[en] The nano-infiltration transient eutectic (NITE) SiC/SiC composites are considered as most promising candidates for accident tolerant fuel (ATF) cladding in light water reactors. However, this method requires very specific mold so that it can hardly fabricate long size cladding tubes. To solve the problem, this work presents an improved mold-free NITE method to produce long size tubular SiC/SiC composites. To add some PCS to the classic NITE-SiC slurry, so that the cross-linked SiC precursor can hold together the β-SiC powders onto the fabric. This allows the hot isostatic pressing at 1780 ℃ and 20 MPa to produce dense cladding tubes of SiC/SiC composites. By this means, the complicated NITE-mold is no longer needed, enabling the capability to fabricate long size cladding tubes of SiC/SiC composites, and the corresponding density is higher than that of the CVI-SiC/SiC composites. (authors)

[en] The vacuum induction smelting and casting technology of zirconium-uranium- erbium alloy is introduced in this paper. Four furnaces are carried out by changing the processing parameter such as percentage composition, temperature and time of smelting, temperature of casting temperature of mold etc,the results are as following:the addition of alloy elements are determined to guarantee the accuracy of component, the addition of uranium is 30%, the addition of orbium is 2.05%; The uniformity of alloy element is improved with the increasing of time of refining and the time of refining determined is 8-11 min; The coating of graphite crucible can make the impurity content satisfactory such as C,Y etc ; The major problem of casting quality is introduced specially and explained according the analysis of influencing factor on the flowing property. The suggestion to improve casting quality in the next stage is presented. (authors)

[en] The new CVI + moldless NITE technology combines the advantages of chemical vapor infiltration (CVI) technology and nano-infiltration eutectic transformation (NITE) technology, and is with the potential to prepare long size SiCf/SiC composite cladding tubes. This study has shown that the short-term CVI infiltration can strengthen the fiber preform and keep the inner pores open for the NITE infiltration step; meanwhile, adding polycarbosilane (PCS) to the NITE slurry can effectively reduce the sintering difficulty of the NITE process, so that SiCf/SiC composite tubes can be obtained through hot isostatic pressing method. The maximum density of SiCf/SiC short tubes in this study reaches 2.77 g/cm³, and can still be improved. (authors)

[en] The precipitation of copper-enriched clusters was induced into pressure vessel model steel (with higher Cu content) of nuclear reactors by water quenching and thermal aging. The mechanical property tests showed that the presence of copper-enriched clusters led to a large shift of the ductile-to-brittle transition temperature, a tiny increase in the yield strength and tensile strength,and a tiny decrease of plasticity. In addition, this paper also studied the effect of the presence of Nickel element on the ductile-to-brittle transition temperature. Three-dimensional atom probe test revealed that the number density of enriched clusters was about 10²³ m^-3, and the size of copper-enriched clusters was in the range of 1 nm to 3 nm in diameter. (authors)

[en] Uranium silicide is formed from ingot of uranium and silicon in near stoichiometric quantities by arc melting. And then uranium silicide pellets were produced by conventional powder metallurgy. The effect of pellet compression molding and sintering on density and the microstructure of U₃Si₂ pellets were studied. It turned out that, 0.5% of PEG was added to be binder and the green pellets was got with a pressure ranging from approximately 260 to 300 MPa, then the pellets were sintered with a temperature of 1550℃ for 2-4 h. To this end, high phase purity U₃Si₂ with density 11.4 g/cm³, which is above 93% of theory density, is produced. The pellet size is uniform and the average grain size is about 60μm, but there is a little U or UO₂ impurity in sample U₃Si₂ pellet. The thermal conductivity of U₃Si₂ pellet is superior to UO₂, and rise approximate linearity with the increasing of temperature. (authors)

[en] The microstructure of the alloy specimens which were melted with the impure uranium and pure uranium respectively, and their hydrided specimens were analyzed by OM and SEM, moreover, the composition of the hydrided specimens were studied by SEM-EDS. The results showed that the contents of impurity elements of Fe and C were both higher in the impure uranium-contained specimen than in the pure uranium-contained specimen, in which the elements were more homogeneously distributed in the zirconium hydride matrix. There was great difference of expansion coefficient between the precipitate which consisted of the elements of U, C, a little Fe and zirconium matrix in the impure uranium-contained hydrided specimen, thus when the volume of zirconium matrix increased due to absorbing hydrogen, the precipitate as a secondary phase pinned in the matrix so that the stress was concentrated resulting in the hydrided specimen cracking. In the pure uranium-contained hydrided specimen, the elements of U and C which existed in the form of zirconium carbide relatively homogeneously distributed in the zirconium hydride matrix, and the stress in the hydrided specimen did not concentrate so that the hydrided specimen did not cracked. (authors)

[en] Uranium-zirconium hydride fuel pellets were manufactured by the method of melting and casting U-Zr alloys and then hydrogenating the U-Zr alloys. The casting quality and yield were improved by changing the parameters of melting and casting process. U-Zr alloys were hydrogenated by using different parameters. The H/Zr atomic ratio of uranium-zirconium hydride fuel pellets was ranged from l.41 to 1.71. The size of specimens was increased after hydrogenation process. The fuel pellet was composed by several phases, and uranium was present as metallic inclusions in a matrix of zirconium hydride. In addition, the concentration of hydrogen at fuel pellet brim was higher than that at fuel pellet center. (authors)

[en] FeCrAl cladding and UN fuel pellet are important accident tolerant fuel (ATF) candidates, it's necessary to analyze the performance of FeCrAl cladding and UN fuel pellet under PWR operation condition. Based on the latest FeCrAl cladding and UN fuel physical property data and behavior model at home and abroad, the fuel performance analysis program FUPAC is redeveloped to analyze the in-reactor performance of FeCrAl/UN, FeCrAl/UO₂, Zr-4/UN and Zr-4/UO₂ fuel rods under different linear power densities. Through comparison, the results showed that FeCrAl/UN fuel rod has good performance in aspects like pellet temperature, fission gas release, fuel rod internal pressure, etc. But due to low creep rate of FeCrAl cladding, once the cladding-pellet gap closes, the cladding stress increases rapidly. This phenomenon needs to be paid attention during the following research. (authors)

[en] SiC_f/SiC composites are considered as one of the ideal candidates for accident resistant fuel cladding due to their excellent properties. However, as a new material system, there are still many problems to be studied in order to realize its application in the nuclear field. In this paper, the 24 hours oxidation test of SiC_f/SiC composites cladding with different coating under the condition of 1300 ℃, 100% water vapor was conducted. The weight changes of different coating samples after steam oxidation were studied, and by using SEM, XRD and XPS the microstructure and compositions were analyzed. The research results show that the different coating sample have similar weight change law, and the weight gain rate is around 2%. After oxidation, glassy oxide film appears on the surface of the coating, and there are holes and cracks on the oxide film. The oxidation products for the specimens whose coatings were deposited at 1050 ℃ and 1150 ℃ are amorphous SiO₂ and SiC_xO_y, and for the specimens whose coating was deposited at 1250 ℃ the oxidation products are mainly amorphous SiC_xO_y. (authors)

[en] FeCrAl coating was prepared by the magnetron sputtering at different deposition temperature. Effects of deposition temperature on the microstructure, mechanical properties, hydrophilicity and oxidation resistance of FeCrAl coatings were investigated. In addition, the oxidation behavior of the FeCrAl coating was discussed. The results show that FeCrAl coatings are formed by body-centered cubic (BCC) Fe-Cr phase structure, and all of them have a hydrophilic surface. The deposition temperature has a significant effect on the adhesion of FeCrAl coating, and it has good mechanical properties when the deposition temperature is 400℃. High-temperature air oxidation tests at 800℃ indicate that the FeCrAl coating with the deposition temperature of 400℃ has excellent air oxidation resistance and can effectively protect Zr-4 alloy substrate from oxidation. (authors)