摘要:
A fuel assembly included a plurality of fuel rods, fuel spacers for maintaining gaps between the fuel rods and a channel box. The channel box includes spacer support portions projecting inwardly from an inner surface of the channel box and supporting the fuel spacer in a transverse direction and creep deformation inhibition portions disposed at the lower end portion of the channel box and projecting inwardly. The distance between the spacer support portions disposed to oppose one another in a horizontal direction is smaller than the distance between the creep deformation inhibition portions opposing one another in the horizontal direction.
摘要:
An object of the present invention is to provide a boiling water reactor wherein two phase flow instability in a fuel assembly occurs scarcely.A bottom flow path is formed beneath a partition plate which is supported by control rod driving mechanism housings in a reactor pressure vessel, and coolant guide tubes which open beneath the partition plate stands perpendicularly on the partition plate. An upper end portion of the coolant guide tube is restrained at outer periphery by a fixing portion of a square grid, and a coolant entrance of a fuel assembly is connected through to the coolant guide tube.Pressure loss of the coolant decreases and flow instability of the coolant in the fuel assembly occurs scarcely, lowering of a critical power ratio at a pump trip can be suppressed.
摘要:
In a fuel assembly having fuel rods inserted into regularly arranged cells of a fuel spacer which keeps the fuel rods correctly spaced from one another and has spacer elements disposed in a plurality of stages in the longitudinal direction of the fuel rods, the fuel spacer comprises vanes formed on the cells in such a manner that each vane is bent from a cut formed in a part of the side wall of the cell. The vanes obliquely project into the corresponding spaces between adjacent fuel rods and allow a coolant flowing through the spaces and forming two-phase flows to generate swirling flows toward the fuel rods. The fuel spacer may alternatively comprise either thin-walled cylinders having built-in vanes or spiral vanes, which are fixed to the spacer that has not been subjected to any direct machining. Also disclosed is a fuel assembly provided with any of the above-described fuel spacers. The arrangement of the present invention enables, while assuring a sufficient strength for maintaining fuel rods in their correct position, the transfer of heat from the fuel rods to the coolant to be promoted so as to raise the allowable power level of the fuel assembly, and enables the void ratio to be lowered so as to increase the reactivity.
摘要:
A fuel assembly has a water rod which consists of a coolant ascending path and a coolant descending path, the coolant ascending path opening below a fuel support of a lower tie plate, the coolant descending path opening above the fuel support and adapted to guide downwardly the coolant that has flowed up the coolant ascending path to the upper portion of the water rod. The lateral cross section of the coolant ascending path is more than 25 times that of the coolant descending path.The nuclear reactor with these fuel assemblies loaded in the core is operated as follows. After startup of the reactor when the reactor power is low, all the control rods inserted in the core are withdrawn completely. Then, the reactor power is controlled by regulating a liquid level formed in the water rods. This reactor operation method prolongs the lifetime of the control rods, thereby reducing the number of times they have to be replaced.
摘要:
The lower end of each of a plurality of fuel rods is supported by a fuel supporting portion of a lower tie plate. The fuel supporting portion includes a plurality of second coolant paths for supplying a coolant from below the fuel supporting portion to a first coolant path defined above the fuel supporting portion and between the fuel rods. The total cross-sectional area of all the second coolant paths is smaller than the cross-sectional area of the first coolant path. A water rod disposed between the fuel rods each includes an ascending tube path having therein a coolant ascending path having a coolant inlet port opening to a region below the fuel supporting portion, for guiding upward the coolant supplied through the coolant inlet port, and a descending tube having therein a coolant descending path having a coolant delivery port opening to said first coolant path, for guiding downward the coolant guided by said coolant ascending path and discharging the coolant through the coolant delivery port to the first coolant path. The descending tube path is so disposed outside the ascending tube path as to define a gap, through which the coolant inside the first coolant path flows, between it and the ascending tube path.
摘要:
The lower end of each of a plurality of fuel rods is supported by a fuel supporting portion of a lower tie plate. The fuel supporting portion includes a plurality of second coolant paths for supplying a coolant from below the fuel supporting portion to a first coolant path defined above the fuel supporting portion and between the fuel rods. The total cross-sectional area of all the second coolant paths is smaller than the cross-sectional area of the first coolant path. A water rod disposed between the fuel rods each includes an ascending tube path having therein a coolant ascending path having a coolant inlet port opening to a region below the fuel supporting portion, for guiding upward the coolant supplied through the coolant inlet port, and a descending tube having therein a coolant descending path having a coolant delivery port opening to said first coolant path, for guiding downward the coolant guided by said coolant ascending path and discharging the coolant through the coolant delivery port to the first coolant path. The descending tube path is so disposed outside the ascending tube path as to define a gap, through which the coolant inside the first coolant path flows, between it and the ascending tube path.
摘要:
A fuel assembly in accordance with the present invention comprises a plurality of first fuel rods and a plurality of second fuel rods having a length shorter than a length of the first fuel rod, and these two kinds of fuel rods are arranged in a fuel rod array of 10 rows by 10 columns. Two water rods are arranged in regions capable of arranging 8 fuel rods. The second fuel rods are not arranged in the outermost tier of the fuel rod array. Which satisfies the following conditions, that is, B≧60 (Equation 1) 15≦n≦20(n: integer) (Equation 2) Awr/Ach≦0.149 (Equation 3) Lp/Lf≧11/24 (Equation 4) Awr/Ach≧(3.00×10−4×n2+6.00×10−4×n−1.2×10−2)×(Lp/Lf−1)+1.75×10−1 (Equation 5) Awr/Ach≦(8.63×10−4×n2−6.09×10−2×n+1.33×10−1)×(Lp/Lf−8.32×10−1) (Equation 6) where Awr is a total sum of horizontal sectional areas of said water rods, Ach is a horizontal sectional area of a coolant flow passage in a bottom portion of said fuel assembly, Lf is an effective fuel length of said first fuel rod, n is number of said second fuel rods, Lp is an effective length of said second fuel rod, and B (GWd/t) is an average burn-up.
摘要:
A fuel assembly is provided with a coolant ascending path for making coolant rise and a water rod having a coolant descending path for conducting the coolant.A ratio of a flow area in a coolant inlet port of the smallest in coolant ascending path 13 on the downstream side than large diameter tube portion 3E to a flow area of the largest in the axial direction of coolant ascending path 13 in large diameter tube portion 3E is set to be 0.2-20%.In the normal operation, the declination degree from the liquid level in the coolant ascending path, corresponding to the coolant flow rate of the liquid level formed in the coolant ascending path can be controlled. Further, at the time of the excess the change speed of the liquid level can also be controlled.
摘要:
A fuel assembly comprises a plurality of fuel rods, tie plates for holding both ends of these fuel rods, and spacers which support these fuel rods. The spacer comprises a plurality of cells into which the fuel rods are inserted respectively, the adjacent cells being joined to each other at axial ends thereof, whereby a space between these cells being held or retained, and a plurality of loop springs held respectively on the cells. Each of the loop springs has a pair of resilient members which are located within the pair of adjacent cells and which urge the fuel rods in a radial direction, and a pair of connections which connect axial ends of the resilient members to each other. Each of the connections have a passage through which coolant flows axially and which is defined by a closed peripheral wall. The closed peripheral wall is not uniform in thickness. The pair of adjacent cells have at axial end portions of peripheral walls openings for accommodating or receiving the connections of the loop spring.
摘要:
A second fuel rod positioned at each corner of a channel box and second fuel rods adjacent to the former are formed to have a smaller outer diameter than that of ordinary first fuel rods, so that a pitch between the second fuel rods is narrower than a pitch between the first fuel rods. Making the outer diameter of the second fuel rods smaller than that of the first fuel rods reduces the power per unit length of the second fuel rods. The narrower pitch between the second fuel rods than the pitch between the first fuel rods provides two effects. First, a unit lattice cell becomes so small as to avoid an increase in the H/U ratio. Secondly, a new moderator region is formed between the second fuel rods and the first fuel rods adjacent thereto, the moderator region acting to intensify thermal neutron flux around those first fuel rods. These two effects enable a further reduction in the power per unit length of the second fuel rods. As a result, a fuel assembly intended for higher burn-up can be realized by increasing enrichment, while suppressing an increase in the local power peaking factor at corners of the fuel assembly.