The status of studies using RAMONA and NEPTUN models on decay heat removal by natural convection for the European Fast Reactor

An extensive Research and Development Program is being carried out to support the Direct Reactor Cooling System which relies solely on natural convection for decay heat removal during all loss of station service power. Experiments have been performed in water test rigs of different scales. RAMONA is a 1:20 and NEPTUN a 1:5 scaled three dimensional model. Similar steady state tests have been carried out in both models. For the RAMONA test facility about 100 transient experiments have been performed. These experiments allow to study the in-vessel thermohydraulics in the transition regime from forced nominal to natural convection conditions after scram. All these experiments provide a basis for the verification of computer programs. It is demonstrated by experimental results, that the decay heat can be removed safely by means of natural convection under different variations of parameters. It is also shown by the calculations performed with the 3-D computer code FLUTAN that the steady state process and transition regime is mastered both qualitatively and quantitatively even for the very complex geometry of the NEPTUN model. (author)