Abstract: A fuel assembly according to the present invention includes an end plug disposed on both upper and lower end portions of a fuel rod, and a tie plate that supports at least an upper portion of the end plug. The end plug includes a plurality of support protrusions on a surface of the end plug, and a closed-loop spring having a portion that is inserted through an opening portion formed in the end plug and is stored in a single space formed in the end plug, and a remaining portion protruding to the outside of the end plug. The end plug is supported by the plurality of support protrusions and the closed-loop spring in a state in which the plurality of support protrusions and the closed-loop spring are in contact with an inner wall of an insertion hole formed in the tie plate.

Abstract: In a fuel assembly, a plurality of fuel rods are arranged in an array of 10 rows and 10 columns in the cross section of the fuel assembly. A flow resistance member is disposed in a central portion in the cross section at upper end portions of partial length fuel rods which are a part of the fuel rods. In the flow resistance member, resistance members are each disposed between ferrules arranged in an array of 6 rows and 6 columns in the diagonal direction of the flow resistance member. Resistance members are each disposed between the ferrules in a peripheral portion of the flow resistance member. By disposing the resistance members, the pressure loss in an inner region in the cross section of the fuel assembly is increased, and the flow rate of a gas-liquid two-phase flow in an outer region surrounding the inner region is increased.

Abstract: In a fuel assembly, a plurality of fuel rods are arranged in an array of 10 rows and 10 columns in the cross section of the fuel assembly. A flow resistance member is disposed in a central portion in the cross section at upper end portions of partial length fuel rods which are a part of the fuel rods. In the flow resistance member, resistance members are each disposed between ferrules arranged in an array of 6 rows and 6 columns in the diagonal direction of the flow resistance member. Resistance members are each disposed between the ferrules in a peripheral portion of the flow resistance member. By disposing the resistance members, the pressure loss in an inner region in the cross section of the fuel assembly is increased, and the flow rate of a gas-liquid two-phase flow in an outer region surrounding the inner region is increased.

Abstract: A fuel assembly with a plurality of fuel rods, extending along a uniform direction, disposed inside a channel box assuming a quadrangular duct shape, wherein: the plurality of fuel rods that are disposed on sides of a plurality of hypothetical concentric quadrangles of various sizes with shapes similar to a cross-sectional shape of the channel box viewed from an end along which the fuel rods extend, and include at least outermost fuel rods disposed on the sides of a largest hypothetical concentric quadrangle among the hypothetical concentric quadrangles and second layer fuel rods disposed on the sides of a second largest hypothetical concentric quadrangle among the hypothetical concentric quadrangles; and the outermost fuel rods are disposed so that consecutive outermost fuel rods are set apart from each other over equal intervals which are greater than intervals setting apart consecutive fuel rods among the second layer fuel rods.

Abstract: A fuel assembly has a constitution in which plural fuel rods are arranged in 10 rows by 10 columns in a channel box, and includes plural fuel rods G containing gadolinium and plural partial length fuel rods P. In the fuel assembly, average enrichment of lower portion cross section is approximately 4.6 wt %, and average enrichment of upper portion cross section is approximately 4.7 wt %. The average enrichments at the outermost layer are approximately 5.6 wt % both in the upper portion and the lower portion. Ratios e/x of the average enrichment of the outermost layer e (wt %) to the average enrichment of the fuel assembly cross section x (wt %) are 1.19 in the upper portion and 1.22 in the lower portion, and the ratios satisfy equation (1). [ Equation ? ? 1 ] ? e x ? - 18.3 ? ( x 10 ) 5 + 68.766 ? ( x 10 ) 4 - 101.77 ? ( x 10 ) 3 + 74.428 ? ( x 10 ) 2 - 27.372 ? ( x 10 ) + 5.