control however is not different from the prior art the lower overll reactivity worth reduces power peaking and serves to flatten the power distribution axially and radially within the core the lower reactivity worth of the control rod cluster allows the fuel assemblies associated with the control rod clusters when the control rod cluster is inserted within the fuel assembly to operate at a higher power output and since the overall power output of the core remains the same for any given power level of operation the remaining fuel assemblies may then operate at a lower individual power output another beneficial effect is realized since the hottest spot in the core will also operate at a lower power and temperature for a given peak hot spot relative power this in turn will allow the reactor to operate at a higher average power thereby increasing the power capacity of the reactor combinations other than that shown in fig1 are possible thus more or fewer stainless steel rods may be used also the relative reactivity worth between the stainless steel rods 14 and the absorber rods 15 may be decreased by decreasing the amount of absorber material in absorber rods 15 and or adding higher worth absorber material to the stainless steel rods such as for example by coating alloying or intermixing of stainless steel with absorber materials the main consideration as to how much the reactivity worth of the control rod cluster may be reduced is primarily controlled by the reactor shutdown margin constraints calculations have shown that the configuration in fig1 still provides an acceptable shutdown margin fig2 schematically depicts a cross section of a core of a four loop plant having.