Fuel elements remain in cooling ponds after their operation in nuclear reactors until they are being transferred to interim storage. The cooling pond is filled with water well over the top edge of the fuel rods in order to shield radioactivity and to discharge afterheat.

The test plant ADELA serves for experimental research on heat release of the fuel rod surface under cooling pond conditions. The plant provides the means to simulate scenarios of cooling water ebullition and falling water level below the top edge of the fuel rods.

A 3x3 bundle of electrically heated rods simulates the fuel rods. The heating rods are 10 mm in diameter and 3740mm in length and thus are equal to nuclear reactor fuel rods. The rod spacers are built up of segments of original parts. With the help of an inner and outer channel flow conditions in the fuel elements can be simulated with a good approximate. The additional heating rod in the outer channel reduces heat loss in radial direction. The output of the heating rods is continuously adjustable up to 2kW.

The test plant is equipped with 12 thermo elements to measure the water and rod surface temperature, a pressure difference sensor for level indication and a power measuring device. An observation window allows the visual observation of the bi-phase flow conditions in the region of the spacers.