section as shown in fig1 or extend to the complete end an inspection hole 55 fig1 is used to visually verify proper placement of the neutron absorber material also it will be noted that each alternate cell on the module periphery is closed by a panel 58 fig4 which extends the cell complete length to form a spent fuel rack all the l shaped sections are assembled into cells as described above and with this construction the interior of each cell other than those cells located on the module periphery is bounded by walls having neutron absorbing material located either on the inside or the outside walls of a particular cell since the corner cells of the module do not require neutron absorbing material on its outside walls the l shaped sections 56 located at the corners comprise only stainless steel plate having their longitudinal edges welded to adjacent l shaped sections on the module when thus welded each corner cell is then of a size and configuration to accept a fuel assembly fig4 6 illustrate how the l shaped sections are welded together to form cells variations in the characteristics of the stainless steel material after being exposed to varying temperatures and stresses during the manufacturing process produces slight distortion in the material such that the l section longitudinal edges do not always fall in a vertical plane usually the longitudinal edges can be welded along their complete length as shown in fig5 and 6 wherein weld 2 metallurgically joins adjacent l shaped sections 34 in the event the adjacent l sections of adjacent cells to be joined are spaced a distance greater than that which can be bridged by a single weld such as weld 63 0 18 inch spacer wire 68 shown in fig5 is welded in.