Development of a Program Routine for Parameter Optimization and Creation of Program Flowcharts for the Hydrogen Recombiner Simulation Program REKO-DIREKT

[Automatically extracted and translated] In the event of incidents in water-cooled reactors, hydrogen (H2) can form. After a loss of coolant in the core and a failure of the residual heat removal, the cooling water in the core evaporates after a certain time. The resulting water vapor reacts with the zirconium of the fuel element cladding and at a later time (after the corium has melted through) with the iron of the concrete foundation. In addition to the formation of zirconium oxide (or Fe2O3), large amounts of hydrogen (H2) are produced. This can form an explosive mixture with the air oxygen in the containment at sufficient concentration and lead to the formation of a large overpressure in the reactor containment. To reduce these dangers in the reactor, hydrogen recombiners have been developed to catalytically recombine the hydrogen in the air. Since the late 1990s, power plant operators have begun retrofitting their facilities with hydrogen recombiners. About 40 recombiners per plant are necessary to counteract a maximum possible release of H2. Hydrogen recombiners cause a controlled, exothermic reaction of hydrogen with air oxygen in the presence of a catalyst, thus filtering out the excess hydrogen from the air (the chemical formula is: 2H2 + O2 -> 2H2O). There are various concepts for the construction of a recombiner. In this system, the air-hydrogen mixture enters the lower part of the recombiner and flows upwards between the catalyst plates. The hydrogen is recombined, and the altered gas mixture exits the upper part of the recombiner. The reaction takes place without external energy supply and starts at H2 concentrations of 1.0 vol-%.