Abstract: Disclosed is a zirconium alloy material having high corrosion resistance regardless of thermal history during its manufacturing process. The zirconium alloy material is obtained by providing a zirconium alloy containing on the mass basis: 0.001% to 1.9% of Sn, 0.01% to 0.3% of Fe, 0.01% to 0.3% of Cr, 0.001% to 0.3% of Ni, 0.001% to 3.0% of Nb, 0.027% or less of C, 0.025% or less of N, 4.5% or less of Hf and 0.16% or less of O with the remainder being inevitable impurities and zirconium, being formed of a bulk alloy and a surface layer, in which the surface layer has a plastic strain of 3 or more or a Vickers hardness of 260 HV or more and an arithmetic mean surface roughness Ra of 0.2 ?m or less.

Abstract: Disclosed is a zirconium alloy material having high corrosion resistance regardless of thermal history during its manufacturing process. The zirconium alloy material is obtained by providing a zirconium alloy containing on the mass basis: 0.001% to 1.9% of Sn, 0.01% to 0.3% of Fe, 0.01% to 0.3% of Cr, 0.001% to 0.3% of Ni, 0.001% to 3.0% of Nb, 0.027% or less of C, 0.025% or less of N, 4.5% or less of Hf and 0.16% or less of O with the remainder being inevitable impurities and zirconium, being formed of a bulk alloy and a surface layer, in which the surface layer has a plastic strain of 3 or more or a Vickers hardness of 260 HV or more and an arithmetic mean surface roughness Ra of 0.2 ?m or less.

Abstract: A method for monitoring the performance of internal pumps in a plant in which a coolant is driven through plural internal pumps, said method comprising measuring the pump motor power input to the motor driving said pump; estimating the power input to said pump motor during a test performed outside said plant corresponding to the pump speed and the pump flow measured within said plant; computing a pump motor input power ratio based on said measured value and said estimated value; and detecting the variation in the performance of said internal pumps.

Abstract: A method for monitoring the performance of internal pumps in a plant in which a coolant is driven through plural internal pumps, said method comprising measuring the pump motor power input to the motor driving said pump; estimating the power input to said pump motor during a test performed outside said plant corresponding to the pump speed and the pump flow measured within said plant; computing a pump motor input power ratio based on said measured value and said estimated value; and detecting the variation in the performance of said internal pumps.

Abstract: A fuel assembly and a reactor core using same which are able to increase size of the fuel assembly with ensuring thermal margin and reactor shut down margin.A distance between centers of adjacent fuel assemblies is about 23 cm, which is enlarged about 1.5 times of conventional fuel assemblies. A thickness of water gap region is about 16 cm, which is relatively thinner than that of prior art. While, H/U ratio is about 5 as same as that of the prior art, and decreasing amount of non-boiling water in the water gap region is arranged in a channel box as water rods. Consequently, a ratio of transversal cross section area of the water rods to transversal cross section area of the fuel rods becomes about 0.6, and local power peaking factor can be decreased and thermal margin can be increased. Further, the transversal cross section area of the water rod is selected to be 15 cm.sup.2 so as to ensure the reactor shut down margin by reducing excess reactivity.

Abstract: A mean uranium enrichment of fuel rods is set to not less than 4 wt% and preferably 4.25%, a percentage in number of Gd rods to all the fuel rods is set in the range of 20 to 30% and preferably 23%, and an enrichment 4.45 wt% of the Gd rods is between a pellet maximum uranium enrichment and a pellet minimum uranium enrichment. A percentage in number of those fuel rods having a maximum uranium enrichment of 5.0% to all the fuel rods except the Gd rods is set to not less than 75% and preferably 82%. A mean uranium enrichment in the enriched fuel section except blanket regions at upper and lower end portions is 4.75 wt% and a ratio e.sub.max /e.sub.mean of the pellet maximum uranium enrichment to that mean uranium enrichment is not larger than 1.16 and preferably 1.105. Accordingly, when the maximum uranium enrichment is limited to 5.0 wt%, the mean uranium enrichment can be raised to attain mean discharged exposure not less than 45 GWd/t without causing any problems in gadolinia containing fuel rods.

Abstract: When a spatial distribution of a physical quantity to be displayed is given, a value range showing the three-dimensionally distributed physical quantity is divided into a plurality of small value ranges to obtain the distribution of the spatial positions where the physical quantity has the value equal to that in the small value range for every small value range to display the physical quantity, and to repeat the operation by successively changing the small value range.

Abstract: The fuel assembly has fuel arrangement of a square lattice of 10 lines by 10 rows. Four water rods having a large diameter are arranged in central region of horizontal cross section wherein arrangement of 12 fuel rods is possible. The four water rods having a large diameter are so arranged adjacently in a circle as to form an internal between each other. First coolant flow path which is extended toward axial direction is formed by surrounded with the water rods having a large diameter. The first coolant flow path leads to third coolant flow path which is formed around the fuel rods through second coolant flow path which is the interval between the water rods having a large diameter.The fuel assembly is able to optimize the moderator to fuel atom number density ratio and to reduce the pressure loss because a portion to be an excessively moderated region is utilized as the first coolant flow path.