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The corrosion resistance of uranium has always been an important issue in the wide use of uranium materials. Surface nitriding has been proved to be one of the best surface anti-corrosion modification methods. In the present study, the nitrided layer with different nitrogen content was prepared on the surface of uranium by laser nitriding technique. The surface morphology and lattice structure were characterized by scanning electron microscopy (SEM) and X-ray diffractometry (XRD). The electronic structures and oxidation behaviors were analyzed by X-ray photoelectron spectroscopy (XPS). Corrosion resistance was analyzed by electrochemical test. The results show that the main phase in the nitrided layer is UN and metal uranium. The nitrogen always exists in the oxidized state of the nitrided layer. The nitrogen element in the crystal lattice may enhance the oxidation resistance of uranium surface. The electronic structure and valence band structure of UNx films with different nitrogen content and their depth-dependent information were obtained. Excessive nitrogen content will lead to the initiation of microscopic cracks, which destroy the integrity of nitrided layer and reduce the corrosion resistance in solution. UN0.35 nitrided layer is well matched with lattice of the base metal, and the surface is intact without cracks, showing the best solution corrosion resistance.

Cerium mononitride (CeN) film was fabricated by dual ion beam sputtering deposition method on silicon wafer. The oxidization process of CeN film was monitored by optical microscopy (OM), scanning electron microscopy (SEM), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS), respectively. The results showed that, when the CeN film was exposed to ambient atmosphere, bubbles appeared on the film surface rapidly and then the surface flaked off to powders. Meanwhile, the CeN film changed from polycrystalline to amorphous. XPS analysis indicated that the CeN was oxidized to Ce2O3 initially, and then further oxidized to CeO2. These results indicated that the CeN film degraded easily in ambient atmosphere, exhibiting little or no passivation.

The nitride surfaces of uranium were prepared by the surface glow plasma nitriding (SGPN) and plasma immersion ion implantation (PIII) methods. The initial oxidation behaviors of modified surfaces were studied by X-ray photoelectron spectroscopy (XPS). The SGPN on the uranium surface led to a single layer of uranium sesquinitride (U2N3), while the PIII on the surface resulted in a compound layer composed of U2N3 and uranium dioxide (UO2). The oxygen covered on these modified layers led to the formation of UO2 from U2N3 and U2N3 from UN. The oxidized nitrogen species were also observed on the two types of nitriding layers, with the discussion of the N–O coaction behaviors.

Aluminum overlayers on uranium were prepared by sputtering at room temperature in an ultra-high vacuum chamber. The growth mode of aluminum overlayers and behaviors of the Al/U interface reaction were studied in situ by auger electron spectroscopy, electron energy loss spectroscopy, and X-ray photoelectron spectroscopy. The results suggested that the interdiffusion took place at the Al/U interface during the initial stage of deposition. The U4f spectra of the Al/U interface showed strong correlation satellites at binding energies of 380.4 and 392.7 eV and plasma loss features at 404.2 eV, respectively. The interactions between aluminum and uranium yielded the intermetallic compound of UAl x , inducing the shift to a low binding energy for Al2p peaks. The results indicated that aluminum overlayers were formed on the uranium by sputtering in an island growth mode.

The nitride layer was formed on uranium metal by a glow plasma surface nitriding method. The structure and composition of the layer were investigated by X-ray diffraction and Auger electron spectroscopy. The nitride layer mainly consisted of α-phase U 2 N 3 nanocrystals with an average grain size about 10–20 nm. Four zones were identified in the layer, which were the oxide surface zone, the nitride mainstay zone, the oxide-existence interface zone, and the nitrogen-diffusion matrix zone. The gradual decrease of binding energies of uranium revealed the transition from oxide to nitride to metal states with the layer depth, while the chemical states of nitrogen and oxygen showed small variation.

Uranium nitrides are among the most promising fuels for Generation IV nuclear reactors, but until now, very little has been known about their thermal stability properties under nonequilibrium conditions. In this work, thermal decomposition of nitrogen-rich uranium nitride (denoted as UN2–x) under ultrahigh-vacuum (UHV) conditions was investigated by thermal desorption spectroscopy (TDS). It has been shown that the nitrogen TDS spectrum consists of two peaks at about 723 and 1038 K. The X-ray diffraction, scanning electron microscopy, and X-ray photoelectron microscopy results indicate that UN2–x (UN2 phase) decomposed into the α-U2N3 phase in the first step and the α-U2N3 phase decomposed into the UN phase in the second step.

The effect of Fe and C doping on the thermal release of helium from Al implanted with 10 keV, 4.0 × 1021 ion/m2 He at room temperature (RT) has been investigated by thermal helium desorption spectrometry (THDS) and transmission electron microscope (TEM). The results show that Fe and C doping have significant impact on the release of helium from Al and the extent depends on the doping fluence. Proper fluence of Fe and C doping would lead to the retardation of the release of helium from Al, while excessive fluence of Fe and C doping would result in more desorption peaks and the release of helium in lower temperature ranges. Fe and C doping have different influence on the release of helium from Al, and the difference is related with the secondary phases forming in the samples.

A new pair potential for helium in bulk iron was developed using a method based on the Chen–Mobius lattice inversion in order to study the effect of He in irradiated iron. By means of molecular dynamic (MD), we have examined this interatomic potential. Comparing with the ab initio calculation results, the stability of He-vacancy clusters at zero temperature and migration energy was well reproduced by this potential.

Nitrogen ion was implanted into uranium surface using plasma immersion ion implantation, and the corrosion resistance of modified layer was studied by corrosion experiment. SEM was used to observe variety of samples surface. In atmosphere, the sample surface had not changed during five months. In heat–humid environment, there was dot-corrosion appearing after two months, but it did not influence the integrity of the modified layer. AES was used to study the diffusion of oxygen and nitrogen during hot–humid corrosion, in three months, both of two elements diffused to the substrate, but the diffusion was weak. The structure of modified layer was not changed. Experimental results show that the modified layer formed by plasma immersion ion implantation has good corrosion resistance.

The initial oxidation of uranium–niobium alloy in oxygen atmosphere at 298 K has been studied by X-ray photoelectron spectroscopy (XPS). For comparison, the adsorption of oxygen on pure metal niobium and uranium has also been studied. The changes of U4f, Nb3d and O1s spectra during in situ oxidation indicate that the adsorption of oxygen on uranium–niobium alloy surfaces first leads to the formation of UO2 and NbO; then NbO2 and Nb2O5 are detected with increasing exposures of oxygen. The segregations of U and Nb to the uranium–niobium alloy surfaces are observed at different oxidation stages. The oxide film formation of uranium–niobium alloy is faster than that of pure uranium at initial oxidation stages.