Experimental Investigations on Heat Transfer in Transient Boiling

During reactivity initiated accidents in a core of a nuclear reactor, a power excursion occurs on some fuel rods. The consequent rapid boiling is a matter of study for the nuclear power plants safety evaluation, because of the risk for rod-clad failure. In order to better understand the influence of power excursions and to characterise the phases of the rapid boiling phenomenon, an experimental set-up has been built at the Institut de Mécanique des Fluides de Toulouse (IMFT). The test section is a semi annulus. The inner half cylinder is made of a stainless steel foil, heated by Joule effect. Its temperature is measured by an infrared camera filming the backside of the foil, coupled with a high speed camera for the visualization of the phenomena. Measurements were made when a square current signal is applied to the foil. They showed the influence of the supplied power and of the wall temperature increase rate during boiling.