[en] This report describes the conceptual design of an LWBR based on the technology developed for the Shippingport LWBR. Control of power changes is provided by a neutron-economic system made up of movable and fixed thoria-fueled control rods. These thoria control rods are similar in design to the poison control rods currently used in commercial pressurized water reactors. Poison control rods are also included in the concept for hot and emergency shutdown. The poison rods are completely withdrawn from the core during normal operation. The core is housed in a 256 in. inside diameter pressure vessel, and has a three year lifetime. Annual fuel management, when one-third of the fuel modules are replaced, has been assumed