Underwater spectrometric systems for characterization of radioactive contamination - 5151

The decommissioning and dismantling of reactors and other nuclear facilities requires holding the characterization of contamination in the underwater environment. Since the 2000's, we have used underwater CORAD to characterize sediments in relatively clean water: ponds near the nuclear power plant, pools for storage and operations with spent fuels. The method for the measurement of the characteristics of radioactive contamination of bottom sediments is similar to technique of ¹³⁷Cs soil contamination measurement with collimated radiometer: free length path of 662 keV gamma-rays in water is about 10 cm, so the detector registers mainly radiation inside solid angle from the surface area of about 0.2 m² that corresponds to a spatial resolution of about 50 cm. This underwater spectrometer system has the following parameters: scintillator volume of spectrometric probe: 20 cm³; the energy resolution at 662 keV: < 7 %; sensitivity (minimal measured surface activity with 30% inaccuracy and 30 min exposure time): 20 kBq/m², a measurement range up to 10 GBq/m²; maximum depth of measurements: about 5 m. In recent years, to survey the pools of technology-research reactor we use a new system to find and measure the underwater contamination. The water has significant activity of ¹³⁷Cs. The system uses a semiconductor spectrometric detector CdZnTe, the system has a special collimator. The processing of hardware spectrum of detector allows a high background of water contamination with ¹³⁷Cs (typical fuel storage pools) to register the characteristic X-ray radiation of U excited by gamma radiation of ¹³⁷Cs, gamma-lines of ²⁴¹Am and other nuclides