May-June 2019 NPJ

Nuclear Plant Journal, May-June 2019 NuclearPlantJournal.com 31 operation for a number of reactors. A primary concern during load follow is maintaining fuel integrity as rapid changes in local power, cycled many times over during operation, can result in fuel rod stresses leading to fuel failure. CASL has developed modeling capabilities through the PCI challenge problem to assess the risk of such failures during load follow operation. Novel applications of VERA envisioned by industry end users, unimagined a few years ago, have also become a reality. A recent example is the use of VERA to analyze secondary source signal strength as seen by the source range detectors during refueling. For this application, secondary sources are important during the fuel reload shuffle sequence as the means to amplify the signal coming from the fuel in order to detect a fuel misloading. A fuel misloading has a high consequence for outage delays and reactor downtime. Validation of VERA showed excellent agreement between measured and predicted signal data. The ability of VERA to model with high accuracy the coupled in-core and ex-core problem during the refueling sequence reinforces the adoption of VERA as a reactor digital twin capable of analyzing the core and fuel behavior over a wide range of conditions. Figure 2. (Continued on page 46)