查看更多>>摘要：Helium has profound effects on the microstructure and mechanical property of materials used in nuclear power systems. To understand the interaction between helium and irradiation-induced defects and its effect on bubble formation, single-beam and dual-beam irradiations on nickel were performed with 16 keV helium ions and 1 MeV krypton ions under in-situ TEM observation. For 1 MeV krypton single-beam irradiation, voids were observed at 600 °C but not at 500 °C and 700 °C. For helium single-beam irradiation at 500 °C, helium moved freely and formed bubble-loop complexes. For dual-beam irradiation at 500 °C, helium was trapped by vacancies and formed bubbles homogeneously. The structure of dislocation loops was also affected by the presence of helium. For krypton single-beam irradiation at 500 °C, the microstructure was {100} periodic wall of faulted and perfect dislocation loops. For dual-beam irradiation at 500 °C, periodic wall was not observed, and dislocation loops were predominantly perfect. For single-beam helium at 500 °C, dislocation loops were produced by athermal process of SIAs ejection or loop punching mechanisms. The interplay between helium and vacancies played an important role on the evolution of helium bubbles and defect microstructures.
查看更多>>摘要：As part of a global initiative to reduce the usage of highly enriched uranium (HEU) fuel for research and test reactors, Al-clad U-7Mo/Mg and U-10Mo/Mg pin-type mini-elements with a low-enriched uranium (U-235 enrichment of 19.75 wt%) loading of 4.5 g U/cm3 were fabricated at the Canadian Nuclear Laboratories (CNL). The mini-elements were irradiated in the National Research Universal (NRU) reactor at maximum linear power ratings of 100 kW/m up to 80 at% U-235 burnup. Hot cell macroscopic examination of the discharged fuel elements at 30, 60 and 80 at% U-235 burnup indicated that they were intact without breakaway swelling or fuel cladding failure. The results of interim post-irradiation examination (PIE) that was conducted on mini-elements discharged at 30 at% U-235 burnup are reported in this paper. A follow-up paper will present the PIE results of the mini-elements that achieved burnups of 60 and 80 at% U-235. In the present study, the microstructure and phase composition of the irradiated U-7Mo/Mg and U-10Mo/Mg fuel cores were investigated using optical microscopy and neutron diffraction analysis. The weight fraction of different crystalline phases in U-7Mo/Mg and U-10Mo/Mg fuel cores at low burnup was determined through Rietveld refinement. This paper includes a description of the irradiation tests along with preliminary PIE results from the irradiated U-Mo/Mg mini-elements and describes the results of optical microscopy characterization and neutron diffraction analysis.
查看更多>>摘要：Uniaxial creep of the 316L austenitic steel is studied in static oxygen-controlled lead-bismuth eutectic (LBE) with an oxygen content of 10?6 wt. % decreasing to 10?11 wt. % and in air at 450–550 °C. Dissolution of the steel components (nickel, iron and chromium) in liquid metal with a following formation of a depletion zone and ingress of liquid metal inwards a depleted zone are observed in all LBE-experiments. At 500 and 550 °C, the 316L austeinitic steel ruptured much earlier in LBE than in air, while at 450 °C the specimens were still in-tact after long-term testing in LBE (7,178 h) and air (5,783 h). Dissolution of the steel in LBE at 550 and 500 °C is detected to localize close to the failure and unaffected steel surface close to the screw head of the cylindrical creep specimens where creep rate is comparatively low, while at 450 °C, a surface of the whole LBE-specimen is dissolved in liquid metal during a long-term LBE-test. Reference air-specimens show an insignificant surface oxidation at 450–550 °C and creep rate at least one order lower than for the LBE-specimens. Liquid metal embrittlement effect was not observed in 316L tested in LBE.
查看更多>>摘要：The purpose of the present study is to clarify the instability behavior of M23C6 under irradiation, specifically the occurrence of radiation-induced amorphization (RIA). Ion irradiation of 10.5 MeV-Fe3+ at elevated temperatures from 573 to 623 K was conducted into the reduced activation ferritic/martensitic steels (F82H) and its model alloy (Fe-8Cr-0.1C). A bilayer contrast of the particle consisting of an amorphous-rim phase and inner crystalline core of M23C6 was observed in the irradiated F82H specimen, but not in the model alloy. From the high-resolution electron microscope observation, the preferential occupation site of W into M23C6 lattice was identified as 8c-site prior to irradiation in F82H specimen, which shifted to other sites due to chemical disordering upon irradiation. Evaluation of the intensity ratio between 8c and another site of M23C6, 8c/4a, then revealed that the extent of chemical disordering of W was mitigated at the amorphous-crystal interface region in comparison with the central of the particle. The hypothesis for the formation mechanism of an amorphous-rim in M23C6 was presumed as the deviation from the stoichiometric composition at the local interface due to the irradiation-enhanced diffusion and/or ballistic mixing under the current circumstances, although the efforts from experimental and/or simulation studies are still necessary to achieve a further understanding of the RIA behavior in M23C6.
查看更多>>摘要：This paper describes the results of a systematic sensitivity analysis for silver diffusional release from Tristructural Isotropic (TRISO) fuel particles in the AGR-1 base irradiation test and high temperature safety test database. The BISON code was used to model the diffusional release of silver through the coated particle for a wide range of the irradiation and the high temperature conditions conducted in the AGR-1 tests. The current BISON results agree well with other computations and measurements. We then conducted the systematic sensitivity analysis to identify the impact of Ag diffusion coefficient in the TRISO layer materials on the prediction of Ag release. Sobol indices were computed to indicate the contribution of each input, and the scatter plots were analyzed to investigate the correlations between diffusivity parameters and predicted Ag release. Informed by the Sobol sensitivity analysis, a calibrated set of diffusion coefficients were obtained which gave better predictions. The result of this best-estimate calibration indicates a Ag diffusion pre-factor in the SiC from 3.85 × 10?10 to 3.19 × 10?9 m2/s and Ag activation energy in SiC between 178 and 185 kJ/mole. The outputs are expected to provide the systematic approach for better understanding of Ag transport inside TRISO particle.
查看更多>>摘要：Effect of post-weld heat treatment(as-weld, 615℃/16 h and 615℃/48 h) on microstructure and corrosion behavior in ENiCrFe-7 weld overlay cladding materials had been investigated, the results showed that the heat treatment had an obvious influence on microstructure and corrosion properties. As-weld Alloy ENiCrFe-7 exhibited to be compressive residual stress, and it had a lot of homogeneously distributed microstructure defects(e.g. composition segregation), the pits were evenly distributed on the surface of the sample after polarization, its passive current density was the least due to formation of the densest passive film. With increasing heat treatment time to 16 h, the compressive residual stress was rapidly decreased, the degree of Cr-depletion in the dendrites was obviously increased, and a large number of pits were concentrated in the Cr-depletion area. With increasing heat treatment time to 48 h, the compressive residual stress was slightly increased compared with that at heat treatment time of 16 h, both the degree of Cr-depletion in the dendrites and microstructure defects were improved, the looser passive film was formed, general corrosion was mainly performed during polarization.
查看更多>>摘要：The anisotropic behavior of elastic properties of the low-temperature phase of uranium was studied by theoretical and experimental methods in this work. Firstly, based on the density functional theory, the elastic constants and compliance constants of α-U were obtained. Secondly, Young's modulus, bulk modulus, shear modulus, and Poisson's ratio of polycrystalline α-U were calculated using the Voigt-Reuss-Hill model. Then, according to the crystal symmetry of α-U, the spatial distribution characteristics of its Young's modulus were calculated and displayed. The Young's modulus of α-U in some specific crystal directions (including the typical deformation-induced twinning {1 3 0}, {1 7 2}) were also given. Nanoindentation method combined with electron backscatter diffraction (EBSD) technology were used to measure and characterize the grains with different crystal orientations, to obtain experimental values of Young's modulus of α-U in different crystal orientations. Also, the inverse pole figure of Young's modulus of α-U was given.
查看更多>>摘要：A new route for the synthesis of silver-phosphate based sorbent beads as precursors of final iodine waste form is proposed here. This sorbent is used to entrap gaseous iodine produced during the reprocessing of spent nuclear fuels and to be directly transformed into materials composed of a silver phosphate glass phase considered as high efficient iodine containment matrix for long-term storage in deep geological repository. Using sacrificial organic template method (alginate) and well controlled calcination of the obtained silver phosphate grains materials, this innovative synthesis makes in-situ formation of metallic silver inside them. Ag0 then can easily entrap iodine when in contact with gaseous iodine. The obtained sorbent were tested for iodine trapping in static conditions. They showed great performances with a catch rate of 480 mg.g?1. The iodine-loaded sorbent were finally heat treated at 650 °C with an iodine loss lower than 3% wt. The resulted materials shows the presence of the expected silver phosphate glass matrix with a great iodine incorporation of 9% mol.
查看更多>>摘要：Gadolinium zirconate (Gd2Zr2O7) is a candidate phase of ceramic waste form for immobilizing high-level nuclear waste. Dense fine-grained ceramics is beneficial to improve the irradiation resistance and leaching resistance of the ceramic waste form. In this work, two-step microwave sintering (TSMS) on Gd2Zr2O7 was firstly demonstrated as a considerable approach to fabricate dense nano-grained Gd2Zr2O7 ceramic. Microstructure evolutions and densification processes of the Gd2Zr2O7 samples at various temperatures were investigated. The nano-grained (69.2 nm) Gd2Zr2O7 ceramic with a relative density of 96.9% has been successfully fabricated at 1350 °C - 3 min - 1200 °C - 20 min. TSMS can promote the near complete densification of ceramics while suppressing the growth of crystal grains within nanoscale (<100 nm) by taking advantages of microwave sintering and two-step sintering.
查看更多>>摘要：Post-Loss of Coolant Accident (LOCA) ductility assessments of Cr-coated Zircaloy cladding was conducted in compliance with the United States Nuclear Regulatory Commission (U.S.NRC)’s guidelines. The Equivalent Cladding Reacted (ECR) limit for Cr-coated cladding oxidized on both sides, representing the embrittlement process of an outer-side coated cladding near the burst hole followed by ballooning, is found to be 13.8% at steam oxidation temperature of 1204°C. Ring Compression Test (RCT) induces peak tensile stress at the inner surface of the cladding specimen at which the crack starts to propagate from the brittle phases (ZrO2 and α(O)-Zr). Such characteristic of RCT is responsible for the decrease in the ECR limit for the claddings coated on the external surface as its oxygen-affected brittle phases are developed at the inner cladding surface. Outer-side Cr-coated cladding gives approximately 10 minutes of extra accident coping time at the fixed steam oxidation temperature 1204°C before it reaches the cladding embrittlement limit.
NSTL
Elsevier