PRESS RELEASE

"Tens of thousands of fuel rods are stored in a single nuclear reactor. In the fuel inside, a fission reaction takes place, which causes the rod to heat up strongly. There are only millimetre gaps between them, through which water flows and cools them. In case of insufficient cooling, they can overheat and cause a so-called boiling crisis. Of course, this is not usually the case, but it is part of the safety assessment of a nuclear reactor. Theoretically, the cooling system can fail, so we need to know when such a situation can occur and how the fuel rod coverage behaves at such a moment," Karel Katovský from the Faculty of Electrical Engineering and Communication BUT explained the need for experimental loops.

In the experiments, the researchers gradually heated the loop to 110 °C. As soon as the fuel rod is critically heated, the hot spot lights up and the device switches off automatically. "While we make the equipment to boil in our primary circuit, they definitely do not want to boil in a real pressurized water nuclear power plant. This is already an emergency," Katovský pointed out.

In addition, the scientists from the Brno University of Technology can now study various materials for the production of fuel rods. "There are now 444 nuclear reactors in operation around the world, most of which use zirconium alloys as material to cover the fuel rods. It generally has good properties, but in an emergency, zirconium reacts with superheated steam to form hydrogen. Unfortunately, people may remember the forceful explosions of the reactor halls in Fukushima nine years ago, which were caused by the hydrogen that had just accumulated," Karel Katovský pointed out another sphere of research. Therefore, many researchers are now looking for new ways to prevent this zirconium reaction and come up with new materials or finishes that need to be tested. The equipment from BUT can also help in this.

"In the first set of experiments, we studied critical heat fluxes on a nickel superalloy, which is a very expensive and stable material usable for various extreme environments. Our experiments with this material and the parameters we monitored were the first of their kind in the world," Kamil Števanka, a doctoral student working on an experimental loop as part of his dissertation, added.

The researchers from the Institute of Power Engineering have been cooperating for a long time not only with the largest nuclear university in the United States, Texas A&M University, but also with the Joint Institute for Nuclear Research in Dubno, Russia. In addition, this year, Czech power engineers are commemorating the 35th anniversary of the connection of the first Dukovany nuclear unit to the grid.