Individual assembly powers of a spectral shift controlled reactor

The relative powers achieved by individual fuel assemblies in the core of a spectral shift controlled reactor (SSCR) is a very important consideration, especially in the heterogeneous moderator control mode and/or when there are an unequal number of fuel pins per assembly. Also, during the cycle, as water is introduced to provide positive reactivity in compensation for fuel depletion and fission product buildup, the power peaking must be monitored to ensure that it does not exceed its design limit. The algorithms presented have been incorporated in the RPM program, which can be used to compute beginning-of-cycle (BOC) and end-of-cycle (EOC) core power profiles. A modified version has been developed and used for SSCR analysis. The changes enable the program to handle the V/sub f//V/sub m/ variation and an unequal number of fuel rods per assembly. The revised-version RPM modifications are described. Although convergence problems were experienced in the modified RPM runs for such cores, the results are considered sufficiently reliable to permit the following observations: from the core maps, assembly powers are controlled as well or better than in conventional pressurized water reactor cores with respect to power peaking at both BOC and EOC and the evolution from BOC to EOC