At the end of cycle 1, 64 of the 65 assemblies of lot 1 (called lot 1A) are removed. One of the 1GC assemblies (called lot IB) that had the lowest bumup of the lot 1 group is moved to the central AA position. Residual burnable poison is removed from the remaining lot 2 and lot 3 assemblies, which are shifted to the new positions shown in Fig. 3.21. Sixty-four new assemblies (called lot 4), enriched to 3.2 w/o 235 U and containing no burnable poison, are placed in the positions with heavy borders in this figure. This placement of assemblies was

Center*

line

Assembly Number BOC Burnup, MWd/MT EOC Burnup, MWd/MT BOC Relative Power (Assembly/Average)

Figure 3.20 PWR, assembly power and bumup distribution, cycle 1.

found by Rieck [Rl] to lead to an acceptably low maximum peak-to-average assembly power ratio of 1.34 in assemblies 4DG and 4GD. The burnup at the beginning of cycle 2 is shown in the second row of each square, and the bumup at the end in the third row. The total thermal energy produced in the second cycle is 835.2 GWd, or 20,044 X 106 kWh. At the end of cycle 2, assembly 1GC (called sublot IB) and all assemblies from lot 2 except 2FE (called sublot 2A) are removed.