Study of rewetting and quench phenomena by single pin out-of-pile experiments, with special emphasis on the effect of pin composition

A series of comparative experiments with single electrically heated fuel pin simulators of different compositions is performed under identical boundary conditions simulating emergency core cooling by reflooding. Three types of pins are used. A hollow tube heated directly by Joule heating, an indirectly heated rod with an internal heater and the space between the heater and the cladding filled with aluminaoxide powder, and finally another indirectly heated rod with the space filled with UO2 ring pellets, simulating very closely a real fuel rod. The pins are tested in the same test rig. The outer dimensions of the pins are identical for all three pins, 12 mm diameter and a heated length of 4 m. The pins are placled in a circular shroud with an internal diameter of 22 mm, leaving an annular space of a width of 5 mm for the coolant flow. The shroud can be heated to simulate an array of surrounding pins and to avoid cold wall effects. The test paramters are: initial temperature 600-8000C, liquid flow rate at the inlet 1-10 cm/s, system pressure 1-10 bar. The experimental results have been compared to calculations with the computer code NORCOOL-II. A rather good agreement have been achieved between experiments and calculations for a wide range of parameters (rod composition, flow rate, system pressure)