XEDOR evaluation of PCI fuel failure risk due to loss of feedwater heating in boiling water reactors

XEDOR is a reduced order model that was developed as a maneuvering tool for preventing PCI failures of fuel rods. The model calculates cladding stress and related parameters such as the maximum allowable linear heat generation rate and fuel conditioning state for every rod at every node of a reactor core. This capability was used to investigate the risk for widespread PCI type fuel failure in the case of anticipated power transients that may ramp a large number of fuel rods such as a loss of feedwater heating incident in a BWR. More specifically, the exercise focused on the effect of a power uprate on the risk of PCI under a power ramp associated with loss of feedwater heating. Detailed stress surveys with XEDOR were performed on two equilibrium cycle designs, one with the originally licensed rated power and the other using the uprated power. No significant change of PCI risk was calculated due to power uprate. However, the analysis indicates elevated PCI risk due to unintended power ramping immediately following the completion of control rod sequence exchange maneuvers unless the transient is detected and terminated by operator action