[en] The R and D programme at the Forschungszentrum Karlsruhe in the frame of the Project Nuclear Safety Research is centered on phenomena and processes that would endanger containment integrity of a large pressurized water reactor in the case of a core melt accident. It supports the safety design of next generation reactors like EPR. This paper discusses energetic threats caused by steam explosion and hydrogen combustion. The goal of investigation in the steam explosion field is to prove that interacting masses and energy conversion rates are inherently limited. The QUEOS and PREMIX programmes for heat transfer and premixing mechanisms provide an experimental database. The data are used for model development and validation of the code MATTINA. Energy conversion will be investigated in the forthcoming ECO programme. In the BERDA programme experiments are performed to study consequences of melt slug impact on the RPV head including the dissipating effects of internal structures and processes during slug formation. The hydrogen programme aims at development of validated numerical tools, based on mechanistical models, which allow the complete analyses of NPPs for hydrogen production, distribution and combustion. Hydrogen sources are determined using code systems like SCDAP/RELAP and MELCOR. The 3-D finite element code GASFLOW is being further developed and validated for reliable prediction of hydrogen distribution and mixing. Criteria were developed to identify detonation risks. Similar criteria to quantify the risk of fast turbulent deflagration are under development. Present work concentrates on phenomena like flame acceleration, turbulent combustion and flame quenching. Hydrogen production and trapping during late phase core degradation and reflood processes in an overheated core is studied in the QUENCH facility. Heated preoxidized test bundles are quenched by water and steam, and hydrogen production rates and total masses are measured on line. In the first experiment a cladding temperature of 1700 K was achieved. (author)