Sensitivity analyses on reflooding effect on the TMI-2 accident by the SCDAP code

Sensitivity analyses were performed in order to investigate the effect of reflooding on the hydrogen generation and temperature rise of the fuel cladding due to Zr-water reaction. The sensitivity analyses were conducted for the TMI-2 accident assuming that the reflooding was initiated by an operator action between 100 and 174 minutes after the accident initiation. The following conclusions were obtained from the present sensitivity analyses. (1) There is a possibility of temperature rise of cladding in the upper part of the core during the reflooding as was observed in the CORA-12 experiment at KfK, in the case when the reflooding was assumed to be initiated in the TMI-2 accident by an operator action during 100∼174 minutes after the accident initiation. (2) Reflooding of degraded core could result in hydrogen generation and temperature rise of the upper fuel cladding in the case that the core condition before reflooding was under steam starvation, temperature of the remaining unoxidized Zr was at about 1500 K and the reflooding was slow. (3) For accident management of severe accident, the relationship between hydrogen generation, initiation timing and rate of reflooding should be taken into account. (J.P.N.)