A Post-Processing Method for Control Rod Worth Measurements at Oconee Nuclear Station

摘要

In recent cycles, all three units at the Oconee Nuclear Station have experienced large percent differences between their zero power physics test (ZPPT) control rod worth measurements and predicted rod worths. Individual rod groups acceptance criteria is ±15.0%. One cycle-Unit 2 Cycle 22-exceeded total rod worth acceptance criteria of ±10.0%. Consequently, a root cause investigation was initiated. An identified root cause is a constant voltage offset in the high gain bandpass filter (HGBF). Signals from the excore fission chamber detectors are processed through the HGBF, then sent to the reactimeter. However, the voltage offset causes the HGBF to pass an inappropriate signal to the reactimeter. The true signal is the sum of the inappropriate voltage and the voltage offset. The offset has not been constant over previous cycles. This report shows that post-processing methods which correct ZPPT data for the voltage offset cause a decrease in the measured-to-predicted control rod worth percent difference. Post-processing trends across cycles are used to predict the initial HGBF calibration voltage for Oconee Unit 1 Cycle 24.