Papers by Keyword: Uranium Oxide

Abstract: To study the fuel debris treatment at Fukushima Daiichi NPP, information on the behaviour of fuel and structural materials in severely damaged reactors, i.e., oxides and metals of uranium and zirconium is essential. Since sea water was introduced to the reactors, situation of fuel debris became different from that for TMI case. In this paper, phase relations of uranium and zirconium oxides were analyzed by powder XRD method at high temperatures. By the heat-treatment of the mixture of UO₂ and ZrO₂ (U:Zr=1:1) under 10 torr air, UO₂ was oxidized to U₃O₈ over 800 ^oC, The UO₂ like phase appeared again at 1350 ^oC which may be caused by the decomposition of U₃O₈. The oxidation behavior of the UO₂-ZrO₂ system was also investigated by using solid solution sample with different U/Zr ratios under different steam and oxygen pressures. The oxidation of the UO₂-ZrO₂ mixture seemed to be suppressed with decreasing U/Zr ratio. The behavior of fuel materials in the presence of seawater was also discussed as well as that for other structural materials.

Abstract: Several samples of (U,Nd)O₂ with different Nd content (ranging from 2 to 50 in Nd₂O₃ mass. %) were prepared. For composition ranging from 6 to 20 in Nd₂O₃ mass %, two crystalline phases are unambiguously evidenced by X-ray and neutron diffraction, by optical microscopy, and by SEM-EDX and EPMA. The influence of the preparation route on the distribution of the domains made by these two phases is evidenced and discussed.

Abstract: The ceramics fuel of UO2, irradiated in power reactors, has restructuring at high burnup, around 70MWd/kgU, which is near in the scope of future fuel utilization with improving economy. The original grains are divided into sub-grains of 100 nm scale and segregation of fission gas (Xe, Kr) grows bubbles resulting in volumetric swelling of the fuel. This restructuring was investigated in the field of nuclear engineering of power reactor fuel industry. This presentation briefly provides observations of this restructuring and some of engineering consequences. In a mechanism study a new approach, combing accelerator irradiation and computational science has been started and some of initial results are presented.