Papers by Keyword: Zircaloy

Abstract: As for the fuel cladding in the light-water reactor, silicon carbide fiber reinforced silicon carbide matrix (SiC/SiC) composite is one of the promising candidates as a replacement of Zircaloy due to many superiorities, where it is necessary to develop the end-cap seal of SiC/SiC composite cladding. In this research, the caulking method was employed as the method for sealing the end cap of SiC/SiC composite tube by Zircaloy tube where the titanium micro-powder was inserted between two tubes. The fiber laser was circumferentially irradiated on the outer surface of zircaloy tube, and the insert method of titanium powder was varied by changing the cutting method of SiC/SiC composite tube. The examinations about the slit shape effect for the flat cutting suggested that the hook slit is considered to be the best cutting method for holding the titanium powder during the laser irradiation where the width of slit should be narrower than that of laser irradiation line.

Abstract: Turning chips of zirconium alloys are produced in large quantities during the machining of alloy rods for the fabrication of the end plugs for the Pressurized Water Reactor (PWR) fuel elements parts of Angra II nuclear reactor (Brazil – Rio de Janeiro). This paper presents a study on the search for an efficient way for the cleaning, quality control and Vacuum Arc Remelting (VAR) of pressed zirconium alloys chips to produce a material viable to be used in the production of the fuel rod end plugs. The process starts with cutting oil clean out. The first step in this process consists in soaking a bunch of chips in clean water, to remove soluble cutting oils, followed by an alkaline degreasing bath and a wash with a high-pressure flow of water. Drying is performed by a flux of warm air. The oil free chips are then subjected to a magnet in order to detect and collect any magnetic material, essentially ferrous, that may be present in the original chips. Samples of the material are collected and then melted in a small non consumable electrode vacuum arc furnace for evaluation by Energy Dispersive X-ray Fluorescence Spectrometry (EDXRFS) in order to define the quality of the chips. The next step consists in the 15 ton hydraulic pressing the chips in a die with 40 mm square section and 500 mm long, producing an electrode with 20% of the Zircaloy bulk density. The electrode was finally melted in a laboratory scale modified VAR furnace located at the CCTM–IPEN, producing 0.8 kg ingots. The authors conclude that the samples obtained from the fuel element industry can be melting in a VAR furnace, modified to accommodate low density electrodes, allowing a reduction up to 40 times the original storage volume, however, it is necessary to remelt the ingots to correct their composition in order to recycle the original zirconium alloys chips. in a process to reduce volume and allow the reutilization of valuable Zircaloy scraps.

Abstract: Silicon carbide fiber reinforced silicon carbide composite (SiC/SiC composite) is expected as a potential replacement of the current Zircaloy fuel cladding in the light-water reactor because of its many superiorities, where it is necessary to develop the end-cap seal of SiC/SiC composite cladding. In this research, the applicability of diode laser irradiation for joining between Zircaloy and SiC/SiC composite tubes was examined based on the caulking method. As the method for fitting two tubes, the screw cutting was conducted for the inner face of Zircaloy tube and the outer surface of SiC/SiC composite. In addition, as a method to improve the joinability of Zircaloy and SiC/SiC composite, titanium nanopowder was inserted into a gap between two tubes. The laser beam irradiation was circumferentially applied to the outer surface of Zircaloy tube. Although the mechanical caulking joint was successfully produced, the airtightness was insufficient for the end-caps of SiC/SiC composite cladding. However, the good adhesion between Zircaloy and SiC/SiC composite was partially produced as the result of the generation of all proportional solid solution between titanium and zirconium. Namely, it can be concluded that the circumferential diode laser irradiation with inserting titanium nanopowder between Zircaloy and SiC/SiC composite tubes would have a good potential for producing the caulking joint of two tubes.

Abstract: The texture and microstructure evolution during uniaxial compression of Zircaloy-4 at 500C has been studied. X-ray diffraction was used to measure the bulk texture compressive after strains of 20% and 50%. Early stages of texture evolution involve the strengthening of the fibre through the action of prismatic slip. With further deformation, the basal poles move toward the rolling direction from the normal direction as a result of a non-prismatic slip system. A detailed EBSD study in a small region showed that the grains of the fibre are more stable than those of the fibre. The latter rotates further during deformation and shows a greater spread of grain average misorientation (GAM). This could be due to a greater accommodation of plastic strain in these grains and/or a difference in recovery rates between the two fibres.

Abstract: In the fabrication of nuclear reactor core parts, machining chips of Zircaloy are generated. These alloys are strategic for nuclear technology and cannot be discarded. In the present work are presented two methods for recycling of Zircaloy chips. One of the methods is by melting in VAR furnace and the other by powder metallurgy method. By this method the Zircaloy was submitted to hydriding process and milled in a high-energy ball mill. The powder was cold isostatically pressed and vacuum sintered. The elemental composition of the samples obtained by both ways was determined by XRF and compared to the specifications. The phase composition was determined by XRD. The microstructures resulting of both processing methods, before and after rolling were characterized using optical and scanning electron microscopy. The good results of the powder metallurgy method suggest the possibility of producing small parts, like cladding cap-ends, using near net shape sintering.

Abstract: To investigate the property of a new type of Zircaloy material, a low cycle fatigue (LCF) test has been performed at room temperature (RT) and 375°C. Results show that the new alloy generally displays cyclic hardening followed by a continuous softening behavior. Fatigue lifetime curves as a function of strain range imply that the new alloy has a nearly same lifetime than that of Zr-4 at RT, and superior than that at 375°C.

Abstract: Zirconium (Zr) alloys are best known for their use in nuclear reactor applications. A hexagonally close-packed structure with a low c/a ratio and very limited slip systems leads to strong textures in these alloys during fabrication processes. These alloys are used in cladding applications for encapsulating fuel pellets, and undergo various stress conditions in-service. Hence, it is necessary to understand the creep properties of Zr alloys to predict the life of reactor claddings. Due to the unique texture, the creep deformation of these alloys is anisotropic in nature. The texture of Zircaloys was determined by X-ray diffraction experiments, and expressed in terms of pole figures and crystalline orientation distribution functions. Biaxial creep testing of thin walled tubing was used to study the creep anisotropy. Creep loci evaluation based on the experimental data and model predictions are compared. It is found that the models can predict the creep loci for recrystallized alloy very well. However, they fail to explain the behavior of the cold worked alloys. When stress enhancements due to the grain boundary sliding are taken into account, the predicted creep loci correlated well with that constructed from the experimental data.

Abstract: A series of strain fatigue tests were carried out on small bugle-like slice-specimens of Zr-4 alloy at 20
and 400
. According to Elastic and Plastic Finite Element Analysis
 and assumption of local damage equivalence, a strain formula was given to transform transverse strain of the specimen to uniaxial strain. Based on the test results of the alloy and the strain transform formula, M-C (Manson-Coffin) models to be used for estimating uniaxial fatigue life of Zr-4 alloy were obtained. The results show that, the alloy mainly behaves as cyclic softening at 20
and as cyclic hardening at 400
, and the elevated temperature can lead serious additional fatigue damage of the alloy and the effect of the elevated temperature impairs gradually with increasing of amplitude strain. A conclusion is helpful that prediction life by using M-C model based on traditional strain transform equation is quite conservative when uniaxial strain amplitude is less than 0.5%.

Abstract: A laser ultrasound technique (LUT) is reported for nondestructive characterization of hydrogen concentration (HC) in Zr-4 cladding tubes. With the LUT, ultrasonic waves propagating in the Zircaloy tubes with different HC are generated and detected remotely by optical means. By measuring the dispersion spectra with the LUT, relations between the dispersion spectra and the HC of the Zircaloy tubes are established. HC ranging from 0 to 1200 ppm in the Zircaloy tubes are successfully discriminated by the LUT with a resolution of 200 ppm.

Abstract: Latest post-irradiation experiment results of Zry-2 and HiFi alloy (0.4%Fe-Zry2) showed that iron addition reduces the hydrogen pickup by these alloys compared to oxidation amount. In order to clarify the mechanism of reduced hydrogen absorption rate, (1) autoclave test, (2) surface potential measurement and (3) hydrogen absorption test of the intermetallic compound were carried out. Based on these results, a tentative mechanism for hydrogen absorption by zirconium alloys is proposed, taking into account of both the electrical potential gradient over the oxide film as well as the SPP window for hydrogen absorption.