| 摘要 |
PURPOSE:To enable decrement of void reactivity coefficient without changing water-to-fuel-volume-ratio by making an arrangement of fuel rods and water rods to be of a triangular grid shape by making a rods number ratio of the water rods to a total rods number to be more than 10%. CONSTITUTION:Fuel rods 3 are arranged in a shape of a regular triangle grid in a square channel box CB1. In this case, when a vertical arrangement pitch of the fuel rods 3 is (a), a horizontal arrangement pitch becomes 3<1/2> a/2 = 0.87a. Accordingly, when a ratio of the vertical and horizontal rods numbers is made to be an integer of around 1 to 0.87, the arrangement shape is made to be of an almost square shape and the fuel rods are arranged in the shape of triangular grid shape, the fuel rods 3 can be very effectively arranged. In this occasion, a column number in case of 10 rows becomes 10divided by 0.87 = 11.49, that is, 11 columns, and therewith a moderator flow area can be reduced by around 5%. Also, when number ratio of the water rods WL2 is made to more than 10%, fuel assembly can be intended to be much more enriched. In this case, the WL2 have to be arranged so that moderator and fuel in the fuel assembly may be much evenly distributed.
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