Analysis of a PWR LBLOCA without SCRAM

We analyze a conservative recriticality, scenario to explore the potential risk of fuel damage during a large-break loss-of-coolant accident in a typical U.S. pressurized-water reactor. No SCRAM is assumed, and no credit is taken for injected boron in core neutronics calculations. Although the scenario is conservative, the analysis is best estimate, using TRAC- PF1/MOD2 to model the thermal-hydraulics, coupled with a three-dimensional, transient neutronic model of the core. The simulation can follow complex system interactions during the reflood, which influence the neutronic feedback in the core. In all cases examined, the return of cold water to the core is limited by increased steam production from a marginal (local) return to power. A quasi-steady state is established during low-pressure safety injection cooling in which sufficient core flow exists to maintain rod temperatures to well below the fuel damage limit, but insufficient total inventory is present to result in a full return to power.