AbstractIn the seed-blanket core concept, the major portion of the core power is typically produced in subcritical regions known as“blankets.”The small supercritical regions that drive the blankets are known as“seeds.”The concept lends itself to geometry control in which moving the seeds varies the leakage of neutrons into fertile material, thus avoiding the loss of neutrons to parasitic control devices. As a burner, the seed-blanket concept has significant advantages in the reduction of initial fuel loading and improvement in resource utilization.As a breeder, the seed-blanket concept has further advantages in making it feasible to obtain negative void and moderator reactivity coefficients. A summary is presented of recent studies of the application of the seed-blanket core concept with both heavy water and light water moderation.