None. Firstly 8x8 fuel was phased out starting around 1990 with the introduction of 9x9 fuel, and more recently, BWR 10x10 fuel designs have been introduced. The earliest 8x8 assembly had no water rods. In the late 70's and early 80's, BWR vendors introduced 8x8-1, then 8x8-2, and in the case of GNF and AREVA, during early to mid-80's, to 8x8-4 designs. ABB switched from 8x8 (SVEA-64) to 10x10 (SVEA-100, then SVEA-96) in the mid 90's while GNF and AREVA went to 9x9 designs, then 10x10 designs.
There are water rods/channels/crosses in BWR assembies, not guide tubes or instrument tubes. The objective is increased moderation in the interior fuel rods of the assembly.
GNF uses two water rods in their 10x10 designs, AREVA uses a water box (square channel) in their ATRIUM-10 designs, and Toshiba/Westinghouse (formerly ABB) uses a water cross or four-armed cruciform water channel with a square (diamond) channel in the center.
The BWR control elements are external to the assembly. Four assemblies surround one control rod (control rod blade (CRB) or control blade). Incore instruments are located at the corners of core cells (each cell representing 4 assemblies surrounding one CRB).
Please refer to: