Recent studies on potential accident-tolerant fuel-cladding systems in light water reactors

Accident-tolerant fuel(ATF)has attracted considerable research attention since the 2011 Fukushima nuclear disaster.To improve the accident tolerance of the fuel-cladding systems in the current light-water reactors,it is proposed to develop and deploy(1)an enhanced Zrbased alloy or coated zircaloy for the fuel cladding,(2)alternative cladding materials with better accident tolerance,and(3)alternative fuels with enhanced accident tolerance and/or a higher U density.This review presents the features of the current UO2-zircaloy system.Different techniques and characters to develop coating materials and enhanced Zr-based alloys are summarized.The features of several selected alternative fuels and cladding materials are reviewed and discussed.The neutronic evaluations of alternative fuel-cladding systems are analyzed.It is expected that one or more types of ATF-cladding systems discussed in the present review will be implemented in commercial reactors.

Surface dealuminated Beta zeolites supported WO3 catalyst and its catalytic performance in tetralin hydrocracking

In this study,selective dealumination of Beta zeolites was performed through partially removing the templating agent in Beta zeolites by calcination and then removing the aluminum on the external surface of Beta zeolites with acid treatment.Hydrocracking catalysts were prepared by loading WO_(3)onto these dealuminated Beta zeolites.It was shown that the surface SiO_(2)/Al_(2)O_(3)of selectively dealuminated Beta zeolites was higher than that of conventionally dealuminated samples for the same bulk SiO_(2)/Al_(2)O_(3),and the hydrogenation activity of the catalyst of the selectively dealuminated Beta zeolites was lower than that of conventionally dealuminated Beta zeolites.The experimental results for tetralin hydrocracking to BTX showed that the catalysts based on the selectively dealuminated Beta zeolites had higher BTX selectivity and lower coke formation rate than that the catalysts based on the conventionally dealuminated Beta zeolites.

The surface properties of aluminated meso–macroporous silica and its catalytic performance as hydrodesulfurization catalyst support

Aluminated mesoporous silica was prepared by multiple post-grafting of alumina onto uniform mesoporous SiO2 ,which was assembled from monodisperse SiO2 microspheres.Hydrodesulfurization（HDS）catalyst was prepared by loading Ni and Mo active components onto the aluminated uniform mesoporous SiO2 ,and its HDS catalytic performance was evaluated using hydrodesulfurization of dibenzothiophene as the probe reaction at 300℃ and 6.0 MPa in a tubular reactor.The samples were characterized by N2 physisorption,scanning electronic microscopy,Fourier transform infrared spectrum,X-ray diffraction（XRD）,temperature-programmed desorption of ammonia（NH3-TPD）,^27Al nuclear magnetic resonance（^27Al-NMR）and high-resolution transmission electron microscopy（HRTEM）.The results showed that the Si–OH group content of SiO2 was mainly dependent on the pretreatment conditions and had significant influence on the activity of the Ni Mo catalyst.The surface properties of the aluminated SiO2 varied with the Al2O3-grafting cycles.Generally after four cycles of grafting,the aluminated SiO2 behaved like amorphous alumina.In addition,plotting of activity of Ni Mo catalysts supported on aluminated meso–macroporous silica materials against the Al2O3-grafting cycle yields a volcano curve.

Metathesis of 1-butene and 2-butene to propene over Re_2O_7 supported on macro-mesoporous γ-alumina prepared via a dual template method

Macro-mesoporous γ-alumina support（MMA） was prepared by a sol-gel route in aqueous medium using pseudo-boehmite as aluminum source and polystyrene microspheres and Pluronic P123 as hard and soft dual templates,respectively.MMA had a BET specific surface area of about 259 m2 g-1,total pore volume of about 1.61 cm3 g-1,macropore diameter of about 102 nm,and mesopore diameter of about 14 nm.Re2O7/MMA and conventional Re2O7/Al2O3 were prepared by a incipient-wetness impregnation method,and their catalytic performances in the metathesis of 1-butene and 2-butene were tested in a fixed-bed tubular reactor.The result showed that Re2O7/MMA possessed higher activity and far longer working life-span than conventional Re2O7/Al2O3.

Measurement of pore diffusion factor of porous solid materials

Internal diffusion of molecules in porous materials plays an important role in many chemical processes.However, the pore diffusion capacity of porous materials cannot be measured by conventional catalyst characterization methods. In the present paper, a pore diffusion factor, the ratio of the diffusionconstriction factor to the pore tortuosity of the porous materials, was proposed to measure the diffusion ability of pores inside solid materials, and a method was proposed for measuring the diffusion factor using a well-defined and uniform pore size material as a reference. The diffusion factor was calculated based on the effective diffusion coefficients and the diffusion-constriction factor and pore tortuosity of the reference porous materials. The pore diffusion factor measurement can be performed at room temperature and atmospheric pressure. The pore diffusion factor of conventional porous materials was found to be much smaller than 1, indicating that there is a lot of room for improving the diffusion ability of the conventional catalysts and adsorbents, and could be significantly increased through adding small number of fibers into the conventional porous materials as template.

Low-energy atomic displacement model of SRIM simulations

Radiation-induced atomic displacement damage is a pressing issue for materials.The present work investigates the number of atomic displacements using the Primary Knock-on Atom (PKA) energy E_(PKA)and threshold displacement energy E_(d)as two major parameters via lowenergy SRIM Binary Collision Approximation (BCA) full cascade simulations.It is found that the number of atomic displacements cannot be uniquely determined by E_(PKA)/E_(d )or E_(D) /E_(d)(E_(D) refers to the damage energy) when the energy is comparable with E_(d).The effective energy E_(D,eff)proposed in the present work allows to describing the number of atomic displacements for most presently studied monatomic materials by the unique variable E_(D,eff)/E_(d).Nevertheless,it is noteworthy that the BCA simulation damage energy depends on E_(d),whereas the currently used analytical method is independent of E_(d).A more accurate analytical damage energy function should be determined by including the dependence on E_(d).

Preparation of mesoporous alumina with large pore size and their supported rhenium oxide catalysts in metathesis of 1-butene and 2-butene to propene

Mesoporous γ-aluminas with large pore size （up to 19 nm, denoted as MAI9） are prepared from dispersed pseudo-boehmite using pluronic P123 as template. It is found that these mesoporous alumina supported rhenium oxide catalysts were more active and have far longer working life-span in gas-phase metathesis of 1-butene and 2-butene to propene than rhenium oxide on conventional alumina with small pore size （5 nm）. At 60 ℃ and atmospheric pressure with WHSV = 1 h^-1, the similar stable conversions of butene （ca. 55%） for all the 13 wt% Re207/alumina catalysts were obtained near the chemical equilibrium, and the stable working life-spans of Re2OT/MA19 were far longer than that of Re2O7/A1203, being about 70 h and 20 h, respectively.

A model for transient diffusion in bidisperse pore structures

A bidisperse model for transient diffusion and adsorption processes in porous materials is presented in this paper.The mathematical model is solved by numerical methods based on finite elements combined with the linear driving force approximation.A criterion based on the model to identify the diffusion controlling mechanism(macropore diffusion,micropore diffusion,or both)is proposed.The effects of different adsorption isotherms(linear,Freundlich,or Langmuir)on the concentration profiles and on curves of fractional uptake versus time are investigated.In addition,the influences of model parameters concerning the pore networks on the fractional uptake are studied as well.

In Situ Synthesis of Block Copolymer Nano-assemblies by Polymerization- induced Self-assembly under Heterogeneous Condition

Controlled synthesis of amphiphilic block copolymer nanoparticles in a convenient way is an important and interest topic in polymer science. In this review, three formulations of polymerization-induced self-assembly to in situ synthesize block copolymer nanoparticles are briefly introduced, which perform by reversible addition-fragmentation chain transfer （RAFT） polymerization under heterogeneous conditions, e.g., aqueous emulsion RAFT polymerization, dispersion RAFT polymerization and especially the recently proposed seeded RAFT polymerization. The latest developments in several selected areas on the synthesis of block copolymer nano-assemblies are highlighted.

A big step forward to graphene-based atomic hydrogen storage

Considered as the ultimate solution for the energy and environment crises,hydrogen energy plays a crucial role in the realization of worldwide carbon neutrality.There are three key issues for the practical utilization of hydrogen energy:high-capacity storage,safe transportation and reversible release,among which hydrogen storage is the first step.