Plant for cleaning gases (1) from an incinerator (3) of lightly radioactiveaste. The plant includes a cooler-condenser (6, 100) for cooling gases (1) to a temperature lower than the dew point, a heater (300) for raising the temperature of the gases as they are discharged from the cooler-condenser (6, 100), a filter (200) for recovering solid particles downstream of the heater before the gases are discharged into the atmosphere, a unit (3) for treating condensates, and capable of precipitating radioactive heavy metals for recovery of a radioactive precipitate and an aqueous solution, an a unit (36) for crystallizing salts and concentrating them to dryness in an aqueous solution and recovering water to be recycled in the plant (2).