Pickering NGS B - Unit 6 strategy to remove fuel defects during operation at high power

Unit 6 was operating at high power (100% FP) with all the adjuster rods (AAs) in core when Chemistry sample results of HTS I-131 activity increased from 1.65 μCi/kg (base line) to 5.4 μCi/kg. Sustained elevated activity levels and subsequently numerous significant spikes have lead to the conclusion that the Unit 6 core contains defected fuel bundles. 34 channels have been identified by Reactor Physics, as possible locations containing defective fuel bundles. Reactor Physics has developed a set of criteria, to be used in prioritizing the sequence of channel re-fuelling and defect removal. The refuelling strategy was successfully implemented in February 2009, all the suspect channels were twice fuelled and any potential defected fuel bundle was discharged by end of summer 2009. (author)