Analysis of superheated wall effects during refill at small scale. [PWR]

A semi-empirical analysis is presented to calculate the timing and rate of delivery of emergency core coolant (ECC) to the lower plenum of a pressurized water reactor. Emphasis is given to the physical process of ECC bypass by upward flowing steam in the reactor downcomer and the amplification of this effect by steam produced at the superheated vessel walls. The analysis is successfully compared with over 350 tests at 1/15 scale. Sensitivity studies are reported which quantify modeling uncertainties and display the strengths and weaknesses of the analysis.