Axially shaped channel and integral flow trippers

Abstract

An improved channel is disclosed which has a reduced average thickness in its upper portion. The lesser average thickness corresponds to a lower pressure difference acting on the channel sides, over the upper portion of the channel. The reduction in average thickness is accomplished by cutting flow trippers into the inner surface of the channel walls and/or cutting grooves into the outer surface of the channel. The axial variation of channel average thickness increases water volume adjacent to the upper part of the channel to provide increased neutron moderation, to minimize the steam void reactivity coefficient, and to provide a greater cold shutdown margin. The material removed to produce the flow trippers increases the cross-sectional area inside the channel and reduces pressure drop in the upper portion of the channel. The flow trippers divert water flowing on the channel walls to the fuel rods adjacent to the channel walls, permitting higher reactor power operation. The flow trippers also permit operation at lower flow rates.

What is claimed is: 
     
       1. A fuel assembly comprising a plurality of fuel rods positioned in spaced array by upper and lower tie-plates, an open ended flow channel surrounding said array for conducting coolant upward between a lower support plate having coolant communicated thereto to an upper support grid having a steam/water outlet communicated thereto, said flow channel surrounding said array for conducting coolant about said fuel rods; said open ended channel having a polygon shaped cross section with said channel constituting a closed conduit with flat side sections connected at corners to form said enclosed conduit; means separate from said channel for connecting said upper and lower tie-plates together and maintaining said fuel rods in spaced array independent of said flow channel, the improvement in said flow channel comprising tapered side walls, said tapered side walls extending from an average thick cross section adjacent said lower support plate to an average thin cross section adjacent said upper core grid whereby said channel is reduced in thickness adjacent said upper core grid to correspond with the reduced pressure adjacent said upper core grid. 
     
     
       2. The invention of claim 1 and wherein said channel includes an increased cross section for coolant flow at the upper end of said channel. 
     
     
       3. The invention of claim 1 and wherein said channel includes transverse grooves in its sides, said grooves being wider and/or more closely spaced in the upper part of the channel. 
     
     
       4. The invention of claim 1 and wherein said channel includes longitudinal grooves in its sides, said grooves being wider and/or deeper in the upper part of the channel. 
     
     
       5. The invention of claim 1 including corner sections to said channels, said corner sections being thicker than said side wall sections. 
     
     
       6. A fuel assembly comprising a plurality of fuel rods positioned in spaced array by upper and lower tie-plates, an open ended flow channel surrounding said array for conducting coolant upward between a lower support plate having coolant communicated thereto to an upper support grid having a steam/water outlet communicated thereto, said flow channel surrounding said array for conducting coolant about said fuel rod; said open ended channel having a polygon shaped cross section with said channel constituting a closed conduit with flat side sections connected at corners to form said enclosed conduit; means separate from said channel for connecting said upper and lower tie-plates together and maintaining said fuel rods in spaced array independent of said flow channel, the improvement in said flow channel comprising transverse grooves acting as flow trippers on the interior walls of said channel to trip water flow from a path adjacent the said side walls of said channel to and towards said fuel rods. 
     
     
       7. The invention of claim 6 and including transverse or longitudinal grooves between flow trippers. 
     
     
       8. The invention of claim 6 wherein the flow trippers are confined to the upper portion of the channel and including transverse or longitudinal grooves in the lower portion of the channel. 
     
     
       9. The invention of claim 6 and including corner sections to said channels, said corner sections being thicker than said side sections. 
     
     
       10. The invention of claim 6 and including corrugated side walls in the lower portion of said channel. .Iadd. 
     
     
       11.  The invention of claim 6 and including ramp shaped grooves configured in the inner surface of said channel over the upper portion of said channel, said grooves commencing from a large cross section of wall thickness at the bottom to smaller cross section of wall thickness at the top. .Iaddend. .Iadd. 
     
     
       12.  The invention of claim 6 and wherein the lower edges of said grooves have a taper to allow the water layer to flow smoothly along the wall of said channel and into said grooves. .Iaddend. .Iadd.13. The invention of claim 12 and wherein the taper is at an angle of less than 9°. .Iaddend. .Iadd.14. The invention of claim 6 and wherein the upper edges of said groove provides a sharp discontinuity in said channel wall thickness which forces water passing along said grooves to move away from the channel wall. .Iaddend.