Neutron economic reactivity control system for light water reactors

The combination of a neutron reactivity control system and a light water pre-breeder/breeder reactor comprising:

• a reactor core having a stationary seed-blanket arrangement of a plurality of symmetrical, contiguous hexagonal shaped physics cell regions, each of said cell regions comprising:
• a hexagonal shaped inner fuel module including a hexagonal shaped inner blanket region of stationary blanket fuel rods containing thoria fuel pellets, said inner blanket region centrally positioned in said inner fuel module, and a hexagonal shaped, annular first seed region which surrounds said inner blanket region and which includes stationary seed fuel rods having a mixture of thoria and urania fuel pellets and the combination of a neutron reactivity control system and a light water pre-breeder/breeder reactor comprising:
• movable poison rods of neutron absorption materials which are used to shut down and control the reactor core and which are symmetrically arranged about said inner blanket region;
• and
• a hexagonal shaped, annular outer fuel module which is contigious to and arranged symmetrically about said first seed region of said inner fuel module, said outer fuel module including an outer annular periphal blanket region of stationary blanket fuel rods containing thoria fuel pellets which defines the outer periphery of said physics cell and an annular second seed region which is contiguous with and which surrounds said inner fuel module, said second seed region including stationary seed fuel rods having a mixture of thoria and urania fuel pellets, and a plurality of movable shim control rods containing thoria materials for controlling the reactivity of the reactor core.