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The region from cladding to pellet of the leak rod with the burnup of 41 GW·d/tU and the intact rod with the burnup of 45 GW·d/tU was characterized by nanoindentation, metallurgical microscope, and Raman spectroscopy. The results show that a porous high burnup structure (HBS) appears on the pellet periphery of the intact rod, and this phenomenon results in the decrease of the hardness of periphery of the pellet. The hardness of the pellet of the leak rod decreases along the radial direction towards the centre of the pellet, which is mainly related to the migration of the pores and the reconstruction of the fuel pellet. After the leak of the cladding, coolant enters the gap between the cladding pellets and reacts with the pellets. The porosity of the HBS of the leak rod is less than that of the intact rod, and the hardness of the HBS of the leak rod is slightly higher. Meanwhile, the temperature change leads to grain reconstruction and the formation of large-sized columnar crystals, resulting in the decrease of hardness in the middle and centre of the leak rod fuel pellet. The leak of the cladding does not change the phase composition of the pellets. As a result, the Young's modulus of intact rod and leak rod pellets does not show much difference. The hardness of the FCCI layer of the intact rod increases gradually along the cladding towards the pellet, while the Young's modulus firstly decreases and then increases. The hardness of the FCCI layer of the leak rod increases at first and then decreases, while the change of the Young's modulus is in general similar to the hardness of the leak rod along the cladding to the pellet. The phenomenon arises from the combined effects of phase structure transformation and fission product doping. The hydrogenation and oxidation of the cladding after the leak of the fuel rod results in a significantly higher hardness and Young's modulus of the leak rod cladding than that of the intact rod.

Ephemeral gully (EG) erosion is an important type of water erosion. Understanding the spatial distribution of EGs and other influencing factors at a regional scale is crucial for developing effective soil and water management strategies. Unfortunately, this area has not been sufficiently studied. The present study visually interpreted the EGs based on Google Earth images in 137 small watersheds uniformly distributed in the Loess Plateau, compared them with measured results, and analyzed the factors influencing EG formation and density using GeoDetector. The results showed that visually interpreting EGs from Google Earth images was suitable for EG regional studies. Out of the 137 small watersheds, 33.6% had EG occurrence with an average density of 3.41 km/km2. Rainfall (R) and slope gradient (S) were the primary factors influencing the formation of EGs, while the area proportion of sloping farmland (APSF) and soil erodibility (K) were the main factors affecting EG density. The interaction of dual factors had a greater influence compared to single factors, with the interaction between S and Normalized Difference Vegetation Index (NDVI) having the greatest impact on EG formation and the interaction between K and NDVI on EG density. Although natural forces significantly influence whether EGs can form in a specific area, human activities greatly affect the density of the gullies that develop. This underscores the importance of proper land management in controlling gully erosion. These findings could provide theoretical support for EG prediction models and a scientific basis for soil and water loss control strategies at the regional scale. [ABSTRACT FROM AUTHOR]