[en] The operations of dismantling of nuclear installations are often difficult due to the lack of knowledge about the position, the identification and the radiological characteristics of the contamination. To avoid the manual mapping and simply sampling and radiochemical analysis, which takes time and causes doses new tools are now used: - CARTOGAM to detect the position of the activity and the relative dose rates of the different hot spots, - NaI, CZT or Ge gamma spectrometers to characterize the major radionuclides, - a model with ISOCS gamma attenuation code or MERCURAD-PASCALYS gamma attenuation and dose rate evaluation code CARTOGAM and MERCURAD were developed in collaboration with CEA and COGEMA. All these tools are used to build a complete methodology to give adapted solutions to the nuclear facilities. This methodology helps to prepare for and execute decontamination and dismantling activities. After describing the methodology, examples are given of its use in preparation of repairing at an EDF NPP site and in dismantling operations at a CEA site. These examples give concrete insights into their significance and the productivity gains they offer. (authors)