Fabrication of UO2-Gd2O3 Fuel Pellets

The burnable poison Gadolinium oxide was incorporated into UO2 in two of the 36 elements of the fuel assembly in the reload fuel of BWR Units I & II of Tarapur Atomic Power Station. This enabled loading of higher quantities of fuel and achieving a more flattened neutron flux distribution over a longer period of time in the nuclear reactor core. The UO2-Gd2O3 pellets are made by powder pressing and sintering. In the early days of this author’s experience of the 1970s, the processing of UO2-Gd2O3 turned out to be more complex than that of UO2 alone. The small proportion of Gd2O3 in the powder mixture (1.5%) is to be uniformly distributed in the UO2 before and after sintering and substitutional solid solution formation must be complete prior to densification. The inadequacy of homogeneity in the powder and pressed pellets leads to severe defects in the sintering process. In this paper, the processing of U2-Gd2O3 has been revisited. The defects in the product such as “free gadolinia”, low sintered density and bloating, caused by improper processing, have been brought out. The structural defect chemistry aspects of UO2-Gd2O3 and diffusion processes relevant to sintering have also been discussed.

The chemistry,stability and health effects of phenolic compounds in cultivated hawthorn(Crataegus pinnatifida var.major):a review

Cultivated hawthorn(Crataegus pinnatifida var.major),the principal cultivated hawthorn species in China,is rich in phenolic compounds.These phytochemicals are considered essential bioactive ingredients in different organs of cultivated hawthorn,contributing to its health effects.However,there is lack of a comprehensive review that systematically summarizes the chemistry,health effects,and stability of phenolic substances.This review summarizes recent progress in the characterization,classification,and distribution of phenolic compounds in C.pinnatifida var.major,including procyanidins,flavonoids,phenolic acids,lignans,and others.Importantly,the stability of these compounds was found to be influenced by factors such as the hawthorn development process,postharvest storage,postharvest processing,and the gastrointestinal tract environment.Additionally,the health effects of phenolic compounds in cultivated hawthorn and their underlying mechanisms were discussed.This review provides valuable insights into the utilization of hawthorn resources and the development of the hawthorn industry.

First Investigation of Nonlinear Optical Oxychalcogenide with Three-Dimensional Anionic Framework and Special Windmill-Like Functional Motifs

Oxychalcogenides have been drawn much attention to be explored as nonlinear optical(NLO)materials in recent years.To date,all the NLO oxychalcogenides crystallize in low dimensional structures.Herein,a new oxysulfide K_(2)Ba_(0.5)Ga_(9)O_(2)S_(13) was obtained via three-dimensional(3D){[Ga_(9)O_(2)S_(13)]^(3-)}_(∞)polyanionic framework.As the first oxychalcogenide with 3D NLO-acitve polyanionic framework,K_(2)Ba_(0.5)Ga_(9)O_(2)S_(13) has a wide band gap of 3.72 eV,and exhibits a high laser-induced damage threshold(LIDT,17×AgGaS_(2)).It presents moderate phase-matchable NLO response of 0.5×AgGaS_(2) at 2.1μm and 2×KH_(2)PO_(4) at 1.064μm.The theoretical calculation results indicate that the NLO response is mainly contributed from[Ga(2)S4]unit-built[Ga(2)_(3)S_(10)]windmill-like motif.This work may stimulate the exploration of more NLO oxychalcogenides with balanced performances.

Preparation and Reaction of Naked Metal Clusters for Catalysis and Genetic Materials

Metal clusters that contain a small number of atoms usually present unique properties with dramatic dependence on their sizes,geometric structures,and compositions.The studies of naked metal clusters are devoted to develop new catalysts and functional materials of atomic precision,and enable to improve the fundamental theory of structure chemistry and to understand the basic reactions and properties bridging the gap between atoms and bulk materials.In particular,some interesting superatom clusters have received reasonable research interest indicative of materials gene of clusters.Here in this review,we simply summarize the preparation,stability,and reactivity of naked metal clusters with a few examples displayed.Hopefully it serves as a modest spur to stimulate more interest of related investigations in this field.