Fuel Cycle Extension by Part-Length Control Rod Removal at Rancho Seco

Abstract

The Babcock and Wilcox Company (B&W) normally uses part-length axial power shaping rods (APSRs) for core axial power distribution control. The development and implementation by B&W and the Sacramento Municipal Utility District of a procedure for extending cycle length by removing the APSRs at the end of cycle 3 of Rancho Seco Nuclear Generating Station is explained. Increased core reactivity and hence greater cycle length were successfully achieved. Neither the reactor protection system nor normal operating limits were violated during the APSR withdrawal procedure. Further, pellet-cladding interaction was avoided, and primary coolant feedand bleed requirements were within the capacity of the plant evaporators. During the 22 h at less than full power, the average capacity factor was 81.1%, a reasonable tradeoff in light of the extension of cycle 3 by 10 effective full-power days (EFPDs). Successive use of this technique over following cycles yields average gains of 5 EFPDs per cycle.