Fuel-to-cladding gap evolution and its impact on thermal performance of high burnup fast reactor type uranium-plutonium oxide fuel pins

Drastic evolution of fuel-to-cladding gap is observed in high burnup JOYO Mk-II driver and MONJU type uranium-plutonium oxide fuel pins. The effect of the evolution is examined from viewpoints of fuel restructuring, gaseous FP release and retention and cesium migration behaviors. Its thermal impact on fuel pin performance is also studied by one-dimensional steady state thermal analysis. Threshold condition of the evolution depends on fuel pellet characteristics, burnup and probably temperature. The evolution directly relates to as-fabricated microstructures and to gaseous FP release and retention behavior. A comparison of fuel restructuring with predicted temperature profiles indicates that, even where large residual gaps are observed, non-gaseous filler always improves the heat transfer across the gaps.     

Electronic States of Natural and Metal-ion Doped DNA

Electronic states of pristine and metal ion doped salmon DNA’s are studied with EPR and SQUID. Intrinsically no EPR signal is observed in purified salmon DNA, consistent with a semiconducting nature of the pristine DNA, but inconsistent with a metal or a superconductor as reported previously. Although we obtained successfully the divalent metal ion-DNA complexes with one-dimensional array of ions located in between the bases of a base pair, substantial EPR signal except for the case of 3d transition metal ions is not observed. This leads to the conclusion that divalent metal ions counterbalances two phosphate anions instead of Na counter ions in B-DNA, which contradicts the metallic behavior reported previously (A. Rakitin, et al., PRL 86, 3670 (2001)). A comment will also be given on the recent report: “Intrinsic Low Temperature Paramagnetism in B-DNA” (S. Nakamae et al., PRL 94, 248102 (2005)).     

Weight change mechanism of randomly oriented GFRP panel immersed in hot water

This study deals with the weight changes of the fiber/matrix interface and the weight change mechanisms of the randomly oriented E-glass fiber continuous strand mat reinforced unsaturated polyester panels. The weight changes were evaluated by introducing the weight gain due to water absorption (M_g) and the weight loss due to matrix dissolution (M_l). The weight changes of the fiber/matrix interface (M_gI and M_lI) were obtained from the difference of M_g and M_l between GFRP and neat resin. Water absorption of the interface occurred after water absorption of matrix resin reached saturation. Weight loss due to dissolution of binder on glass-fiber mat and matrix from the interface occurred after water penetration into the interface. The debondings at the fiber/matrix interface occurred due to water penetration, and as a result, the binder and matrix dissolved easily in the water through the interface. The weight changes of the GFRP panel were classified into three phases. In phase I, only the resin matrix absorbed water. In phase II, the fiber/matrix interface absorbed water. After that phase, water absorption into the fiber/matrix interface and matrix dissolution from the interface occurred simultaneously.     

Digital processing to improve image quality in real-time neutron radiography

Real-time neutron radiography (NTV) has been used for practical applications at the Kyoto University Reactor (KUR). At present, however, the direct image from the TV system is still poor in resolution and low in contrast. In this paper several image improvements are demonstrated, such as a frame summing technique, which are effective in increasing image quality in neutron radiography. Image integration before the A/D converter has a beneficial effect on image quality and the high quality image reveals details invisible in direct images, such as: small holes by a reversed image, defects in a neutron converter screen through a high quality image, a moving object in a contoured image, a slight difference between two low-contrast images by a subtraction technique, and so on. For the real-time application a contouring operation and an averaging approach can also be utilized effectively.     

Dispersion of phosphovanadates on silica gel chemically modified with silane coupling agents having an amino group and their catalytic activities for methanol oxidation

Phosphotetradecavanadate (PV14) was dispersed on a silica gel chemically modified with a silane coupling agent (AnPS-SiO₂) by an equilibrium adsorption method. The PV14 contents approximately correlated with the V(IV) spin contents by ESR. PV14 dispersed on AnPS-SiO₂ resulted in a quite high selectivity for formaldehyde such as 97% in methanol oxidation.     

Fabrication of Zirconia-Nickel Functionally Gradient Materials by Slip Casting and Pressureless-Sintering

A powder processing technique has been developed for the fabrication of tetragonal zirconia-nickel functionally gradient materials using slip casting and pressureless-sintering. Rheological behavior of slips was studied. Single-layer zirconia-nickel green compacts with various zirconia/nickel volume ratios were characterized by permeability and pore radius. A multilayer zirconia-nickel green compacts with a stepwise compositional gradient was formed and sintered in argon atmosphere. One of the keys to successful fabrication was to minimize differences in permeability and pore radius between neighbouring layers in a multilayer green compact to avoid fracture during drying in an ambient atmosphere.