Patent Number: 
Section: claims

1. A method of operating a nuclear fission reactor core, the method comprising:providing a plurality of modules of fissile nuclear fission fuel material and a plurality of modules of fertile nuclear fission fuel material in a nuclear fission reactor core;providing reactor coolant to the nuclear fission reactor core;establishing a region of maximized reactivity by initiating a nuclear fission deflagration wave within at least one of the plurality of modules of fissile nuclear fission fuel material;propagating the region of maximized reactivity by propagating the nuclear fission deflagration wave through at least one of the plurality of modules of fertile nuclear fission fuel material;controlling reactivity responsive to change in thermal power demanded from the nuclear fission reactor core during propagation of the region of maximized reactivity; andafter propagating the region of maximized reactivity through at least one of the plurality of modules of fertile nuclear fission fuel material, removing from the nuclear fission reactor core at least a portion of the fertile nuclear fission fuel material through which the region of maximized reactivity has propagated. 2. The method of claim 1, wherein the region of maximized reactivity and the plurality of modules of fertile nuclear fission fuel material are moved relative to each other. 3. The method of claim 2, wherein:the modules of nuclear fission fuel material are stationary; andthe region of maximized reactivity propagates through the modules of nuclear fission fuel material.