Abstract
Axial and lateral pressure loss in a 5 × 5 rod–bundle with a split-type mixing vane spacer grid was experimentally measured using differential pressure transmitters at different sub-channel Reynolds numbers (Re) and orienting angles. The geometrical parameters of the 5 × 5–rod bundle are as follows: they have the same diameter (D = 9.5 mm) and pitch (p = 12.6 mm) as those of real fuel rods of a typical pressurized water reactor (PWR), with a sub-channel hydraulic diameter (Dh) of 11.78 mm. The characteristics and resistance models of pressure loss are discussed. The main axial pressure loss is caused by the spacer grid, and the spacer grid generates additional wall friction pressure loss downstream of the spacer grid. The lateral pressure loss shows strong correlations with orienting angles and distance from the spacer grid. The lateral pressure loss shows a sudden burst in the mixing vanes region and a slight augmentation at z = 3Dh. After 3Dh, the lateral pressure loss decays in an exponential way with distance from the spacer grid, and it becomes constant quickly at z = 20Dh.
Highlights
The mixing vane spacer grids in the fuel assembly of a pressurized water reactor (PWR) highly enhance cross-flow, turbulent mixing, and heat transfer in fuel assembly, improving the departure from nucleate boiling (DNB) conditions in PWRs
Axial and lateral pressure loss in the central inner sub-channels of the 5 × 5–rod bundle were measured from z −20Dh to z 20Dh and from θ −90° to θ 90° under conditions of the Reynolds number from 6,600 to 66,000
When the flow is fully developed upstream of the spacer grid, the wall friction is the main reason of axial pressure loss, which is a decreasing power function of the Reynolds number
Summary
The mixing vane spacer grids in the fuel assembly of a pressurized water reactor (PWR) highly enhance cross-flow, turbulent mixing, and heat transfer in fuel assembly, improving the departure from nucleate boiling (DNB) conditions in PWRs. The impulse pipes are fixed on the channel wall of the rod bundle, which is not the locally axial pressure loss in sub-channels. To measure the pressure loss orienting to different angles, an SUS304 angle dial plate of 63.5 mm FIGURE 5 | Friction factor in the bared rod bundle. 7 and 11 was measured using a YOKOGAWA differential pressure transmitter (EJA110E) (range 5 kPa, accuracy 0.065%) for FIGURE 6 | Spacer grid resistance models. The central impulse pipe can be turned to face a different angle θ ranging from −90° to 90° By this procedure, the lateral pressure loss around the central impulse pipe at different distances from the spacer grid can be measured. The pressure loss is an averaged pressure loss based on a sample size of 1,000 samples at 10 Hz of sample frequency
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