The objective of this study was to investigate the effects of types of motion and loading conditions on the wear of Pressurized Water Reactor (PWR) fuel rod cladding made of Zircaloy-4 in contact with a grid support cell. Fretting-wear tests, for various combinations of motion and preload, were conducted at 310°C and 11.7 MPa using primary circuit water chemistry. Wear coefficients, derived from three-dimensional profilometry, were used to assess the severity of the wear process. The types of motion and the loading conditions were found to have a significant interdependent effect on fuel rod wear coefficients. Scanning Electron Microscope (SEM) examinations were performed on the worn fuel rod cladding specimens to identify wear mechanisms.
To understand the mechanisms at the origin of whisker formation and growth, a Zn-electroplated steel prone to whiskering was studied. Several samples were prepared from different locations of the electroplated plate. Care was taken to extract samples at the root, in the nodule, or away from whiskers. Samples were characterized using electron backscattered diffraction (EBSD). Crystallographic data from EBSD show that recrystallized regions are present at the root of whiskers and in their nodules. These observations support whisker growth models based on recrystallization. In addition, atom probe tomography samples were prepared in the center of whiskers. The distribution of Zn atoms is almost homogeneous and no impurities are present in the whiskers.
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To date, almost all the studies related to component damage have been concerned primarily with dynamic interactions at the interface of contacting components and the subsequent damage due to mechanical wear. Based on the results of examination of a large assortment of photo-micrographs taken from worn reactor components and worn specimens from a broad range of test facilities, it appears that, in many cases, mechanical wear is only a secondary contributing mechanism. With the exception of special cases where severe flow-induced vibration might have occurred, such as in some condensers and primary heat exchangers as well as in the U-bend and inlet regions of some earlier steam generators, resulting in severe component interactions causing substantial wear damage, erosion, corrosion, impacting and perhaps cavitation would seem to be the primary contributing mechanisms.
Coatings of silicon rich silicon carbide are obtained in a plasma assisted device from tetramethylsilane and argon mixture, around 760K under reduced pressure on metallic alloys: FeCrAl and NiCrA1.The atomic composition of the deposits is determined by microprobe analysis and adherence is evaluated by scratch test measurements. These results are discussed in relation with previous determinations obtained when identical films are deposited on low carbon steel substrates. All samples exhibit a similar behavior which denotes a good adherence. The formation of a diffusion zone is responsible for this trend. The qualitative behavior of the coated substrate in air at high temperature (1273 K) is investigated in comparison with the uncoated substrate through cross section examinations by different analysis (EDS mapping, WDS profiles). The heat treatment (lOh, 100h) induces a strong diffusion which is discussed. It is evidenced that the silicon carbide based films drastically change the oxidation mechanism (mainly in the case of NiCrAl) and tend to improve the resistance of the substrate against an oxidizing atmosphere. Futhermore, some solutions to improve the lifetime of such metallceramic junctions are suggested. As for example, the interest of an alumina interlayer between S i c coating and FeCrAl substrate is experimentally shown.
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