a reactivity insertion accident, the temperature and the pressure
rapidly increase inside the rod and can lead to the rupture of the clad
and the ejection of fuel toward the coolant. Since the fuel could be
finely fragmented, the thermal interaction between fuel and coolant
(FCI) could create a pressure wave as well as a large vapor volume.
Safety-related consequences of the FCI may be related to both phenomena.
experimental studies concerning such a RIA related FCI are in-pile
experiments in thermal hydraulics conditions that differ from PWR
conditions. Therefore validation of a simulation tool from these data
and extrapolation to reactors conditions is subject to uncertainties.
experimental study is devoted to the violent thermal interaction
between a hot material and a fluid. An experimental bench has been
designed. It is mainly a cylindrical tube, where the interaction takes
place, connected to a larger vessel as a compressibility tank. To reduce
the required level of energy as well as temperature and pressure
conditions, liquid carbon dioxide has been chosen to simulate water in
PWR conditions. Respect of thermodynamics similarity criteria allows to
lower pressure by a factor 3 and energy per unit mass fluid by a factor
5. To produce the energy pulse, a tungsten wire is heated by Joule
effect from the discharge of a 27 mF capacity. Design of the tank
allows for a relatively long mechanical relaxation of the coolant with
regards to the heat transfer kinetics.
pressure wave is recorded thanks to four dynamic pressure sensors along
the tube. Two dual tip fiber optical probes allow characterizing the
kinetics of vapor formation near the wire. The data acquisition system
operates with a required frequency of the MHz range.
test bench allows to record the local behavior of the fluid such as the
pressurization of the liquid. A very clear pressure wave have been
recorded just after weak energy pulse around 0.2 kJ. The influence of
some major parameters on these quantities have been studied. For
example, the liquid level in the tank is increased between two tests up
to be totally full, so, the influence of the compressibility is
highlighted. Also, three different wire diameters have been used to
modify the heat transfer kinetics. Finally, several intensities of the
energy pulse have been considered. All these studies hel p to im prove
the understanding on the thermal interaction potentially involved in the
nuclear reactor safety context.