Evaluation of Fuel Assembly Bow Penalty Peaking Factors for Ringhals 3 : Based on a Cycle Specific Core Water Gap Distribution

Sammanfattning: In recent years, fuel assembly bow in Ringhals 3 has started to increase again after lower levels of bow. Normally, the fuel assemblies are straight axially. One of the consequences of fuel assembly bow is perturbed power distribution across the core, resulting in smaller margins of safety during operation. A way of ensuring safe operation is add-on margins, penalties, dependent on bow amplitude, added to the power peaking factors. A new method of producing these penalties, based on realistic water gap distribution derived from measurements, was used. By comparing the new penalties with the currently used penalties, the currently used penalties were concluded to be around 10 percent smaller for both FdH, the radial power peaking factor penalty, and FQ, the local power peaking factor penalty. The currently used penalties hence are significantly lower. However, the conclusion should be seen as an indication, rather than directly implementable, since there is potential to evolve the method further and eliminate sources of error.