TRACE Analysis of a Loss of Alternating-Current Power Without Rod Insertion for the NuScale Power Module—I: Basic Event Progression and Long-Term Behavior

The U.S. Nuclear Regulatory Commission (NRC) staff often performs confirmatory analysis to support regulatory decision making. In the current work the TRAC/RELAP Advanced Computational Engine (TRACE) code was used to study the transient system response for the NuScale power module to a beyond-design-basis event where the control rods fail to insert. The regulatory purpose of the current work was to confirm the results of analyses provided by the applicant as part of their probabilistic risk assessment analysis that demonstrates that the core is not damaged under certain conditions when the control rods fail to insert. The NRC staff performed calculations using a TRACE model of the NuScale power module that includes both the primary and secondary systems that simulates a loss of alternating-current power and complete failure of the module protection system to insert control rods. The NRC staff analyses demonstrate that under these conditions the reactor stabilizes at a new stable condition with minor power and pressure oscillations where core power is balanced by passive heat removal.