Investigation of the transition from forced to natural convection in the research reactor Munich II

The new research reactor Munich II (FRM-II), which is under construction at the Technical University of Munich (TUM), Germany, makes use of a compact reactor core consisting of a single fuel element, which is assembled of two concentric pipes. Between the fuel element's inner and outer pipe 113 involutely bent fuel plates are placed rotationally symmetric, forming 113 cooling channels of a constant width of 2.2 mm. At the Department for Nuclear and New Energy Systems of the Ruhr-University of Bochum, Germany, a test facility has been built in order to confirm the concept of the decay heat removal in the FRM-II, to acquire data of single and two phase natural convection flows and to detect the dry out in a narrow channel. All results have proved the possibility to cool the fuel element by means of natural convection.