HGM| + (9.2 ± 8.0) with a correlation factor of 0.99 in the entire solubility interval in the ␣Zr phase, from 15 to 650 wt. ppm-H. The mean enthalpy value determined with two different criteria for T TSSd and Q ␦→␣ measurements is H (Q) ␦→␣ = 39.3 ± 1.5 kJ/mol H. The present method is specially appropriate for alloys where a partition of the overall hydrogen concentration in two phases exists. It is applicable to all hydride forming metals which ideally follows the van't Hoff law.
In this work, the dissolution enthalpy, Delta H delta-->alpha, of the delta hydride phase in t... more In this work, the dissolution enthalpy, Delta H delta-->alpha, of the delta hydride phase in the alphaZr matrix in ZIRCALOY-4 has been determined with a differential scanning calorimeter (DSC) in two different ways: by means of a van't Hoff equation, measuring the terminal solubility temperature in dissolution, TSSd, and by direct measurement of the dissolution heat, Q delta-->alpha, as the area between the base line and the calorimetric curve. The application of the DSC technique to the hydride dissolution heat measurements, a transformation which covers an extended temperature range, is completely original and requires a special treatment of the calorimetric curve. These measurements were done on samples that practically cover the entire solubility range of hydrogen in alphaZr phase (80 to 640 ppm). The values obtained, 36.9 and 39.3 kJ/mol H, respectively, are self-consistent and in good agreement with the values of the more recent revisions, but reduces considerably the scatter of the literature data.
X-ray diffraction diagrams of neutron irradiated Zircaloy-4 were obtained at the Brazilian Synchr... more X-ray diffraction diagrams of neutron irradiated Zircaloy-4 were obtained at the Brazilian Synchrotron Laboratory (LNLS) with the aim to obtain bulk information about the amorphization process in which the Zircaloy-4 second phase particles (SPPs) undergoes due to neutron irradiation. Owing to the low concentration of the SPPs in the alloy (∼ 0.4 V%), no data regarding to the bulk were obtained until now. The synchrotron experiences allowed to detect five of the more intense lines of the phase C14 (SPPs structure) in unirradited Zircaloy-4: b110N θ , b103N θ , b112N θ , b201N θ and b004N θ in the 34°b 2θ b 45°Bragg angle range and others of minor intensity. The diagrams of the samples irradiated at moderate doses (10 20 n/cm 2) show these lines even in the as received samples. In contrast, none of these lines are observed for high fluency samples (∼10 22 neutrons/cm 2), confirming in the bulk what is known by TEM in thin films. In addition, in similar high fluency samples annealed 24 h or 72 h at 600°C the intensity rises just at the 2θ range where the C14 lines were observed, showing a wide peak. That peak is interpreted as a result of the superposition of unresolved diffraction lines corresponding to the Zircaloy SPPs which are in a reconstitution process of crystallization.
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