Vibration of Rods Induced by Water in Parallel Flow

Abstract An experimental determination was made of the type and magnitude of vibration in the simulated fuel rods of a heterogeneous nuclear reactor with water flowing parallel to the rod axes. Triangular lattices with equivalent hydraulic diameters of 0.0708, 0.198, and 0.470 ft were studied at a single rod length. The test rods employed had a range of natural frequencies of vibration in water of 5 to 25 cycles per sec. This range was obtained by using ½ and ⅝-in-diam rods made of brass or aluminum, by making some rods hollow and others solid, and by using fixed and pin-ended support conditions. The water velocity was varied from 6 to 21 fps, at room temperature. It was found that the vibration can be significant for reactor conditions. The rod vibration was observed to be self-excited, resulting in the rods vibrating at their natural frequencies independent of the water velocity. A theoretical study of the forces acting on the rods was made from which it appears that ten variables (of which six were varied in these tests) influence the amplitude of vibration of the rod. A correlation was derived and the resulting equations give a good fit with the test data.