NOVELTY - Method for destroying effluents issuing from a reactor involves treating effluent with plasma source (6) capable of destroying at least certain bonds in molecules of perfluorinated (PFC) or hydrofluorocarbon (HFC) type to generate first species which are then converted to second gaseous, liquid or solid species; reacting first species with at least one hydrogen-containing reagent and/or reducing agent before interaction of the second species with dry or wet purifying unit; removing at least some of these second species by wet purifying e.g. water scrubbing.    USE - For destroying perfluorinated or hydrofluorocarbon containing effluents issuing from a reactor (claimed), particular effluents obtained from reactors used in semiconductor manufacturing processes e.g. etching, deposition, reactor cleaning.    ADVANTAGE - The injection of chemical compounds containing at least one hydrogen atom, preferably at the plasma outlet or, as early as possible, in the plasma but close to the outlet of these compounds from the plasma, generate hydrofluoric acid which then dissolves in the water (or any reducing liquid system), without being obliged to use a dry pollution control system to remove the hydrofluoric acid. It avoids deposition of products e.g. tungsten fluoride (WF6), on the tube walls, which cause its virtually instantaneous failure. The WF6 species upon leaving the plasma reacts with the reducing species injected downstream, this causes a deposition of tungsten metal or other solid tungsten compounds, such as oxides or oxyfluorides, on the generally metal lines located at the plasma outlet, thereby raising no problem of operation of the plasma system. The method additionally involves injecting upstream of the plasma at least one oxygen-containing compound. when an anhydrous additive, particularly oxygen, for example oxygen or air, is injected upstream of the plasma, the additive is dissociated and/or excited and its fragments react very easily with the dissociation fragments of the PFCs and/or HFCs to yield corrosive fluorine-containing compounds such as fluorine, COF2, SO2F2, SOF4: (the first species): these compounds are very stable at the high temperature of the gas in the microwave plasma and, once formed, are very unlikely to be dissociated again. In particular, they are not significantly reconverted to PFC. These corrosive anhydrous fluorine-containing products are much more reactive than PFCs. At the plasma outlet, when the hydrogen-containing compounds are injected, the temperature is still sufficient for them to react more or less completely with the hydrogen-containing additives, to essentially produce HF which is much more stable thermodynamically than the corrosive anhydrous fluorine-containing compounds.    DETAILED DESCRIPTION - Method for destroying effluents issuing from a reactor involves transporting the effluents through at least one pump (1) towards plasma source (6) capable of destroying at least certain bonds in molecules of perfluorinated (PFC) or hydrofluorocarbon (HFC) type, between the fluorine and the other elements of these molecules of the PFC or HFC type, in order to generate first species which are then converted to second gaseous, liquid or solid species; before interaction of these second species with dry or wet purifying means (15), at least one hydrogen-containing reagent and/or reducing agent (that can react with the first species created to form the second species), is injected downstream (8) of the plasma, but upstream of the purifying unit (15); followed by removing at least some of these second species by wet purifying e.g. water scrubbing. The method also additionally involves injecting upstream (5) of the plasma at least one oxygen-containing compound. The hydrogen-containing reagent and/or reducing agent is selected from water, ammonia, methane, and/or alcohols.    DESCRIPTION OF DRAWING(S) - The figure shows section of system used for treating effluents from a reactor manufacturing semiconductors.    Pumps (1)    Oxygen-containing compound stream (5)    Plasma source (6)    Hydrogen-containing reagent and/or reducing agent stream (8)    Purifying unit (15)