Design of CANDU Regional Overpower Protection Fluxshapes Reclassification Scheme

The Regional Overpower Protection（ROP） system is designed to prevent the dryout in any fuel channel of CANDU reactors during a slow loss of regulation（LOR） event. Reactor aging will lead to the reduction of ROP margin. To resolve the deficiency of ROP margin in Third Qinshan Nuclear Power Plant（TQNPP）, four reclassification rules are determined based on review of original ROP fluxshapes classification principle, operational documentation and policy of TQNPP, reactivity device configuration and existing DCC alarms. ZDROP alarm for monitoring axially averaged zone deviation is also developed and installed. Totally 270 fluxshapes are removed outside of ROP normal position HSP#1. The implementation of ROP reclassification scheme in TQNPP indicates nearly 3% to 5% ROP margin can be restored and additionally the economy and safety of reactor will be improved.