| 摘要 |
PROBLEM TO BE SOLVED: To further improve fuel integrity by improving thermal margin and reactor shut down margin by positioning the upper edge of the effective part of a fuel rod of short length to a specific height or less of the longest effective part out of a fuel rod of long length. SOLUTION: In a fuel assembly 1, a fuel rod of long length 2, a fuel rod of short length 3, and a large-diameter water rod 6 are fixed to an upper tie plate 4 and a lower tie plate 5 as a bundle of fuel rods by bundling them in a tetragonal lattice by a spacer 8, and a bundle of fuel rods is surrounded by a channel box 7. The upper edge of the fuel rod of the fuel rod of short length 3 is located near 13/24 and the upper edge of the effective length of the fuel rod of short length 3 is located at 12/24 of the effective length of the fuel rod of long length 3. Also, eight spacers 8 are provided and a spacer gap L2 at the upper part of an area near the upper edge of the fuel rod of short length 3 is arranged shorter than a spacer gap L1 at a lower part, thus improving the marginal output characteristics of the upper part of the fuel assembly, at the same time minimizing the peak of neutron flUx while a reactor is in shut down state and improving a reactor shut down margin drastically. |
