[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 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] 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)