The reprocessing of spent nuclear fuel produces high level liquid waste (HLLW). Due to the decay heat, these concentrated nitric solutions containing fission products are stored in cooled tanks to prevent the solution from boiling, evaporating and drying out. In case of a total loss of cooling, potential large releases of radioactive materials into the environment, especially volatile species derived from ruthenium, can happen. The loss-of-cooling accident on HLLW storage tanks is one of the accident scenarios identified as a very dreaded situation. Besides, an extensive literature review performed at IRSN confirms the lack of reliable data on the behaviour of ruthenium in nitric acid solutions and concerning mechanism of releases. It highlights that research works on this topic can be classified in several categories: ruthenium chemistry in a nitric medium characterized by the formation of nitrosyl ruthenium ion RuNO3+; behaviour of volatile forms of ruthenium in presence of steam, nitric acid vapour and nitrogen oxides (recombination, decomposition, etc.); transfer phenomena and stability of the different gaseous species containing ruthenium through the ventilation network. Subsequently, the efficiency and the performance of various trapping systems that can be used for mitigation of ruthenium release (gas/liquid absorbers/traps, steel filters, porous media such as zeolites etc.), or even various means of preventing its volatilization (recombination, addition of reducing agents in situ, etc.) have been investigated by different authors. Previous experimental work performed at IRSN on severe accident scenarios in nuclear facilities allowed to characterize usual filtration devices such as active charcoals or metallic filters, with respect to gaseous RuO4. It showed that these latter do not trap efficiently RuO4(g). From these findings, IRSN started a research program aiming at improving the knowledge on this topic. A specific test bench has been developed in order to study the volatilization of a nitric acid solution containing Ru nitrosyl, simulating a real HLLW in terms of acidity and ruthenium concentration, and to investigate the possible inhibition of Ru volatilization by addition of specific reducing compounds (nitrogen oxides, sucrose, etc). A first series of tests showed that the quantities of released ruthenium obtained for different temperature levels are consistent with the literature, before testing inhibitors. The experimental setup mentioned before dedicated to gaseous RuO4 is also used to study trapping of RuO4(g) by different porous materials: zeolites, rare earth oxides, etc. Decontamination factors (DF) and RuO4(g) retention capacity have been determined for several of these compounds.