[en] Information in relation to the measurement devices for very low radioactivity, applied in the decommissioning of electronuclear power plants, is scarce and scattered. However, some realistic information can be obtained from the specialists working on nuclear plant dismantling sites. In practice, the in situ measurements deal with two or three radionuclides only. The other containments must be determined on some samples in laboratories by means of radioanalysis and spectrometry technologies. These technologies are briefly described. One of the problems concerns the detection threshold of the measuring instruments. This threshold varies in relation with the detector efficiency, the background and the measurement duration. The application of this concept of threshold to various types of instrument is studied. Tables and graphs are given that sum up the various possibilities of detection for the usual detectors according to their effective area. The possibility of reducing the number of monitoring points using statistical methods is presented

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[en] Many test reactors and some power reactors have already been decommissioned and partially or entirely dismantled. Although some materials are classified as radioactive waste, others may be considered as ordinary waste or re-utilized for nuclear or non-nuclear work. There is no international recommendation on activity limits for the unconditional reutilization of material. The levels applied in the various countries differ according to the materials and their use or destination. In Germany the limits applied for dismantling the Otto Hahn reactor were 10^-4 μCi.g^-1 and 10^-5 μCi.cm^-2. In France there are no statutory limits for release for public use. Each case is submitted for authorization to the Service Central de Protection centre les Rayonnements Ionisants, a department of the Ministry of Health, which decides on the basis of the characteristics of the waste in question. We give examples of release in Germany (GKSS), France (CEA) and the United Kingdom (UKAEA). (author)