Channel - control blade interference in GE boiling water reactor, D-lattice plants with zircaloy-2 channels

This paper provides a summary of the operational experience of Zircaloy-2 channels at three GE BWR D-Lattice plants that experienced channel control-blade interference between 2007 and 2009. Prior to 2007, observations of channel interference were limited to S-Lattice and C-Lattice plants where the channel-to-blade gap is ∼40% and ∼15% smaller, respectively, than in D-lattice plants. The observations were made when control rods failed to settle into the fully inserted location during a shutdown or sequence exchange at Monticello on January 20, 2007, at Brunswick 2 on November 8, 2008 and at Peach Bottom 3 on January 21, 2009. Poolside exams of channels after discharge confirmed that the observations were a result of excessive channel distortion that was linked to shadow corrosion-induced bow, which appears to become more variable as ECBE and exposure increase. In addition, Peach Bottom 3 successfully used the LaSalle channel management strategy that involves inserting control rods to decrease the level of friction in cells with interference.