Answers from Seabrook
1) Surry uses IFBA fuel. Core modeling is performed using the CASMO-4/SIMULATE-3 computer codes. In making comparisons between measured and predicted boron concentrations (corrected for B-10, power, xenon, rod position, and RCS temperature), we notice a tendency to for the core models to underpredict the measured critical boron between 2 and 4 GWD/MTU by 10-20 ppm (about 80-160 pcm) more than at other times in life (such as at BOC equilibrium xenon or between MOC and EOC). Have you observed this tendency at your plant?
Core design is with ANC and we use IFBA. We always see measured boron above predicted for most of core life. Some attributed to B-10 depletion and some to modeling.
2) For the monthly reactivity anomaly calculation, is a B-10 corrected value used to meet Tech Spec requirements, or is the non-corrected value used? (Surry uses the non-corrected value)
We correct for B-10 depletion in the monthly reactivity balance surveillance, shutdown margin curves and ECPs.
3) Does your anomaly procedure have a threshold (such as +/-500 pcm) at which the anomaly would be documented in the corrective action system?
No threshold. Although if we saw something out of the ordinary we would propbably address it in CAPS.
Paul Gurney 603-773-7776