| 摘要 |
PURPOSE: To improve pressure loss and to reduce neutron absorption while limiting the film boiling interval by setting the ratio between the spacing of center and the outside diameter of cladding tube in the range of 1.35-1.37. CONSTITUTION: A fuel pellet 8 has outside diameter D corresponding to conventional dimension of 8.02mm or 9.11mm. A cladding tube 6 has inside diameter d1 of 8.22mm or 9.30mm and also has conventional dimension. Especially, outside diameter da of the cladding tube 6 is selected at a small value of 9.36mm or 10.53mm. Spacing P of two adjacent center lines 4 of the same shape is set at 12.7mm-14.3mm. The ratio p/da between above mentioned spacing P of center line and the outside diameter da of cladding tube 6 is in the range of 1.35-1.37. In the invention, that ratio is set in the range of 1.357-1.358.
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