Experience with check of potentially contaminated materials released to the environment

Full text: Measuring systems with 2 or 4 large area plastic scintillating detectors were tested, which are used to avoid the undesirable and illegal transport of radioactive materials especially at border crossings, in metallurgical works and in plants processing metal scrap. The measuring equipment with 3 germanium detectors was tested, which is used for check of material released from the Dukovany nuclear power plant (in the Czech Republic). The chamber with plastic scintillating detectors was tested, which is used for check of material released from the Kruemmel nuclear power plant (in Germany). This detection system consists of 24 large area plastic scintillating detectors. The conditions of release of materials, substances and objects to the environment from the point of view of the radionuclides content are regulated (in the Czech Republic), by Act on the peaceful uses of atomic energy and ionising radiation (the Atomic Law). For the γ-ray emitting radionuclides (e.g. 60Co, 137Cs), there is a requirement that the sum of the activity concentrations of these radionuclides in the released materials has to be less then 300 Bq/KXg. For monitoring systems equipped with the plastic scintillating detectors, used for loads check on trains or automobiles this limit cannot be achieved and the minimum detectable activity, for 137Cs, resulted 2000 Bq/KXg. Therefore these systems, even if suitable for the check for example in metallurgical works or at border crossings, are not adequate for the check of the material released to the environment. The advantage of the measuring system with the germanium detectors is the direct identification of the γ-ray emitting radionuclides contained in the checked material. The minimum detectable activity concentrations achieved at the testing measuring in the Dukovany nuclear power plant are 50 Bq/KXg for 137Cs and 30 Bq/KXg for 60Co. Measuring equipment is adequate for the check of the material released to the environment. For the scintillating chamber the minimum detectable activity concentrations are 100 Bq/KXg for 137Cs and 60 Bq/KXg for 60Co. It is necessary to accomplish the measurements in the chamber with a nuclide identification by γ-ray spectrometry