Gd burnable poison system for reactivity control of the first cycle of a PWR

Abstract

The reactivity control of a PWR core may be performed by a system of burnable poison (BP) rods. In such a case, the soluble B system may be eliminated and the BP rods will be responsible for the excess reactivity provided for fuel depletion and fission products accumulation. A strong negative moderator temperature coefficient is a desirable safety feature, inherent to a poison-free moderator. The design objective of a PWR core controlled completely by a system of BP rods is achieved by utilization of Gd as the poison material and annular geometry of a BP rod. The proposed concept is tested as a retrofittable option for the current generation, as well as new PWR plants. A plausible incore fuel-management scheme is demonstrated, with planar power distribution, close to an acceptable range. The fuel-cycle penalty due to the residual poison content at EOC is relatively small.